Opening and closing are the other two primary operators of mathematical morphology. They are both derived from the two base operations—erosion and dilation. Like those functions, they are normally used on binary or grayscale images.

From a technical perspective, opening and closing can be described in the following ways:

• Opening: This is the dilation of the erosion
• Closing: This is the erosion of the dilation

It is essential to note that erosion is not the inverse of dilation. In general, eroding and dilating produces an image different than the original, and identical results are created by chance.

As with base morphological operators, the exact operation is determined by a structuring element, which in Julia is fixed to a 3x3 block.