Canny Edge Detector

extensions [gst-video bitmap]

globals [cam-is-inited? xconv yconv max-grad]
patches-own [bw new-bw grad gx gy]

to start-webcam
  if (not (cam-is-inited? = true)) [
    gst-video:camera-init
    set cam-is-inited? true
  ]
  gst-video:camera-start
end 

to stop-webcam
  gst-video:camera-stop
end 

to display-mirror-to-patches
  cam-mirror-to-patches
  display
end 

to cam-mirror-to-patches
  if (gst-video:camera-is-rolling?) [
    bitmap:copy-to-pcolors gst-video:camera-image false
  ]
end 

to go
  no-display
  cam-mirror-to-patches
  ask patches [set bw brightness set new-bw bw]
  if horizontal-blur [ask patches [apply-horiz-gaussian]]
  if vertical-blur [ask patches [apply-vert-gaussian]]
  ask patches [set bw new-bw]
  ifelse detection-method != "None" [
    ask patches [gradient]
    set max-grad max [grad] of patches
    ;ask patches [set pcolor scale-color white grad 0 max-grad]
    ask patches [color-patch]
  ]
  [
    ask patches [set pcolor scale-color white bw 0 255]
  ]
  display
end 

to-report brightness
  report mean pcolor
end 

to color-patch
  ifelse grad <= high-thresh or (non-max-suppress and not max-edge?) [set pcolor black] [
    ifelse color-gradient
      [set pcolor hsb (255 * atan gx gy / 360) 128 (255 * grad / max-grad)]
      [set pcolor scale-color white grad 0 max-grad]
  ]
end 

to apply-horiz-gaussian
  let p1 [bw] of patch-at -2 0
  let p2 [bw] of patch-at -1 0
  let p4 [bw] of patch-at 1 0
  let p5 [bw] of patch-at 2 0
  
  set new-bw (2 * p1 + 4 * p2 + 5 * bw + 4 * p2 + 2 * p1) / 13
end 

to apply-vert-gaussian
  let p1 [bw] of patch-at 0 -2
  let p2 [bw] of patch-at 0 -1
  let p4 [bw] of patch-at 0 1
  let p5 [bw] of patch-at 0 2
  set new-bw (2 * p1 + 4 * p2 + 5 * bw + 4 * p2 + 2 * p1) / 13
end 

to-report max-edge?
  if grad < high-thresh [report false]
  let angle 45 * round ((atan gy gx) / 45)
  let x sin angle
  let y cos angle
  report grad >= [grad] of patch-at x y and grad >= [grad] of patch-at (- x) (- y)
end 

to gradient
  let p1 [bw] of patch-at -1 1
  let p2 [bw] of patch-at 0 1
  let p3 [bw] of patch-at 1 1
  let p4 [bw] of patch-at -1 0
  
  let p6 [bw] of patch-at 1 0
  let p7 [bw] of patch-at -1 -1
  let p8 [bw] of patch-at 0 -1
  let p9 [bw] of patch-at 1 -1
  if detection-method = "Scharr" [
    ; Scharr
    set gx (3 * p1 + 10 * p2 + 3 * p3) - (3 * p7 + 10 * p8 + 3 * p9)
    set gy (3 * p3 + 10 * p6 + 3 * p9) - (3 * p1 + 10 * p4 + 3 * p7)
  ] 
  if detection-method = "Sobel" [ 
    ; Sobel
    set gx (p1 + 2 * p2 + p3) - (p7 + 2 * p8 + p9)
    set gy (p3 + 2 * p6 + p9) - (p1 + 2 * p4 + p7)
  ]
  if detection-method = "Prewitt" [
    set gx (p1 + p2 + p3) - (p7 + p8 + p9)
    set gy (p3 + p6 + p9) - (p1 + p4 + p7)
  ]
  set grad abs(gx) + abs(gy)
  ;report abs(gx) + abs(gy)
end