Re: [CinePaint] strange handling of SIGTERM

Am 18.08.09, 00:11 +0100 schrieb Gene Selkov:

> understanding color management. Whatever I tried to do during the last
> couple days left me with a suspicion that my display profile is
> applied twice. First when it is loaded into my display's LUT. And the

You are familiar with the two stage colour correction for monitors?
ArgyllCMS not only sets the ICC profile in X but as well loads a embedded 
vcgt tag into the graphic card. Vcgt is a triple of linear LUTs to alter 
gray balance and over all response of a monitor. This is often called 
the device calibration stage. This cheap and very fast manipulation brings 
the whole desktop in one consitent state. The biggest plus is it works for 
almost all computers including elder ones.

The drawback is, a calibration eats some bits of the available shades. So 
with a monitor exposing steppings alredy in the still typical 8-bit mode 
will expose even more obvious stepping due to the omitted shades from the 
vcgt calibration stage. It may or may not harm on a laptop monitor as most 
of these displays are said to be dithered 6-bit devices.

Colour corrections are done by a CMM, in CinePaint by littleCMS or 
short lcms. Lcms can handle whatever ICC profile a image is tagged with. 
Ok Gray should still be a problem in CinePaint. Lab, Cmyk, Yuv and so on 
can not correctly be displayed with a simple linear calibration approach 
but should be correctly displayed with CinePaints colour management.

> second time, when Cinepaint opens my image. The reason I believe so is
> because the same image looks very different when I view it with a
> non-color-managed tool. To be exact, it looks right in evince, for
> example, which is not color-managed. To make sure I knew what's right
> and what's not, I took a shot of a reflective IT8 in direct sunlight,
> saved it into an sRGB tiff with ufraw, using my camera's internal
> matrix (which is a more trustworthy calibration source than any
> profile I managed to produce so far), and when I view that in any
> profile-agnostic tool on my newly calibrated screen, it does look
> right. Which means, I believe, that Argyll did a great job, and that
> my camera isn't too bad either. Now, when I open that image in

I am in doubt that the Gnome desktop has a real desktop colour management.
This would mean it had to colour correct all desktop content through a 
CMM. While this is possible and exists as a working prototype for the 
Compiz window manager in Oyranos git, its still far from every day 
usability.

A false colour image tagged with the according ICC profile can detect 
ICC style colour corrections.

> Cinepaint (regardless of the profile assigned), It looks too bright
> and too red -- which is what I would expect from my current display
> profile, if it were applied twice (I know the direction and
> approximately the amount of change it effects, from the uncalibrated
> state,  and the change I observe in Cinepaint is in the same
> direction, and by about as much).

Did you veryfy your calibration with Argyll? I think Graeme has some 
routines in his tools to test a applied ICC profile. But thats best asked 
on the Argyll mailing list.

> Another curious observation is that when I open my raw file with
> Cinepaint, it does look right, but only until I try to something
> useful to it. I cannot save it or make any changes, or add a layer, or
> copy it to another image; whatever I do to it make it look wrong. It
> becomes too dim and too blue.

Perhaps the colour correction is not running instantly. A plain zoom 
should not alter the images colour appearance.

> There is something profoundly wrong in my toolchain, because when I
> consider all these effects together, they add up to something like
> Escher's straircase. Does any of this seem familiar to anyone? Is
> there a rational way of sorting it out?

:-) Yes its someties hard to nail things down with colour management due 
to the often many components involved. A step by step verification 
is unfortunedly often laborious. But you seems to have a colorimeter which 
might be a helpful tool.

Frank Peters had already mentioned some test images. Here are a pair of 
false colour and sRGB images:
http://www.oyranos.org/wiki/index.php?title=Test_Images
They can be used to find out about double colour corrections.


kind regards
Kai-Uwe Behrmann
-- 
developing for colour management 
www.behrmann.name + www.oyranos.org


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