Psychtoolbox>Screen.{mex*} subfunction

oldclut = Screen(‘LoadCLUT’, ScreenNumber [, clut] [, startEntry=0] [, bits=8]);

Load or query the hardware gamma table of the specified screen. If you pass a
new ‘clut’ hardware gamma table, then ‘clut’ needs to be a matrix with 1 to
(256-startEntry) rows and 3 columns. Each row corresponds to a single color
index value and contains the Red- green- and blue values to use for output of a
pixel of that color. If you provide ‘startEntry’ then the hardware clut is
overwritten by your table starting at color index ‘startEntry’ instead of
starting at index 0. You are free to provide a clut with only a few rows if you
only want to update a subset of the color indices in the hardware clut. Column 1
is the red value, column 2 is the green value and column 3 is the blue value
that you want to load into the hardware clut for a specific index. Values in the
table have to be in range between 0 (for dark pixel) and ‘max’ (for maximum DAC
output intensity), where ‘max’ depends on the number of bits that the RAMDAC of
your graphics hardware supports. Psychtoolbox currently has no way of knowing
the bit-resolution of your RAMDAC, so you have to provide it in the optional
argument ‘bits’. If you don’t provide a ‘bits’ setting, it defaults to a safe
default of 8-Bits. Some examples for ‘bits’ vs. ‘max’: 8 bits (default) –> max
= 255. 9 bits –> max=511. 10 bits –> max=1023. 12 bits –> max = 4095. On
MacOS-X and Linux, this function takes arbitrary clut-tables which makes it
suitable for fast CLUT animation. On Microsoft Windows, only tables with
monotonically increasing values are considered valid. Other tables get rejected
by the operating system – there’s nothing we can do about this incredibly wise
decision of the Microsoft system designers :( , so this function is not suitable
for CLUT animation, but only for linearizing or calibrating display devices.
PLEASE NOTE: LoadCLUT is only provided to keep old code from OS-9 PTB and old
Windows PTB working. It is just a wrapper around ‘LoadNormalizedGammaTable’. Use
‘LoadNormalizedGammaTable’ for new code. That function is independent of DAC
resolution as it takes values in a normalized range between 0.0 and 1.0 and
always gives you the highest possible resolution for your gamma table, despite
not knowing the real DAC resolution. This function returns the old CLUT as
optional return argument. If you don’t pass a clut, then it only returns the old

###See also: LoadNormalizedGammaTable ReadNormalizedGammaTable