The Morphological image processing reference article from the English Wikipedia on 24-Apr-2004
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Morphological image processing

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A collection of techniques for digital image processing based on Mathematical morphology. Since these techniques rely only on the relative ordering of pixel values, not on their numerical values, they are especially suited to the processing of binary images and grayscale images whose light transfer function is not known.

Some morphological operations are:

By combining these operators one can obtain algorithms for many image processing tasks, such as feature detection, image segmentation, image filtering, granulometry and distance transforms.