Constant variance enhancement: A digital processing technique
Abstract
An imageenhancement process is one in which the image is manipulated for the purpose of increasing the information extractable by the human visual system. Constantvariance enhancement is a technique which employs highpass filtering to reduce the local average to zero for all regions of the picture and then applies a gain factor equal to the reciprocal of the local standard deviation to produce an output picture in which all local regions have equal variance. An example of constantvariance enhancement is presented with pictures illustrating the various mathematical stages of the processing operations. The concept of differential luminance gain is introduced as a crude measure of enhancement effectiveness and is numerically evaluated for the illustrative processing. The significance of negative differential luminance gain is considered, and ways of dealing with these spurious results are considered.
 Publication:

Applied Optics
 Pub Date:
 May 1977
 DOI:
 10.1364/AO.16.001268
 Bibcode:
 1977ApOpt..16.1268H
 Keywords:

 Digital Techniques;
 High Pass Filters;
 Image Enhancement;
 Optical Data Processing;
 Cathode Ray Tubes;
 Image Contrast;
 Luminance;
 Variance (Statistics);
 Instrumentation and Photography;
 IMAGE ENHANCEMENT;
 IMAGE PROCESSING