Re: [CinePaint] strange handling of SIGTERM

Am 18.08.2009, 8:02 schrieb Kai-Uwe Behrmann <[email protected]>:

> You are familiar with the two stage colour correction for monitors?

Not yet, but I intend to be -- give me a week to catch up. I am just
beginning to explore along the lines you suggested.

> 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.

I grasped that much form Frank's explanation, but I still don't know
enough to explain everything I see.

> The drawback is, a calibration eats some bits of the available shades.

How many bits does it eat?

> 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.

I am looking at the test image generated by Argyll's "timage", the
default one with two views of the cube. It doesn't show any steppings
when rendered by unmanaged viewers. Maybe it does, but I really have
to work to convince myself I see them. But when I view it in
Cinepaint,
the color cubes look as if they were painted in half-a-dozen distinct
zones. The gray stripe in the middle remains smooth. Is that the
effect of the bits consumed by the calibration, or could it be
something else? I can post a picture somewhere, instead of explaining
what I see.

> 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.

I am not following: why is Gray a problem?

> 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.

You're scaring me: I hope I don't have to worry about gnome and compiz
adding their stuff to the pot. In fact, I use both.

> 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.

Not with Argyll yet, but visually it doesn't look terribly off. I have
another display calibrated with the same colorimeter (but different
software), and they look pretty close when viewed side-by-side. I also
compared a color target with it's image on the display, and that's
pretty close, too. By the way, my other display is a Macbook Pro, and
I used Spyder's own software to calibrate it. It took suspiciously
short time to do the calibration, but the result is not unreasonable.
The only conspicuous difference is that the same image looks more
saturated on the Mac, but it shows the same gradations and the same
overall balance.

>> 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.

A zoom doesn't but every real change does. I think I can articulate it
better this time. There was an option in the raw image loader that I
overlooked. The option is "Convert to WideRGB", which is set by
default. I admit I don't understand the meaning of this conversion,
but whatever it is, it doesn't stick. It looks like it gets lost after
any change is applied to the image afterwards. The quickest way to
reproduce this is to open a raw image with this option enabled, select
all and copy it to a new image. The pasted selection becomes nearly
black, but that's the way it looks if I don't select the WideRGB
conversion in the first place. Another similar effect is the reversal
of the layer icon to the "unconverted" state after a couple
manipulations with layers -- layer duplication and such. It makes me
wonder what that is all about, because the initial WideRGB conversion,
projected through all those enigmatic transforms onto my display seems
to render so accurately that I don't even feel like adjusting it in
any way (usually have to, with most of my raw images).

> :-) 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.

Grasping how things hang together (if they do) in this entire system
is certainly beyond the ability of an unaided human brain, and mine in
particular is not very good at verbal thinking. One thing that could
help is some sort of diagram depicting all the actors and
relationships between them, and all data flows with possible
alternative paths (such as with and without color management), and all
dependencies -- various config files and parameters. If such diagram
doesn't exist, I will feel compelled to make one.

> 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.

These do look identical in Cinepaint. Does it mean I'm in a good shape?

Thanks a lot,

--Gene

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