# Alpha blending + CreateProceduralGabor or CreateProceduralSineGrating

**URL:** <https://psychtoolbox.discourse.group/t/alpha-blending-createproceduralgabor-or-createproceduralsinegrating/456>\
**Category:** Uncategorized\
**Created:** [January 26, 2012, 10:00pm UTC](https://psychtoolbox.discourse.group/t/alpha-blending-createproceduralgabor-or-createproceduralsinegrating/456 "2012-01-26T22:00:28Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![xrli2002](https://avatars.discourse-cdn.com/v4/letter/x/48db29/32.png) [@xrli2002](https://psychtoolbox.discourse.group/u/xrli2002)\
**Post date:** [January 26, 2012, 10:00pm UTC](https://psychtoolbox.discourse.group/t/alpha-blending-createproceduralgabor-or-createproceduralsinegrating/456/1 "2012-01-26T22:00:28Z")

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When I use CreateProceduralGabor or CreateProceduralSineGrating together with alpha blending enabled, I found I don't have a way to set backgroundColorOffset correctly. After I took a look at the shader, it seems that the alpha in backgroundColorOffset is also modulated sinusoidally. My understanding is that the alpha should be a constant. If it is a sine wave or gabor, the image will lose its mean luminance. Am I right?  
  
-Xiangrui