SPIE PRESS This full-color book begins with a detailed study of the nature of color images–including natural, multispectral, and pseudocolor images–and covers acquisition, quality control, and display of color images, as well as issues of noise and artifacts in color images and segmentation for the detection of regions of interest or objects. The book is primarily written with the (post-)graduate student in mind, but practicing engineers, researchers, computer scientists, information technologists, medical physicists, and data-processing specialists will also benefit from its depth of information. Those working in diverse areas such as DIP, computer vision, pattern recognition, telecommunications, seismic and geophysical applications, biomedical applications, hospital information systems, remote sensing, mapping, and geomatics may find this book useful in their quest to learn advanced techniques for the analysis of color or multichannel images. P.O. Box 10 Bellingham, WA 98227-0010 ISBN: 9780819485649 SPIE Vol. No.: PM206 Library of Congress Cataloging-in-Publication Data Rangayyan, Rangaraj M. Color image processing with biomedical applications / Rangaraj M. Rangayyan, Begona Acha, Carmen Serrano. p. ; cm. -- (Press monograph 206) Includes bibliographical references and index. ISBN 978-0-8194-8564-9 1. Imaging systems in medicine--Data processing. 2. Diagnostic imaging-- Digital techniques. 3. Color photography. 4. Image processing. I. Acha, Begona. II. Serrano, Carmen, Ph. D. III. Title. IV. Series: SPIE monograph ; 206. [DNLM: 1. Image Processing, Computer-Assisted--methods. 2. Staining and Labeling--methods. W 26.55.C7] R857.O6R36 2011 616.07'54--dc23 2011021979 Published by SPIE P.O. Box 10 Bellingham, Washington 98227-0010 USA Phone: +1 360.676.3290 Fax: +1 360.647.1445 Email: [email protected] Web: http://spie.org Copyright © 2011 Society of Photo-Optical Instrumentation Engineers (SPIE) All rights reserved. No part of this publication may be reproduced or distributed in any form or by any means without written permission of the publisher. The content of this book reflects the work and thoughts of the author(s). Every effort has been made to publish reliable and accurate information herein, but the publisher is not responsible for the validity of the information or for any outcomes resulting from reliance thereon. Printed in the United States of America. First Printing Bellingham, Washington USA Dedication To Mayura, my wife, for adding color to my life Raj To my father Bego To my big and colorful family Carmen Todo es de color (Lole y Manuel) Contents Preface xi Acknowledgments xvii Symbols and Abbreviations xxi 1 The Nature and Representation of Color Images 1 1.1 Color Perception by the Human Visual System . . . . . . . . 3 1.1.1 The radiant spectrum . . . . . . . . . . . . . . . . . . 4 1.1.2 Spectral luminous efficiency . . . . . . . . . . . . . . 7 1.1.3 Photometric quantities . . . . . . . . . . . . . . . . . 7 1.1.4 Effects of light sources and illumination . . . . . . . . 10 1.1.5 Color perception and trichromacy . . . . . . . . . . . 12 1.1.6 Color attributes . . . . . . . . . . . . . . . . . . . . . 12 1.1.7 Color-matching functions . . . . . . . . . . . . . . . . 14 1.1.8 Factors affecting color perception . . . . . . . . . . . . 17 1.2 Representation of Color . . . . . . . . . . . . . . . . . . . . . 30 1.2.1 Device-independent color spaces and CIE standards . 31 1.2.2 Device-dependent color spaces . . . . . . . . . . . . . 38 1.2.3 Color order systems and the Munsell color system . . 52 1.2.4 Color-difference formulas . . . . . . . . . . . . . . . . 53 1.3 Illustrations of Color Images and Their Characteristics . . . . 60 1.3.1 RGB components and their characteristics . . . . . . 60 1.3.2 HSI components and their characteristics . . . . . . . 62 1.3.3 Chromatic and achromatic pixels . . . . . . . . . . . . 65 1.3.4 Histograms of HSI components . . . . . . . . . . . . 73 1.3.5 CMYK components and their characteristics . . . . . 76 1.4 Natural Color, Pseudocolor, Stained, Color-Coded, and Mul- tispectral Images . . . . . . . . . . . . . . . . . . . . . . . . . 81 1.4.1 Pseudocolor images of weather maps . . . . . . . . . . 84 1.4.2 Staining . . . . . . . . . . . . . . . . . . . . . . . . . . 84 1.4.3 Color coding . . . . . . . . . . . . . . . . . . . . . . . 88 1.4.4 Multispectral imaging . . . . . . . . . . . . . . . . . . 91 1.5 Biomedical Application: Images of the Retina . . . . . . . . . 97 1.6 Biomedical Application: Images of Dermatological Lesions . . 99 1.7 Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 vii viii Color Image Processing 2 Acquisition, Creation, and Quality Control of Color Images 103 2.1 Basics of Color Image Acquisition . . . . . . . . . . . . . . . 103 2.1.1 Color image sensors . . . . . . . . . . . . . . . . . . . 103 2.1.2 Dark current correction . . . . . . . . . . . . . . . . . 106 2.1.3 Demosaicking . . . . . . . . . . . . . . . . . . . . . . . 106 2.1.4 White balance . . . . . . . . . . . . . . . . . . . . . . 109 2.1.5 Color transformation to unrendered color spaces . . . 110 2.1.6 Color transformation to rendered color spaces. . . . . 115 2.2 Quality and Information Content of Color Images . . . . . . 117 2.2.1 Measures of fidelity . . . . . . . . . . . . . . . . . . . 118 2.2.2 Factors affecting perceived image quality: contrast, sharpness, and colorfulness . . . . . . . . . . . . . . . 121 2.3 Calibration and Characterization of Color Images . . . . . . 124 2.3.1 Calibration of a digital still camera. . . . . . . . . . . 125 2.3.2 Characterization of a digital still camera. . . . . . . . 127 2.3.3 International Color Consortium profiles . . . . . . . . 128 2.4 Natural and Artificial Color in Biomedical Imaging . . . . . . 129 2.4.1 Staining in histopathology and cytology . . . . . . . . 131 2.4.2 Use of fluorescent dyes in confocal microscopy . . . . 143 2.4.3 Color in fusion of multimodality images . . . . . . . . 146 2.4.4 Color coding in Doppler ultrasonography . . . . . . . 150 2.4.5 Use of color in white-matter tractography . . . . . . . 155 2.5 Biomedical Application: Endoscopy of the Digestive Tract . . 162 2.6 Biomedical Application: Imaging of Burn Wounds . . . . . . 163 2.6.1 Influence of different illumination conditions . . . . . 166 2.6.2 Colorimetric characterization of the camera . . . . . . 168 2.7 Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 3 Removal of Noise and Artifacts 173 3.1 Space-Domain Filters Based on Local Statistics . . . . . . . 174 3.1.1 The mean filter . . . . . . . . . . . . . . . . . . . . . . 175 3.1.2 The median filter . . . . . . . . . . . . . . . . . . . . 177 3.1.3 Filters based on order statistics . . . . . . . . . . . . 181 3.2 Ordering Procedures for Multivariate or Vectorial Data . . . 184 3.2.1 Marginal ordering . . . . . . . . . . . . . . . . . . . . 185 3.2.2 Conditional ordering . . . . . . . . . . . . . . . . . . 185 3.2.3 Reduced ordering . . . . . . . . . . . . . . . . . . . . 187 3.3 The Vector Median and Vector Directional Filters . . . . . . 188 3.3.1 Extensions to the VMF and VDF . . . . . . . . . . . 190 3.3.2 The double-window modified trimmed mean filter . . 190 3.3.3 ThegeneralizedVDF–double-window–α-trimmedmean filter . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 3.4 Adaptive Filters . . . . . . . . . . . . . . . . . . . . . . . . . 191 3.4.1 The adaptive nonparametric filter with a Gaussian kernel . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 Table of Contents ix 3.4.2 The adaptive hybrid multivariate filter. . . . . . . . . 194 3.5 The Adaptive-Neighborhood Filter . . . . . . . . . . . . . . 196 3.5.1 Design of the ANF for color images . . . . . . . . . . 196 3.5.2 Region-growing techniques . . . . . . . . . . . . . . . 197 3.5.3 Estimation of the noise-free seed pixel . . . . . . . . . 201 3.5.4 Illustrations of application . . . . . . . . . . . . . . . 203 3.6 Biomedical Application: Removal of Noise Due to Dust in Fundus Images of the Retina . . . . . . . . . . . . . . . . . . 210 3.7 Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 4 Enhancement of Color Images 215 4.1 Componentwise Enhancement of Color Images . . . . . . . . 216 4.1.1 Image enhancement in the RGB versus HSI domains 216 4.1.2 Hue-preserving contrast enhancement . . . . . . . . . 217 4.1.3 Enhancement of saturation . . . . . . . . . . . . . . . 219 4.1.4 Selective reduction of saturation . . . . . . . . . . . . 220 4.1.5 Alteration of hue . . . . . . . . . . . . . . . . . . . . . 221 4.2 Correction of Tone and Color Balance . . . . . . . . . . . . . 223 4.3 Filters for Image Sharpening . . . . . . . . . . . . . . . . . . 229 4.3.1 Unsharp masking. . . . . . . . . . . . . . . . . . . . . 229 4.3.2 Subtracting Laplacian . . . . . . . . . . . . . . . . . . 234 4.4 Contrast Enhancement . . . . . . . . . . . . . . . . . . . . . 235 4.5 Color Histogram Equalization and Modification . . . . . . . . 239 4.5.1 Componentwise histogram equalization . . . . . . . . 244 4.5.2 3D histogram equalization. . . . . . . . . . . . . . . . 246 4.5.3 Histogram explosion . . . . . . . . . . . . . . . . . . . 250 4.5.4 Histogram decimation . . . . . . . . . . . . . . . . . . 251 4.5.5 Adaptive-neighborhood histogram equalization . . . . 251 4.5.6 Comparative analysis of methods for color histogram equalization . . . . . . . . . . . . . . . . . . . . . . . . 257 4.6 PseudocolorTransformsforEnhancedDisplayofMedicalIm- ages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265 4.7 TheGamutProblemintheEnhancementandDisplayofColor Images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 4.8 Biomedical Application: Correction of Nonuniform Illumina- tion in Fundus Images of the Retina . . . . . . . . . . . . . . 269 4.9 Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272 5 Segmentation of Color Images 275 5.1 Histogram-based Thresholding . . . . . . . . . . . . . . . . . 275 5.1.1 Thresholding of grayscale images . . . . . . . . . . . 276 5.1.2 Thresholding of color images . . . . . . . . . . . . . . 279 5.2 Color Clustering . . . . . . . . . . . . . . . . . . . . . . . . . 283 5.2.1 Color feature spaces and distance measures . . . . . . 285 5.2.2 Algorithms to partition a feature space . . . . . . . . 286