Re: A color space puzzle
Re: A color space puzzle
- Subject: Re: A color space puzzle
- From: Rolf Gierling <email@hidden>
- Date: Thu, 07 Feb 2002 11:52:50 +0100
Hello Bruce,
this is a very simplified description of what happens
(easy to think about for me, but difficult to describe,
if you dont want to mention the math behind it).
If you want to solve it mathematicly, you may
want to take a look at an article Tom Lianza
wrote (www.sequelimaging.com).
(Technical Paper: Converting XYZ to RGB by Tom Lianza.)
>
Tom Lianza wrote there:
>
RWNS (Read When Not Sleepy)
The conversion you do uses (monitor)profiles.
Their profile connection space is XYZ.
So the conversion is sRGB - XYZ - AdobeRGB and vice versa.
If you simplify it, X is a kind of red, Y a kind
of green and Z a kind of Blue.
But, by definition, Y is the luminance of the color,
and both spaces have the same white with a luminance
of 1.
If you want to keep the luminance of the color unchanged,
the conversion G(sRGB) - Y - G(AdobeRGB) must result
in the same values for green. So red and blue must change.
Again, this is very simplified.
Rolf Gierling
"Bruce J. Lindbloom" wrote:
>
A popular color space among those on this list is Adobe RGB (1998). A less
>
popular one is sRGB. If you compare their two definitions, you will find
>
that they both have the same gamma (2.2), they both have the same white
>
point (D65), they both have the same red primary (0.64, 0.33) and they both
>
have the same blue primary (0.15, 0.06). In fact, the ONLY difference
>
between them is in the green primary: Adobe RGB (1998) is (0.21, 0.71) and
>
sRGB is (0.30, 0.60). And yet, if you convert an sRGB image to Adobe RGB
>
(1998) or vice versa, you will find that it is the red and blue channels
>
that change -- green remains completely unchanged. That doesn't seem right.
>
How do you explain it?
--
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--Rolf Gierling Multitools--
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52064 Aachen
Germany
Tel. +49/241/4012579
Fax +49/241/4012583
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