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Color management in ink jet printing
Color management in ink jet printing
Half drop repeat of droplet motif with abstract overlay.
Ink Jet Textile Printing. http://dx.doi.org/10.1016/B978-0-85709-230-4.00004-2 Copyright © 2015 Elsevier Ltd. All rights reserved.
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4.1
Introduction
Color is not a surface or an object. Color is the phenomenon of light reflected from a surface or object as it is received by the eye and processed by the brain. Light and surfaces will vary, but even the same conditions can result in differing mental interpretations and verbal descriptions by a viewer. As the mental interpretation of a physical process, “color is in the eye of the beholder,” and if there is more than one beholder, it is likely that their views will vary. This chapter aims to detail those issues in color management relevant to printing on textiles by ink jet, rather than being an exhaustive detailing of the entire field of color management. It considers both the production of color and the perception of color with the need for individuals to agree on the perception of a color when in a commercial situation and not all operating with calibrated equipment. As even different parts of an office can change the perception of a color due to the quality of the light in that area, this becomes particularly problematic when the individuals in question are located in different parts of the world.
4.2
The perception of color
The perception of color is complex, very individual, and could be categorized as “light” and “sight”: l
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“Light” concerns the production of color, perhaps by ink or light. “Sight” might be defined by two activities: reception by the eye and perception by an individual’s physiology and psychology.
Light enters the eye, and a corresponding electrical signal is received by the brain of an individual. The quality of this light may be affected by regional and seasonal differences in brightness, or by a physical location offering shading or reflection. These may all affect the perception of a particular color, but so might fatigue or even the emotional state of the individual. Depression or grief is often described as being a “dark” place. Humans will physiologically react to certain colors, and colors often have profound cultural as well as personal associations that affect this perception and any subsequent reaction to colored objects or spaces (Drew and Meyer, 2008, pp. 196-199). It is not enough to assume that an apparently appealing colorway will sell well. Seasonal variations are well understood in textile design, with summer ranges including lighter colors and textures compared to the heavier, dark warmth of winter. Effective color management can include cultural considerations of the intended marketplace as well as how the local light will affect a color. Definition is one thing, but appeal is another. Using color remains an art as well as a science.
4.3
The production of color
Color theory has a long and varied history, reflecting its importance to humans for identification, emotions, and increasingly measurement. For a subject intrinsically generated by mixing and blending, a lot of words try to define what can be very difficult to delineate. A “light” color could be either pale and washed out, or bright and
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cheerful. This section gives the working definitions used in this book. The definitions also introduce concepts involved in color and its reproduction. Some terms used have specifically defined meanings, but these are rarely used consistently outside of the scientific study of color. Color is as cultural as it is scientific, and other systems also exist for understanding color. The two systems used for color reproduction in ink jet printing are: l
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CMYK (or a greenish-blue “cyan”; a bluish-red or pink “magenta”; a yellow; and a black, represented by a K). This system mixes these colors as pigments or dyes for color printed onto a surface. Printing usually begins with a white substrate, perhaps as paper or fabric. An area printed with a particular color ink reflects only that color’s wavelengths of light as color, absorbing or “subtracting” everything else. Ironically, the color produced is the color it rejects, or reflects. This is known as “subtractive” color mixing. It starts with all of the colors and removes or subtracts them until only the color needed is left. RGB (or red, green, blue). This system mixes these colors as light for the emission of color to a viewing screen. The computer monitor starts from no light or “black,” and adds colors in as light, mixing to make colors, then emitted as light on a screen as individual spots of red, green, and blue, so closely packed that the observer only sees their combined effect. This is known as “additive” color mixing. It starts with nothing and adds in color as needed.
A “gamut” refers to the range of colors capable of being reproduced by any system of color mixing. The gamuts of CMYK and RGB overlap; however, it is not an exact overlap, as each system begins from different starting points. CMYK using its magenta and RGB using its red will probably each mix a different color. Crucially, as these two systems work differently, they can mimic each other rather than exactly reproduce each other’s range of colors. In addition, many printers use “light” versions of the CMYK inks or an additional set of primaries, such as red, orange, blue, and a deep or dark black to extend the range of possible colors (SPGPrints, n.d.). Many design software programs use three variables in an interface, often in two steps to allow users to select colors. These often correspond to three principle activities involved in producing a color: l
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Hue Saturation Value
4.3.1
Color mixing: hue
“Hue” is perhaps the easiest to understand, as it often employs the words many know and have used since childhood, such as paint primaries of blue, red, or yellow. These are generally considered to be three primary colors, not including white and black as colors, that largely correspond to the three different types of cells that view and make color in the human eye. Essentially, mixing for hue is just adjusting the proportions of these primaries, even when adding “secondary” colors such as purple (red + blue), orange (red + yellow), or green (blue + yellow), or tertiaries: aqua ¼ primary blue + secondary green (blue + yellow). Differing cultural associations with hue must not be underestimated, particularly when it comes to describing or interpreting colors between different peoples.
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Color dilution: saturation
“Saturation” describes how much of a color is in the color; this refers to the mixed hue, rather than the proportions of its component primaries. This isn’t quite as confusing as it sounds. The primary color, or “hue,” blue may be increasingly “desaturated” so that, proportionately, there is less blue in the mix than when it was 100% blue. Painting the graduations in color at twilight could range from using lots of blue and just a little water (saturated) to lots of water and just a little blue (desaturated). Water is a neutral or colorless carrier and thus does not technically adjust the hue, although it may appear more or less pale. Increasing saturation can appear to make a color brighter by making it more intense; saturation is also sometimes used to refer to the brightness or dullness of a color. One way of thinking of this is like a volume control for sound, with pale as quiet and bright as loud. Intensely saturated colors, particularly several used together, are often described as “loud.”
4.3.3
Color highlights: value
A “gray scale” version of an image uses a mix of black and white to represent the “value” of the colors. Value could be described as the amount of light a color absorbs or reflects, or how light or dark. Value is related, but only related, to color; a fully saturated light blue may be of the same value as a desaturated purple. Three dimensional drawing techniques use white or light colors as highlights to show where the light hits, or dark or black to create shade. A color can be moved along the value scale toward white, by adding white (often then described as tint and useful for highlights). Adding black will move a color in the opposite direction on the scale (described as a shade and used for shading). Adding a mix of black and white as a gray, described as a tone, will fine-tune values in the midpoint area.
4.4
Defining color
Red is considered one of the primary colors. However, colors vary; both blood and a lipstick could be described as red, but they are often not the same red. For consistency across media, the red must be defined so all can use the “same” red. Organizations such as the International Commission on Illumination (CIE) develop standards for the measurement and use of light and color (Commission international de l’e´clairage, 2011). “Metamerism” refers to the phenomenon whereby two colors that appear the same subsequently appear different when viewed under a different light source. The quality of light, as well as the amount, is enormously influential on the color information as received by the eye and must always be considered when presenting color for inspection and comparison. It is so important that several large retail chains specify particular commercial lighting products for use by both their product suppliers and their store builders (HunterLab, 2008b, p. 4). By 1931, CIE had developed one of the first mathematically defined color spaces, considering principally the perception of color. In 1993, commercial members
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founded the International Color Consortium (ICC), concerned with the production, particularly printing, of color. Color “models” such as RGB and CMYK can be described as “device-dependent,” so the default red or magenta depends on the device or ink that is generating that color. Rather than negotiating between these different methods, a better system is the use of a neutral “color space.” Based on the CIE system, the ICC color space is “device-independent.” It works as a translator or intermediary in a “profile connection space” using “look-up tables” (LUT) as reference for the different embedded languages used by input, display, and then output devices (JISC Digital Media, 2008). Interestingly, the ICC member companies did not try to monopolize or maximize market share by producing a “closed” or vendor specific system. Its “open” and cross-platform color management system has meant that, as a result, ICC-based color management has become the default standard in many industries (Loser and Tobler, 2006, p. 196).
4.4.1
Measuring difference: tolerance
A significant development in the CIE system was informed by the earlier work of Dorothy Nickerson and her measurements of fading between textile samples when testing for durability and quality (Hunter, 1975, p. 139; Nickerson, 1936). This matched color differences as steps within a particular hue as perceivable by humans, with a mathematical difference in the mathematical color space (HunterLab, 2008a, p. 1). A crucial component in the quality control of color, or color matching, is the determination of how much colors differ and how or why they differ, along with a permissible range of difference known as “tolerance.” Communicating degrees of difference is important for applications where color is used diagnostically as well as for commercial applications, where the consistency of color is an issue. “Tolerance” also recognizes the difficulties of trying to exactly match colors in differing viewing conditions, to a commercial agenda and timeframe. It can be understood that some color models such as RGB produce colors outside of the range or “out of gamut” of other color models such as CMYK, because the red in RGB and the magenta in CMYK were not the same color to begin with. If the color scale is considered as a mathematical space, then it can be understood how some colors can be produced that are outside of human perception. We might not see infrared or ultraviolet light, but this does not mean they do not exist or have no effect on us. This can also give false impressions of the number of visible colors that can be produced. Also, while there may be a large number of visible colors able to be produced, there are limits as to the steps between colors as distinguishable by the average human eye. A wide mathematical range of green is pointless if they all look the same to most observers. None of the color spaces also address the phenomena of related color, or how neighboring colors affect one another. This is particularly important in textile design, as the color viewed in isolation may look quite different when combined in a pattern among other colors. The ICC color space defines options of what to do if a color cannot be matched between two systems (ICC, 2006, pp. vii-viii). Each of the four “rendering intents”
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generally relates to a common requirement encountered in graphic design print production. Differing intents can be assigned within a single design file, reducing the unsatisfying compromises that a printer may be forced to make (King, 2005, p. 18). “Relative” or “absolute” colorimetric rendering prioritize individual colors and use gamut “clipping” to prioritize in-gamut colors, rendering out-of-gamut colors to the nearest possible hue: l
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“Proof or relative colorimetric.” Reproduces out-of-gamut colors to the nearest reproducible hue. It preserves lightness but not saturation. “Match or absolute colorimetric.” Converts out-of-gamut colors to the nearest hue but sacrifices saturation and lightness.
Alternatively, “saturation” or “perceptual” rendering prioritizes the overall color scheme and uses gamut “compression” to prioritize the relationship between colors, shifting most if not all of the hues so as to reproduce all of them within a particular gamut (Anderson and Krogh, 2011). These types of rendering can be described as follows: l
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“Graphic or saturation.” Maps the saturated primary colors in the source to those in the destination irrespective of differences in hue, saturation, or lightness. Often used for business display graphics. “Picture or perceptual.” Generally recommended for photographic reproduction because it applies the same gamut compression to all images, thus maintaining the same overall relative color rendering balance.
4.5
Workflow for the design, print, and sale of printed textiles
Color matching was always a challenge, even when comparing “hard copies” of painted and printed designs, both generated by the same “subtractive” color systems although using different media. RGB color production on an electronic monitor added a different “additive” color production method and a new viewing system, so color matching is now conducted across two very different systems of color production, with different media and even different monitors producing different colors. The need to standardize across a diverse range of color production systems is color management, with “calibration” as its principle method.
4.5.1
Workflow, with digital devices
The workflow for color management or coordination across the design, print, and retail of textiles may now include some or all of the following steps, and some repeatedly. Color management, with calibration, is essentially the attempt to secure a single agreed color all along this staged workflow and across all of these different devices and circumstances:
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Design generation Cameras: preferably producing images in “raw” (RAW) format, but otherwise including its own color determinants. Hand-drawn designs: perhaps colored with “subtractive” mixes of the red yellow blue (RYB) paint primaries. “Glare” from substrate and its color may affect color reproduction when scanned or photographed. Scanners: converting to RGB, usually according to manufacturer’s set of default color specifications. RGB-based monitor: file will be loaded for viewing, and both computer and monitor usually run according to their manufacturer’s set of default color specifications. Design manipulation: in a software program such as Adobe Photoshop, often using software’s default color management system. May conflict with color management in monitor used to view file. Design files: ink formulations for ink jet or screen-based print processes are not the same. Files should be prepared at the design stage to print effectively on either the ink jet or the screen-based systems, or both if sample printing with ink jet, but printing bulk runs with screen-based system. This will significantly affect design decisions such as the gamut to be used and will help to avoid significant and costly mistakes. Save and despatch: digital design file saved in one of various formats (e.g., TIFF, PDF) to send to printer. Each format has its own color specifications. l
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Print production Printer software: converting file as necessary for CMYK-based production system, such as ink jet printers. Ink: colors may vary between manufacturers. Sampling: printing onto cloth that has been prepared for print by bleaching, dyeing, and pretreating with chemical agents to varying degrees according to the cloth. Cloth and climate: circumstantial factors such as age of the cloth, temperature, and humidity of the surroundings may affect color uptake and appearance. Fixing and finishing: these may affect color appearance, both immediately and in the long term. Quality control: on-site, or swatches sent remotely. Color viewing conditions will vary between countries and may vary between different spots in the same office, according to illuminating, shading, and reflecting conditions both inside and from outside through doors and windows. Conversion: if sample is ink jet but bulk production is by screen-based print system. Ink jet printing uses “process” color, mixing as required. Screen-based printing is a “spot” color system, premixing colors beforehand. Fixing, finishing, storage: bulk production is more likely to be transported by sea. Finishing may include treatments to preserve and protect appearance of textiles during transportation.
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Retail Wholesale purchase: often from sample swatches. Bulk production must match these samples. Selection: some international brands strive to standardize color globally, others stock color selections according to local tastes, as defined by local culture and quality of light.
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Marketing: increasingly includes color images of items across wide range of media platforms. Websites are RGB, with newsprint and gloss-stock magazines both CMYK, but on very different substrates. Retail: increasingly occurs at night as well as day. Stores must consider lighting specific to their location to ensure color appeal throughout long opening hours. Retail websites: viewed through different browsers and on different RGB monitors, most set to their various manufacturers’ default color specifications. Returns after remote purchasing due to dissatisfaction will impact the brand profile as well as the profits. Postpurchase consumer care: includes a wide range of washing and drying techniques, machines, and products. All can have an impact on the short- and long-term appearances of color.
4.6
Calibration
Each of the devices in the digital workflow has its own system of color management. To “calibrate” means to check against a definitive scale used to synchronize all devices. The scale can be a printed example, or could be a set of digital definitions. Calibration involves analysis of what a scanner or monitor or ink manufacturer may consider to be, for example, a standard red against where those reds sit in a master “look-up” table. The comparison can occur either by eye comparing a monitor to the printout or by using a colorimeter or spectrophotometer to measure color, working in conjunction with specialist software packages. The most effective and efficient use of calibration for color will benefit from knowledge of how different systems make color, how color is measured and defined, and how to analyze its importance to the final printed output. Calibration of monitors may be achieved by the use of small “clip-on” spectrophotometers operated with specific software. The calibration of scanners requires the provision of special test cards as a set of multicolored panels whose color coordinates are known. Digital printers can be fed with data for a similar test card; the printed result can then be measured photometrically. Both systems require the provision of appropriate software.
4.6.1
Automated calibration
The selection of a calibration system is often made on price, but should also consider some other factors, as any system is only as effective as its operator. Mundane factors should not be overlooked. Calibration of the monitor must be considered in conjunction with the color management system used by the design software and by the computer itself. These may need to be disabled, and the easily accessible user settings such as for brightness and contrast should not be forgotten. “CRT” or bulky, older cathode ray tube monitors produce color differently to newer, slimmer, liquid crystal display “LCD” monitors (Dawson, 2006, p. 163). Relocating the monitor is likely to result in different viewing conditions, so color may again look different. Appropriate purchases require some research, including background knowledge to explain the significance of some of the more technical terms. It may pay to purchase the best profiling equipment and software within budget, but it will only pay if it is used correctly. Not
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only its ease of use and effectiveness should be discussed with others in the same industry, but also consideration given to how easily scheduling for its use can be fitted into an existing organizational schedule. “Frequent” calibration can be required monthly or even weekly, due to time-related “drift” (Dawson, 2006, p. 171). The knowledge of how to use any system should be shared among several employees, although the responsibility for upkeep and updating should rest with one employed position. As well as the product offering, the service offering behind the system and software should be considered. Once purchased, what is the access to advice for maintenance and use, and how understandable and costly is any such advice? Longevity and experience may mean good service, or instead complacency, with new entrants to the field keener to secure market position. The bottom line is that if the product is not used properly, it is often a waste of money.
4.6.2
“Systemic” calibration
Automated calibration maintains professional accuracy, but lacks the flexibility needed in a changing commercial situation often dealing with some unknowns. Each time something is altered anywhere in the chain of input, display, or output, all the devices in an entire system may require recalibration. Printing on textiles occurs across a wide range of substrates, and conditions may vary even between batches of the same substrate, for example, due to age or storage. Such additional complications are why many shy away from even the mention of calibration. Continuous perfect calibration may prove impossible, but an appropriate level of calibration maintained across a system offers the best chance to reduce repetition and waste, while increasing the frequency of a satisfying result. Effective calibration for color management does not solely involve standardizing across devices, but recognizes that these operate within a workflow. The final print output onto cloth for retail is the true measure of calibration. As a commercial product, it is upon the sales based on its appearance that the success or failure of the entire print workflow is judged. The end therefore is where calibration across the workflow could begin.
4.7
Color print production
One rarely asked but significant question is why one color must match another. Asking this question allows for an appropriate allocation of resources according to the response, as there are degrees of justification for expensive and extensive calibration practices. In “batch matching,” there may be little or no allowance for difference and tolerance, particularly for applications such as military parade uniforms or rolls of curtaining. In this case, calibration deserves the appropriate amount of time, money, and attention. Some choose to recognize discrepancies between processes and colors as part of the creative process and an inherent part of print production. For color schemes, matching may be more relevant across the relative colors contributing to the overall complimentary look, along with a fast and financially effective color
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solution. Detailed color profiling also offers greater accuracy, but does not increase the overall range of the color gamut. Profiling does not add different color gamuts together. It disregards colors not reproducible by all, leaving the reduced range of only the shared hues; however, avoiding calibrating will not change this.
4.7.1
Design generation
Design programs such as Adobe Photoshop and Illustrator or others specifically tailored for textile design are usually formulated in two ways, reflecting the “in computer” or “by hand” methods now used for designing textiles. Manipulating images sourced from a camera or scanned files usually involves software programs with origins in photographic editing techniques such as Adobe Photoshop: l
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These programs tend to be “raster” based—that is, the picture is built with individual pixels arranged in a grid format. Manipulation often includes picture editing and color balancing before putting the image into repeat, or fitting the image to a particular size or shape for a “placement” print. Placement prints are similar to those seen on the front of T-shirts but are not limited to this format or size. Pixels present a challenge when scaling up designs. Unless originals are scanned or set at a very high resolution, designs can “pixelate,” leaving “jaggies,” or jagged or stepped edges if the image is enlarged so far that the individual square pixels of the image can now be seen. Camera and scanned images often show color that at a distance looks acceptable, yet the color mixing occurs at a pixel level. “Dithering” uses several colors to simulate a single color. At a distance this is not an issue, but if the file is to be printed as a large format, it can become very noticeable. Working directly from a complex image involving significant numbers of colors, gradients, and fine detail, this digital design pathway aligns itself more easily with ink jet printing. Broadly speaking, it lends itself less to conversion for screen-based printing, along with the established industry practices for textile printing, such as multiple colorways.
Designing directly into computer software is essentially sophisticated drawing; for example, many of the tools in Adobe Illustrator relate directly to their real-life counterparts, such as pencils and pens: l
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Drawing programs such as Adobe Illustrator tend to be “vector” based, recognizing that drawing paper is rarely a grid full of squares, but blank to accommodate freeform curves and random angles. Vector-based graphics work much like drawing a line between two points, defined but not restricted by the mathematics of an xy grid. This enables vector images to be enlarged to any size with no loss of resolution. Colors tend to be selected within the software, giving a “clear and clean” effect. Fewer colors tend to be used overall, often as a set palette of colors for a particular design, which makes it easier to change hues and generate multiple colorways. Ink jet printing can be the most effective at capturing a “painterly” style, involving washes and gradients. Overall, however, this design pathway tends to be more aligned to established screen-based methods of textile print production and therefore print design.
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If conversion for printing is done by software for raster image processing, then this, as well as the format in which the converted file is saved, can also be a source of color shift.
4.7.2
Monitors
The monitor tends to act as a “filter” for images between the stages of design generation and print production. As a result, the monitor is often used as the “fulcrum” from which the calibration process is leveraged along the chain of production. The monitor and indeed the entire supply chain may be calibrated and use the most sophisticated fabric simulations, but success will still be judged by the final product. This will eventually be viewed in a range of different lighting conditions, although all initial shade comparisons should be assessed under standard lighting conditions, such as in a matching cabinet fitted with standard “daylight,” or store-specified, fluorescent tubes. Differences of opinion among viewers across different cultures will also affect the result. Communication is essential for calibration, particularly if it includes a degree of realism. “Tolerance” is a measure of how much difference to accept, often forced by time shortages. Politics may be involved in color matching; aiming for accuracy maintains standards but good relationships among all in the supply “network” also gives the best chance of accuracy. In commercial negotiations, there is an art to knowing when to push for more and how much difference to accept. “Tolerance” is a commercial decision, as good commerce grows long-term profit from professional relationships.
4.7.3
Scanners and cameras
Many textile designers still produce designs by hand, often scanning artwork into a computer program for clean-up and manipulation into a repeat. Colors can be immediately compared to an original and any necessary adjustments made. Scanners, as well as printers, tend to be more reliable than computer monitors in terms of “time-related” drift in color, but a regular program for checking color calibration is still advised as best practice (Dawson, 2006, p. 171). Calibration for scanners usually involves an ICC profile and can occur with purchased printed test images that include a gray scale as well as a range of colors and some test images. Each of these colors has specific and measurable mathematical coordinates. The resolution, or size, of an image means how much information it holds and is also affected by the storage format for that information. Cameras, scanners, monitors, and ink jet printers “sample” information in steps, rather than as a continuous flow. “Samples per inch” or “spi” might be a better term than “dpi” or “ppi” (dots or pixels per inch). It is around this that issues and confusion about resolution revolve. Apparently high resolutions may not be the “optical” resolution, which is how many samples are taken from an inch, but an “interpolated” resolution. This inserts estimated information between the samples, giving an impression of higher resolution without actually taking any more detail from the original. The ideal resolution for an image depends on its final output. The measure of “good enough” is truly good enough for images that will only be printed as small, or serve as small elements in an overall design. Data storage has reduced in cost,
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and so “master” images or final files justify being captured and archived at the highest possible resolution. Some textile designers use digital cameras as their sketchbook and incorporate these images directly into their work. Each model or brand has its own way to capture and hold image information. Such diversity brings the risk that original files may no longer be accessible as various formats become obsolete. Formats such as JPEG (developed by the “Joint Photographic Experts Group”) or TIFF (“Tagged Image File Format,” offering less compression and more variety of storage than JPEG) were developed as standards for digital image files in response to such issues. “RAW” is a format available on most middle to higher-end digital cameras. The term Raw or RAW does not stand for anything, but means just that, raw or unprocessed. It refers collectively to image data, including color data, that has been minimally processed and compressed by any suitably enabled digital camera or scanner. It does not refer to a particular software or file format. Instead, the raw file is like a digital negative; it is not immediately usable as an image but contains all the information necessary to generate one. Conversion from raw data for image editing and storage means an extra step in the workflow and usually results in a larger file. Over-compressing a larger file results in some information being lost. Different file formats compress to different degrees, with the ideal being a balance between “lossy” or “lossless” compression compared to human perception of this according to the final printed format. Good results also mean getting information about the final printing process before creating the initial images.
4.7.4
Paper printers
Many designers find a “proof” stage with a desktop paper printer useful for intermediary print development and checking. Looking at the image on paper rather than a screen usually results in faster and more effective quality checks, particularly for the “flow” in a repeat. Calibration can be attempted, despite the likely additional light primaries used in many commercial scale textile printers. Two color profiles, and thus two copies of the same file may be developed, with one calibrated for the test paper print and the second for the cloth print. The number of variables involved in textile printing can result in many different profiles and calibrations. Developing a system of labeling profiles that includes as much immediately accessible information about the specifics involved in that particular profile may require some interesting abbreviations, but will avoid time-wasting and frustration.
4.7.5
Color maps, charts, tables, matrix, or matrices
Printers can supply printed versions of “look-up” tables as charts that can be used to calibrate back across the design workflow, either by eye or by equipment and software—some also offer related software (Spoonflower Inc., 2011). No matter what descriptive term is used, the charts are usually grids, with each square containing incrementally altering blends of colors. Some printers add in “light” versions of the standard CMYK inks to increase the range of producible colors. More primaries,
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such as a cyan and a light cyan, require more squares. These charts can be timeconsuming to generate, and it is worth considering the format used. All charts and standardized design or image test files should be printed on and finished as close as possible to the standard materials, methods, and machinery used for bulk production. Yarn structure with slubs or hairiness, and weave or knit structure can also affect image graininess or “noise,” and different types of inks may produce slightly different colors. Whether synthetic or natural in origin, fiber is subject to environmental factors such as light, humidity, and time, with later bulk lots possibly affected differently. The physical size of the squares themselves is significant, as too small may not generate enough visual information for the observer, but too large may cause the overall grid to be unwieldy. Blending increments can range between 2% and 10%. Greater steps than this may leave too many gaps, but equally the smaller the increment, the more numerous the squares and the larger and more unwieldy the grid. Much like software-based profiling and calibration, while larger files with more information offer greater accuracy, they also take much more time and space. The grids may be printed as large sheets or cut into smaller individual grids, depending on individual working methods. Such grids are also only a guide, as color is rarely generated in neatly divisible numbers. The color charts can also be useful when developing colorways. A dull mid-gray card viewer with corresponding square windows can be useful when assessing single colors as well as viewing colors in a scheme. The grids can be used to explore the tints and shades of individual colors to “push” a scheme that bit further. Sample design or image files are additionally recommended for test and analysis printing, and should be selected with unashamed bias. The “standard” will reflect individual or company design preferences. It should include some challenging areas of browns, dark navy, and black, including at least one large area, some saturated red, green, and blue, neutral grays and gradients, and some flesh tones, perhaps from a human portrait. It may also be relevant to test print using files saved in different formats as well as discussing which formats are most suitable with the printer. Another popular tool specifies colors using a recognized color system such as the Pantone system. Pantone has partnered with textile dye producer Clariant to offer dye formulations for fabric that should match specific Pantone colors (Pantone LLC, 2011). Highly accurate, electronically measured color matching using Pantone’s textile-based system would, however, require the use of Clariant products and specific fabrics, finishing, and pretreatments in order to match the Pantone sample swatch exactly, even before differences in viewing conditions are considered. Ironically, using the paper-based Pantone products developed for graphic designers as many do, may result in a more realistic outcome due to the clear awareness that there are two different methods as well as different substrates being compared. “Uncoated” paper may give a better result when used in conjunction with most textiles, although the smooth shine of “coated” may be more aligned to fabric types with a sheen such as for swim or performance wear. Printed charts or chips will deteriorate in quality depending on age and storage, even if kept stored away from light. They will need to be refreshed periodically, especially if any component is changed in the print workflow of fabric/pretreatment/ink/finishing.
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4.7.6
Ink Jet Textile Printing
Ink jet textile printers
Much commercial manufacturing is dedicated to eradicating differences, but standardization can be difficult to maintain for many valid reasons. Outsourcing printing, particularly internationally, has come to be seen as a normal part of a supply chain. “Supply chain” is the term most commonly used to describe the commercial, mutually reliant relationships contributing to a workflow, but Web or network may be a more useful metaphor. These relationships extend out beyond the final printer of the textile to include its ink supplier, even the software controlling its machinery. If an ink brand has to change, then colors may change, and the calibration of the entire system may consequently have to be adjusted. Any change in significant factors in the print workflow may change the color outcome of the print, causing color management to be adjusted accordingly. Information about any changes will come from positive and well-managed relationships with suppliers along the various networks of supply. Ink-jet printing is not a simple substitute for screen-based printing. If the final output is to be on a screen-based system, then the initial design, even if completed on computer software and proofed on an ink-jet printer, must be designed around the restrictions that define screen-based printing, such as a smaller range of solid colors, restricted by the number of screens. Proofing on an ink-jet printer means there will also be additional restrictions, such as its limited range of inks. Conversely, those used to developing designs for screen-based printing methods need to understand the differences inherent in the ink jet method. Ink jet methods can be very efficient and economical with ink. This makes good claims for environmental sustainability but also offers some challenges to print and design expectations. Due to issues such as ink density, extremely dark, bright, or saturated colors can be difficult to achieve, as are large solid areas of dark colors. Subtle graduations in shade do not always replicate as well as they appear on the monitor, and toning down expectations as well as colors may be a good policy in a commercial situation, while still experimenting with new technological developments.
4.8
Conclusion
The personalized nature of the experience of color questions both our ability and our need to control color. Much of the need for calibration is about control, and this is understandably necessary when mistakes can be extremely costly. However, calibration across all of the components in the supply chain for ink jet printing on textiles is enormously difficult and remains tricky at best, so it might be argued that this need for control can also be costly. Sometimes a valid question is whether there is a sound financial reason for the control, or whether it is in fact driven by emotion. In color management, context is more crucial than control. Must a particular product match repeatedly across the ranks, or briefly across the racks? Calibration needs to be undertaken with an understanding of the final context and a realistic assessment of possibilities and probabilities, of what might happen, and what will happen. There are producers who aim to standardize a product for a market, yet according to seasonal
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variations, along with climactic and other conditions, there is an inevitable variety that other producers instead embrace and exploit. For the former, standardization is their selling point. For the latter, regional variation is their selling point, often along with exclusivity. Textile production often involves constantly changing product information and complex and variable web-like networks of personal and professional relationships. Designers through to printers need to maintain relationships to ensure effective commercial outcomes, in marked contrast to notions of outsourcing as “distance with disinterest.” Rather than any simplistic “order, pay, and walk away” arrangement, effective color management requires participants as partners, and commercial involvement in this field requires long-term commitment from all.
References Anderson, R.W., Krogh, P., 2011. Color Space and Color Profiles. dpBestflow—American Society of Media Photographers. Available at: http://www.dpbestflow.org/color/colorspace-and-color-profiles (accessed 01.09.11). Commission international de l’e´clairage, 2011. CIE—International Commission on Illumination: General information. CIE. Available at: http://www.cie.co.at/index.php/LEFTMENUE/ About+us/General+Information (accessed 28.08.11). Dawson, T.L., 2006. Digital colour management. In: Ujiie, H. (Ed.), Digital Printing of Textiles. Woodhead, Cambridge, England, pp. 163–179. Drew, J., Meyer, S.A., 2008. Color Management: A Comprehensive Guide for Graphic Designers. RotoVision, Hove, England. Hunter, R.S., 1975. The Measurement of Appearance. Wiley-Interscience, USA. HunterLab, 2008a. CIE L*a*b* color scale. Insight Color 8 (7), 1–4. Available at: www.hun terlab.com/appnotes/an07_96a.pdf. HunterLab, 2008b. Equivalent white light sources and CIE illuminants. Insight Color 17 (5), 1–5. Available at: www.hunterlab.com/appnotes/an05_05.pdf. ICC, 2006. ICC Specification—ICC.1: 2004-10. Available at: http://www.color.org/icc_ specs2.xalter (accessed 06.10.11). JISC Digital Media, 2008. Colour Management in Practice: Still Images. JISC Digital Media. Available at: http://www.jiscdigitalmedia.ac.uk/stillimages/advice/colour-managementin-practice/ (accessed 29.03.12). King, J.C., 2005. Tutorial on Color Management. Available at: http://www.color.org/info_pro files2.xalter. Loser, E., Tobler, H.-P., 2006. ICC color management for digital inkjet textile printing. In: Ujiie, H. (Ed.), Digital Printing of Textiles. Woodhead, Cambridge, England, pp. 180–198. Nickerson, D., 1936. The specification of color tolerances. Text. Res. J. 6, 505–514. Available at: http://trj.sagepub.com/cgi/doi/10.1177/004051753600601202 (accessed 28.10.11). Pantone LLC, 2011. Pantone Color Fabric Products. Pantone. Available at: http://www.pantone. com/pages/pantone/category.aspx?ca¼4 (accessed 10.11.11). SPGPrints. Flare Inks [Epson printheads]. Available at: http://www.spgprints.com/textile+print ing/screens%2C+lacquers+and+digital+inks/digital+inks?product_id¼95 (accessed 30.06.14). Spoonflower Inc., 2011. Spoonflower Help Center. Spoonflower. Available at: http://www. spoonflower.com/help#help4b (accessed 26.10.11).
Half drop repeat of droplet motif with abstract overlay.
Ink Jet Textile Printing. http://dx.doi.org/10.1016/B978-0-85709-230-4.00004-2 Copyright © 2015 Elsevier Ltd. All rights reserved.
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4.1
Introduction
Color is not a surface or an object. Color is the phenomenon of light reflected from a surface or object as it is received by the eye and processed by the brain. Light and surfaces will vary, but even the same conditions can result in differing mental interpretations and verbal descriptions by a viewer. As the mental interpretation of a physical process, “color is in the eye of the beholder,” and if there is more than one beholder, it is likely that their views will vary. This chapter aims to detail those issues in color management relevant to printing on textiles by ink jet, rather than being an exhaustive detailing of the entire field of color management. It considers both the production of color and the perception of color with the need for individuals to agree on the perception of a color when in a commercial situation and not all operating with calibrated equipment. As even different parts of an office can change the perception of a color due to the quality of the light in that area, this becomes particularly problematic when the individuals in question are located in different parts of the world.
4.2
The perception of color
The perception of color is complex, very individual, and could be categorized as “light” and “sight”: l
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“Light” concerns the production of color, perhaps by ink or light. “Sight” might be defined by two activities: reception by the eye and perception by an individual’s physiology and psychology.
Light enters the eye, and a corresponding electrical signal is received by the brain of an individual. The quality of this light may be affected by regional and seasonal differences in brightness, or by a physical location offering shading or reflection. These may all affect the perception of a particular color, but so might fatigue or even the emotional state of the individual. Depression or grief is often described as being a “dark” place. Humans will physiologically react to certain colors, and colors often have profound cultural as well as personal associations that affect this perception and any subsequent reaction to colored objects or spaces (Drew and Meyer, 2008, pp. 196-199). It is not enough to assume that an apparently appealing colorway will sell well. Seasonal variations are well understood in textile design, with summer ranges including lighter colors and textures compared to the heavier, dark warmth of winter. Effective color management can include cultural considerations of the intended marketplace as well as how the local light will affect a color. Definition is one thing, but appeal is another. Using color remains an art as well as a science.
4.3
The production of color
Color theory has a long and varied history, reflecting its importance to humans for identification, emotions, and increasingly measurement. For a subject intrinsically generated by mixing and blending, a lot of words try to define what can be very difficult to delineate. A “light” color could be either pale and washed out, or bright and
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cheerful. This section gives the working definitions used in this book. The definitions also introduce concepts involved in color and its reproduction. Some terms used have specifically defined meanings, but these are rarely used consistently outside of the scientific study of color. Color is as cultural as it is scientific, and other systems also exist for understanding color. The two systems used for color reproduction in ink jet printing are: l
l
CMYK (or a greenish-blue “cyan”; a bluish-red or pink “magenta”; a yellow; and a black, represented by a K). This system mixes these colors as pigments or dyes for color printed onto a surface. Printing usually begins with a white substrate, perhaps as paper or fabric. An area printed with a particular color ink reflects only that color’s wavelengths of light as color, absorbing or “subtracting” everything else. Ironically, the color produced is the color it rejects, or reflects. This is known as “subtractive” color mixing. It starts with all of the colors and removes or subtracts them until only the color needed is left. RGB (or red, green, blue). This system mixes these colors as light for the emission of color to a viewing screen. The computer monitor starts from no light or “black,” and adds colors in as light, mixing to make colors, then emitted as light on a screen as individual spots of red, green, and blue, so closely packed that the observer only sees their combined effect. This is known as “additive” color mixing. It starts with nothing and adds in color as needed.
A “gamut” refers to the range of colors capable of being reproduced by any system of color mixing. The gamuts of CMYK and RGB overlap; however, it is not an exact overlap, as each system begins from different starting points. CMYK using its magenta and RGB using its red will probably each mix a different color. Crucially, as these two systems work differently, they can mimic each other rather than exactly reproduce each other’s range of colors. In addition, many printers use “light” versions of the CMYK inks or an additional set of primaries, such as red, orange, blue, and a deep or dark black to extend the range of possible colors (SPGPrints, n.d.). Many design software programs use three variables in an interface, often in two steps to allow users to select colors. These often correspond to three principle activities involved in producing a color: l
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Hue Saturation Value
4.3.1
Color mixing: hue
“Hue” is perhaps the easiest to understand, as it often employs the words many know and have used since childhood, such as paint primaries of blue, red, or yellow. These are generally considered to be three primary colors, not including white and black as colors, that largely correspond to the three different types of cells that view and make color in the human eye. Essentially, mixing for hue is just adjusting the proportions of these primaries, even when adding “secondary” colors such as purple (red + blue), orange (red + yellow), or green (blue + yellow), or tertiaries: aqua ¼ primary blue + secondary green (blue + yellow). Differing cultural associations with hue must not be underestimated, particularly when it comes to describing or interpreting colors between different peoples.
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4.3.2
Ink Jet Textile Printing
Color dilution: saturation
“Saturation” describes how much of a color is in the color; this refers to the mixed hue, rather than the proportions of its component primaries. This isn’t quite as confusing as it sounds. The primary color, or “hue,” blue may be increasingly “desaturated” so that, proportionately, there is less blue in the mix than when it was 100% blue. Painting the graduations in color at twilight could range from using lots of blue and just a little water (saturated) to lots of water and just a little blue (desaturated). Water is a neutral or colorless carrier and thus does not technically adjust the hue, although it may appear more or less pale. Increasing saturation can appear to make a color brighter by making it more intense; saturation is also sometimes used to refer to the brightness or dullness of a color. One way of thinking of this is like a volume control for sound, with pale as quiet and bright as loud. Intensely saturated colors, particularly several used together, are often described as “loud.”
4.3.3
Color highlights: value
A “gray scale” version of an image uses a mix of black and white to represent the “value” of the colors. Value could be described as the amount of light a color absorbs or reflects, or how light or dark. Value is related, but only related, to color; a fully saturated light blue may be of the same value as a desaturated purple. Three dimensional drawing techniques use white or light colors as highlights to show where the light hits, or dark or black to create shade. A color can be moved along the value scale toward white, by adding white (often then described as tint and useful for highlights). Adding black will move a color in the opposite direction on the scale (described as a shade and used for shading). Adding a mix of black and white as a gray, described as a tone, will fine-tune values in the midpoint area.
4.4
Defining color
Red is considered one of the primary colors. However, colors vary; both blood and a lipstick could be described as red, but they are often not the same red. For consistency across media, the red must be defined so all can use the “same” red. Organizations such as the International Commission on Illumination (CIE) develop standards for the measurement and use of light and color (Commission international de l’e´clairage, 2011). “Metamerism” refers to the phenomenon whereby two colors that appear the same subsequently appear different when viewed under a different light source. The quality of light, as well as the amount, is enormously influential on the color information as received by the eye and must always be considered when presenting color for inspection and comparison. It is so important that several large retail chains specify particular commercial lighting products for use by both their product suppliers and their store builders (HunterLab, 2008b, p. 4). By 1931, CIE had developed one of the first mathematically defined color spaces, considering principally the perception of color. In 1993, commercial members
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founded the International Color Consortium (ICC), concerned with the production, particularly printing, of color. Color “models” such as RGB and CMYK can be described as “device-dependent,” so the default red or magenta depends on the device or ink that is generating that color. Rather than negotiating between these different methods, a better system is the use of a neutral “color space.” Based on the CIE system, the ICC color space is “device-independent.” It works as a translator or intermediary in a “profile connection space” using “look-up tables” (LUT) as reference for the different embedded languages used by input, display, and then output devices (JISC Digital Media, 2008). Interestingly, the ICC member companies did not try to monopolize or maximize market share by producing a “closed” or vendor specific system. Its “open” and cross-platform color management system has meant that, as a result, ICC-based color management has become the default standard in many industries (Loser and Tobler, 2006, p. 196).
4.4.1
Measuring difference: tolerance
A significant development in the CIE system was informed by the earlier work of Dorothy Nickerson and her measurements of fading between textile samples when testing for durability and quality (Hunter, 1975, p. 139; Nickerson, 1936). This matched color differences as steps within a particular hue as perceivable by humans, with a mathematical difference in the mathematical color space (HunterLab, 2008a, p. 1). A crucial component in the quality control of color, or color matching, is the determination of how much colors differ and how or why they differ, along with a permissible range of difference known as “tolerance.” Communicating degrees of difference is important for applications where color is used diagnostically as well as for commercial applications, where the consistency of color is an issue. “Tolerance” also recognizes the difficulties of trying to exactly match colors in differing viewing conditions, to a commercial agenda and timeframe. It can be understood that some color models such as RGB produce colors outside of the range or “out of gamut” of other color models such as CMYK, because the red in RGB and the magenta in CMYK were not the same color to begin with. If the color scale is considered as a mathematical space, then it can be understood how some colors can be produced that are outside of human perception. We might not see infrared or ultraviolet light, but this does not mean they do not exist or have no effect on us. This can also give false impressions of the number of visible colors that can be produced. Also, while there may be a large number of visible colors able to be produced, there are limits as to the steps between colors as distinguishable by the average human eye. A wide mathematical range of green is pointless if they all look the same to most observers. None of the color spaces also address the phenomena of related color, or how neighboring colors affect one another. This is particularly important in textile design, as the color viewed in isolation may look quite different when combined in a pattern among other colors. The ICC color space defines options of what to do if a color cannot be matched between two systems (ICC, 2006, pp. vii-viii). Each of the four “rendering intents”
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generally relates to a common requirement encountered in graphic design print production. Differing intents can be assigned within a single design file, reducing the unsatisfying compromises that a printer may be forced to make (King, 2005, p. 18). “Relative” or “absolute” colorimetric rendering prioritize individual colors and use gamut “clipping” to prioritize in-gamut colors, rendering out-of-gamut colors to the nearest possible hue: l
l
“Proof or relative colorimetric.” Reproduces out-of-gamut colors to the nearest reproducible hue. It preserves lightness but not saturation. “Match or absolute colorimetric.” Converts out-of-gamut colors to the nearest hue but sacrifices saturation and lightness.
Alternatively, “saturation” or “perceptual” rendering prioritizes the overall color scheme and uses gamut “compression” to prioritize the relationship between colors, shifting most if not all of the hues so as to reproduce all of them within a particular gamut (Anderson and Krogh, 2011). These types of rendering can be described as follows: l
l
“Graphic or saturation.” Maps the saturated primary colors in the source to those in the destination irrespective of differences in hue, saturation, or lightness. Often used for business display graphics. “Picture or perceptual.” Generally recommended for photographic reproduction because it applies the same gamut compression to all images, thus maintaining the same overall relative color rendering balance.
4.5
Workflow for the design, print, and sale of printed textiles
Color matching was always a challenge, even when comparing “hard copies” of painted and printed designs, both generated by the same “subtractive” color systems although using different media. RGB color production on an electronic monitor added a different “additive” color production method and a new viewing system, so color matching is now conducted across two very different systems of color production, with different media and even different monitors producing different colors. The need to standardize across a diverse range of color production systems is color management, with “calibration” as its principle method.
4.5.1
Workflow, with digital devices
The workflow for color management or coordination across the design, print, and retail of textiles may now include some or all of the following steps, and some repeatedly. Color management, with calibration, is essentially the attempt to secure a single agreed color all along this staged workflow and across all of these different devices and circumstances:
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Design generation Cameras: preferably producing images in “raw” (RAW) format, but otherwise including its own color determinants. Hand-drawn designs: perhaps colored with “subtractive” mixes of the red yellow blue (RYB) paint primaries. “Glare” from substrate and its color may affect color reproduction when scanned or photographed. Scanners: converting to RGB, usually according to manufacturer’s set of default color specifications. RGB-based monitor: file will be loaded for viewing, and both computer and monitor usually run according to their manufacturer’s set of default color specifications. Design manipulation: in a software program such as Adobe Photoshop, often using software’s default color management system. May conflict with color management in monitor used to view file. Design files: ink formulations for ink jet or screen-based print processes are not the same. Files should be prepared at the design stage to print effectively on either the ink jet or the screen-based systems, or both if sample printing with ink jet, but printing bulk runs with screen-based system. This will significantly affect design decisions such as the gamut to be used and will help to avoid significant and costly mistakes. Save and despatch: digital design file saved in one of various formats (e.g., TIFF, PDF) to send to printer. Each format has its own color specifications. l
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Print production Printer software: converting file as necessary for CMYK-based production system, such as ink jet printers. Ink: colors may vary between manufacturers. Sampling: printing onto cloth that has been prepared for print by bleaching, dyeing, and pretreating with chemical agents to varying degrees according to the cloth. Cloth and climate: circumstantial factors such as age of the cloth, temperature, and humidity of the surroundings may affect color uptake and appearance. Fixing and finishing: these may affect color appearance, both immediately and in the long term. Quality control: on-site, or swatches sent remotely. Color viewing conditions will vary between countries and may vary between different spots in the same office, according to illuminating, shading, and reflecting conditions both inside and from outside through doors and windows. Conversion: if sample is ink jet but bulk production is by screen-based print system. Ink jet printing uses “process” color, mixing as required. Screen-based printing is a “spot” color system, premixing colors beforehand. Fixing, finishing, storage: bulk production is more likely to be transported by sea. Finishing may include treatments to preserve and protect appearance of textiles during transportation.
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Retail Wholesale purchase: often from sample swatches. Bulk production must match these samples. Selection: some international brands strive to standardize color globally, others stock color selections according to local tastes, as defined by local culture and quality of light.
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Marketing: increasingly includes color images of items across wide range of media platforms. Websites are RGB, with newsprint and gloss-stock magazines both CMYK, but on very different substrates. Retail: increasingly occurs at night as well as day. Stores must consider lighting specific to their location to ensure color appeal throughout long opening hours. Retail websites: viewed through different browsers and on different RGB monitors, most set to their various manufacturers’ default color specifications. Returns after remote purchasing due to dissatisfaction will impact the brand profile as well as the profits. Postpurchase consumer care: includes a wide range of washing and drying techniques, machines, and products. All can have an impact on the short- and long-term appearances of color.
4.6
Calibration
Each of the devices in the digital workflow has its own system of color management. To “calibrate” means to check against a definitive scale used to synchronize all devices. The scale can be a printed example, or could be a set of digital definitions. Calibration involves analysis of what a scanner or monitor or ink manufacturer may consider to be, for example, a standard red against where those reds sit in a master “look-up” table. The comparison can occur either by eye comparing a monitor to the printout or by using a colorimeter or spectrophotometer to measure color, working in conjunction with specialist software packages. The most effective and efficient use of calibration for color will benefit from knowledge of how different systems make color, how color is measured and defined, and how to analyze its importance to the final printed output. Calibration of monitors may be achieved by the use of small “clip-on” spectrophotometers operated with specific software. The calibration of scanners requires the provision of special test cards as a set of multicolored panels whose color coordinates are known. Digital printers can be fed with data for a similar test card; the printed result can then be measured photometrically. Both systems require the provision of appropriate software.
4.6.1
Automated calibration
The selection of a calibration system is often made on price, but should also consider some other factors, as any system is only as effective as its operator. Mundane factors should not be overlooked. Calibration of the monitor must be considered in conjunction with the color management system used by the design software and by the computer itself. These may need to be disabled, and the easily accessible user settings such as for brightness and contrast should not be forgotten. “CRT” or bulky, older cathode ray tube monitors produce color differently to newer, slimmer, liquid crystal display “LCD” monitors (Dawson, 2006, p. 163). Relocating the monitor is likely to result in different viewing conditions, so color may again look different. Appropriate purchases require some research, including background knowledge to explain the significance of some of the more technical terms. It may pay to purchase the best profiling equipment and software within budget, but it will only pay if it is used correctly. Not
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only its ease of use and effectiveness should be discussed with others in the same industry, but also consideration given to how easily scheduling for its use can be fitted into an existing organizational schedule. “Frequent” calibration can be required monthly or even weekly, due to time-related “drift” (Dawson, 2006, p. 171). The knowledge of how to use any system should be shared among several employees, although the responsibility for upkeep and updating should rest with one employed position. As well as the product offering, the service offering behind the system and software should be considered. Once purchased, what is the access to advice for maintenance and use, and how understandable and costly is any such advice? Longevity and experience may mean good service, or instead complacency, with new entrants to the field keener to secure market position. The bottom line is that if the product is not used properly, it is often a waste of money.
4.6.2
“Systemic” calibration
Automated calibration maintains professional accuracy, but lacks the flexibility needed in a changing commercial situation often dealing with some unknowns. Each time something is altered anywhere in the chain of input, display, or output, all the devices in an entire system may require recalibration. Printing on textiles occurs across a wide range of substrates, and conditions may vary even between batches of the same substrate, for example, due to age or storage. Such additional complications are why many shy away from even the mention of calibration. Continuous perfect calibration may prove impossible, but an appropriate level of calibration maintained across a system offers the best chance to reduce repetition and waste, while increasing the frequency of a satisfying result. Effective calibration for color management does not solely involve standardizing across devices, but recognizes that these operate within a workflow. The final print output onto cloth for retail is the true measure of calibration. As a commercial product, it is upon the sales based on its appearance that the success or failure of the entire print workflow is judged. The end therefore is where calibration across the workflow could begin.
4.7
Color print production
One rarely asked but significant question is why one color must match another. Asking this question allows for an appropriate allocation of resources according to the response, as there are degrees of justification for expensive and extensive calibration practices. In “batch matching,” there may be little or no allowance for difference and tolerance, particularly for applications such as military parade uniforms or rolls of curtaining. In this case, calibration deserves the appropriate amount of time, money, and attention. Some choose to recognize discrepancies between processes and colors as part of the creative process and an inherent part of print production. For color schemes, matching may be more relevant across the relative colors contributing to the overall complimentary look, along with a fast and financially effective color
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solution. Detailed color profiling also offers greater accuracy, but does not increase the overall range of the color gamut. Profiling does not add different color gamuts together. It disregards colors not reproducible by all, leaving the reduced range of only the shared hues; however, avoiding calibrating will not change this.
4.7.1
Design generation
Design programs such as Adobe Photoshop and Illustrator or others specifically tailored for textile design are usually formulated in two ways, reflecting the “in computer” or “by hand” methods now used for designing textiles. Manipulating images sourced from a camera or scanned files usually involves software programs with origins in photographic editing techniques such as Adobe Photoshop: l
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These programs tend to be “raster” based—that is, the picture is built with individual pixels arranged in a grid format. Manipulation often includes picture editing and color balancing before putting the image into repeat, or fitting the image to a particular size or shape for a “placement” print. Placement prints are similar to those seen on the front of T-shirts but are not limited to this format or size. Pixels present a challenge when scaling up designs. Unless originals are scanned or set at a very high resolution, designs can “pixelate,” leaving “jaggies,” or jagged or stepped edges if the image is enlarged so far that the individual square pixels of the image can now be seen. Camera and scanned images often show color that at a distance looks acceptable, yet the color mixing occurs at a pixel level. “Dithering” uses several colors to simulate a single color. At a distance this is not an issue, but if the file is to be printed as a large format, it can become very noticeable. Working directly from a complex image involving significant numbers of colors, gradients, and fine detail, this digital design pathway aligns itself more easily with ink jet printing. Broadly speaking, it lends itself less to conversion for screen-based printing, along with the established industry practices for textile printing, such as multiple colorways.
Designing directly into computer software is essentially sophisticated drawing; for example, many of the tools in Adobe Illustrator relate directly to their real-life counterparts, such as pencils and pens: l
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Drawing programs such as Adobe Illustrator tend to be “vector” based, recognizing that drawing paper is rarely a grid full of squares, but blank to accommodate freeform curves and random angles. Vector-based graphics work much like drawing a line between two points, defined but not restricted by the mathematics of an xy grid. This enables vector images to be enlarged to any size with no loss of resolution. Colors tend to be selected within the software, giving a “clear and clean” effect. Fewer colors tend to be used overall, often as a set palette of colors for a particular design, which makes it easier to change hues and generate multiple colorways. Ink jet printing can be the most effective at capturing a “painterly” style, involving washes and gradients. Overall, however, this design pathway tends to be more aligned to established screen-based methods of textile print production and therefore print design.
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If conversion for printing is done by software for raster image processing, then this, as well as the format in which the converted file is saved, can also be a source of color shift.
4.7.2
Monitors
The monitor tends to act as a “filter” for images between the stages of design generation and print production. As a result, the monitor is often used as the “fulcrum” from which the calibration process is leveraged along the chain of production. The monitor and indeed the entire supply chain may be calibrated and use the most sophisticated fabric simulations, but success will still be judged by the final product. This will eventually be viewed in a range of different lighting conditions, although all initial shade comparisons should be assessed under standard lighting conditions, such as in a matching cabinet fitted with standard “daylight,” or store-specified, fluorescent tubes. Differences of opinion among viewers across different cultures will also affect the result. Communication is essential for calibration, particularly if it includes a degree of realism. “Tolerance” is a measure of how much difference to accept, often forced by time shortages. Politics may be involved in color matching; aiming for accuracy maintains standards but good relationships among all in the supply “network” also gives the best chance of accuracy. In commercial negotiations, there is an art to knowing when to push for more and how much difference to accept. “Tolerance” is a commercial decision, as good commerce grows long-term profit from professional relationships.
4.7.3
Scanners and cameras
Many textile designers still produce designs by hand, often scanning artwork into a computer program for clean-up and manipulation into a repeat. Colors can be immediately compared to an original and any necessary adjustments made. Scanners, as well as printers, tend to be more reliable than computer monitors in terms of “time-related” drift in color, but a regular program for checking color calibration is still advised as best practice (Dawson, 2006, p. 171). Calibration for scanners usually involves an ICC profile and can occur with purchased printed test images that include a gray scale as well as a range of colors and some test images. Each of these colors has specific and measurable mathematical coordinates. The resolution, or size, of an image means how much information it holds and is also affected by the storage format for that information. Cameras, scanners, monitors, and ink jet printers “sample” information in steps, rather than as a continuous flow. “Samples per inch” or “spi” might be a better term than “dpi” or “ppi” (dots or pixels per inch). It is around this that issues and confusion about resolution revolve. Apparently high resolutions may not be the “optical” resolution, which is how many samples are taken from an inch, but an “interpolated” resolution. This inserts estimated information between the samples, giving an impression of higher resolution without actually taking any more detail from the original. The ideal resolution for an image depends on its final output. The measure of “good enough” is truly good enough for images that will only be printed as small, or serve as small elements in an overall design. Data storage has reduced in cost,
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and so “master” images or final files justify being captured and archived at the highest possible resolution. Some textile designers use digital cameras as their sketchbook and incorporate these images directly into their work. Each model or brand has its own way to capture and hold image information. Such diversity brings the risk that original files may no longer be accessible as various formats become obsolete. Formats such as JPEG (developed by the “Joint Photographic Experts Group”) or TIFF (“Tagged Image File Format,” offering less compression and more variety of storage than JPEG) were developed as standards for digital image files in response to such issues. “RAW” is a format available on most middle to higher-end digital cameras. The term Raw or RAW does not stand for anything, but means just that, raw or unprocessed. It refers collectively to image data, including color data, that has been minimally processed and compressed by any suitably enabled digital camera or scanner. It does not refer to a particular software or file format. Instead, the raw file is like a digital negative; it is not immediately usable as an image but contains all the information necessary to generate one. Conversion from raw data for image editing and storage means an extra step in the workflow and usually results in a larger file. Over-compressing a larger file results in some information being lost. Different file formats compress to different degrees, with the ideal being a balance between “lossy” or “lossless” compression compared to human perception of this according to the final printed format. Good results also mean getting information about the final printing process before creating the initial images.
4.7.4
Paper printers
Many designers find a “proof” stage with a desktop paper printer useful for intermediary print development and checking. Looking at the image on paper rather than a screen usually results in faster and more effective quality checks, particularly for the “flow” in a repeat. Calibration can be attempted, despite the likely additional light primaries used in many commercial scale textile printers. Two color profiles, and thus two copies of the same file may be developed, with one calibrated for the test paper print and the second for the cloth print. The number of variables involved in textile printing can result in many different profiles and calibrations. Developing a system of labeling profiles that includes as much immediately accessible information about the specifics involved in that particular profile may require some interesting abbreviations, but will avoid time-wasting and frustration.
4.7.5
Color maps, charts, tables, matrix, or matrices
Printers can supply printed versions of “look-up” tables as charts that can be used to calibrate back across the design workflow, either by eye or by equipment and software—some also offer related software (Spoonflower Inc., 2011). No matter what descriptive term is used, the charts are usually grids, with each square containing incrementally altering blends of colors. Some printers add in “light” versions of the standard CMYK inks to increase the range of producible colors. More primaries,
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such as a cyan and a light cyan, require more squares. These charts can be timeconsuming to generate, and it is worth considering the format used. All charts and standardized design or image test files should be printed on and finished as close as possible to the standard materials, methods, and machinery used for bulk production. Yarn structure with slubs or hairiness, and weave or knit structure can also affect image graininess or “noise,” and different types of inks may produce slightly different colors. Whether synthetic or natural in origin, fiber is subject to environmental factors such as light, humidity, and time, with later bulk lots possibly affected differently. The physical size of the squares themselves is significant, as too small may not generate enough visual information for the observer, but too large may cause the overall grid to be unwieldy. Blending increments can range between 2% and 10%. Greater steps than this may leave too many gaps, but equally the smaller the increment, the more numerous the squares and the larger and more unwieldy the grid. Much like software-based profiling and calibration, while larger files with more information offer greater accuracy, they also take much more time and space. The grids may be printed as large sheets or cut into smaller individual grids, depending on individual working methods. Such grids are also only a guide, as color is rarely generated in neatly divisible numbers. The color charts can also be useful when developing colorways. A dull mid-gray card viewer with corresponding square windows can be useful when assessing single colors as well as viewing colors in a scheme. The grids can be used to explore the tints and shades of individual colors to “push” a scheme that bit further. Sample design or image files are additionally recommended for test and analysis printing, and should be selected with unashamed bias. The “standard” will reflect individual or company design preferences. It should include some challenging areas of browns, dark navy, and black, including at least one large area, some saturated red, green, and blue, neutral grays and gradients, and some flesh tones, perhaps from a human portrait. It may also be relevant to test print using files saved in different formats as well as discussing which formats are most suitable with the printer. Another popular tool specifies colors using a recognized color system such as the Pantone system. Pantone has partnered with textile dye producer Clariant to offer dye formulations for fabric that should match specific Pantone colors (Pantone LLC, 2011). Highly accurate, electronically measured color matching using Pantone’s textile-based system would, however, require the use of Clariant products and specific fabrics, finishing, and pretreatments in order to match the Pantone sample swatch exactly, even before differences in viewing conditions are considered. Ironically, using the paper-based Pantone products developed for graphic designers as many do, may result in a more realistic outcome due to the clear awareness that there are two different methods as well as different substrates being compared. “Uncoated” paper may give a better result when used in conjunction with most textiles, although the smooth shine of “coated” may be more aligned to fabric types with a sheen such as for swim or performance wear. Printed charts or chips will deteriorate in quality depending on age and storage, even if kept stored away from light. They will need to be refreshed periodically, especially if any component is changed in the print workflow of fabric/pretreatment/ink/finishing.
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4.7.6
Ink Jet Textile Printing
Ink jet textile printers
Much commercial manufacturing is dedicated to eradicating differences, but standardization can be difficult to maintain for many valid reasons. Outsourcing printing, particularly internationally, has come to be seen as a normal part of a supply chain. “Supply chain” is the term most commonly used to describe the commercial, mutually reliant relationships contributing to a workflow, but Web or network may be a more useful metaphor. These relationships extend out beyond the final printer of the textile to include its ink supplier, even the software controlling its machinery. If an ink brand has to change, then colors may change, and the calibration of the entire system may consequently have to be adjusted. Any change in significant factors in the print workflow may change the color outcome of the print, causing color management to be adjusted accordingly. Information about any changes will come from positive and well-managed relationships with suppliers along the various networks of supply. Ink-jet printing is not a simple substitute for screen-based printing. If the final output is to be on a screen-based system, then the initial design, even if completed on computer software and proofed on an ink-jet printer, must be designed around the restrictions that define screen-based printing, such as a smaller range of solid colors, restricted by the number of screens. Proofing on an ink-jet printer means there will also be additional restrictions, such as its limited range of inks. Conversely, those used to developing designs for screen-based printing methods need to understand the differences inherent in the ink jet method. Ink jet methods can be very efficient and economical with ink. This makes good claims for environmental sustainability but also offers some challenges to print and design expectations. Due to issues such as ink density, extremely dark, bright, or saturated colors can be difficult to achieve, as are large solid areas of dark colors. Subtle graduations in shade do not always replicate as well as they appear on the monitor, and toning down expectations as well as colors may be a good policy in a commercial situation, while still experimenting with new technological developments.
4.8
Conclusion
The personalized nature of the experience of color questions both our ability and our need to control color. Much of the need for calibration is about control, and this is understandably necessary when mistakes can be extremely costly. However, calibration across all of the components in the supply chain for ink jet printing on textiles is enormously difficult and remains tricky at best, so it might be argued that this need for control can also be costly. Sometimes a valid question is whether there is a sound financial reason for the control, or whether it is in fact driven by emotion. In color management, context is more crucial than control. Must a particular product match repeatedly across the ranks, or briefly across the racks? Calibration needs to be undertaken with an understanding of the final context and a realistic assessment of possibilities and probabilities, of what might happen, and what will happen. There are producers who aim to standardize a product for a market, yet according to seasonal
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variations, along with climactic and other conditions, there is an inevitable variety that other producers instead embrace and exploit. For the former, standardization is their selling point. For the latter, regional variation is their selling point, often along with exclusivity. Textile production often involves constantly changing product information and complex and variable web-like networks of personal and professional relationships. Designers through to printers need to maintain relationships to ensure effective commercial outcomes, in marked contrast to notions of outsourcing as “distance with disinterest.” Rather than any simplistic “order, pay, and walk away” arrangement, effective color management requires participants as partners, and commercial involvement in this field requires long-term commitment from all.
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