├── test_image.jpg
├── test_result.jpg
├── README.md
└── contour detection.py


/test_image.jpg:
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https://raw.githubusercontent.com/RajdeepMondal/Contour-Detection/HEAD/test_image.jpg


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/test_result.jpg:
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https://raw.githubusercontent.com/RajdeepMondal/Contour-Detection/HEAD/test_result.jpg


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/README.md:
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1 | # Contour-Detection
2 | This is an implementation of the contour detection algorithm proposed in the paper Topological Structural Analysis of Digitized Binary Images by Border Following by Suzuki and Abe 1985.
3 | The function raster_scan() requires a zero-padded binary input image.
4 | The outputs are the contour coordinates, hierarchy of the contours and the corresponding border types. The images are assumed to be four-connected.
5 | # Results
6 | ![](test_image.jpg)
7 | ![](test_result.jpg)
8 | 


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/contour detection.py:
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  1 | import numpy as np
  2 | import ast
  3 | # four-connected case
  4 | """
  5 |     Direction Reference:
  6 | 
  7 |                 1
  8 |                 |
  9 |                 |
 10 |          2 <- - | - -> 0
 11 |                 |
 12 |                 |
 13 |                 3
 14 |     """
 15 | def next_cell(curr_pixel,curr_dir):
 16 |     i,j=curr_pixel
 17 |     save=None
 18 |     if curr_dir==0:
 19 |         r=i-1
 20 |         c=j
 21 |         new_dir=1
 22 |         save=[i,j+1]
 23 |     elif curr_dir==1:
 24 |         r=i
 25 |         c=j-1
 26 |         new_dir=2
 27 |     elif curr_dir==2:
 28 |         r=i+1
 29 |         c=j
 30 |         new_dir=3
 31 |     elif curr_dir==3:
 32 |         r=i
 33 |         c=j+1
 34 |         new_dir=0
 35 |     return r,c,new_dir,save
 36 | 
 37 | def border_follow(img,start,prev,direction,NBD):
 38 |     curr=list(start)
 39 |     exam=list(prev)
 40 |     save=None
 41 |     save2=list(exam)
 42 |     contour=[]
 43 |     contour.append(list(curr))
 44 |     while img[exam[0]][exam[1]]==0:
 45 |         exam[0],exam[1],direction,save_pixel=next_cell(curr,direction)
 46 |         if save_pixel!=None:
 47 |             save=list(save_pixel)
 48 |         if save2==exam:
 49 |             img[curr[0],curr[1]]=-NBD
 50 |             return contour
 51 |     if save!=None:
 52 |         img[curr[0]][curr[1]]=-NBD
 53 |         save=None
 54 |     elif (save==None or (save!=None and img[save[0]][save[1]]!=0)) and img[curr[0]][curr[1]]==1: img[curr[0]][curr[1]]=NBD
 55 |     else: pass
 56 |     prev=list(curr)
 57 |     curr=list(exam)
 58 |     contour.append(list(curr))
 59 |     if direction>=2: direction=direction-2
 60 |     else: direction=2+direction
 61 |     flag=0
 62 |     start_next=list(curr)
 63 |     while True:
 64 |         if not(curr==start_next and prev==start and flag==1):
 65 |             flag=1
 66 |             exam[0],exam[1],direction,save_pixel=next_cell(curr,direction)
 67 |             if save_pixel!=None:
 68 |                 save=list(save_pixel)
 69 |             while img[exam[0]][exam[1]]==0:
 70 |                 exam[0],exam[1],direction,save_pixel=next_cell(curr,direction)
 71 |                 if save_pixel!=None:
 72 |                     save=list(save_pixel)
 73 |             if save!=None and img[save[0]][save[1]]==0:
 74 |                 img[curr[0]][curr[1]]=-NBD
 75 |                 save=None
 76 |             elif (save==None or (save!=None and img[save[0]][save[1]]!=0)) and img[curr[0]][curr[1]]==1: img[curr[0]][curr[1]]=NBD
 77 |             else: pass
 78 |             prev=list(curr)
 79 |             curr=list(exam)
 80 |             contour.append(list(curr))
 81 |             if direction>=2: direction=direction-2
 82 |             else: direction=2+direction
 83 |         else:
 84 |             break
 85 |     return contour
 86 |         
 87 | def raster_scan(img):
 88 |     rows,cols=img.shape
 89 |     LNBD=1
 90 |     NBD=1
 91 |     contours=[]
 92 |     parent=[]
 93 |     parent.append(-1)
 94 |     border_type=[]
 95 |     border_type.append(0)
 96 |     for i in range(1,rows-1):
 97 |         LNBD=1
 98 |         for j in range(1,cols-1):
 99 |             if img[i][j]==1 and img[i][j-1]==0:
100 |                 NBD+=1
101 |                 direction=2
102 |                 parent.append(LNBD) 
103 |                 contour=border_follow(img,[i,j],[i,j-1],direction,NBD)
104 |                 contours.append(contour)
105 |                 border_type.append(1)
106 |                 if border_type[NBD-2]==1: parent.append(parent[NBD-2])
107 |                 else:
108 |                     if img[i][j]!=1: LNBD=abs(img[i][j])              
109 |             elif img[i][j]>=1 and img[i][j+1]==0:
110 |                 NBD+=1
111 |                 direction=0
112 |                 if img[i][j]>1: LNBD=img[i][j]
113 |                 parent.append(LNBD)
114 |                 contour=border_follow(img,[i,j],[i,j+1],direction,NBD)
115 |                 contours.append(contour)
116 |                 border_type.append(0)
117 |                 if border_type[NBD-2]==0: parent.append(parent[NBD-2])
118 |                 else:
119 |                     if img[i][j]!=1: LNBD=abs(img[i][j])
120 |     return contours,parent,border_type
121 | 
122 | img=np.array(ast.literal_eval(input()))
123 | contours,parent,border_type=raster_scan(img)
124 | print(contours)
125 | print(parent)
126 | print(border_type)
127 | 


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