This may be of some use?
http://www.blitzbasic.com/codearcs/codearcs.php?code=515
You could use it to find the picked texel colour/alpha, and use that to calculate the lumel intensity. Is that what you mean?
http://www.blitzbasic.com/codearcs/codearcs.php?code=515
You could use it to find the picked texel colour/alpha, and use that to calculate the lumel intensity. Is that what you mean?