[argyllcms] Re: Comparison of Monitors on Linux and Mac
- From: "Hal V. Engel" <hvengel@xxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Fri, 10 Oct 2008 17:51:50 -0700
On Friday 10 October 2008 17:11:07 Timothy Hattenberger wrote:
> I need to be able to view the same image on Mac and Linux and have
> them look the same. I've eliminated as many variables as possible.
>
> 2- 20" Apple Cinema - One on the Linux and one on the Mac
> ArgyllCMS used to calibrate and profile on each OS (latest version,
> v1.0.03 I believe)
>
> After creating the profiles using the same settings, on each platform,
> I then load them using ColorSync on the Mac and dispwin on Linux.
> When I compare a set of images they are pretty close, but there is
> definitely a color difference and it's more pronounced in some images
> over others (to be expected). For example, one monitor is more red
> than the other.
>
> My current understanding is that on Linux, when I run dispwin, it's
> loading RGB VCGT calibration curves into the xserver somewhere (i.e.
> not into the graphics card) and the rest of the profile is never
> used. So, in order to make sure it's exactly, the same, I'm using
> untagged images on the Mac. So essentially only the VCGT curves are
> being 'used' there as well. I verified this on the Mac side by
> comparing the same untagged image loaded in Preview (a color managed
> app) and Shake (a non-color managed app) and they look identical.
> I've been working on this a while and am getting a little frustrated.
>
> In fact, I got better results when I used Eye-One match on the Mac,
> and RSR cineProfiler on the Linux box, not only in comparison, but in
> overall profile performance (e.g. there was a lot less contouring). I
> believe I could probably tweak the argyllcms settings eventually to
> get a better looking profile, but I'm not even at the point of having
> the images match yet.
>
> I have a suspicion that this could be related to the monitors, but
> don't know how to eliminate that. If I run dispcal -yl -R and look at
> the native responses of the monitors, what I get (roughly) is that one
> of the monitors has a native white point of ~6850K and the other is
> ~6300K. I would guess the same monitors should have much closer
> native responses.
If these were really high end monitors (IE. ones costing several thousand
dollars) they might but the monitors you are using are somewhat nicer consumer
grade devices. I have done some testing with with a pair of Samsung 245BW
monitors and the native response of these monitors are significantly different
from each other. Although the native white points can be adjusted to a closer
match than your monitors there is still about a 200K different. But the
native response curves of the individual channels of these two monitors are
way different. In each case two of the channels have very similar and smooth
gamma curves and the third gamma curve has a significant amount of inflection.
In both cases the inflection is in the upper part of the curve. For one
monitor this is the green channel and for the other one it is the red channel.
I suspect that this is because one of the places where the vendors can reduce
the cost of these consumer grade monitors is to use a faster but less accurate
calibration process at the factory. There is probably lower standards for the
back lights as well which would explain the differences in the native white
points of two "identical" monitors.
> What I would like to do is be able to make an
> input .ti1 file with just a few patches, measure the XYZ values and
> calculated CIEDE94 values. The only question is if it's possible to
> make those measurements with the calibration in place (i.e. w/o
> blowing away the VCGT LUTS). Is that possible?
>
>
> So, does anyone have any clues?
How about creating a tiff file with some "patches" and using an imaging
application to display the patches and using spotread to take the
measurements. If it is a small number of patches that should be doable.
>
> Thanks,
> Tim H.
>
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