- Email: [email protected]
Digital image signal processing
Book reviews
"Digital Image Signal Processing", by F. M. Wahl, Artech House Inc., 685 Canton Street, Norwood, MA 02062, U.S.A. 1987, viii+183 pp., ISBN 0-89006-227-7
The book is the straight English translation of Digitale Bildsignalverarbeitung published in 1984 by Springer-Verlag, with no change or addition. The approach and the content of the book more or less correspond to the aims expressed in the foreword to the original version, i.e. to give an introduction to digital image processing with great emphasis on the signal aspects and with the help of many simulation examples (mostly developed by the author and his group) to link theory with intuition. Therefore, all the aspects related to image analysis and understanding, to 3-D image processing and to computer vision are explicitly excluded from the contents. For this reason, in conjunction with the fact that the book is four years old (the references too being dated no later than 1983, with a minority more recent than 1980) the reader should not expect to find any recent research advance or state-of-the-art updating in the field. On the other hand, the book represents a sort of "compendium" of fundamentals of 2-D signals and the systems and of classical techniques for image processing. According to the chosen approach, about one third of the text (Chapter 2) is devoted to an extensive presentation of signal theory in two dimensions for the continuous and discrete case: the Fourier transform with properties and examples, image sampling and reconstruction in the deterministic and stochastic case, DFT with its properties, applications, and a radix-2 (l-D) FFT algorithm, a brief mention to other discrete transforms, including Karhunen-Loeve. Though not complete nor uniform in the depth level, the coverage provides a great deal of the needed information for the reader approaching the field: he will be helped by the pictorial examples and probably a bit discouraged by the heavy notation and the numerous formulae.
185
Image enhancement and restoration are considered in Chapters 3 and 4. For subjective image improvement, a set of basic pixel and local operators and spatial frequency filterings is illustrated for gray scale manipulation, noise smoothing and edge sharpening, and a very short discussion is given of nonlinear techniques (e.g. median filtering) and of space-variant, or signaldependent, smoothing, as well as of homomorphic processing. In the chapter devoted to image restoration, after a short discussion of the linear model with additive noise, the basic idea of inverse filtering is presented and then the approaches of the constrained optimum filter and of Wiener filtering are extensively described in two sections quite dense of formulae, concepts and examples. Also space-variant and signal-dependent restoration techniques are briefly explained, again with the help of some examples. The last two chapters deal with segmentation and some image analysis methods. Segmentation is treated from the viewpoint of very basic techniques, divided into region-oriented (fixed and variable threshold, region growing) and edgeoriented (classical and intensity weighted gradient operators, Hueckei and Shaw edge models, contour following) methods, strictly with a bottom-up approach. In ten pages are then mentioned some image analysis tools, like pixel labeling, simple binary feature measures, Fourier and moment representations, matched filtering, local spectrum and co-occurrence matrices. A short appendix on the Hankel transform and a set of 237 references conclude the volume. As a general comment, the choice of the presentation level for the various subjects, and therefore of the needed reader prerequisites, does not seem uniform throughout the book: sometimes details are presented that can be appreciated only by an experienced reader, sometimes important techniques are only mentioned. The analytical apparatus may be considered heavy by many non specialists (though compensated by the many simulation examples), as well as the frequent reference pointing used to keep short a presentation. Vol. 17, No. 2, June 1989
186
Book reoiews
There are also various minor errors (one in a section title), that however do not diminish the great value of the book seen as a sort o f " p a n o r a m i c introduction, with inhomogeneities" to a basic subset of the wide and fast-evolving field of image processing. Certainly, the book does not represent (as it did not in 1984) a novelty in the panorama of image processing books, where obsolescence is soon induced by such a fast evolution rate. This undesirable effect is partly avoided in this case, due to the choice of the author to concentrate a large amount of basic signal aspects (not all: topics
often included in this set, like vision psychophysics, image formation and representation/coding, sequence/motion analysis, image processing architectures and computer graphics are not covered) in a thin, handy volume.
"Signal Analysis and Estimation", by R. L. Fante,
reader to check how he can handle the basic notions. This is why I think this book can be very useful for engineers working in signal processing area, not because of the originality of its content, but because it presents it very practically, including a lot of examples. But I am not sure it can be easily used by students. Indeed, as mentioned before, the author wants to avoid any sophisticated mathematical background. This is a very interesting approach, showing that he is more interested in the application of the tools to signal processing problems rather than in the development of a beautiful mathematical theory. But, in some cases, this can be perhaps dangerous, and I think it is particulary true for Chapter 2, dealing with the Dirac "function". I absolutely agree with a physical presentation of it and Dirac's introduction, although mathematically absolutely heretic, provides an interesting idea of what this notion represents. But using symbolic writing with distribution can be very dangerous: it is well known that some relations, although not meaningful for functions, can be extended to distributions, but others absolutely cannot be generalized. The knowledge qf the basic theory makes these limits clearer. For example, relations (23) and (24), p. 45, can be easily misused. This is true too for relation (37b), p. 48, and formula (44), containing the product of two Dirac functions. Some equations
Textron Defence Systems, Wilmington, Massachusetts, U.S.A. Publishers: John Wiley & Sons Ltd., Baflins Lane, Chichester, West Sussex, PO19 1UD, United Kingdom, 1988, xiv+448 pp., ISBN 0-471-62425-X This book contains all the fundamentals and basic materials about deterministic continuous and discrete signals, Fourier transform, random signals and estimation. The author decided to use a formulation and a presentation for practicians, substituting generally physical and intuitive explanations to mathematical definitions or statements. For example, he shows that Fourier series gives the best mean square fit of a periodic function by minimizing a quadratic form (p. 15), but he does not describe it as an expansion over a complete set of orthonormal functions in an Hilbert space. The notion of probability is introduced starting from very practical situations, as flipping a die. Each notion is illustrated by many examples relative to different domains and applications. These examples contain numerical values, allowing the reader to understand how the basic results can be effectively applied practically: for instance, example 4.1 p. 134 shows clearly how band limitation affects the temporal behaviour of a signal. Numerous exercises at the end of the chapters provide additional illustrations and allow the Signal Processing
Professor C. BRACCINI Instituto di Elettrotechnica Universita di Genova Via Froncesco Causa 13 1-16145 Genova Italy
"Digital Image Signal Processing", by F. M. Wahl, Artech House Inc., 685 Canton Street, Norwood, MA 02062, U.S.A. 1987, viii+183 pp., ISBN 0-89006-227-7
The book is the straight English translation of Digitale Bildsignalverarbeitung published in 1984 by Springer-Verlag, with no change or addition. The approach and the content of the book more or less correspond to the aims expressed in the foreword to the original version, i.e. to give an introduction to digital image processing with great emphasis on the signal aspects and with the help of many simulation examples (mostly developed by the author and his group) to link theory with intuition. Therefore, all the aspects related to image analysis and understanding, to 3-D image processing and to computer vision are explicitly excluded from the contents. For this reason, in conjunction with the fact that the book is four years old (the references too being dated no later than 1983, with a minority more recent than 1980) the reader should not expect to find any recent research advance or state-of-the-art updating in the field. On the other hand, the book represents a sort of "compendium" of fundamentals of 2-D signals and the systems and of classical techniques for image processing. According to the chosen approach, about one third of the text (Chapter 2) is devoted to an extensive presentation of signal theory in two dimensions for the continuous and discrete case: the Fourier transform with properties and examples, image sampling and reconstruction in the deterministic and stochastic case, DFT with its properties, applications, and a radix-2 (l-D) FFT algorithm, a brief mention to other discrete transforms, including Karhunen-Loeve. Though not complete nor uniform in the depth level, the coverage provides a great deal of the needed information for the reader approaching the field: he will be helped by the pictorial examples and probably a bit discouraged by the heavy notation and the numerous formulae.
185
Image enhancement and restoration are considered in Chapters 3 and 4. For subjective image improvement, a set of basic pixel and local operators and spatial frequency filterings is illustrated for gray scale manipulation, noise smoothing and edge sharpening, and a very short discussion is given of nonlinear techniques (e.g. median filtering) and of space-variant, or signaldependent, smoothing, as well as of homomorphic processing. In the chapter devoted to image restoration, after a short discussion of the linear model with additive noise, the basic idea of inverse filtering is presented and then the approaches of the constrained optimum filter and of Wiener filtering are extensively described in two sections quite dense of formulae, concepts and examples. Also space-variant and signal-dependent restoration techniques are briefly explained, again with the help of some examples. The last two chapters deal with segmentation and some image analysis methods. Segmentation is treated from the viewpoint of very basic techniques, divided into region-oriented (fixed and variable threshold, region growing) and edgeoriented (classical and intensity weighted gradient operators, Hueckei and Shaw edge models, contour following) methods, strictly with a bottom-up approach. In ten pages are then mentioned some image analysis tools, like pixel labeling, simple binary feature measures, Fourier and moment representations, matched filtering, local spectrum and co-occurrence matrices. A short appendix on the Hankel transform and a set of 237 references conclude the volume. As a general comment, the choice of the presentation level for the various subjects, and therefore of the needed reader prerequisites, does not seem uniform throughout the book: sometimes details are presented that can be appreciated only by an experienced reader, sometimes important techniques are only mentioned. The analytical apparatus may be considered heavy by many non specialists (though compensated by the many simulation examples), as well as the frequent reference pointing used to keep short a presentation. Vol. 17, No. 2, June 1989
186
Book reoiews
There are also various minor errors (one in a section title), that however do not diminish the great value of the book seen as a sort o f " p a n o r a m i c introduction, with inhomogeneities" to a basic subset of the wide and fast-evolving field of image processing. Certainly, the book does not represent (as it did not in 1984) a novelty in the panorama of image processing books, where obsolescence is soon induced by such a fast evolution rate. This undesirable effect is partly avoided in this case, due to the choice of the author to concentrate a large amount of basic signal aspects (not all: topics
often included in this set, like vision psychophysics, image formation and representation/coding, sequence/motion analysis, image processing architectures and computer graphics are not covered) in a thin, handy volume.
"Signal Analysis and Estimation", by R. L. Fante,
reader to check how he can handle the basic notions. This is why I think this book can be very useful for engineers working in signal processing area, not because of the originality of its content, but because it presents it very practically, including a lot of examples. But I am not sure it can be easily used by students. Indeed, as mentioned before, the author wants to avoid any sophisticated mathematical background. This is a very interesting approach, showing that he is more interested in the application of the tools to signal processing problems rather than in the development of a beautiful mathematical theory. But, in some cases, this can be perhaps dangerous, and I think it is particulary true for Chapter 2, dealing with the Dirac "function". I absolutely agree with a physical presentation of it and Dirac's introduction, although mathematically absolutely heretic, provides an interesting idea of what this notion represents. But using symbolic writing with distribution can be very dangerous: it is well known that some relations, although not meaningful for functions, can be extended to distributions, but others absolutely cannot be generalized. The knowledge qf the basic theory makes these limits clearer. For example, relations (23) and (24), p. 45, can be easily misused. This is true too for relation (37b), p. 48, and formula (44), containing the product of two Dirac functions. Some equations
Textron Defence Systems, Wilmington, Massachusetts, U.S.A. Publishers: John Wiley & Sons Ltd., Baflins Lane, Chichester, West Sussex, PO19 1UD, United Kingdom, 1988, xiv+448 pp., ISBN 0-471-62425-X This book contains all the fundamentals and basic materials about deterministic continuous and discrete signals, Fourier transform, random signals and estimation. The author decided to use a formulation and a presentation for practicians, substituting generally physical and intuitive explanations to mathematical definitions or statements. For example, he shows that Fourier series gives the best mean square fit of a periodic function by minimizing a quadratic form (p. 15), but he does not describe it as an expansion over a complete set of orthonormal functions in an Hilbert space. The notion of probability is introduced starting from very practical situations, as flipping a die. Each notion is illustrated by many examples relative to different domains and applications. These examples contain numerical values, allowing the reader to understand how the basic results can be effectively applied practically: for instance, example 4.1 p. 134 shows clearly how band limitation affects the temporal behaviour of a signal. Numerous exercises at the end of the chapters provide additional illustrations and allow the Signal Processing
Professor C. BRACCINI Instituto di Elettrotechnica Universita di Genova Via Froncesco Causa 13 1-16145 Genova Italy