04. Chromaticity diagram - 2011

04. Chromaticity diagram - 2011 - ECE 638: Principles of...

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ECE 638: Principles of Digital Color Imaging Systems Lecture 4: Chromaticity Diagram
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Goal is to understand the origins and meaning of everyday chromaticity diagrams, such as the CIE xy diagram
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Synopsis Brief review of trichromatic theory Develop chromaticity diagram Examine conditions for prediction of response of one sensor based on another Limitations of trichromatic theory
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Review: Development of trichromatic theory Sensor model Reinterpretation of conditions for color match Metamerism Linearity of sensor model Response to monochromatic stimuli Chromaticity diagram
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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: Metamerism Stimuli and are said to be metameric with respect to the sensor if they elicit identical responses Metamerism is both a blessing and a curse for color imaging systems designers S 1 ( λ ) S 2 ( ) 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: Chromaticity diagram For a particular set of nonorthognal axes, the lengths of the perpendiculars illustrated below can be shown to satisfy ( r , g , b ) r = R R + G + B g = G R + G + B b = B R + G + B r + g + b = 1
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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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Notation Use upper case symbols for sensor response Use lower case symbols for corresponding chromaticity coordinates C = ( R , G , B ) c = ( r , g , b )
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Effect of shape of senor response functions on sensor performance Consider again the ideal block sensor Intuitively, we might expect that this would be a good sensor full coverage of spectral band at uniform sensitivity no overlap of response from different channels minimize cross-talk or “confusion”
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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 University-West Lafayette.

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04. Chromaticity diagram - 2011 - ECE 638: Principles of...

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