Erosion (morphology)

Erosion (usually represented by ⊖) is one of two fundamental operations (the other being dilation) in morphological image processing from which all other morphological operations are based. It was originally defined for binary images, later being extended to grayscale images, and subsequently to complete lattices.

In binary morphology, an image is viewed as a subset of a Euclidean space ${\displaystyle \mathbb {R} ^{d}}$ or the integer grid ${\displaystyle \mathbb {Z} ^{d}}$, for some dimension d.

The basic idea in binary morphology is to probe an image with a simple, pre-defined shape, drawing conclusions on how this shape fits or misses the shapes in the image. This simple "probe" is called structuring element, and is itself a binary image (i.e., a subset of the space or grid).

...
Wikipedia