got colors

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got colors?

• Color Quantization Techniques
• Joo Hyun Song

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Outline

• Overview
• Implementation
• Results and Discussion
• Concluding Remarks

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Overview

• What is color quantization?
• Color quantization is applied when the color
  information of an image is to be reduced. 1
• The most common case is when a 24-bit color
  image is transformed into an 8-bit color image.
  1
• Used when high-depth color is not supported or
  necessary.
• 1 http//www.dai.ed.ac.uk/HIPR2/quantize.htm

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Overview (contd)

• Main issues concerning color quantization
• What are the criteria for colors that are
  retained in the resulting image?(How are the
  important colors selected?)
• How accurate is the resulting image?(How well
  are the important features of the image preserved
  in the resulting image?)
• How fast is the quantization process?

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Implementation

• Diversity Algorithm 2
• Color quantization algorithm devised by John
  Bradley, the creator of the popular UNIX-based
  imaging software xv.
• The algorithm starts by picking the most populous
  color (the overall color) of the original image.
• Then the most distant colors from the colors in
  the new color table are picked until the new
  color table is filled.
• Results in the most diverse selection of colors
  surrounding the overall color.
• 2 http//www.trilon.com/xv/manual/xv-3.10a/diversi
  ty-algorithm.html

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Implementation (contd)

• Modified Diversity Algorithm 2
• Improvement over the original Diversity Algorithm
  suggested by Tom Lane of the Independent JPEG
  Group.
• The modification aims to better balance the
  allocation between diverse colors and populous
  colors.
• The alternation strategy is subjective some
  strategy works better in certain images while not
  as good in other.
• Examples in this presentation use the
  10-div-pop/div rule. ?

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Implementation (contd)

• ImageMagickTM 3 libraries and tools
• Provides readily available libraries and tools
  for reading, manipulating and writing most of the
  popular image formats.
• Programming Language of choice C
• C has stdvector and stdmap datatypes that
  made the histogram and colorMap implementation
  simpler.
• C has a built-in optimized sort() function that
  can be used for sorting elements in stdvector
  datatypes.
• Not Java. -)
• 3 http//www.imagemagick.org/

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Test Images
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Results

• Tested Algorithms
• Diversity Algorithm
• Modified Diversity Algorithm
• Tested Color Spaces
• RGB
• YUV
• YIQ
• XYZ
• UVW

(not really)
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Original Diversity vs. Modified Diversity
Original Diversity Algorithm (RGB)
Modified Diversity Algorithm (RGB)
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Original Diversity vs. Modified Diversity (contd)
Original Diversity Algorithm (RGB)
Modified Diversity Algorithm (RGB)
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Original Diversity vs. Modified Diversity (contd)
Original Diversity Algorithm (RGB)
Modified Diversity Algorithm (RGB)
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Color Space Comparisons
Original
RGB
YUV
XYZ
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Color Space Comparisons
Original
RGB
YUV
XYZ
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Color Space Comparisons
Original
RGB
YUV
XYZ
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Weird
UVW (supposedly)
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My UVW Implementation

• double DecodeUVW(const unsigned int color, const
  char opt)
• double X DecodeXYZ(color, 'x')
• double Y DecodeXYZ(color, 'y')
• double Z DecodeXYZ(color, 'z')
• double x X/(XYZ)
• double y Y/(XYZ)
• double u 4x/(-2x12y3)
• double v 6y/(-2x12y3)
• double W 25pow(100Y, 1/3)-17
• // Get reference white
• X DecodeXYZ(0xFFFFFF, 'x')
• Y DecodeXYZ(0xFFFFFF, 'y')
• Z DecodeXYZ(0xFFFFFF, 'z')
• x X/(XYZ)

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Future Interest

• Investigate more advanced color spaces (such as
  Luv or IHS).
• Investigate other color metrics (e.g. Riemannian
  color space).
• Investigate more advanced color quantization
  algorithms (such as the Neural Networks color
  quantization algorithm).

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Performance of other programs

• ImageMagicks built-in quantizeColors() algorithm

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Performance of other programs (contd)

• Gimp

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What I Have Learned

• Start EARLY ?
• Subjectivity of image quality.
• Different Color Spaces.
• Dont use ImageMagick

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Any Questions?