Question : Calculating RGBA given different RGB colours.

Hello,

I have three RGB colours, background, foreground and target. The target colour is always between the background and foreground colours. Now, given these three RGB colours, I want to find out what the alpha channel of the foreground colour should be to give the closest approximation of the target colour that only had the RGB channels.

Any ideas on where I can even start this thing???

Thanks,
Uni

Answer : Calculating RGBA given different RGB colours.

depending n how you define closest, it may be
(rt+gt+bt)-(rb+gb+bb)/((rf+gf+bf)-(rb+gb+bb))
or
((rt-rb)/(rf-rb)+(gt-gb)/(gf-gb)+(bt-bb)/(bf-bb))/3
perhaps with gamma or other correction