[argyllcms] Re: perceptual black too light

Graeme Gill wrote:
Furthermore, since paper usually has a reflectance of < 100%, the luminance of paper white, after transformation to the monitor space, becomes implicitly lower than the monitor white luminance, which also helps to reduce out-of-gamut probles if tinted paper white is simulated on the monitor).
Right, but it doesn't work properly the other way around.

That's indeed true, it does not work the other way round (at least not without additional luminance downscaling by the CMM). Furtunately, softproofing a print on a monitor seems to be more usual than vice versa.

The same effect could have been achieved by simply linking your paper source in absolute, to the display in relative, if that's the effect you wanted.

Right, basically this would have the same effect (except if an exceptional display profile would assume that the observer is not adapted to monitor white, and thus would have a wtpt tag != D50).

I'm not sure that's true. If you make a conscious effort to compare the book to other things in the environment, then yes, I'm sure you can make a judgement about it's paper color, relative to the appearance of other white references you can see. But
if you are actually reading the book, I don't think you would interpret it as being other than "white".

I'm not sure, whether an explicit white reference is stringently necessary; I think it's probably even sufficient to see enough familiar objects in the surround in order to trigger the cognitive mechanisms for discounting the illuminant. But I also have doubts, whether it would work as well in an artificial environment with only unusually colored, artificial objects. It also won't work if the tint of the paper to judge isn't strong enough. And it also seems to work better in daylight, than under e.g. tungsten light.

The effect is purely subjective. If you flip an edge of the paper over to lie beside the highlight in a photo, it is clear that they are the same color. It's interesting that broader areas of the paper do not look so white. Simultaneous contrast helps accentuate the appearance of white in the photographs.

Yes, it's interesting. Under "normal newspaper reading conditions" I think I would not judge the paper color of a significantly tinted newspaper (like e.g. the pink Financial Times, or others) as "white". But I agree, in printed images the vision seems to be obviously more inclinable to accept the color of unprinted paper as white. Yes, this seems to be a simultaneous contrast issue.

With ICC-absolute intent, such an absolute match (for a side-by-side comparison) can only be achieved with a D50 calibrated monitor (or in the general case, with a monitor whose WP is calibrated to the illuminant color used to view the print).
I think it can be achieved without this, if the application uses full screen display, and if the CMM is smart enough to avoid clipping the white. There would be more flexibility using this sort of approach.

I meant, if a true absolute match (same XYZ) to a D50-illuminated print is required, and if ICC-absolute intent is used for the proofing transformation (strictly according to the ICC spec, without any additional smartness of the CMM), then the absolute match can only be achieved with a monitor whose WP is calibrated to D50 - that's a limitation of this intent.

Regards,
Gerhard



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