Re: [Openexr-devel] Colour space

[gary demos]

Chris,

Thanks for your comments.  With respect to CIE 1931 XYZ (and xy), there 
are some who agree with you,
that it is adequate, and there are some who feel that the errors are 
significant.  I have attached an interesting
example using the Judd/Vos 1978 correction to the x_bar, y_bar, and 
z_bar functions.  This example is
using LED color primaries.  Note that the white/grey match is centered 
in the inter-person variation point-cloud
using Judd/Vos1978, whereas CIE 1931 XYZ is at the lower-left of the cloud.

It is also worth mentioning that Judd/Vos 1978 only corrects cyan and 
blue, and there are also know disparities
in the average in red, yellow, and green.

I have also seen an unpublished result testing Metal-Halide (UHP) lamps 
vs Xenon in white matching, show
a similar systematic average error when using CIE 1931 XYZ.  Note that 
white matching is not likely to
be the most stressful match, so there are probably cases, using a few 
spikey spectra where CIE 1931 XYZ
is further from the average viewer.

I am not sure that CIE 1931 XYZ is inadequate.  However, I suspect that 
this is the case.

Again, these opinions are my own, and do not represent any group.

-Gary Demos


Chris Cox wrote:

> Yet neither RIMM nor ERIMM are linear (gamma 1.0) colorspaces. OpenEXR 
> files are supposed to be gamma 1.0.    So  you can't apply those 
> colorspaces as-is.
>
>
> > The problem with RIMM and ROMM, as well as with XYZ and most other 
> > systems (e.g. Rec 709 HDTV) is
> >  that the color primaries are specified in terms of CIE 1931 xy 
> > chromaticity coordinates.  This is also true for
> >  the primaries in the OpenExr header.
>
>
> That's not a problem - that's the standard, with good reason.
>
>
> > CIE 1931 xy chromaticity relies upon x_bar, y_bar, and z_bar spectral 
> > matching functions, which are known to
> >  have some errors in certain color regions (especially near cyan at 
> > 500nm, but also at other places in the spectrum).
>
>
> Not much error according to the reasearch I've seen.
> Yes, it could better account for women with a fourth primary sensor 
> and color deficient viewers.
>
>
> >  I have been inquiring of color scientists concerning a) how much of 
> > a problem are the errors in CIE 1931 XYZ,
> >  and b) how much benefit is there from going to more than three color 
> > primaries for the device-independent space.
>
>
> a) not much
> b) more than 3 primaries would present some mathematical difficulties 
> (N->1->N mappings anybody?)
>
>
> Chris
>
>
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LED color match test.pdf
Description: Adobe PDF document