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Re: GaMapICC

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Re: GaMapICC

Subject: Re: GaMapICC
From: Klaus Karcher <email@hidden>
Date: Thu, 16 Oct 2008 12:45:32 +0200

Hi Martin,

you wrote:

I have also seen this problem and can show you an example.
This is a small section of an image that I am working on that is in AdobeRGB:
<http://www.web36531.clarahost.co.uk/filedump/16665_aRGB.tif>
This is a similar section cropped from a device link conversion to ISO Coated v2 using Argyll:
<http://www.web36531.clarahost.co.uk/filedump/16665_ISOv2_DL.tif>
And here is the same section cropped from a conversion using Argyll's gamut mapping:

<http://www.web36531.clarahost.co.uk/filedump/16665_ISOv2GM.tif>

Thanks for sharing your example. I'm not quite sure about the differences between 16665_ISOv2_DL.tif and 16665_ISOv2GM.tif. Can you please specify the steps/commands that led to the results? I guess 16665_ISOv2GM.tif is an image specific conversion with 100% popularity filtering -- but what is 16665_ISOv2_DL.tif?

From a retoucher's perspective there's too little information in the weak channels in the gamut mapped version. Without small amounts of cyan and black you end up with no detail in the magenta.

A pixel count shows that the original RGB has 62,569 colours. The device link conversion creates an image with 95,623 colours whereas the gamut mapped conversion only has 51,383 colours :-(

This trick (counting unique colors) appears to be a practical measure of entropy correlated with the perceived richness of detail IMHO (at least as long as you compare transformations of the same source image to the same target colorspace).

I'm using Argyll all the time to create device link profiles and apply them to images but I'm not convinced by the gamut mapping features at all.


Thank you,
  Klaus

--
Klaus Karcher * Eichenallee 18
26203 Wardenburg * Germany
Tel. +49 441 8859770
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References:  
  >Re: GaMapICC (From: Don Hutcheson <email@hidden>)
  >Re: GaMapICC (From: Klaus Karcher <email@hidden>)
  >Re: GaMapICC (From: Martin Orpen <email@hidden>)




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