Understanding ‘Selective Color’ `?

H
Posted By
hannes
Jul 13, 2006
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863
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1
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Closed
Hi,

i’m tryng to understand the ‘Selective Color’ command in photoshop. I managed to figure out how the command changes the ‘control’ colors (yellow, green, blue, red, cyan, magenta, black, grey, white). E.g. mode ‘relative’ transforms the color to CMY, multiplies the (C,M,Y) factor with the (C,M,Y) value of the respective color and re-transforms the color to RGB.
But i couldn’t figure out how the command changes the ‘intermediate’ colors. Must be some sort of interpolating, but there are many possible choices for interpolation, and in which color model is interpolated ?

Is there some ‘selective color’ expert who can give me a hint ?
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Mike Russell
Jul 13, 2006
"Hannes F." wrote in message
Hi,

i’m tryng to understand the ‘Selective Color’ command in photoshop. I managed to figure out how the command changes the ‘control’ colors (yellow, green, blue, red, cyan, magenta, black, grey, white). E.g. mode ‘relative’ transforms the color to CMY, multiplies the (C,M,Y) factor with the (C,M,Y) value of the respective color and re-transforms the color to RGB.
But i couldn’t figure out how the command changes the ‘intermediate’ colors. Must be some sort of interpolating, but there are many possible choices for interpolation, and in which color model is interpolated ?
Is there some ‘selective color’ expert who can give me a hint ?

Probably not, since Adobe does not document their color algorithms, nor discuss them publicly. My guess is that Selective color is implemented in Lab mode, and that ranges of a and b are used to define a particular range of hues. Most of the other color calculations use Lab, with the exception of layer blending calculations, which seems to be mostly based on HSB.

The free LabMeter download at curvemeister is a good experimental image – for example you can use Select>Color Range and see the resulting square selection regions on the Lab image.
http://www.curvemeister.com/tutorials/LabMeter/index.htm —
Mike Russell
www.curvemeister.com/forum/

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