• red: original image
• white: blurred (C+N+S+E+W)
• black: desaturated
• gray: solid gray

Moving the mouse between the red-white dots shows blurring. (interpolation.)
Moving it to the left of red shows sharpening. (extrapolation.)
Moving between red and black shows saturation. Moving above red shows negative saturation.
Moving along white-gray or black-gray shows contrast. Above white, or to the left of black shows negative contrast.