Re: Re[2]: fundamental question - monitor profile as working RGB?
Re: Re[2]: fundamental question - monitor profile as working RGB?
- Subject: Re: Re[2]: fundamental question - monitor profile as working RGB?
- From: Chris Murphy <email@hidden>
- Date: Wed, 10 Dec 2003 15:20:09 -0700
On Dec 10, 2003, at 7:22 AM, Peter Karp wrote:
Mmh, I doubt that this is a vaild test for a profiling software to
determine if it assumes gray-balance.
It's a valid test for determining what LAB values the profile+CMS
report back for given equal RGB values. That's how a CMS works. You can
do it in reverse too if you want. Create a LAB black to white gradient
and convert to RGB using the same profile and you will get equal
amounts of RGB as a result. This is something that just happens with
matrix profiles where the TRC's are identical for each channel.
I agree with Graeme that most if
not all "monitor measuring software" try to create a perfect gray
balance
in the step of creating correction values for the LUT of the video
card.
Yes. I don't think this is in dispute. Some have options to just make a
profile, but by default most of them do calibrate and gray balancing
the display is one of the aspects of display calibration.
In the second step when the display is profiled the current color
values
for the calibrated display could be measured and would make it into the
profile. But I think Graeme has no other chance then to be horrified
;-),
because the calibration packages I know just show the color patches
_once_ in the uncalibrated state of the display (this means, they
flatten
the LUT before the measurements). So I assume that the profiling part
of
the software assumes a perfect gray balance applying the correction
values to the LUT. Otherwise the profiling step would have to be a
divided part where the color patches would be measured a second time --
but this time with the calibration done in the hardware of a display
and
with the calibration values loaded on the LUT.
That's right. That's essentially what most packages are doing. They
calibrate first, and then most do a cursory confirmation that the
intended white point was hit, and a middle neutral to confirm gamma,
and maybe they will re-read the primaries if the top end of R, G or B
were modified in calibration. But that's basically it.
It defeats the purpose of profiling.
That's a good "question". It depends on how accurate the calibration
part
of the display really works.
Yes and having relied on the video card to do this successfully,
especially uniformly, is not necessarily a good assumption. I do not
believe it's time to panic and suggest all such products are doing a
bad job when in fact we know this stuff works amazingly well. But at
the same time, it might point to a possible area of improvement if we
depend less on the video card, and also make fewer assumptions about
how displays behave - which means taking more measurements than most
packages do now. Since the devices have gotten faster and more accurate
than just a few years ago I don't think this is impractical.
Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
---------------------------------------------------------
Co-author "Real World Color Management"
Published by PeachPit Press (ISBN 0-201-77340-6)
_______________________________________________
colorsync-users mailing list | email@hidden
Help/Unsubscribe/Archives:
http://www.lists.apple.com/mailman/listinfo/colorsync-users
Do not post admin requests to the list. They will be ignored.