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Author Topic: Lab vs aRGB midpoint question  (Read 1868 times)
Jonathan Wienke
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« on: July 25, 2005, 01:35:02 AM »
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LAB and Adobe RGB do not have the same luminance gamma.
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Hermie
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« Reply #1 on: July 25, 2005, 01:14:59 AM »
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Can someone help me out on this one?

A Lab luminance value of 50% in Adobe RBG space equals RGB 118,118,118 and a brightness of 46% in HSB.
Now aRGB is a perceptual uniform color space with gamma 2.2, so why isn't a luminance of 50% situated at RGB 128,128,128? Does this mean that aRGB is not as uniform as Lab?

When I do the math on 18% reflectance I also arrive at 46%: 0.18^0.4545=46% (0.4545 = function of lightness sensation, the inverse of a gamma of 2.2). Or am I mixing up things?

Thanks

Herman
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