Posterization issue

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  • This topic has 30 replies, 2 voices, and was last updated 6 years ago by MW.
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  • #11057

    MW
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    I did two things, not sure which solved it: #1 Moving the ArgyllCMS folder to the drive root. #2 Installed the display profiles as system-wide instead of per-user.

    None of these are related ?

    Here’s the run-down of the actual cause of the problem: When measuring with video levels set in DisplayCAL (doesn’t matter if autodetected or explicitly selected), ArgyllCMS quantizes the test patch device RGB values in the resulting measurement file to 8 bits by default. Normally this doesn’t cause an issue, but when doing a verification with a simulation profile (not using it as display profile), the input CIE values are looked up through the display profile to obtain the target device RGB values, but these device RGB values are not quantized to 8 bits. So, if by chance these values end up not lining up with the quantized test values for white (which depends on the display profile), there’s an unexpected mismatch between the measurement file and the looked up device RGB values. The solution is to quantize the target device RGB values in the same way as the device values in the resulting measurement data. This will be fixed with the next update.

    Thanks for the explaination. I couldn’t find the exact sequence to reproduce the error in fact. FWIW moving the main Displaycal window to a different display would trigger the error sometimes, I remember seeing the ouput level setting being set incorrectly whenever the error happened, which makes sense considering your explanation.

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