hi Mart�,
 
good news for you.
conversion with icctrans works quite well - in both directions.
  now i know how to deal with it :-) values are the same as in
  photoshop - except for rounding differences.
 
i must admit - hmmh - i made a beginners mistake...
when choosing color values with photoshop 'color picker' i was in
  L*a*b* color space - and so was very often out of RGB gamut...
  got a hot flush when i realised this.
 
sorry Mart� for this false alarm, my only excuse is that i _am_ a
  newbie to color models and color handling.
 
maybe you like to know how i came to lcms...
i intend to make a tool to adjust brightness of each individual pixel
  of a picture - for now JPEGs.
to do so i modified the IJG source code - needed three days of
  hard work...
when i came to the point where i had access to the sample data i
  wondered how to modify the RGB values in order to modify
  brightness - but without changing the 'color' or at least my
  perception of a color becoming 'lighter'.
whatever this _really_ means - need to find out more about it -
  i figured this must be difficult modifying three independent color
  values at once.
in that situation i threw my eyes upon the L*a*b* color model which
  hopefully gives me what i want - at least it has one value to adjust
  'lightness'.
but how to convert RGB to L*a*b* from within C code? now i know
  the answer and am very happy with it.
 
thank you Mart� and all others involved in lcms project!
 
andreas
 
----- Original Message -----
Sent: Saturday, March 16, 2002 3:14 PM
Subject: Re: [Lcms-user] conversion sRGB to L*a*b* fatal error

Hi,
 
> i am trying to validate the 'icctrans'-values for sRGB IEC61966-2.1 to L*a*b* conversion.
 
Humm... I have checked this utility extensively, and seemed to work.
Are you sure Photoshop is using sRGB as workspace (Edit-Color settings-Working spaces RGB)?
 
I'm also attaching latest source, with some small additions. But anyway the old one did work properly to me...
 
This would give sRGB to Lab
 
icctrans -v
 
And this Lab to sRGB
 
icctrans -i*Lab
 
If this don't work to you, could please send any values that makes it fail? Thanks.
 
Regards,
Mart� Maria
The little cms project
http://www.littlecms.com
[EMAIL PROTECTED]
 
 
 
 
 
----- Original Message -----
Sent: Friday, March 15, 2002 5:10 PM
Subject: [Lcms-user] conversion sRGB to L*a*b* fatal error

hello marti,
 
i am trying to validate the 'icctrans'-values for sRGB IEC61966-2.1 to L*a*b* conversion.
i want to validate against adobe photoshop - i simply use the 'color picker' to get values.
i am unlucky :(
neither the built in profile 'cmsCreateLabProfile(NULL)' nor 'lcmstiff8.icm' nor 'tifflab8spac.icm' give me the photoshop values.
 
i built lcms 1.08 with cygwin on win2000, build looked ok.
 
what do you think?
maybe i missed something?
i'm not sure whether i use the right profiles.
 
regards,
andreas

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