[Cin] psychtoolbox vs HDR

Andrew Randrianasulu randrianasulu at gmail.com
Thu Jun 8 04:04:25 CEST 2023

Found this tidbit


in 3.0.18 beta

16 bit native (effective 12 bit) framebuffer support for Linux with AMD
Polaris and later.


This commit switches PsychImaging() to only expose 16 bpc framebuffers on
such Linux + X11 + AMD Polaris+ + amdvlk + Linux 5.14 systems, but then at
much better reliability and performance than our old dead code.

It allows to get up to 12 bpc per color-channel color output, ie. 4096
intensity levels for red, green, blue, grayscale/luminance and a total of
64 billion shades of color, either on suitable 12 bpc capable high-end
displays, or via spatial dithering by the gpu on the more common 10 bpc
capable displays or even - at a lower quality - standard 8 bpc capable

This makes Linux the first operating system to my knowledge to support this
color precision on out of the box on commodity graphics hardware and
displays, natively at full performance without any compromise in timing
precision or reliability.

Basic testing has been performed with a CRS ColorCal-2 on a HDR-10 10 bpc
capable monitor and on a MacBookPro 2017 Retina display under Linux, with
AMD RavenRidge and Polaris.


test apps apparently even include gstreamer-based movie player (never
thought I'll find HDR player in medical software ...)




If the optional flag ‘hdr’ is specified as non-zero, then the demo
expects the onscreen window to display on a HDR-10 capable display device
and system, and tries to switch to HDR mode. If the operating system+gpu
driver+gpu+display combo does not support HDR, the demo will abort with
an error. Otherwise it will expect the movies to be HDR-10 encoded and
try to display them appropriately. A flag of 1 does just that. A flag of 2
manually force the assumed EOTF of movies to be of type PQ, iow. assume the
is a HDR-10 movie in typical Perceptual Quantizer encoding. This is useful
if you
want to play back HDR content on a system with a [GStreamer
<http://psychtoolbox.org/docs/%28GStreamer%29> version older than
1.18.0 installed, where [GStreamer <http://psychtoolbox.org/docs/GStreamer>]
(GStreamer) <http://psychtoolbox.org/docs/%28GStreamer%29> is not fully HDR
capable, but this hack may
get you limping along. Another restriction would be lack of returned HDR
so if your HDR display expects that, you will not get the best possible
Upgrading to [GStreamer <http://psychtoolbox.org/docs/GStreamer>](GStreamer)
<http://psychtoolbox.org/docs/%28GStreamer%29> 1.18 or later is advised for
HDR playback.
A flag of 3 or 4 will use an alternative HDR display method only available
Linux/X11, with 4 applying the same hack to cope with older [GStreamer
<http://psychtoolbox.org/docs/%28GStreamer%29> versions
as a setting of 2.


happy psyching! (???)
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