In Photoshop you can adjust the hue, saturation and lightness of an image with three sliders. ImageMagick you can modulate the brightness, saturation, and hue. Minimizing the saturation correctly produces a black and white image in both programs. Maxing out the saturation appears close, but ImageMagick appears to soften some of the blown out edges while Photoshop will expose more the the compression artifacts. How can I accurately reproduce Photoshop's saturation changes from within ImageMagick, or other command line tool.