[argyllcms] Re: Unable to access VideoLUT
- From: Graeme Gill <graeme@xxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Tue, 23 Aug 2016 16:05:59 +1000
This seems to imply, that 11 significant bits
per color specifications is indeed correct? Can
you give me a pointer where to read about the
meaning and usage of this eleventh bit?
Unless you can find nVidia documentation on this
(and public nVidia technical documentation seems sparse),
then no information seems to be available.
The way I have assumed it behaves is simply as 11 bits
(i.e. nothing special about the 11th bit), with any
mismatch between different bit widths being covered
by interpolation HW in the graphics chip.
also puzzled by the TrueColor and DirectColor
distinction in X, and that TrueColor is
read-only. Does this mean, that a TrueColor
may allow read-access to the Video LUT but not
to change it?
Don't get confused. X11 was written when 24 bit color
was somewhat exotic, and 8 bit frame buffers that used
8 -> 24 bit lookup tables were the standard for color.
So there is an allowance for X11 driven lookup table setting
and management of sharing those lookup tables between applications.
This extends to 24 bit color, where there is an allowance
for per channel lookup tables. So DirectColor allows writing
to those tables, whereas TrueColor does not.
These writable lookups may or may not be the same as the VideoLUTs that
are accessed via XRANDR, and it is the latter that ArgyllCMS uses for setting
calibration curves, not the former, since the former are application controlled.
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