Believe it or not, this shitty algorithm is the one most digital cameras use for taking “grayscale” photos. CCDs in digital cameras are comprised of a grid of red, green, and blue sensors, and rather than perform the necessary math to convert RGB values to gray ones, they simply grab a single channel (green, for the reasons mentioned in Method #2 – human eye correction) and call that the grayscale one. For this reason, most photographers recommend against using your camera’s built-in grayscale option. Instead, shoot everything in color and then perform the grayscale conversion later, using whatever method leads to the best result.
It is difficult to predict the results of this method of grayscale conversion. As such, it is usually reserved for artistic effect.
Method 6 – Custom # of gray shades