Lecture 3: Digital Image Representation and Color Science

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Lecture 3 Digital Image Representation and Color
Science
Instructor Tiecheng Liu
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Image Sampling and Quantization
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Image Sampling
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Gray Level Image Representation
Mathematical representation 2-d matrix, 2-d
signal Programming representation 2-d array or
1-d array Storage different file formats
PBM/PGM/PPM BMP, GIF, JPEG, etc.
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• Color Image
• Color Space
• Color Matching

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Introduction to Color Science
Light and Spectra Light is an electromagnetic
wave. Its color is characterized by the
wavelength content of the light. (a) Laser light
consists of a single wavelength e.g., a ruby
laser produces a bright, scarlet-red beam. (b)
Most light sources produce contributions over
many wavelengths. (c) However, humans cannot
detect all light, just contributions that fall in
the visible wavelengths". (d) Short wavelengths
produce a blue sensation, long wavelengths
pro-duce a red one.
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Spectrum of visible color
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Spectral Power Distribution (SPD)
The symbol for wavelength is ? . The energy
distribution is E(?).
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Human perception of color
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Then the human perception of R, G, B color can be
represented in the form of integral.
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Surface Spectral Reflectance
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Surface Spectral Reflectance of Sample objects
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Image Formation Model
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Image Formation Equations
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RGB Color Cube
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Complements on Color Circle
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RGB Color Space and Primary colors
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Transformation from RGB Color Space to CMY Color
Space
here 1 is the maximum value. If using 256 levels
of color, change 1 to 256.
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CMYK Color Space

• Why CMYK instead of RGB colors for printing?
• Why introducing K?
• Undercolor removal. Sharper and cheaper printer
  colors calculate that part of the CMY mix that
  would be black, remove it from the color
  proportions, and add it back as real black.

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CIE Chromaticity Diagram
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HSI Color Space
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Complement Transforms