vedgex − edge operator cleanup by non-maximum suppression, and thresholding with hysteresis

vedgex if=infile of=outfile [lt=low-threshold] [ht=high-threshold] [-s] [-t] [-d]

Vedgex performs non-maximum suppression and thresholding with hysteresis on the result of an edge operator. The input file must be a VisionX unsigned byte or float image, and must be composed of two channels, edge magnitude and edge direction. The resulting image is unsigned byte.

Only byte and float image types are accepted for input. A second channel containing edge direction is required. The direction must be of the following form : East=0, North=64, West=128 and South=192

lt=low-thresh

ht=high-thresh

The lt= and ht= parameters specify the low and high thresholds of the thresholding with hysteresis function. All points above the high threshold are set high, and all points which are on the same contour as the high points and lie above the low threshold are also set high. This elegant scheme prevents contours from being segmented, and provides higher noise immunity. The default for the high-threshold is 76.5 (equivalent to 0.3 in a normalized 0-1 scale). The default for the low-threshold is ht/3.0.

-s

If the -s option is selected, non-maximum suppression is not performed.

-t

If the -t option is selected, thresholding is not performed. Note that -s and -t cannot be specified at once.

-d

If the -d option is selected, the angle information is output on channel two (copied from the input file), and the output file will have two channels.

D. Griegel, D. Roitman

vderiche(1), vsobel(1)