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RE: YUV/RGB Color Space Issues

On 18 Dec 97, Pete Mountanos <petemo wrote:
> If I read the posting from Discreet Logic correctly I am surprised.
> What I heard was that to solve the problem they reduce the size of the
> color space to fit into the YUV color space.  Please tell me this isn't
> true.
> Here's why.
> 1. RGB space is "larger" than YUV space.  Consider it a cube.  YUV can
> be considered a rectangular shaped box inside YUV rotated around so that
> projects a hectagon in 2-D space.

You are right. The RGB color space has a larger gammut than the YUV space.
BUT, because the end-of -the-line display devices, CRTs are RGB devices,
this greatly influences how we define a signal as being legal or not (I
know it's not the only factor..). So it is safe to assume that an approach
where the RGB color space is fit within the YUV space is safe and will
cover the vast majority of the colors which we can safely assume will
display accurately on the end projection devices.

The biggest challenges with YUV/RGB conversion are:

* High-precision computation matrices

* Ability to accomodate an extended range of YUV signal including what is
known in NTSC as super black and white

* Avoid RGB clipping by offering the user options in bringing out-of-scope
YUV values within the supported range.

     We now feel that the last generation of SGI computer platforms, for
which we develop software (that's what we do!), now offer us the tools to
intelligently adress these issues. I would hate to think that most of you
would not realize that the Discreet Logic systems are far from being the
only ones out there being faced with these issues; there are many other RGB
based systems and there are also many so-called YUV based systems that show
an RGB processing path somewhere. We want to deal with this issue
intelligently and openly as we try to do with everything. We recognize
these issues and they are being treated as top priorities by both Discreet
Logic and SGI. In the meantime, we feel confident that for most
post-production situations, our systems allow our clients (and they rank in
the hundreds and amongst the top post-production houses in the world) to
make money because this is what matters in the end. We've brought tools to
the post-production community that were innovative and allowed our
customers to be more creative and productive than ever before and bring the
quality of productions to new levels. No, we're not waiting on the future
to solve these issues, as someone seemed to insinuate, we are working on
them today and we believe that the wide-spreading of digital technology
will eventually bring new working habits and leave these problems behind
us, as has happened with many industries faced with the advent of computers
and other digital technologies.


Stephane Blondin

Editing Product Specialist, Discreet Logic

thanks to Neil Kempt for support of the TIG in 1998
TIG subscriber count is 910 on Thu Dec 18 14:07:18 PST 1997
complete information on the TIG website http://www.alegria.com/tig3/