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 getting brightness from RGB tuple?
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Reply Quoting This MessageEdit Message lemour9907    Member since: 5/2/2007
 Posted - 5/18/2007 4:10:03 PM
I am trying to analyze brightness of a picture, but I have no idea how to extract the brightness value given the Red, Green, Blue tuple... Does anyone know of some kind of formula or method to do this? I am working in Python.
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Reply Quoting This MessageEdit Message win_crook    Member since: 10/7/2005  From: Blackpool, United Kingdom
 Posted - 5/18/2007 4:24:25 PM
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
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Reply Quoting This MessageEdit Message lemour9907    Member since: 5/2/2007
 Posted - 5/18/2007 4:35:50 PM
that worked like a charm! thank you
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Reply Quoting This MessageEdit Message Lode  GDNet+  Member since: 3/29/2002  From: Belgium
 Posted - 5/19/2007 8:52:13 AM
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.
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Reply Quoting This MessageEdit Message TheAdmiral    Member since: 4/15/2004  From: London, United Kingdom
 Posted - 5/19/2007 10:44:51 AM
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 . I find this reference invaluable for these finicky matters.

Admiral
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