<> <> Digital halftones Contouring ? figure from stanford talk Pair of idealized spectra Pair of real spectra (?) More PrintervsMonitor process diagram New GamutMapping based on TOG picture? Color Imaging and Reproduction Color Production Color Reproduction Same Image Different Device Color Measurement CIE Colorimetry CIE Color Standards Calibrated Color Reproduction What is Color? Red, Green, Yellow, ... Hue, Tone, Tint ... Response of Eye to Stimulus Perception of Stimulus Anything not a Mask Color Devices Additive (Monitors) Subtractive (Printers, photograpy) Device Primaries RGB, CMY(K) Bilevel or Multilevel Color Monitors Three Phosphor Dots/Pixel (Picture of single pixel) Full Color (8 bits/color) (Picture of pixels 24bpp) Color Lookup Tables (8 bits/pixel) (Picture of pixels 8 bpp) Primaries are Pure 50% R+50% G + 50% B = 50% gray Gamma Correction Linear in Intensity Color Printing Three or Four Colors Halftones Bilevel 50 to 170 lines/inch Primaries are not Pure 50% C+50% M + 50% Y NOT = 50% gray Gray Balancing Linear in Density BW halftones Color halftones Classic Separation, Black-printer Sequence Digital Color Printing Bilevel Technologies Inkjet Electrostatic Xerography, Electrophotography Thermal Transfer Offset Printing Multilevel Technologies Photographic Processes Thermal Sublimation Digital Halftones Multiple Printer Pixels/Halftone Dot Gray Levels vs. Sharp Edges 10:1 typical 10 by 10 = 101 gray levels 150 lines = 1500 spi Typical Resolutions: 150 to 400 spi Poor Resolution, but good Alignment Digital halftones Contouring Color Reproduction Same Image Different Output Devices Same Appearance Graphic Arts Rules-of-Thumb Customer Satisfaction Color Names don't Change Gray Wedge is Smooth and Gray Good Contrast Designing on Monitors for Printers Additive vs Subtractive Color Different Viewing Environments User Model Functional Color Select Percentage CMYK RGB to CMY(K) automatically RGB to CMY(K) If Inks were Ideal Filters C = 1-R, M = 1-G, Y = 1-B Inks are not Ideal Filters Spectra Overlap Not Inverse of Monitor Spectra Color Correction Required figure from stanford talk Pair of idealized spectra Pair of real spectra (?) Color Correction Map Input to Output Colors Compensate For Impurity For Color of Primaries Different Gamuts Techniques Simple Linear Transformation Piecewise Interpolation Mik's sequence Color Measurement What is Color? Colorimetry Instruments Measure the Stimulus Empirically Derived Metrics Standardized by the CIE What is color measurement Diagrammed image from colorimetry Radiometer with Spectrum showing TV Color Analyzer Mik's colorimeter Device Calibration Define Device Properties in Colorimetric Terms Model Measure Gamut is the Set of all Possible Colors PrintervsMonitor PrinterGamuts MonitorGamuts Introduction to Colorimetry (7) CIEColorimetry CIEStandards TristimulusValues tristimulusEqns ChromaticityEqns CDAdditive Printer vs Monitor Calibrated Color Reproduction Color Correction based on Colorimetric Information Calibrated Devices Possible Reproduction Levels Match Surfaces Match Tristimulus Values Match Chromaticity Coordinates Match Appearance AIC Experiment (show some examples) Bits to Color Separations Different images with different problems 3 slides (tape, seps, cromalin) process diagram Gamut Mapping Appearance Match is the Correct Goal Map to Control Appearance Map to Control Out-of-Gamut Colors Don't Match Tristimulus Values Don't Match Chromaticity Coordinates Conclusions Increasing Number of Digital Color Devices Many are Poor Quality Many are Badly Used Color Reproduction Important Issue for Computer Graphics Community Scholarly Publishing Desktop Publishing Community needs to be Educated Color Measurement Key to Quality Reproduction