Normalization method for eliminating false detections in side scan sonar images

A system for eliminating false detections at the water column boundary in side scan sonar images consisting of a matrix of pixels, each pixel having a known greyness level, comprising:

• a. a median filter which computes the median greylevel value of a pixel and its four adjacent pixels and produces a median image;
• b. a first linear filter which receives said median image and produces an edge image;
• c. a second linear filter which receives said edge image and produces an edge-smoothed image having a plurality of rows and columns;
• d. edge detecting means which searches each row of said edge-smoothed image for the maximum greylevel;
• e. means for defining a transition region between said detected edge and a preselected right boundary, said transition region having a plurality of rows and columns and computing the average greylevels over the rows and columns in said transition region;
• and
• f. means for normalizing the image by computing the image mean greyness level of each pixel in the image.