Erosion is a method used in image processing to enlarge the black areas of the binary image. The structuring element is a 3x3 rectangle (using the 8 nearest pixels). Combining erosion and dilation allows you to perform opening and closing operations, which remove individual black or white pixels, or smooth out the borders.
It is generally adviced to use the same number of dilation and erosion interations.
Number of erosions to apply on the image.