Why do prisms appear in some of the SSI images?
The SSI takes color images by placing a red filter in front of the CCD and taking an image, then a green, then a blue. The three are combined on the ground to make a color image. This has the side effect that the Sun moves between images. This is usually not a problem, but when the camera shadow or lander shadow are in view, they will be in different positions for the three colors. The most interesting shadow is the wiry camera mast–that gives a red, green and blue imprint on the ground. Consumer digital cameras don’t have this problem, because they have filters permanently built onto the CCD. They use some pixels for red, others for green, and other for blue. SSI doesn’t do this because we need to use all of the pixels for individual colors sometimes, and also we need to use the camera to look at other colors, including ones the eye cannot see.
