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List:       kde-kimageshop
Subject:    Re: Off-by-many error
From:       Boudewijn Rempt <boud () valdyas ! org>
Date:       2005-08-22 6:54:49
Message-ID: 200508220854.50317.boud () valdyas ! org
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On Sunday 21 August 2005 16:21, Boudewijn Rempt wrote:

> The slower code works correctly, the clever code doesn't -- and I cannot
> find out what exaclyt doesn't work there, so I'll just checkin the correct
> code for now... 

I discovered what was wrong... It was not the code in KisPaintDevice; we used 
the wrong lcms type for cmyk. We used type_cmyk_8, which doesn't provide for 
the alpha byte at the end of the cmyk pixel (cmyka). So, converting one pixel 
always worked, but converting more than one pixel gave very amusing errors, 
because of the increasing off-ness -- which was reset on every tile boundary.

Anyway, it appears the right lcms type to use is type_cmyk5_8. This may give 
is grief in future, though, because with this type, lcms doesn't check 
whether the colorspace is correct for a given transform.

-- 
Boudewijn Rempt 
http://www.valdyas.org/fading/index.cgi

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