Test proper function of the T-Lock mechanism on CRS devices and PSYNC
mechanism on VPixx devices, as well as proper loading of identity gamma
tables into the GPU, and for bad interference of dithering hardware
with the DVI stream. This test is meant for Mono++ mode of Bits+/Bits# or
M16 mode of DataPixx, ViewPixx, ProPixx. It requires a modern graphics card
which supports at least OpenGL-2.1 and therefore supports these modes.
If you only have older graphics hardware that can only drive Bits++ or
L48 clut display mode, or you have an old CRS Bits+ device switched to
Bits++ mode and don’t want the hassle of setting it to Mono++ mode then
this test script can also perform a slightly more limited test in Bits++
mode or L48 clut mode. Set the optional parameter ‘useclutmodeonly’ to 1
to use this simpler test mode.
Disclaimer: This test only exists because of the huge number of serious &
embarassing bugs in the graphics drivers and operating systems from
Microsoft, Apple, AMD and NVidia. All problems diagnosed here are neither
defects in the Bits+ device or similar devices, nor Psychtoolbox bugs. As
such, sadly they are mostly out of our control and there is only a
limited number of ways we can try to help you to workaround the problems
caused by miserable workmanship and insufficient quality control at those
BitsPlusIdentityClutTest([whichScreen=max][, usedpixx=0][, winrect=][, useclutmodeonly=0][, useVulkan=0]);
How to test:
Make sure your Bits+ box is switched to Mono++ mode by uploading the
proper firmware. Or make sure your DataPixx/ViewPixx/ProPixx or CRS
Bits# is connected, both DVI cable and USB cable. Alternatively set
‘useclutmodeonly’ to 1 to test in Bits++ mode on a CRS device or L48
mode on a VPixx device. In useclutmodeonly = 1 case, skip to step 3.
Run this script, optionally passing a screenid. It will test the
secondary display on a multi-display setup by default, or the external
display on a laptop. For a DataPixx device or similar, set the
optional ‘usedpixx’ flag to 1. Set ‘useclutmodeonly’ flag to 1 if you
want to test in Bits++ or L48 mode instead of Mono++ or M16 mode.
‘useVulkan’ Defaults to 0. If set to 1, use Vulkan display
backend, instead of standard OpenGL backend.
If everything works, what you see onscreen should match the description
in the blue text that is displayed.
If a wrong gamma lut is uploaded into your GPU due to operating system
and graphics driver bugs, you can try to toggle through different
alternative lut’s by repeatedly pressing the SPACE key and seeing if the
display changes for the better. Should you find a setting that works, you
can press the ‘s’ key to save this configuration and Psychtoolbox will
use this setting in all future sessions of your experiment scripts.
You can exit the test by pressing the ESCape key, regardless if it was
successfull or not. The test will then ask you if you rate the results
as success or failure and use your feedback for further operation.
What could also happen is that you get a partial success: The display
behaves roughly as described in the text, but you see the T-Lock color
code line at the top of your display erratically appearing and
disappearing - flickering. You also don’t see a smooth animation of the
drifting horizontal red gradient or a regular cycling of the “COLORFUL”
words, but some jerky, irregular, jumpy animation, which may only update
a few times per second, or even only once every couple seconds or at very
irregular intervals. You may also see the display overlayed with random
colorful speckles, or you may not see the gray background image and gray
rotating gradient patch at all. In that case, the lut uploaded in your
GPU may be correct, but due to some serious graphics driver or operating
system bug, the GPU is applying spatial or temporal dithering to the
video stream which will confuse your display device and cause random
artifacts and failure of the T-Lock or PSYNC mechanism, as well as display
of wrong or inaccurate color or luminance values!
You should also double-check the cabling and connections to rule out
connection problems and other defects.