1.4.5. Double Threshold
Some of the edge pixels might be caused by noise and color variations or texturing artefacts. The design uses two thresholds to discern between a true edge and a pseudo edge. The design classifies pixel edge intensities below the low threshold value as not an edge; those between the low and high threshold as weak edges. The design classifies those above the high threshold value as strong edges. The design gives strong edge pixels the maximum value of 255; weak edge pixels the high threshold value. Pixels that the design reclassifies as not an edge are suppressed to 0.