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List:       koffice-devel
Subject:    Problems with the conversion formulas of RGB to CMYK and back.
From:       Tim Beaulen <tbscope () gmail ! com>
Date:       2005-12-22 11:05:08
Message-ID: dd1e9b170512220305n72b7bef2h98a50e40a30eb5f3 () mail ! gmail ! com
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Hello,


I tried to use the Krita color dockers in Karbon and this went well,
but there was no Krita CMYK color docker yet. So I tried to create
one.

I used the formulas in the following PDF to convert between RGB and CMYK:
http://www.poynton.com/PDFs/coloureq.pdf

But something is going wrong when calculating the black level (k).

When all three C, M and Y sliders are not 0 anymore, the K level will
change (according to the formulas). But this is, in my opinion, wrong.
The result is that if I change C and M and Y are not 0, then all the
sliders will move.

But everywhere I look, I find a similar formula.


It would be great if someone could take a look at
/lib/kopainter/ko_cmyk_widget.*
I looked at it for two days and whatever I did, the only conclusion I
could make was that the formulas are wrong. And conversion / rounding
errors (between float and int).


Thanks,

Tim
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