Convert full RGBA to grayscale

[Sam_Rowlands]

@424614:@Tim Jones

Before I reinvent the wheel yet again, does anyone have a function to convert a standard RGBA PNG image to a grayscale image? MBS or Einhugur are quite acceptable.

How do you want to convert it to grayscale?

Luminosity, average, brightness or maximum, minimum, value (HSV), or a custom implementation where you can fiddle with the RGB channels?