[argyllcms] Re: Custom Illuminant

  • From: Brad Funkhouser <brad.funkhouser@xxxxxxxxxxx>
  • To: "argyllcms@xxxxxxxxxxxxx" <argyllcms@xxxxxxxxxxxxx>
  • Date: Mon, 07 Jul 2014 17:27:49 -0500

I agree, BetaRGB is also D50, which I like versus the D65s.  I'll check out 
eciRGB... That's not one I'm familiar with.  

Thanks for the suggestion.

- Brad

> On Jul 7, 2014, at 3:13 PM, Roger Breton <graxx@xxxxxxxxxxxx> wrote:
> Also, what I like about eciRGB is the fact there is never any issues with
> chromatic adaption since everything happens on a pure-D50 scale, from PCS to
> RGB to XYZ to "infinite and beyond!" -- sorry, got carried away...
> / Roger
> -----Original Message-----
> From: argyllcms-bounce@xxxxxxxxxxxxx [mailto:argyllcms-bounce@xxxxxxxxxxxxx]
> On Behalf Of Brad Funkhouser
> Sent: 7 juillet 2014 14:40
> To: argyllcms@xxxxxxxxxxxxx
> Subject: [argyllcms] Re: Custom Illuminant
> When AdobeRGB is a little too small, and ProPhotoRGB is just too big, try
> Bruce Lindbloom's BetaRGB, it might be just right.
> - Brad
>> On Jul 7, 2014, at 9:18 AM, <robert@xxxxxxxxxxxxxxxxxx> wrote:
>> << How does the gamut mapping know that no mapping is required ? If 
>> you tell it the source gamut is ProPhoto, then it will think that lots 
>> of gamut mapping is needed, since the ProPhoto gamut is so much larger 
>> than a printer !>>
>> Well that has finally clarified that point for me!  So with Perceptual 
>> the whole source gamut is squashed down to the destination gamut, even 
>> if all the colors are within the destination gamut.  This means that 
>> in a Perceptual mapping from ProPhoto to print, colors will be 
>> compressed resulting in desaturation of the image, particularly of the 
>> more saturated colors nearer the print gamut boundary.
>> So the following strategy might make sense for a Relative intent
> conversion:
>> - Going from ProPhoto to print, make sure the colors are more or less 
>> within the destination space to avoid too much clipping.
>> And the following for Perceptual:
>> - Do a Relative conversion from ProPhoto to AdobeRGB (making sure the 
>> colors are more or less within the AdobeRGB space before the 
>> conversion to avoid too much clipping).
>> - Do a Perceptual mapping from AdobeRGB to print.
>> I did a comparison of a 1-step ProPhoto [Perceptual to Print 
>> conversion] with a 2-step [ProPhoto to AdobeRGB conversion, followed 
>> by an AdobeRGB Perceptual to print conversion]:
>> - If the original image colors are all within the AdobeRGB gamut there 
>> is quite a difference if the print gamut is much smaller than 
>> AdobeRGB, but none if it is of similar size.
>> - If the original image colors are outside the AdobeRGB gamut, the 
>> 2-step approach is significantly better even if the print gamut is 
>> very close to the AdobeRGB gamut.
>> This is a bit puzzling because I would have expected a difference in 
>> all cases (if the full ProPhoto gamut is squashed down in a Perceptual 
>> conversion).
>> What would be nice would be to be able to make the smaller 
>> intermediate working color space using tiffgamut/colprof (from a range 
>> of typical images), but I don't see how that could be done.
>> Robert

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