non-maximum suppression

• suppress edges that are non maximal (to get rid of false positives of thicker edges)
• We assume that an edge occurs where gradient is maximum, even if their Gradient magnitude is above the threshold
• Suppress non-maxima neighboring edges
  • Only suppress edges that are in the same direction nearby
  • Don’t suppress other edges

example

• we have neighboring points p,q,r
• q has largest gradient, so p and r are not real edges and should be suppressed (set to 0)

problem

• due to image sampling and quantization, we have values as pixels
  • p and r may not be an actual pixel
  • FIX: find top k closest pixel locations, represent p and r as average of neighboring pixels (bilinear interpolation)

implementation

• calculate Gradient magnitude