Lab to RGB

G
Posted By
grigi
Aug 10, 2007
Views
247
Replies
3
Status
Closed
I have L*A*B colour: L+58, a+25, b+22. I fill a new document (in LAB). Now I need convert colors to RGB (relcol and ACE module). OK, it’s possible. But then I pickup someones pixels and compare the color… Ouch, RGB is diferent. With levels I make contrast (www.grigi.cz/forum/cs3-labrozklad.jpg) Very nice 🙂

With Adobe CMM modul is all OK. It is bug? Thanks.
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GH
Gernot_Hoffmann
Aug 10, 2007
grigi,

the experts here can tell you, how Lab
is converted into sRGB or AdobeRGB(98),
but they cannot tell you, how someone’s
pixels might appear in these color spaces.

Furtheron, the colors in your link are not
the least related to the Lab values.

Please define your example, as usual by
numbers in a source space and by numbers
in a destination space.

Best regards –Gernot Hoffmann
G
grigi
Aug 10, 2007
OK (sorry, my english is terrible).

I have color in LAB – L+58, a+25, b+22. I have a new document in Lab and I fill space 100 x 100 px with the Lab color (defined with Lab valu) and after I convert this document to sRGB with relative colometric method and with Adobe ACE module. After convert I have document in sRGB, but any pixels have color (sorry, now I’m at home and I have not exact values) 188/122/102 and others pixel have color 189/122/102. After contrast (see www.grigi.cz/forum/cs3-labrozklad.jpg) is possible this "noice" catch.

With module Adobe CMM is convert from Lab to sRGB (relcol) correct. And now – is bug in Adobe Ace module, or the noice is rounding in the convert or is it any other?
J
Jim
Aug 10, 2007
wrote in message
OK (sorry, my english is terrible).

I have color in LAB – L+58, a+25, b+22. I have a new document in Lab and I fill space 100 x 100 px with the Lab color (defined with Lab valu) and after I convert this document to sRGB with relative colometric method and with Adobe ACE module. After convert I have document in sRGB, but any pixels have color (sorry, now I’m at home and I have not exact values) 188/122/102 and others pixel have color 189/122/102. After contrast (see www.grigi.cz/forum/cs3-labrozklad.jpg) is possible this "noice" catch.
With module Adobe CMM is convert from Lab to sRGB (relcol) correct. And now – is bug in Adobe Ace module, or the noice is rounding in the convert or is it any other?
It could easily be that r=189, g=122, and b=102 in sRGB space correctly correspond to l=58, a=25, and b=22 in Lab space. The a and b values define a color while the l value defines lightness.
However, the RGB values define both a lightness and a color. So direct correlation is difficult at best especially since there are lots of colors in Lab space which can only be approximated in
sRGB space.

Jim

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