The filter represents an optimized version of Erosion filter, which is aimed for binary images (containing black and white pixels) processed with 3x3 structuring element. This makes this filter ideal for removing noise in binary images – it removes all white pixels, which are neighbouring with at least one blank pixel.
See Erosion filter, which represents generic version of erosion filter supporting custom structuring elements and wider range of image formats.
The filter accepts 8 bpp grayscale (binary) images for processing.