COLOUR ENGINEERING. Achieving Device Independent Colour. Edited by. Phil Green

Transcription

1 COLOUR ENGINEERING Achieving Device Independent Colour Edited by Phil Green Colour Imaging Group, London College of Printing, UK and Lindsay MacDonald Colour & Imaging Institute, University of Derby, UK JOHN WILEY & SONS, LTD

2 Contents Colour plate captions Contributors Series Preface Preface xv xvii xxi xxiii 1 Light and colour 1 Arthur Tarrant 1.1 Luminous Flux Illuminance Luminous Intensity Luminance Units Obsolete units Radiometric units Transmission Measurements Direct transmission Diffuse transmission Transmittance Optical density and absorbance The Beer-Lambert law Reflection Measurements Specular and diffuse reflection Surface texture Reflectance Colour Rendering and Metamerism Colour rendering Metamerism 16 References 17 2 Instruments and methods for colour measurement 19 Danny Rich 2.1 Introduction The need for colorimetry 19

3 2.1.2 The principles of colorimetry Making the transition from what we 'see' to quantifying how we 'match' a colour Visual Colorimetry A method to uniquely map the colour of lights and objects Development of the CIE method of visual colorimetry Applications of visual colorimetry Disadvantages of visual colorimetry Analogue Simulation of Visual Colorimetry Replacing the human eye with an optoelectronic sensor Substituting coloured filters to approximate the CIE colour-matching functions Assessing the 'goodness of fit' of a set of colorimeter filters Schematic description of analogue filter colorimeters Disadvantages of analogue filter colorimeters Digital Simulation of Visual Colorimetry Replacing the analogue filters with an abridged spectrometer Assessing the 'goodness of fit' of abridged spectrometers Schematic description of digital spectrocolorimeters Advantages and disadvantages of digital spectrocolorimeters Selecting and Using Colorimeters and Spectrocolorimeters Reading and understanding specifications and technical literature Verifying performance specifications Standards of colour and colour-difference Sources of error and uncertainty in the measurement of reflectance, transmittance and radiance Geometric Requirements for Colour Measurements Colour measurements from self-luminous objects Colour measurements from reflecting or transmitting objects Conclusions and Expectations Current CIE activities in colour and colour-difference measurements Quality management systems and colour measurements 45 References 46 3 Colorimetry and colour difference 49 Phil Green 3.1 Introduction Colorimetry Calculation of chromaticity Calculation of CIE 1976 L* a* b* Inversion of colorimetric transforms Implementation issues 56

4 Vli 3.3 Colour Difference Problems with using UCS colour difference Acceptability of colour differences Overcoming the Limitations of UCS Colour Difference with Advanced Colour Difference Metrics CMC BFD CIE CIEDE Advanced Colour Difference Metrics in Colour Imaging Basis conditions Colour difference in complex images Acceptability and perceptibility Large vs. small differences Deriving Colour Difference Tolerances Sample preparation Psychophysical experiments Observer variability and experience Calculating colour tolerances from experimental data Calculation of discrimination ellipsoids and tolerance distributions Calculation of parametric constants in weightings functions Calculation of acceptability thresholds Conclusion 74 References 75 4 The CIE 1997 colour appearance model: CIECAM97s 79 M. Ronnier Luo 4.1 Introduction CIE 1997 Colour Appearance Model: CIECAM97s Structure of the model Colour attributes Colour appearance phenomena predicted by the model Testing Colour Appearance Models Using Colour Appearance Data Sets Colour appearance data sets Psychophysical methods Testing colour appearance models' performance Recent Modifications to CIECAM97s Conclusion 95 References 95 Appendix 1. Computation Procedures for CIECAM97s 97 Forward CIECAM97s colour appearance model 97

5 ViH Reverse CIECAM97s colour appearance model 101 Worked examples for the CIECAM97s colour appearance model Colour notation systems 105 Peter A. Rhodes 5.1 Introduction Colour Fidelity Colour Notation Systems Introduction and definitions Defining colour notation systems Device-dependent specification systems CIELAB and CIELUV TekHVC Munsell The DIN colour system Natural colour system The OSA-UCS colour system Colour naming systems Other colour notation systems Interrelating Multiple Notation Systems Implementing computer-based systems Summary 124 References Overview of characterization methods 127 Phil Green 6.1 Introduction Numerical Models Regression methods used in characterization Domain Training sets Look-up Tables with Interpolation Interpolation LUT implementation Evaluating Model Accuracy 138 References Methods for characterizing displays 143 Roy Berns and Naoya Katoh 7.1 Introduction GOG Model for CRT Displays 143

6 IX 7.3 The Extended GOGO Model Calibration, Characterisation, and Gamma Determining the colorimetry of each channel Determining the OETF of each channel Numerical Example of A Colorimetric Characterization Characterization summary Conclusions 163 References Methods for characterizing colour scanners and digital cameras 165 Tony Johnson 8.1 Introduction Colour management of device-dependent and device-independent systems Principles of scanner characterization Use of the ANSI/ISO Scanner Characterization Target Use of the Target in Scanner Characterization Evaluation of colour digitizers Evaluation of 'gamut compressed' colour digitizer Signal-to-noise ratio Scanner repeatability Characterization Procedures Analytical solution to first-order equations Least-squares fitting to a first-order model Least-squares fitting to a higher-order model Non-linear transformation Dye modelling algorithms Look-up table with interpolation Summary 177 References Color processing for digital photography 179 Jack Holm, Ingeborg Tastl, Larry Hanlon and Paul Hubel 9.1 Introduction Background Color processing approaches: uncalibrated versus calibrated image data Dealing with calibrated and uncalibrated image data in a common architecture The meaning of device-independent color as applied to digital photography 183

7 9.3 Open Systems Architecture and Workflow Options Digital camera image processing steps related to the three different workflow options Device-independent color via exchange of standard output-referred image data and application of color rendering Device-independent color via deferred processing Digital Camera Image Processing Choices: Component Selection, Characterization Methods, and Processing Algorithms Capture of raw image data Linearization to focal plane irradiance Flare removal Adopted white selection White balancing Demosaicing Determination of transformations to scene-referred colorimetry estimates Color rendering to standard output-referred representations Encoding, compression, and file formats for exchange Color rendering for output 213 References 213 Appendix 1: Terminology Characterizing hard copy printers 221 Phil Green 10.1 Introduction Halftoning Printer Models Block dye model Physical Models Density Dot area models Colorant models Numerical Models and Look-up Tables Black Printer Spectral grey-component replacement Black Generation Algorithm The Reverse Model RGB Printers 242 References Color management and transformation through ICC profiles 247 Dawn Wallner 11.1 The Need for Color Management The PCS The ICC Profile 250

8 XI ICC profile types Use of ICC profiles The ICC Profile Structure ICC profile creation ICC device models ICC rendering intents Required processing tags Private tags Profile Use Color management on the web and ICC profiles Sample ICC profile interfaces ICC profile validation software What to look for in the future at the ICC website Conclusion 261 References i Colour gamut determination 263 Marc Mahy 12.1 Introduction Overview of Gamut Calculations Terminology A General Printer Model The Neugebauer model A localised Neugebauer model Gamut Calculations Introduction Boundaries of a 3-ink process Boundaries of a 4-ink process Analytical gamut calculation: well-behaved Neugebauer model without ink limitations Gamut of a well-behaved localised Neugebauer model Gamut of a less well-behaved model Gamut Representations Conclusions 282 References 283 Appendix 1. Neugebauer Equations 285 Neugebauer equations for a 1-ink process 285 Neugebauer equations for a 2-ink process 285 Appendix 2. Analytical Gamut Calculation: Weil-Behaved Neugebauer Model with Linear Ink Limitation Colour gamut mapping 297 Jan Morovic 13.1 Introduction Gamut mapping aims 299

9 Xii 13.2 Terminology Factors Affecting Gamut Mapping Colour reproduction system Gamut boundary calculation Colour space Media Images Parameters of Gamut Mapping Type of mapping Choice of original gamut Gamut Mapping and Colour Rendering Intents Colour rendering intents Relationship between gamut mapping and rendering intents Overview of Gamut Mapping Algorithms Gamut Mapping Algorithms and Colour Management Frameworks Recommended gamut clipping algorithm Recommended gamut compression algorithm Summary Acknowledgements 314 References Implementation of device-independent color at Kodak 319 Kevin Spaulding and Edward Giorgianni 14.1 Introduction Image States Standard Image State Color Encodings Criteria for selection of R1MM/ROMM RGB color encodings ROMM RGB color encoding ROMM RGB conversion matrix Nonlinear encoding of ROMM RGB R1MMRGB color encoding RIMM RGB conversion matrix Nonlinear encoding of RIMM RGB ERIMM RGB color encoding Nonlinear encoding of ERIMM RGB Image States in a Color-Managed Architecture Implementation with JPEG References Engineering color at Adobe 341 James King 15.1 Introduction The Early Black and White POSTSCRIPT Days 341

10 Xiii 15.3 A Little Bit about POSTSCRIPT POSTSCRIPT Procedures Typical Workflow for Making Black and White Film POSTSCRIPT Level Handling Black in CMYK Workflows Destination Profiles in POSTSCRIPT Differences Between ICC Processing and POSTSCRIPT Processing 'The Tail Wagging the Dog' The Formation of the International Color Consortium Portable Document Format (PDF) Color Management in Other Adobe Products When Things Go Wrong The Future Acknowledgements 369 References Colour management in digital film post-production 371 Wolfgang Lempp and Leonardo Noriega 16.1 Introduction Traditional Film Post-production The film process chain The tools of the cinematographer Digital Visual Effects Digitising the negative Scanner encoding scheme Matching the original negative Colour management: a potential solution The Digital Studio Telecine processing The cinematic experience Colour appearance models Gamut mapping Digital Cinema A standard for digital cinema distribution An architecture for film colour management Conclusion 383 References Managing color in digital image libraries 385 Sabine Susstrunk 17.1 Image Representations in Digital Image Libraries Digital Image Color Workflow Sensor encoding Input-referred image encoding 392

11 XIV Output-referred image encoding Output device specific encoding The use of ICC Color Management in Image Libraries ICC profiles and master files ICC profiles and derivative files Color Spaces and Color Encodings Color space and color encoding characteristics Compression and File Formats Compression File formats Other Issues in Building and Maintaining a Digital Image Library Storage Text metadata Content-based image retrieval (CBIR) Database architecture Summary References Standards activities for colour imaging 421 David Q. McDowell 18.1 Introduction The Initial Graphic Arts Colour Standards Scanner targets CMYK output data set Colour measurement and computation Viewing Standards Hardcopy viewing Softcopy viewing Densitometry and Related Metrology Standards Related metrology standards ISO Output Characterization Printing process definition Reference printing conditions Test Images Other Related Standards Work Where Are We Going? More Information 437 References 437 Appendix 1. Partial Listing of Colour Imaging Standards 438 Appendix 2. Bibliography 441 Author biographies 443 Index 449