This filter converts an image to a grayscale image. To do this it finds the brightness of each pixel and sets the red, green and blue of the output to the brightness value. But what is the brightness? The simplest answer might be that it is the average of the RGB components, but that neglects the way in which the human eye works. The eye is much more sensitive to green and red than it is to blue, and so we need to take less acount of the blue and more account of the green. The weighting used by GrayscaleFilter is:
luma = 77R + 151G + 28B
There are no parameters to this filter.