Characteristics and Limitations of Digital Color Photography
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Transcript of Characteristics and Limitations of Digital Color Photography
Characteristics and Limitations of Digital Color Photography
Harald BrendelMunich, 21 September 2012
Light is Electromagnetic Radiation
Short wavelength (~400nm)
Long wavelength (~700nm)
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Radiometry
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Incandescent Light
Spectral Power Distribution
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3200K
2000K
Incandescent Light
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Daylight
5600K
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6500K
Daylight
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Photoreceptor
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Retina
http://www.cis.rit.edu/people/faculty/montag/vandplite/pages/chap_9/ch9p1.html
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Color Receptors
x =
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Tristimulus
Brightness
Color Sensation
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Primary Colors
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Additive Color Mixture
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Additive Color Mixture: Red and Green
+
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Additive Color Mixture: Blue and Green
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Additive Color Mixture: Red and Blue
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Additive Color Mixture: Red, Green, and Blue
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RGB forms White
=
=
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Metamerism
Two Different Spectra
Same Tristimulus Values
Same Color Perception(For Average Observers)
Colors Are No Physical Attributes
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Color Reproduction
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Additive Display
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Color Gamut
Spectral (monochromatic) locus
Primary colors
Mixtures of two colors
Mixtures of three colors
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Digital Camera
http://en.wikipedia.org/wiki/File:Bayer_pattern_on_sensor.svg
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Cameras See Different
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Two Observers
Stimuli that look the same for one observermay look different for another
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Color Reproduction: Good
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Color Reproduction: Bad
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Color Reproduction: Ugly
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Color Reproduction: Mission Impossible
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A Camera Has No Gamut
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Red Rose
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Blue Lacquer
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Summary
• Colors are no physical attributes.• Physically different stimuli can produce the
same color sensation.• Two stimuli that produce the same color
sensation may look different when photographed with a camera.
• Two light sources that have the same color temperature may produce different object colors.
• Digital cameras have no gamut.• The color encoding defines the gamut.
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Future Prospects
• Cameras with spectral response more similar to the eye– Loss of dynamic range and sensitivity– Future sensor technology will compensate– Multi channel imaging
• Scene encoding without gamut limits– Floating point numbers– Wide virtual primaries– AMPAS ACES
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