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Gamma correction

I’m doing a gamma correction on my Viewpixx monitor screen using a Minolta CS-100 photometer. I measured the luminance values manually and entered them into the table from the Monitor centre.
Something has changed, because the colours now look different when I run my experiment, however the gamma values in the linearisation table are not 1. The option to click on Gamma Test is greyed out, and when I click on Plot gamma, I get the following error:

/Applications/ MatplotlibDeprecationWarning: axes.hold is deprecated.
    See the API Changes document (
    for more details.
Traceback (most recent call last):
  File "/Applications/", line 1019, in plotGamma
    if lumsPre != None:
ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

Clearly the calibration has not worked, but I’m not sure why. Does anyone have any suggestions on what I need to do?

Thank you very much,


Hi Mubaraka,
Did you ever find a solution for your problem?
I have re-installed an early version of PsychoPy (1.85.2) on my Windows 10 computer because of problems I was experiencing with the newest one regarding gamma corrections via the monitor center.
I am however getting the exact same error message as you now.
It is strange because it works fine on my macOS but not on my windows computer.

Thank you very much,


Hi Coralie,

Are you using a secondary monitor screen? if I remember correctly, i was having an issue with macOS, and this ultimately came down to not being able to use fullscreen on the secondary monitor. So I switched to Windows 10, and changed the monitor settings to set Monitor 2 (the Viewpixx screen) as the primary and only screen, and now everything works fine.

Hope that helps?