MDenham wrote:
> Eh, negative luminance + positive Cr/Cb = <+,-,+> potentially (forgive the
> massively bastardized variation on standard color syntax ;-D) - and negatives
> on green are, from looking at normal "RGB vs. real coloring" gamut diagrams,
> probably the most common colors that exist but aren't displayable.  Also, the
> engine already handles "impossible" colors (components all negative,
> hypersaturated colors that extend outside the gamut in the opposite direction,
> &c.) so it's not like that's necessarily an issue other than the obvious "it'll
> look weird and may not behave entirely correctly".
> 

Jpeg's YCbCr is a 1:1 adaption of the European standard tv signal 
encoding (CCIR/ITU Rec. 601 IIRC) with the advantage that you can just 
drop the CbCr part. This did make people happy who couldn't afford a 
color tv. Sending a signal with negative Y would have made people quite 
unhappy 'cause you just imploded their brand new tv set ;)
Seriously, jpeglib uses a strict range checking anyway (to avoid such 
issues as the DCT compression might introduce some noise) and YCbCr is 
just not *designed* to represent anything outside the gamut of a tv 
monitor from this time. Thats not as bad as it sounds because, if I'm 
not mistaken, this gamut was even defined wider than the currently 
accepted sRGB gamut.


> Isn't the "formula" for CMYK->RGB essentially specific to an "ideal" ICC
> profile?

An "ideal" CMYK ICC profile is somehow meaningless and does not exist.
Therefor such a 'formula' cannot exist and this was from the very 
beginning my point ;)
What we have is a bunch of numerous international standards within the 
printing business and an ICC profile is used to make clear to what 
standard the CMYK separation does refer, tells something about the 
intended ink set, raster...  and *a lot* more things.


> *goes off to figure out a good syntax for true spectral
> lighting and pigmenting, which is probably more in the realm of additions to
> 4.0 or later but would allow for "true" conversions both ways as well as other,
> odder effects*
> 

This is of course also something I would like to have, but as I'm not so 
patient I'll wait with such things until computing power evolves much 
more...


-Ive

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