getting brightness from RGB tuple?

I'm not sure if this is what you need but you can calculate the luminance of a pixel with this formula:

Luminance = (0.2126*R) + (0.7152*G) + (0.0722*B)

Good Luck,
David

that worked like a charm! thank you

You can also simply use (R+G+B) / 3. The true brightness is monitor dependent anyway. Though win_crook is right that the eye is much more sensitive to green than to blue.

Quote:

Original post by Lode You can also simply use (R+G+B) / 3. The true brightness is monitor dependent anyway. Though win_crook is right that the eye is much more sensitive to green than to blue.

That's a formula for lightness. It has its place in the world, but when determining perceived lightness of an image (say, for HDR) it's always best to go with the weighted mean (as they both amount to a dot-product). There are indeed a few standards, and they disagree when used on different display devices, but they are all in the same ball-park.

Lightness, perceived lightness, brightness, luminance and intensity are all different things (some more subtly than others), and give rise to different formulas. In the situation, though, we're talking about either luminance or perceived lightness and it would be a crime to equally weigh the three colour components [smile]. I find this reference invaluable for these finicky matters.

Admiral