As I understand,
A local mean filter is the one in which we take a pixel and calculate the mean of color-values of the pixels around them (but in a certain range of area) and the center pixel is replaced by that mean value.
The filter always has a specific size. For instance, 3x3, 5x5, and so on.
The filter sweeps the whole image row by row to achieve a filtered image (spatial domain), or, the FT of the image is multiplied by the FT of the filter (frequency domain).
But, I could not understand the case of a Non-Local Mean (or, median, or whatever) filter.
- How is the the value of the non-local mean calculated?
- How does that value replaces a pixel?
- How does that filter sweeps the image?