05. Primaries - 2011

05. Primaries - 2011 - ECE 638: Principles of Digital Color...

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ECE 638: Principles of Digital Color Imaging Systems Lecture 5: Primaries
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Synopsis Brief review of sensor concepts Spectral model for additive primary mixtures Computation of match amounts Transformation between primaries Color matching functions
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Review: development of chromaticity diagram Shape of spectral response functions for sensor Consider three example sensors Spectral locus Mixture stimuli Polar coordinate interpretation of chromaticity coordinates Chromaticity gamut Spectral response functions for the HVS
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Review: Trichromatic sensor model are spectral response functions that characterize the sensor R S = S ( λ ) Q R ( ) d G S = S ( ) Q G ( ) d B S = S ( ) Q B ( ) d λ Q B ( λ ) λ Q G ( λ ) λ Q R ( λ ) Q R ( ), Q G ( ), Q B ( )
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Review: Plane where R+G+B=1 Represents points of roughly equal lightness All colors that differ by a scalar multiple will intersect this plane at the same point α
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Review: polar coordinate representation of color This suggests a polar coordinate interpretation of color Origin of system is at center of chromaticity diagram – corresponding to intersection of neutral axis in RGB sensor space with chromaticity plane Angle of chromaticity coordinate with respect to horizontal axis is a correlate of hue Distance from origin is a correlate of saturation
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Review: sensor with three channel overlap Sensor response functions Spectral locus
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Primaries Recall color matching experiment In order to understand this process, we need to develop a spectral model for the match stimulus
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Additive mixture of primaries Consider a mixture of three primaries, each of which is described by its spectral density The amounts of the three primaries are given by the constants For convenience, we identify the primaries as R,G, and B. However, at this point, their corresponding spectral densities are completely arbitrary P ( λ ) = p R P R ( ) + p G P G ( ) + p B P B ( ) ( p R , p G , p B )
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What kinds of output devices can be modeled as additive? Additive devices CRT monitor Rear projection TV LCD Of these three, only one is additive at the microscopic level Which one is it? Why? How can we describe the others as being additive? Questions for group discussion: Which of the above display technologies is truly additive? Why? How can the other display technologies be described as additive?
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What kinds of output devices can be modeled as additive? Additive devices CRT monitor Rear projection TV LCD Of these three, only one is additive at the microscopic level Which one is it?
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This note was uploaded on 02/19/2012 for the course ECE 638 taught by Professor Staff during the Fall '08 term at Purdue.

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05. Primaries - 2011 - ECE 638: Principles of Digital Color...

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