Common names: Erode, Shrink, Reduce
Erosion is one of the two basic operations in mathematical morphology (the other being dilation). The effect is to enlarge the boundaries of regions of foreground pixels. Thus areas of foreground pixels grow in size while holes (background) within these regions become smaller. Erosion is the dual of Dilation.
The kernel is a mask used as follows. For binary images, for every 1 in the kernel the image pixels are ANDed. For grey scale images the MINimum of the image pixels is taken where the kernel is 1.