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[Groff] CMYK <-> RGB
From: |
Werner LEMBERG |
Subject: |
[Groff] CMYK <-> RGB |
Date: |
Thu, 04 Oct 2001 17:51:02 +0200 (CEST) |
Looking into the jpegtopnm program which is part of the netpbm
package, I see the following two algorithms to convert from CMYK to
RGB:
CMYK_NORMAL_COLORSPACE:
r = ((maxval-k)*(maxval-c))/maxval;
g = ((maxval-k)*(maxval-m))/maxval;
b = ((maxval-k)*(maxval-y))/maxval;
CMYK_ADOBE_COLORSPACE:
r = (k*c)/maxval;
g = (k*m)/maxval;
b = (k*y)/maxval;
This differs from the formula used in groff (as submitted by Gaius; to
be available soon from the CVS):
r = maxval - min(maxval, c*(maxval-k)/maxval + k);
g = maxval - min(maxval, m*(maxval-k)/maxval + k);
b = maxval - min(maxval, y*(maxval-k)/maxval + k);
[Gaius, your original formula was incorrect; it missed the division by
`maxval'.]
Which one is the `best' or the `correct' one?
Werner
- [Groff] CMYK <-> RGB,
Werner LEMBERG <=
- [Groff] Re: CMYK <-> RGB, Keith Packard, 2001/10/05
- Re: [Groff] Re: CMYK <-> RGB, Ralph Corderoy, 2001/10/05
- Re: [Groff] Re: CMYK <-> RGB, Tadziu Hoffmann, 2001/10/05
- Re: [Groff] Re: CMYK <-> RGB, Keith Packard, 2001/10/05
- Re: [Groff] Re: CMYK <-> RGB, Larry Jones, 2001/10/05
- Re: [Groff] Re: CMYK <-> RGB, Ralph Corderoy, 2001/10/05
- Re: [Groff] Re: CMYK <-> RGB, Larry Jones, 2001/10/05
- Re: [Groff] Re: CMYK <-> RGB, Larry Jones, 2001/10/05
- [Groff] Re: CMYK <-> RGB, Werner LEMBERG, 2001/10/05
Re: [Groff] CMYK <-> RGB, Ralph Corderoy, 2001/10/05