Loading gamma table

Coding
1

Hi all,
In Psychtoolbox, it is possible to load a specific gamma table that will be used when displaying images or movies, using the Screen(‘LoadNormalizedGammaTable’) function. Is this possible within PsychoPy, or when using moviestim?
Thank you
ilkay

2

You would usually do this using psychopy.monitors:

http://www.psychopy.org/api/monitors.html#psychopy.monitors.Monitor.setGammaGrid

3

I also have a similar question.

I understand that psychopy.monitors is where to set specific monitor values, but I’m confused how to translate between Psychtoolbox’s ‘LoadNormalizedGammaTable’ and pschopy.monitors.setGammaGrid.

In Psychtoolbox, you give it a whole set of values (255 values) [0 - 1] (consider this an x-value) and corrected gamma values where each value is a y value s.t. y = A*x^(1/gamma) (where you fit A and gamma from measurements).

In Psychopy.monitors.setGammaGrid, all this wants is min, max, and gamma. I don’t see how this is equivalent. Could someone please explain?

4

I think you could achieve something similar by setting win.gammaRamp after opening a window. See psychopy.visual.gamma.setGammaRamp for details.

5

Thank you for your response! I’m sorry but I have an additional question: I’m reading that win.gammaRamp is 3x256 (or 3x1024). Is there a reason it’s not 4x256 (for ‘gray’, ‘r’, ‘g’, ‘b’)?

Thanks!

6

It is setting the output of the three monitor channels (red, green, blue) for a given input - there is no grey channel as such. This is presumably the same in PsychToolbox’s LoadNormalizedGammaTable.