Erosion is one of the fundamental operations in the mathematical morphology. It is usually applied to black and white images, but can also be applicable to grayscale images. The basic effect of the operation is to erode away the boundaries of regions of foreground pixels (white pixels). Thus areas of foreground pixels shrink in size, and holes within those areas become larger. Applying this to the grayscale image will make bright objects smaller, that is, the image will be darker.

Both erosion and dilation work by translating the structuring element to various points in the input image, and examining the intersection between the translated kernel coordinates and the input image coordinates. For instance, in the case of erosion, the output coordinate set consists of just those points to which the origin of the structuring element can be translated, while the element still remains entirely "within" the input image. In the case of dilation, the effect is the opposite.

For more information, see the IG_IP_erode and IG_IP_NR_ROI_mask_erode functions.