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The images that came from the Viking Orbiter were raw electronic data. These images included transmission errors between the satellite and the antennae on earth, and Ruseau marks.

The first step in image processing is to correct for any lens distortion. Prior to the mission, Ruseau marks -- actually painted small dots -- were applied at regular intervals to the lens itself. Any changes in lens shape caused by magnetic radiation or physical effects can be corrected by examining the position of the marks.


"Bit-correction" follows, where any pixels that do not match neighboring pixels within an established range of light-dark are examined. "Problem" pixels are then changed to the average of the nearest neighbors.

Image contrast is also adjusted. Bright areas are lightened while the dark areas are made darker to reveal hidden highlights and features otherwise invisible to the human eye.

A further technique called sharpening is then applied. Each pixel of image data is contrasted to a degree against its neighboring pixels, creating even greater visual contrast.

Ultimately, the images returned from Mars have been processed more for scientific study than for their visual appeal. As such, features that appear sharp in these images may be quite vague if viewed from closer with a better camera.

 

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