Pruning (morphology)
technique in digital image processing for removing unwanted components to allow better characterization
The pruning algorithm is a technique used in digital image processing based on mathematical morphology. It is used as a complement to the skeleton and thinning algorithms to remove unwanted parasitic components (spurs). In this case 'parasitic' components refer to branches of a line which are not key to the overall shape of the line and should be removed. These components can often be created by edge detection algorithms or digitization. Common uses for pruning include automatic recognition of hand-printed characters. Often inconsistency in letter writing creates unwanted spurs that need to be eliminated for better characterization.
Mathematical Definition
The standard pruning algorithm will remove all branches shorter than a given number of points. If a parasitic branch is shorter than four points and we run the algorithm with n = 4 the branch will be removed. The second step ensures that the main trunks of each line are not shortened by the procedure.
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{\displaystyle B_{1}={\begin{bmatrix}x&0&0\\1&1&0\\x&0&0\end{bmatrix}}B_{2}={\begin{bmatrix}x&1&x\\0&1&0\\0&0&0\end{bmatrix}}B_{3}={\begin{bmatrix}0&0&x\\0&1&1\\0&0&x\end{bmatrix}}B_{4}={\begin{bmatrix}0&0&0\\0&1&0\\x&1&x\end{bmatrix}}}
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{\displaystyle B_{5}={\begin{bmatrix}1&0&0\\0&1&0\\0&0&0\end{bmatrix}}B_{6}={\begin{bmatrix}0&0&1\\0&1&0\\0&0&0\end{bmatrix}}B_{7}={\begin{bmatrix}0&0&0\\0&1&0\\0&0&1\end{bmatrix}}B_{8}={\begin{bmatrix}0&0&0\\0&1&0\\1&0&0\end{bmatrix}}}
The x in the arrays indicates a “don’t care” condition i.e.
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