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Re: ColorSync CMM differences
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Re: ColorSync CMM differences

I'm just running the RGB color values from the Mac system palette using
Generic RGB -> Generic CMYK and looking at the results. As for white
only the Heidelburg and Apple CMMs map white to white. The Kodak and Agfa
CMMs make white go a little cream.

When it comes to full testing, we'll be basically be trying to tweak based
on appearance.

I'd love to use a third party library source code library but that
unfortunately, that's been abandoned because we can't gaurantee the results
will be the same. We have to use the CMM specified in the profile header,
and Kodak, Agfa, and Heidelburg will never open source their CMMs.


on 10/30/00 8:20 PM, Martm Marma at email@hidden wrote:

> Hi,
>
> This is amazing. I did some checking on this subject comparing ColorSync,
> KCMS, Photoshop
> built-in CMM and my own open source CMM. As you tell, results are different,
> but no so different.
> KCMS seems to map white with white and black on black always, ColorSync seems
> to use the "smart
> CMM" approach, using some sort of gamut remapping. Anyway, the differences are
> small, of 3-4 over
> 65536 ( I checked differences using 16 bps). There are technicall reasons for
> these differences on absolute
> intents, but on perceptual ones, results should be same. Could you explain
> more about how you are chcking
> differences?
>
> About your query of cross-platform, perhaps my engine would be of use:
> http://www.lcms.coloraid.de
>
> Marti Maria
> The little cms project
> http://www.abaforum.es/martim/lcms.htm
> mailto:email@hidden
>
>
> ----- Original Message -----
> From: Tom Beckenham <email@hidden>
> To: <email@hidden>
> Sent: Monday, October 30, 2000 1:24 AM
> Subject: ColorSync CMM differences
>
>
>> Hi, I've been developing a piece of software that uses ColorSync for color
>> conversion. The results so far seem pretty good using the Apple CMM, but
>> I've noticed that the other CMMs provided (Heidelburg, Agfa, and Kodak)
>> produce slightly different results. I've also used the free open source
>> library - icclib (http://web.access.net.au/argyll/color.html) and again got
>> different results.
>>
>> I've always assumed that an ICC profile provided all the necessary color
>> matrixes/look up tables to perform color conversion calculations. I was
>> wondering why each CMM produces different results. I thought the ICC color
>> conversion method was fairly well defined, but it seems that everyone has
>> their own interpretion of it.
>>
>> I would like to know the technical reasons for these varying results, what
>> adjustments are made, and where in the conversion process these calculations
>> are performed. Why alter the CMM when the profile could be altered?
>>
>>
>>
>> --
>> Tom Beckenham
>> Advanced Development Group
>> QuickCut Pre-Press Network Pty Ltd
>> email@hidden
>> http://www.quickcut.com.au/
>> _______________________________________________
>> colorsync-dev mailing list
>> email@hidden
>> http://www.lists.apple.com/mailman/listinfo/colorsync-dev
> _______________________________________________
> colorsync-dev mailing list
> email@hidden
> http://www.lists.apple.com/mailman/listinfo/colorsync-dev

References: 
 >RE: ColorSync CMM differences (From: Martí María <email@hidden>)



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