Mine
public text v1 · immutable// I = 0.299R + 0.587G + 0.114B
for(int i = 0; i < (width*height); i++) {
((uint8 *)data)[i] = (uint8)((0.299 * (colordata[i].r))
+ (0.587 * (colordata[i].g))
+ (0.114 * (colordata[i].b)));
}