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MODERN IMAGE
QUALITY ASSESSMENT
i
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Copyright © 2006 by Morgan & Claypool
All rights reserved. No part of this publication may be reproduced, stored in a retrieval sys-
tem, or transmitted in any form or by any means—electronic, mechanical, photocopy, recording, or
any other except for brief quotations in printed reviews, without the prior permission of the publisher.
Modern Image Quality Assessment
Zhou Wang and Alan C. Bovik
www.morganclaypool.com
ISBN: 1598290223
ISBN: 1598290231
paper Wang/Bovik
ebook Wang/Bovik
Modern Image Quality Assessment
Modern Image Quality Assessment
doi
10.2200/S00010ED1V01Y2005081VM003
Library of Congress Cataloging-in-Publication Data
10 9 8 7 6 5 4 3 2 1
Printed in the United States of America
ii
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MODERN IMAGE
QUALITY ASSESSMENT
Zhou Wang
The University of Texas at Arlington
Alan C. Bovik
The University of Texas at Austin
M&C Morgan & Claypool Publishers
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ABSTRACT
This Lecture book is about objective image quality assessment—where the aim is to
provide computational models that can automatically predict perceptual image qual-
ity. The early years of the 21st century have witnessed a tremendous growth in the
use of digital images as a means for representing and communicating information.
A considerable percentage of this literature is devoted to methods for improving
the appearance of images, or for maintaining the appearance of images that are
processed. Nevertheless, the quality of digital images, processed or otherwise, is
rarely perfect. Images are subject to distortions during acquisition, compression,
transmission, processing, and reproduction. To maintain, control, and enhance the
quality of images, it is important for image acquisition, management, communi-
cation, and processing systems to be able to identify and quantify image quality
degradations.
The goals of this book are as follows; a) to introduce the fundamentals of
image quality assessment, and to explain the relevant engineering problems, b) to
give a broad treatment of the current state-of-the-art in image quality assessment,
by describing leading algorithms that address these engineering problems, and
c) to provide new directions for future research, by introducing recent models and
paradigms that significantly differ from those used in the past.
The book is written to be accessible to university students curious about
the state-of-the-art of image quality assessment, expert industrial R&D engineers
seeking to implement image/video quality assessment systems for specific applica-
tions, and academic theorists interested in developing new algorithms for image
quality assessment or using existing algorithms to design or optimize other image
processing applications.
KEYWORDS
Image quality assessment, Perceptual image processing, Visual perception,
Computer vision, Computational vision
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1.
2.
Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1
Subjective vs. Objective Image Quality Measures . . . . . . . . . . . . . . . . . 1
1.2 What’s Wrong with the MSE? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 Classification of Objective Image Quality Measures . . . . . . . . . . . . . 11
1.3.1
Full-Reference, No-Reference and Reduced-Reference
Image Quality Measures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
1.3.2 General-Purpose and Application-Specific
Image Quality Measures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
1.3.3 Bottom-Up and Top-Down Image Quality Measures . . . . 14
1.4 Organization of the Book . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.3
Bottom-Up Approaches for Full-Reference Image
Quality Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.1 General Philosophy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.2 The Human Visual System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.2.1 Anatomy of the Early HVS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.2.2
Psychophysical HVS Features . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Framework of Error Visibility Methods . . . . . . . . . . . . . . . . . . . . . . . . 26
2.3.1
Preprocessing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.3.2 Channel Decomposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.3.3 Error Normalization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2.3.4 Error Pooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Image Quality Assessment Algorithms . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.4.1 Daly Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.4.2 Lubin Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.4.3
Safranek–Johnson Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
2.4.4 Teo–Heeger Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2.4.5 Watson’s DCT Model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
2.4.6 Watson’s Wavelet Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
2.5 Discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37
2.5.1 The Quality Definition Problem . . . . . . . . . . . . . . . . . . . . . . . 37
2.4
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2.5.2 The Suprathreshold Problem . . . . . . . . . . . . . . . . . . . . . . . . . . 38
2.5.3 The Natural Image Complexity Problem . . . . . . . . . . . . . . . . 38
2.5.4 The Dependency Decoupling Problem. . . . . . . . . . . . . . . . . .39
2.5.5 The Cognitive Interaction Problem. . . . . . . . . . . . . . . . . . . . .39
Top-Down Approaches for Full-Reference Image Quality Assessment . . 41
3.1 General Philosophy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Structural Similarity Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.2
Structural Similarity and Image Quality. . . . . . . . . . . . . . . . .43
3.2.1
3.2.2
Spatial Domain Structural Similarity Index . . . . . . . . . . . . . 44
3.2.3 Complex Wavelet Domain Structural
3.3
Similarity Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
3.2.4 Remarks on Structural Similarity Indices . . . . . . . . . . . . . . . . 64
Information-Theoretic Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
3.3.1
Information Fidelity and Image Quality . . . . . . . . . . . . . . . . 65
3.3.2 The Visual Information Fidelity Measure . . . . . . . . . . . . . . . 66
3.3.3 Remarks on Information-Theoretic Indices. . . . . . . . . . . . . .73
3.4 Discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74
No-Reference Image Quality Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
4.1 General Philosophy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
4.2 NR Measures for Block Image Compression . . . . . . . . . . . . . . . . . . . . 81
Spatial Domain Method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82
Frequency Domain Method . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
4.3 NR Measures for Wavelet Image Compression . . . . . . . . . . . . . . . . . . 93
4.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
4.2.1
4.2.2
Reduced-Reference Image Quality Assessment . . . . . . . . . . . . . . . . . . . . . . 103
5.1 General Philosophy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
5.2 Wavelet Domain RR Measure Based on Natural
Image Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
5.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .121
6.1
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
6.2 Extensions and Future Directions. . . . . . . . . . . . . . . . . . . . . . . . . . . . .124
Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
3.
4.
5.
6.
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Preface
Although the topic of image quality assessment has been around for more than
four decades, there has, until recently, been relatively little published on the topic.
Certainly this omission is not for lack of need or paucity of interest, since most
image-processing algorithms and devices are, in fact, devoted to maintaining or
improving the apparent quality of digitized images for human visual consumption.
Traditionally, image quality has been evaluated by human subjects. This
method, though reliable, is expensive and too slow for real-world applications. So
this book is about objective image quality assessment, where the goal is to provide
computational models that can automatically predict perceptual image quality. Per-
haps the first notable work in the field of objective image quality assessment was
the pioneering work of Mannos and Sakrison, who proposed image fidelity criteria,
taking into account human visual sensitivity as a function of spatial frequency [1].
Other important early work was documented in a book edited by Watson [2]. Yet,
until the past few years, the field of image quality assessment has received relatively
little attention, despite its recognized importance.
Indeed, image quality assessment has paradoxically remained not only both
something of a Holy Grail for image-processing engineers and vision scientists
but also a No-Man’s Land of research and development work. Indeed, a recent
Web search, as we write this, reveals that 100 times as many articles are found
for “image restoration” as for “image quality assessment” and nearly 400 times
as many articles are found for “image enhancement.” How do we explain this
discrepancy? It would seem that quality assessment should be a necessary ingredient
in developing restoration and enhancement algorithms. Is image quality assessment
such a daunting problem, or an insoluble one, that researchers have avoided wasting
their efforts?