# Reduce brightness of all screen output by a factor?

**URL:** <https://psychtoolbox.discourse.group/t/reduce-brightness-of-all-screen-output-by-a-factor/32>\
**Category:** Uncategorized\
**Created:** [March 21, 2019, 10:02pm UTC](https://psychtoolbox.discourse.group/t/reduce-brightness-of-all-screen-output-by-a-factor/32 "2019-03-21T22:02:43Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![mattjdunn](https://avatars.discourse-cdn.com/v4/letter/m/67e7ee/32.png) [@mattjdunn](https://psychtoolbox.discourse.group/u/mattjdunn)\
**Post date:** [March 21, 2019, 10:02pm UTC](https://psychtoolbox.discourse.group/t/reduce-brightness-of-all-screen-output-by-a-factor/32/1 "2019-03-21T22:02:43Z")

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I wonder is there a way to restrict luminance output to a range of a monitor's total output capability? I need to reduce the luminance of all monitor output in an experiment to operate within the bottom 10% of the total monitor's capacity, i.e. as if I had just turned the brightness down to 10% (unfortunately, just turning down the brightness is not an option). In other words, I need a global reduction in luminance of 90%. My blacks should be the same as before, whites will be 10% of total monitor output, and 'grey' would be in the middle. The monitor is properly calibrated already. I know that I could manually adjust all my stimuli pixel values to simulate this, but I wonder if there is a built-in function in PTB (perhaps at the time of Screen('OpenWindow')?) that just applies a global luminance transformation in this way?

  

I note the function Screen('ColorRange'), but this looks to \*clamp\* colours ourside of a specific range. I don't think this is what I'm trying to achieve, as I wish to globally affect all luminance values sent to the monitor. Furthermore, I don't think it would be appropriate to use Screen('LoadNormalizedGammaTable'), since the monitor is already gamma corrected, and what I need is a global 90% reduction to \*all\* luminance values output, rather than a nuanced curve.

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**Author:** ![mattjdunn](https://avatars.discourse-cdn.com/v4/letter/m/67e7ee/32.png) [@mattjdunn](https://psychtoolbox.discourse.group/u/mattjdunn)\
**Post date:** [March 22, 2019, 9:08am UTC](https://psychtoolbox.discourse.group/t/reduce-brightness-of-all-screen-output-by-a-factor/32/2 "2019-03-22T09:08:38Z")

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Brilliant! This is exactly what I was looking for. Huge thanks.
  

Best,

Matt