Can a graphics card lookup table be read back, or is it write only?

G
Posted By
Greg
Jan 21, 2004
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757
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Is there a utility that can unobtrusively *read* the current gamma correction lookup tables from the display adaptor?
I’m using Windows XP.

Thanks,
Greg.

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H
hoffmann
Jan 21, 2004
"Greg" …
Is there a utility that can unobtrusively *read* the current gamma correction lookup tables from the display adaptor?
I’m using Windows XP.

Thanks,
Greg.

Greg,

you can download the Vesa-Vbe3 stuff
http://www.vesa.org/vbelink.html

but the programming is not a pleasure.

Best regards –Gernot Hoffmann
G
Greg
Jan 22, 2004
Thanks Gernot. I’ve actually managed to find a utility which will do it – it’s called Powerstrip.
http://www.entechtaiwan.net/ps.htm
This can interrogate the LUT, and save it. (it saves it in the registry, but it’s easy to export)
So I have managed to avoid some unpleasurable programming – phew. ;^)

Greg.

"Gernot Hoffmann" wrote in message
"Greg" wrote in message
news:<lkkPb.12678$>…
Is there a utility that can unobtrusively *read* the current gamma correction lookup tables from the display adaptor?
I’m using Windows XP.

Thanks,
Greg.

Greg,

you can download the Vesa-Vbe3 stuff
http://www.vesa.org/vbelink.html

but the programming is not a pleasure.

Best regards –Gernot Hoffmann
H
hoffmann
Jan 22, 2004
"Greg" …
Thanks Gernot. I’ve actually managed to find a utility which will do it – it’s called Powerstrip.
http://www.entechtaiwan.net/ps.htm
This can interrogate the LUT, and save it. (it saves it in the registry, but it’s easy to export)
So I have managed to avoid some unpleasurable programming – phew. ;^)
Greg.

Greg,

thanks for the feedback.
My experiences with Matrox Graphics Cards:
the results are NOT according to the VBE specs.
Maybe my error.
I´m going to test your suggested utility.

Best regards –Gernot Hoffmann
G
Greg
Jan 23, 2004
Gernot,
Feel free to drop me an email if you have trouble using it – I found it a bit unintuitive. But in the end
I got it to work properly, and it’s a very useful utility.

Greg.
"Gernot Hoffmann" wrote in message
"Greg" wrote in message
news:<HfQPb.12788$>…
Thanks Gernot. I’ve actually managed to find a utility which will do
it –
it’s called Powerstrip.
http://www.entechtaiwan.net/ps.htm
This can interrogate the LUT, and save it. (it saves it in the registry,
but
it’s easy to export)
So I have managed to avoid some unpleasurable programming – phew. ;^)
Greg.

Greg,

thanks for the feedback.
My experiences with Matrox Graphics Cards:
the results are NOT according to the VBE specs.
Maybe my error.
I
G
Greg
Jan 24, 2004
Powerstrip actually does not retrieve the LUT on my system, if I have used the Windows control panel to change the gamma of the display adaptor. In Powerstrip, there is an option "Write directly to palette DAC". I think the Windows control panel must use this method to
write the LUT. There must be some other indirect method of writing the LUT, which puts the info in a read/write buffer somewhere.
When this method is used, Powerstrip is able to read back the LUT data. When I use the Eye One display profiler loader to load the LUT (i.e, to write the vcgt tag from the ICC file into the LUT), Powerstrip is able to read back the LUT data successfully. (of course, I could have simply dumped the data directly from the ICC file)

Greg.
G
Greg
Jan 24, 2004
Ah, Powerstrip does actually retrieve the LUT successfully after I’ve loaded it from the Windows control panel,
but *only* if Powerstrip is invoked with the "Write directly to palette DAC" already checked. If it’s not
checked before having changed the LUT in Windows, Powerstrip seems to reset the LUT as soon as
the setting is checked, to whatever LUT data Powerstrip currently has in it’s own tables. Very tricky.

Greg.
H
hoffmann
Jan 24, 2004
"Greg" …
Ah, Powerstrip does actually retrieve the LUT successfully after I’ve loaded it from the Windows control panel,
but *only* if Powerstrip is invoked with the "Write directly to palette DAC" already checked. If it’s not
checked before having changed the LUT in Windows, Powerstrip seems to reset the LUT as soon as
the setting is checked, to whatever LUT data Powerstrip currently has in it’s own tables. Very tricky.

Greg.

Greg, in the moment I don´t have the time to check Powerstrip. I had tried to read and write the LUTs according to the Vesa-Vbe specs, but this didn´t work for my Matrox cards (it´s assembly programming).
I suspect that these specs are not accurately cast into software, because the Windows programmers who know the direct access to the graphics card´s registers don´t care anymore about the Vesa specs. On the other hand I had success programming the pixel clock (vbe-3.0 for Matrox G550).

See you later ..

Best regards –Gernot Hoffmann
T
thebitbucket
Feb 11, 2004
Greg,

Long time. You and I chatted some time ago about something similar.

I just replaced a Matrox G550 with a P650. The P650 comes with a program called Coloreal that can be used to calibrate (via eyeball) a dual monitor config. Any, I too am having a bit of a difficult time understanding the relationship between AdobeGamma, the AdobeGamma Loader, XP and Coloreal. Here is my situation.

I created a profile with Coloreal which has one monitor very bright and the other very dark (for test purposes); lets refer to this monitor setup as "DL" for short. I delete the Coloreal profile from Properties-Settings-Advanced-Color Management. I reboot and the DL appearance returns. I can I add and profile I want via
Properties-Settings-Advanced-Color Management and reboot and I still get the DL appearance. I suspect the LUT value the make up DL are being saved in the Registry. I gather you investigated this and found that to be true, yes?

If I run (by hand) the AdobeGamma Loader "AGL" it will change the monitor appearance based on the Default monitor profile. I think this makes sense. However when I reboot (again), I’m back to DL. I gather that running AGL does not update the Registry. Note anything about the Registry is pure conjecture on my part. What ar your thoughts?

As a related question, I gather that XP does nothing with the info in Properties-Settings-Advanced-Color Management, other than to keep in there for any piece of software that cares? Is this consistent with you understanding?

I also notice, that I can change the default profile in
Properties-Settings-Advanced-Color Management run AGL then change the default profile to something else and rerun AGL but this time nothing visibly changes. Almost like it will only do something the first time. Very strange.

I’d be interested in you experience with regard to any of this.

Jerry

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