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Principles of Digital Color Imaging Systems

Learn about digital color imaging systems, including cameras, scanners, mobile phones, and displays. Study color science, image capture, display, printing, processing, quality models, and applications in computer vision.

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Principles of Digital Color Imaging Systems

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  1. ECE 638: Principles ofDigital Color Imaging Systems Jan P. Allebach School of Electrical and Computer Engineering allebach@purdue.edu

  2. What is a digital color imaging system?

  3. What else besides printers? • Digital cameras • Flatbed scanners • Mobile phones • Flat panel displays

  4. How do we organize all this? • Cameras • Scanners Image output devices Image capture devices Interconnection space and processing • Smart phones • Tablets • Personal computers • Cloud • Displays • Printers

  5. What do we need to study in order to understand digital color imaging systems? • Color science • Image capture • Image display • Image printing • Image processing • Image quality models • Applications of color in computer vision problems

  6. Color science topics • Transformation between color spaces • White point • Color space interpolation • Gamut mapping • Color appearance models • Color management practices • What is color? • Trichromatic model for human vision • Opponent channel models for human vision • Standard color spaces • Models for color imaging devices • Device gamma • Color imaging systems calibration

  7. Image capture topics • Sensors • Technologies • Characteristics and models • Scanners • Architecture • Illuminations • Scan bar motion • Spatial analysis of scanning and sampling • Calibration of image capture devices • Descreening • Page classification

  8. Image display topics • Display technologies • Cathode ray tube • Liquid crystal • Plasma panel • E-paper • Calibration of image display devices • Spatial analysis of image display • Color image quantization

  9. Image printing topics • Color trapping • Digital halftoning • Calibration of printing systems • Printing technologies • Silver halide-based systems • Ink-based systems • Plate-based systems • Inkjet systems • Toner-based systems • Dry electrophotography • Wet electrophotography • Colorant-media-light interaction

  10. Image quality models and assessment topics • Image quality terminology • Basic psychophysical methods • Image artifact assessment • Image quality metrics • Image quality rulers

  11. Applications of color to computer vision problems • Garment color extraction • Separation of people from background • Color transfer

  12. What is color?

  13. Let’s see what Microsoft has to say about color

  14. Click on “More Font Colors…”

  15. HSV

  16. HSL

  17. Crayon Picker

  18. CMYK Picker

  19. What did we learn? • Lots of different ways to talk about color • Ordering and naming systems • Crayon picker • Coordinate systems • HSV • HLS • CMYK

  20. Many questions remain… • How were these attributes chosen? • Hue • Saturation • Lightness • Value • Which CMYK are we talking about? • Rendering device • Capture device

  21. CMYK Magenta (M) Yellow (Y) Cyan (C) Black (K)

  22. Which CMYK? – effect of rendering device HP DJ 970Cse IPP Driver HP DJ 970Cse Mac Driver Monitor

  23. Which CMYK? – effect of capture device Olympus C3000 Digital Camera Heidelberg Scanner

  24. Different color representations • Are they all equivalent? • How do we get from one to the other? • Can we get from one to the other? • Even if we can, what do all these numbers mean?

  25. Example: capture to capture Given RGB values from one capture device, can we predict RGB values for a second capture device? Olympus C3000 Digital Camera Scanner RGB values (?, ?, ?) (?, ?, ?) (?, ?, ?) (?, ?,?) RGB values (23, 136, 180) (203, 11, 52) (219, 186, 33) (7, 7, 7)

  26. Discussion topic • What is the basis for the equations that underlie color transformations?

  27. So what is color? Color is a sensation experienced by a human being in response to a visual stimulus.

  28. What are the key parts of this definition? Color is a sensation experienced by a human being in response to a visual stimulus.

  29. Sensation – human being • Need to understand something about the human visual system • physiology • perception • psychophysics • Relevant courses • ECE 511 Psychophysics (Prof. Hong Tan)

  30. Visual stimulus • Need to understand interaction of illuminant and object Illuminant Viewer Object

  31. Why should we care about color? • Important aspect of everyday experience • New imaging and information technologies provide unprecedented ability to manipulate and use color • Capture devices • digital cameras • scanners • Output devices • CRT and LCD displays • Inkjet and laser printers • Intermediaries • PCs, smartphones, tablets • applications • internet and cloud

  32. Why should we care… • Color provides valuable information about the world around us • Application areas • manufacturing • medicine • agriculture • environmental • Contexts • image analysis for inspection • machine vision for robotics, unmanned aerial vehicles, driverless cars, etc. • remote sensing

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