🔒 Locked

glGetTexImage with GL_LUMINANCE?

Started by Puppet Nov 11, 2006 at 11:56 AM 2 replies 1.9k views

Original Post

Nov 11, 2006 at 11:56 AM

Would glGetTexImage with GL_LUMINANCE give me a grayscale texture where the pixel result is the sum of the components or the mean of the components? I.e. is it (R+G+B) or (R+G+B)/3? On my machine (nvidia 7600Go) it seems to be the mean, like a grayscale conversion. At the same time, I'm getting otherwise unexplainable reports from other machines that I don't have on-site debug access to (intel integrated gfx), that the textures are read back overbrightened. Could this possibly be attributed to different cards giving different results with GL_LUMINANCE?

Brother Bob

Nov 11, 2006 at 7:37 PM

The specification says L = R+G+B. If you want channel weighting, you can set the scale factors for R, G and B as you like with glPixelTransfer and GL_RED/GREEN/BLUE_SCALE. Scaling occurs before the sum.

Puppet

Nov 14, 2006 at 10:55 AM

Thanks, strangely enough, it doesn't seem to be the sum on my card, but the mean. Perhaps, the default scales are set differently between cards. Anyways, as it was in grayscale, I decided to just pick up the R channel instead.

Brother Bob

Nov 14, 2006 at 11:15 AM

All default values are well specified, and the scale values are 1 by default. Anything else is a broken driver.

Topic Locked

This topic has been locked by a moderator. New replies are not allowed.