[argyllcms] Re: sRGB/AdobeRGB98 vs Lab (was Verifying profile quality...)


I can see it would be useful perhaps to have two shapes then, i.e keep them separate. One for 'safe emissive conditions', and one for typical reflective conditions, assuming D50 white point with optimal lighting, perhaps as you might find in a gallery [and not the average home loungeroom]. 

For some purposes, yes. The emissive one is still pretty arbitrary
however (how much light to you assume it can generate at an individual
wavelength, compared to the white point ?), and even the reflective
one has a degree of arbitrariness, in the choice of illuminant.

Yes I agree that there is an arbitrariness to this, but it must be possible to settle on some safe energy limits (that correspond to the typical energy for 'white' on a good LCD (250 cd/m2 ?) regardless of the color?

And yes, reflective of course is dependent on the choice of illuminant, but since the objective - well what I personally I think would be a useful objective - is to figure out the gamut of the eye in practical terms, I would be picking a reasonably high level of illumination that corresponded with reasonably bright sunlight or nice bright lighting indoors. (Probably not 1kW Halogen flood lamps plastered all around the room though). And as far as color temp, I would be happy if it was either D50 or D65 so long as it was stated. Once again, the lighting conditions may be 'theoretical' only, in the sense that they may be far too ideal to be achieveable in practice, but that doesn't matter.

Having two "visible gamuts" defeats the original purpose I think,
since it was to compare different types of output devices.

I still see value in having them as two separate shapes for gamut comparison purposes, but there's nothing to stop you - if it was seen as useful - from then taking the union of the two, representing the gamut of human vision for all practical purposes. Mathematically that might well have discontinuties in it, but that's probably a lot easier than trying to model both gamuts in one set of transforms?

You could still compare the gamuts of the various devices with both 'eye' gamuts...in fact it may be more useful because you would be able to see what parts of the gamut the device might produce that were for all practical purposes irrelevant.

What I'm still wondering is how you go about measuring the gamut of the eye anyway? Presumably the IEC have done all these sorts of tests over the last few decades?

An associated factor (which is largely being overlooked in
all this I think), is that the color gamut of an emissive
device can be manipulated by the choice of white point.

Using display calibration to set maximum brightness defeats
this idea, and the normal ICC way of storing relative colorimetric
information also works against it, but if the
maximum brightness was set in the profile (and
this might be something as simple as setting a
white point below the level of the maximum output,
depending on how the profile was subsequently used),
the effective gamut of a display can be boosted
considerably in the area of bright saturated colors.
I'm not sure this would help much in making a display
encompass more of a printing gamut (since printers tend to
be large in the darker saturated colors area), but
it could help (particularly when modern LCD monitors have
brightness to burn.)

Yes that's true, but I don't see a problem with that. If you do this with an LCD, and it's set to maximum backlight brightness you're doing this anyway since any adjustment in the monitor's white balance color temp is just ultimately fiddling with the input values, so one might as well let the profile do it all.

This is similar to a point made in the other thread about playing with the sliders in a printer driver to get the best possible gamut. You end up with a wider gamut, but the printer ends up being totally 'uncalibrated'. This is fine so long as the profile can straighten all that out!

..Milton

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