Freeman code

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The Freeman code (also chain code or chain code ) is the pixel-by-pixel coding of a contour or line by specifying

in which direction the next pixel is. It is named after its inventor Herbert Freeman . There are different variants for defining the code.

Starting from the current position

Based on the current position, the directions east, northeast, north etc. are assigned a value from 0 to 7:

 3  2  1 

 4  *  0 

 5  6  7

With a central pixel

The current pixel is set to 0, whereby the directions are then determined by the numbers 1 to 8 using the following matrix:

 4  3  2 

 5  0  1 

 6  7  8