Calibration. The following two images are deteriorated after enhancement due to generic vignetting. They are the space shuttle images STS51B-038-0095 and STS51F-035-0011, Columbia River, Oregon and Washington. They were acquired in May and August, 1985 respectively. The raw image size is 640(h)x640(v) and reduced to 320(h)x320(v) in the following presentation. The quality of the enhanced image is badly deteriorated by vignetting, and causes difficulties in image interpretation. 

The vignetting can be compensated with XBit image processing command rimagesmetric. For the above two images, a script could be 

rimage smetric -in inputImage -outoutputImage -o XY -w 128 -l 322 -h 220 

In the script, option -o XY specifies a compensation based on 2D statistical analysis, and option -w 128 specifies a window size of 128 rows and columns in statistics calculation, options -l 32 and -h 220 restrict the sample values from 32 to 220 in statistics calculation. A default additional model is chosen for brightness compensation. The results show a significant improvement after calibration.