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Spie Press Book

Analysis and Evaluation of Sampled Imaging Systems
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Book Description

Advancing technology in detector arrays, flat panel displays, and digital image processing provides new opportunities to expand imaging applications and enhance system performance. Technical managers and design engineers are faced with evaluating the cost, weight, and performance of an ever-expanding selection of technology options. This tutorial text provides the theory, procedures, and information necessary to evaluate and compare the performance of available imaging technologies. Part I updates the earlier work presented in Analysis of Sampled Imaging Systems (2000). Part II discusses performance evaluation of electro-optical imagers. Part III provides computer programs (on a supplemental CD-ROM) and up-to-date information on detector arrays, optics, and display options.

The book covers a variety of display formats and interfaces, and provides detailed information on available focal plane arrays (FPAs). Particular emphasis is placed on theory and practice for the wide variety of available infrared FPAs. Technologies represented include InSb, HgCdTe, QWIP, and uncooled thermal arrays. Information is provided on the quantum efficiency, blur, crosstalk, and noise characteristics of each technology. The detector and array dimensions of available FPAs are provided. The information on optics, display, and FPA subassemblies allows the model user to make quick and realistic performance assessments of electro-optical imager designs.


Book Details

Date Published: 8 March 2010
Pages: 304
ISBN: 9780819480774
Volume: TT87

Table of Contents
SHOW Table of Contents | HIDE Table of Contents
Preface /xi
Acronyms and Abbreviations /xiii
Part I: Analysis of Sampled Imaging Systems /1
1 The Sampling Process /3
1.1 Description of a Sampled Imager /3
1.2 Description of the Sampling Process /6
1.3 Linarity and Shift Invariance /9
1.4 Signal Reconstruction /13
1.5 Three Ways of Viewing the Sampling Process /15
    1.5.1 The displayed image as the sum of its parts /16
    1.5.2 The display as a filter of the image samples /18
    1.5.3 The display as a filter of the sampled image /20
1.6 The Sampling Theorem /24
    1.6.1 Theory /24
    1.6.2 Example /26
    1.6.3 Discussion /29
Bibliography /29
2 Fourier Integral Representation of an Optical Image /31
2.1 Linear Shift-Invariant Optical Systems /31
2.2 Equivalence of Spatial and Frequency Domain Filters /34
2.3 Reducing LSI Imager Analysis to One Dimension /36
2.4 Perspectives on One-Dimensional Analysis /42
2.5 Imager Modulation Transfer Functions /45
    2.5.1 Imager components /45
    2.5.2 Line-of-sight jitter /48
      2.5.2.1 Reduction of line-of-sight jitter by eye tracking /50
      2.5.2.2 Effect of temporal sampling on line-of-sight jitter /53
    2.5.3 Electronic stabilization /54
    2.5.4 Motion blur /55
    2.5.5 Field replication /56
    2.5.6 Analog electronic filters /57
    2.5.7 Display MTF /48
Bibliography /59
3 Sampled Imager Response Function /61
3.1 Fourier Transform of a Sampled Image /63
3.2 The Sampled Imager Response Function /67
3.3 Examples of Sampled Imager Response Functions /69
    3.3.1 Example 1: The pictures of Lena in Chapter 1 /69
    3.3.2 Example 2: Effect of changing sample rate /71
    3.3.3 Example 3: Midwave thermal imager /79
    3.3.4 Example 4: Two-dimensional SIR example /81
Bibliography /85
4 Sampled Imager Optimization /87
4.1 Interpolation Implementation /89
Bibliography /97
5 Interlace and Dither /99
5.1 Sampling Improvement With Static Scene /102
5.2 Resolution and Sensitivity /108
5.3 Effect of Scene-to-Sensor Motion /111
Bibliography /112
Part II: Evaluating the Performance of Electro-Optical Imagers /113
6 Quantifying Visual Task Performance /115
6.1 Specifying and Evaluating Field Performance /118
6.2 Factors That Influence Target Identification /120
6.3 Measuring Target Signatures /121
6.4 Experimental Procedure /122
6.5 Field Test Procedure /125
6.6 Test Sets Other Than Tactical Vehicles /127
6.7 Field Testing Using Bar Targets /129
7 Evaluating Imager Resolution /131
7.1 Imager Evaluation Procedure /132
7.2 Modeling Gain, Level, and the User Interface /134
7.3 Observer Vision /138
7.4 Predicting Probablity of Identification /143
    7.4.1 Test Sets Other Than Tactical Vehicles /146
Bibliography /147
8 Quantifying the Effect of Aliasing on Visual Task Performance /149
8.1 Model Treatment of Spatial Noise /150
8.2 Treatment of Temporal Noise in Detectivity Versus Photon-Counting Methods /152
8.3 Relating Target and Imager Coordinate Systems /155
8.4 Spatial Scaling of Aliasing Noise /161
Bibliography /163
9 Thermal Imager Topics /165
9.1 Effective Blackbody Temperature /168
9.2 Signal Noise in the Setectivity Model /172
9.3 Thermal Imager Contrast Threshold Function /175
9.4 Adding Aliasing Noise /177
9.5 Predicting Range Performance /179
9.6 Modeling Contrast Enhancement and Boost /179
9.7 Minimum Resolvable Temperature /181
    9.7.1 Predicting minimum resolvable temperature /183
    9.7.2 Predicting sampled imager minimum resolvable temperature /186
    9.7.3 Improving the minimum resolvable temperature procedure /189
Bibliography /191
10 Imagers of Reflected Light /193
10.1 Calculating Target Set Contrast /193
10.2 System Contrast Threshold Function /196
    10.2.1 Interlace /200
    10.2.2 Snapshot and frame integration /201
10.3 Predicting Range Performance /202
Bibliography /202
Part III: Applications /205
11 Computer Programs and Application Data /207
11.1 Optics Modulation Transfer Function /208
    11.1.1 Thermal imagers /208
    11.1.2 Imagers of reflected light /211
11.2 Display Modulation Transfer Function /213
    11.2.1 Cathode ray tubes /213
    11.2.2 Liquid crystal displays /216
    11.2.3 Display interface format /218
11.3 Atmospheric Transmission and Turbulence /218
    11.3.1 Atmosphere in the Reflective model /219
    11.3.2 Atmosphere in the Thermal model /221
    11.3.3 Atmospheric turbulence /223
11.4 Detector Calculations /223
    11.4.1 Detector noise /223
    11.4.2 Detector modulation transfer function /226
11.5 Computer Program Description /227
11.6 Imager Analysis Using the Programs /235
    11.6.1 Imager resolution /235
    11.6.2 System contrast threshold function /236
    11.6.3 Range plots /237
References /240
Bibliography /240
12 Infrared Focal Plane Arrays /241
12.1 Photon Detector Infrared Focal Plane Arrays /241
    12.1.1 Photon detector basic principles /241
    12.1.2 Readout integrated circuit /246
    12.1.3 Photon detector dark current /247
12.2 IR FPA Performance Characterization /251
    12.2.1 Responsivitity and detectivity background-limit performance /252
    12.2.2 Flux-based signal-to-noise ratio /255
12.3 Commonly Available Photon Detector FPAs /258
    12.3.1 Indium antimonide (InSb) detectors /258
    12.3.2 Quantum well infrared photoconductor (QWIP) detectors /261
    12.3.3 Mercury cadmium telluride (HgCdTe) detectors /264
12.4 Uncooled Detectors /269
    12.4.1 Introduction /269
    12.4.2 Signal-to-noise ratio and performance limits /271
    12.4.3 Typical uncooled detectors /273
References /274
Appendix: Observer Vision Model /277
A.1 Contrast Threshold Function /277
A.2 Engineering Model of the Eye /278
References /282
Index /285

Preface

This tutorial is written for the design engineer or system analyst interested in quantifying the performance of electro-optical imagers. Advancing technology in detector arrays, flat panel displays, and digital image processing provide new opportunities to expand imaging applications and enhance system performance. Technical managers and design engineers are faced with evaluating the cost, weight, and performance of an ever-expanding selection of technology options. This book provides the theory and procedures for performance assessment.

This book supersedes Analysis of Sampled Imaging Systems, which was published by SPIE Press in 2000. Part I updates the earlier work. Part II discusses performance evaluation of electro-optical imagers. Part III provides computer programs and up-to-date information on detector arrays, optics, and display options. This book provides the theory, procedures, and information needed to evaluate and compare the performance of available imaging technologies.

Our prior work Analysis of Sampled Imaging Systems focused on the mathematical formulism needed to analyze sampled imagery. That book described the sampled imager response (SIR) function. SIR quantified sampled imager aliasing as well as the system transfer response. Fourier transform theory was used to describe and quantify sampling artifacts such as display raster, blocky images, and the loss or alteration of image detail due to aliasing.

However, the metrics provided by the earlier book were "rules of thumb." Sampled imager design rules were based on experience and experimentation. No theory existed to quantify the effect of aliasing on visual task performance. The earlier work provided guidance on how to optimize sampled imagers by minimizing aliasing. Analysis of Sampled Imaging Systems did not provide a procedure to quantify the impact of aliasing on performance.

In the intervening years since the first book, we have discovered that the effect of aliasing on targeting performance is predictable by treating aliasing as noise. This book presents a resolution metric that predicts the effect of imager blur, noise, and sampling on the probability of correctly identifying targets. This new publication includes quantitative procedures for evaluating target acquisition performance.

Part I of this book includes all of the pertinent material from Analysis of Sampled Imaging Systems. The first five chapters remain substantially the same as the previous work. These chapters introduce sampling concepts and describe the differences between shift-variant and shift-invariant systems. Chapter 2 on Fourier optics is extensively rewritten. The errors associated with assuming separability in Cartesian coordinates are discussed and examples given. The blurs associated with vibration and electronic stabilization are described. In Chapter 3 additional examples are added to better describe the SIR function. The focus of Chapters 1 through 5 remains the same, however. They provide the mathematical tools needed to analyze sampled imagers.

Part II of this new book includes Chapters 6 through 10. This new material describes electro-optical imager evaluation. Chapter 6 describes target identification experiments. These experiments quantify visual task performance. Chapter 7 describes a resolution metric that predicts the probability of identifying targets. Chapter 7 also discusses the relationship between imager resolution and field performance. Chapter 8 explains aliasing as noise theory. For some years, we have known how to predict the effect of noise on target acquisition. Aliasing as noise theory predicts the effect of aliasing on target acquisition. Chapters 9 and 10 provide details on analyzing thermal imagers and imagers of reflected light, respectively.

Part III provides computer programs that implement the theory. These programs calculate the resolution of thermal and reflected light imagers. The programs are used to evaluate expected target acquisition performance and to compare imagers and assess the benefit or penalty of design changes.

Information is also provided to help make realistic assessments of imager performance. The book discusses optical performance and provides the characteristics of typical, good, and ideal lens systems. The book also contains information on a variety of display formats and interfaces. Detailed information on available focal plane arrays (FPAs) is also provided. The information is presented in written form and is also coupled to the computer programs.

Particular emphasis is placed on theory and practice for the wide variety of available infrared FPAs. Technologies represented include InSb, HgCdTe, QWIP, and uncooled thermal arrays. Information is provided on the quantum efficiency, blur, crosstalk, and noise characteristics of each technology. The detector and array dimensions of available FPAs are provided. The availability of current information on optics, display, and FPA subassemblies allows the model user to make quick and realistic performance assessments of electro-optical imager designs.

Richard H. Vollmerhausen
Donald A. Reago, Jr.
Ronald G. Driggers

February 2010


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