Re: [Lcms-user] Soft proofing problems with gamut checks

[Elle S. <ell...@ni...>]

On 11/03/2016 05:59 PM, mar...@li... wrote:
> You are right, gamut check was not intended to work in unbounded mode
> and also, due to the way it works, it needs a space perceptually uniform
> to perform good. This is because gamut check uses a LUT driven by CIE
> L*a*b* to hold the distance of each color to gamut boundary. Works well
> for traditional 8-bit imaging but definitevely not for linear spaces
> close to XYZ.
>
> This is not a bug, but a limitation due to the algorithm used. I take
> two action items: fully de-activate gamut check on unbounded mode and
> document the limitation. Will happen in 2.9

Hi Marti,

Regarding "de-activate gamut check on unbounded mode",

1. Does this mean that in LCMS 2.9, if the source color space is capable 
of being used to encode out of gamut colors using floating point values, 
then the user won't be able to activate an LCMS gamut check?

2. Will the gamut check be de-activated even if the image itself is at 
integer precision, but the source color space itself does support 
encoding out of gamut floating point values?

3. Will the 2.9 code check to see if the source color space is a linear 
gamma color space, and then also de-activate the gamut check? Well, I 
guess usually there wouldn't be a need to check (depending on the answer 
to the first two questions), because parametric and gamma curve linear 
gamma profiles support floating point unbounded editing. Although there 
are linear gamma ICC profiles available that have 4096-point TRCs.

No gamut check at all is probably better than an inaccurate gamut check. 
But soft proofing without the option to activate a gamut check does 
limit the information available to the user when preparing an image for 
conversion to another ICC profile.

Best regards,
Elle