Erosion

Erosion[image, ker] gives the morphological erosion of image with respect to the structuring element ker.

Erosion[image, r] gives the erosion with respect to a range-r square.

Examples

Erode a binary image:

img = Binarize[Import["ExampleData/lena.tif"]]
Erosion[img, 2]

With disk structuring element:

Erosion[img, DiskMatrix[3]]

Please visit the official Wolfram Language Reference for more details.