Re: Are gamma discrepancies relevant? [was: UGRA/UDACT-conforming displays]
Re: Are gamma discrepancies relevant? [was: UGRA/UDACT-conforming displays]
- Subject: Re: Are gamma discrepancies relevant? [was: UGRA/UDACT-conforming displays]
- From: Klaus Karcher <email@hidden>
- Date: Fri, 03 Apr 2009 03:00:03 +0200
In a message dated 4/1/09 4:56 AM, Thomas Holm/pixl wrote:
My experience tells me that you will see various degree of banding
especially, in the two windows with a tone curve/gamma setting
workspace which is different from your monitor calibration.
Marco Ugolini wrote:
Sorry, but I don't agree that this test actually provides incontrovertible
evidence of the theory's validity.
Disclaimer: my monitor does not have a built-in LUT.
Ok, here is another experiment that eliminates the influence of the
video card LUT and other possible sources of error:
Download an extract the file
<http://digitalproof.info/colorsync-users/ramps.zip>
it contains 4 files:
ramp-ProPhotoRGB.tif
ramp-eciRGBv2.tif
ramp-appleRGB.tif
ramp-adobeRGB.tif
The files are exactly the same except for the embedded profile. They
contain a RGB gray ramp with 256 steps, each two pixels wide.
Open them in Photoshop and view them one below the other at 200%.
Now open system preferences, make a mental note of your current monitor
profile, then change it to AdobeRGB (this will also reset your graphics
card LUT as AdobeRGB does not contain a VCGT tag).
Switch back to Photoshop. You will see that the AdobeRGB ramp is
banding-free while the others are not.
Now use AppleRGB as display profile and switch back to Photoshop: only
the AppleRGB and ProPhotoRGB ramps are banding-free -- both profiles
have a gamma 1.8 TRC.
When you use eciRGB v2 as display profile, only the eciRGBv2 ramp will
be bandig-free (you can get eciRGB from
<http://www.eci.org/lib/exe/fetch.php?media=downloads:icc_profiles_from_eci:ecirgbv20.zip>
if you don't have it yet).
Don't forget to restore your original display profile when you are done.
Klaus
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