by Isick on Mon Jun 25, 2007 8:11 pm
If you have an image and you want the brightest color to be most transparent and the darkest color to be least transparent it sounds like all you have to do is set the blend mode of that layer to either "Multiply" or "Darken".
It does exactly what you described, the brighter the color the more transparent, the darker the color the more opaque.
"Photoshop is a powerful tool, but like all tools it still needs a powerful artist to release its potential."