Pixel types

A central vectorization problem is how best to handle junctions.

ShapeLogic has approached the problem by developing an extensive catalogue of different pixel types.

Pixel type catalogue

  • P: Normal point, 2 neighbors, cross index of 4
  • E: End or extreme point, 1 neighbor, cross index of 2
  • N: More neighbors, more than 2 neighbors, cross index of 4
  • J: Junction point, more than cross index of 4
  • L: L corner, 2 neighbors with modulo distance either 2 or 6, cross index of 4
  • V: A corner, 2 neighbors, cross index of 2, should always be next to a junction
  • B: Border of solid, cross index of 2
  • S: Solid, 8 neighbors or 7 where the last on is an even number.

Pixel types examples

Junctions

 P P    P 
  J     P
  P     N
  P   PNJNP
  E     N

Corners

 P      
  N     
 VJNPP

 P
 N
 LNP
 P      
  N     
 VJNPP

V points

V points are angle junctions (as in the letter "V")

   P     
  N     
 VJNPPE

   P     
  N     
 VJNPPE
  N
   P

   P     
  N     
 VJNPPE
 NN 
 P P

Problematic V point 

  P  P    
  N P    
  JN
  V

N points

N points have more than 2 neighbors, but can only be traversed in one reasonable way.

 P  P
  NN
  NN
 P  P

 P P
 NN
 NN
 P P

Edge and inner points

Edge and inner points are not yet handled in ShapeLogic.

 BBBB      
 BSSB     
 BBBB
 BBB      
 BSSB     
 BBBB
 BBB B      
 BSSBB     
 BBBBB
 BBBBB      
 BB BB     
 BBBBB