This filter has produced the correct result. It looks at each channel separately and then creates new colours that contain the results. I assume that your two pixels are rgb(37,62,88), rgb(10,132,255) (I really don't know what you mean by GRB, unless it's a typo). In which case, here is a summary of the min and max: min(r) = 10, max(r) = 37 min(g) = 62, max(g) = 132 min(b) = 88, max(b) = 255 Putting all of this together into two pixels gives us min(rgb) = (10,62,88) max(rgb) = (37,132,255) ... which is exactly that CIAreaMinMax is producing.