View Single Post
  #1  
Old July 11th, 2011, 06:49 PM
Doug Kerr Doug Kerr is offline
Senior Member
 
Join Date: May 2006
Location: Alamogordo, New Mexico, USA
Posts: 8,607
Default The Unified Color Beyond RGB (GMWAS) color space

[GMWAS: gag me with a spoon]

Unified Color Technologies (UCT), in their line of HDR image processing software, uses a color space they call "Beyond RGB". Just what is that?

Well, it turns out that the native file format for BRGB is BEF, and I suspect that describes a color space as well (Bef, actually).

One chart that appears here and there in the UCT documentation, "illustrating" the BRGB color space, is labeled "Bef2" (maybe an editorial slip). So maybe "Beyond RGB" is also "(a little) beyond Bef".

It appears that this color space is either a luminance-chrominance color space or a pseudo-luminance, pseudo-chrominance color space (I actually suspect the former). For reference, the L*a*b* color space is a pseudo-luminance, pseudo-chrominance color space.

Evidently, the coordinates of the color space are B, e, and f (fancy that). B is apparently the luminance (or pseudo-luminance) coordinate; the symbol is doubtless evocative of "brightness".

The coordinates e and f are apparently broadly similar in concept to the coordinates a* and b* of the L*a*b* color space (often called just "a" and "b").

Apparently 32-bit floating point representations of the coordinates are used (probably per IEEE-754).

This figure appears here and there in the UCT stuff:


Copyright Unified Color Technologies (I guess). Fair use for review purposes.

It is apparently a section through the color space of the Bef2 color space at some value of B (a chrominance plane). Apparently it shows a section through the sRGB color space as plotted in the Bef2 color space. Its gamut boundary is apparently the boundary of the gamut of human visibility at that value of B.

In all their literature, they use the word "color" to mean either chromaticity or chrominance. (As I say in my papers on color models, "as lay people, unaware of the technical meaning of color, do".)

In one piece, they say:

Beyond RGB is similar in concept to the Lab color space, in that it is also a three dimensional space with brightness or luminance on one axis and color information on the other two. In practical application however they differ significantly. Brightness changes in Lab can often introduce changes in color too, where as Beyond RGB maintains the integrity of the color data as brightness is changed. [Color keying added.]

What does the red passage mean? It might mean this:
In the L*a*b* color space, if we change L* but leave a* and b* the same, the chromaticity of the represented color changes.
[True.]

or maybe this:
In the L*a*b* color space, if we change L* but leave a* and b* the same, the chrominance of the represented color changes.
[A little true.]

Or maybe something else.

What does the green passage mean? It might mean this:
In the BRGB color space, if we change B but leave e and f the same, the chromaticity of the represented color does not change.
[Hard to believe, if e and f define a chrominance plane.]

or maybe this:
In the BRGB color space, if we change B but leave e and f the same, the chrominance of the represented color does not change.
[Easy to believe, but so what.]

Or maybe something else (but no doubt very desirable).

It's also possible that e and f are chromaticity, rather than chrominance, coordinates. In that case, presumably, if we change B but not e or f, the chromaticity of the represented color does not change.

That's all I know so far.

Best regards,

Doug
Reply With Quote