Lourens Veen wrote:
On Friday 17 March 2006 23:16, Timothy Miller wrote:
On 3/17/06, James Richard Tyrer <[EMAIL PROTECTED]> wrote:
Timothy Miller wrote:
On 3/17/06, James Richard Tyrer <[EMAIL PROTECTED]> wrote: Tech
Source and plenty of others have been doing it for ages with
medical LCD displays at 60Hz.
Interesting but ... I think that gamma correction/color matching
software works by loading a palate.
Well, the standard X way of adjusting your gamma settings is through
XGamma. The X server queries the monitor for its current gamma
setting as well at startup. The gamma value is just a triplet of
floats, one for the gamma value for each colour.
Yes, that is to set Gamma. One Gamma setting for each color. But, what
I am talking about is Gamma correction. Adjusting a non-log Gamma curve
for the monitor to match a printer. The same for color. Printers have
non linearities in their color rendering and color matching needs to
correct for this.
I think that the ATI cards use a small (8-16 entry) lookup table, and
the RAMDAC does linear interpolation between these points to generate
the final conversion curve.
Unfortunately, I can't just read the ATI documentation since it seems to
be a secret. I can't see how this could work unless they just use this
to load the lookup table since linter interpolation requires two
subtractions and a division.
What I am familiar with is the VGA documentation and the documentation
for RAMDACs (BrookTree) when they were separate chips.
One of the design requirements is that OGA should be very good
for 90% or more of desktop users. Very few are going to be
overly concerned about gamma correction at all, let alone how
many bits of precision on the DAC.
Yes, you are correct on this. The only real market for fine
control of gamma and color is pre-press color work. Perhaps most
of those people still use Macs. :-)
Yes, but wouldn't we like them to all move over to Linux? :)
Also, different platforms have different gamma standards. Mac
monitors do gamma 1.5 I think, while on the PC the standard is more
like 1.8, and sRGB is 2.2. And if you want good antialiasing, having
good gamma correction is a big help.
I think that what this refers to is the expected setting of the monitor
(contrast) not anything happening on the graphics board.
Digital cameras are everywhere now, and people edit and print their
photos at home. It would be nice if what they see on screen is a
decent preview of what will come out of the printer, and for that,
you need at least half decent gamma settings. Windows has had
built-in support for device profiles and everything since 98 or so.
It's time the open desktop catches up.
We have the basic color matching software: LCMS. The issue here is that
when you try to match the printer color rendering using only 8 bits per
color that you lose colors and this causes distortions in the color
image displayed on the screen. With extra bits, you can do this without
losing (as many) colors.
--
JRT
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