Image calibration and quality

Assembling the global maps shown here required the production of and combining of image mosaics from numerous observations by Voyager and Galileo obtained over periods of years. Before making a true global map, the images must be calibrated to remove background features inherent to the cameras. Unusual characteristics of both Voyager and Galileo cameras and the nature of each mission plan also affect the location and quality of these images, characteristics that must be taken into account during calibration and global map construction.

Voyager

The Voyager vidicon tube (old-style television) imagers were designed in the late 1960s and used an electron beam to read out the image data. Although robust and relatively stable, the Voyager cameras suffered from problems typical of vidicon cameras. On occasion, the upper left corner of the image was anomalously bright. This unpredictable phenomenon is not accounted for in standard calibration tools, and the corner must be either deleted or smoothed. Near Io, the radiation environment created a temporary background surge in the detector, occasionally saturating bright parts of the image. This can be corrected by knowing the timing and intensity of the exposure anomaly.