Saturday, September 3, 2011

The Black Point

Covering the white point and the color end points (red, green and blue) in previous post, I forgot about the black point.

It's the reference point for 'black'.

I tried to incorporate it, but I only have a few profiles which contain a black point setting.

And the problem is: all values for XYZ are zero in those profiles.

And zero for all values is a problem, because the conversion functions (from XYZ (3D) to xyY (2D) and then back) all result into zero if the big Y is zero.

It means: dragging the point doesn't lead to updated XYZ values. The zero Y (which is used unchanged in the conversion from xyY to XYZ) spoils it.

To actually still see the effect I fiddled a bit with Y (give it a value bigger than zero) but it doesn't seem to matter for the color conversion. XYZ then do update, but there's no changes in my proofing photo in none of the rendering intents (perceptual, relative, saturation or absolute).

It seems the black point isn't taken into consideration at all.

Could be that it only does 'something' in say Output profiles (for printers for instance). The color conversion functions in the Windows API only handle Display profiles, not Output profiles, but it could also be that it only has an effect when changed in the start profile (which I have to find out by using the multi-profile proofing, which isn't in place yet for the editors).

I'll investigate this a bit further, see if the photo should update or not and if I'm at fault here...

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