As each R,G and B have different "intensity" values when for example converting a color image to a greyscale image I would suggest using different weights for each compoment.
Usual weights are like this:
intensity = 0.3*R + 0.59*G + 0.11*B
Try both methods, It would be nice to see what kind of difference you get.
Usual weights are like this:
intensity = 0.3*R + 0.59*G + 0.11*B
Try both methods, It would be nice to see what kind of difference you get.