This is a version of the Median filter that takes a 5×5 matrix instead of a 3×3 one. The strong smoothing is especially efficient on analog video (e.g. captured from VHS) with chroma noise, rainbow effects (e.g. white credits on black background at the end of a movie) etc.(nbsp)(ndash) Median 5×5 applied only on chroma greatly reduces these artifacts.
Example - analog video with strong chroma noise:
Convolution filters applied on chroma clean it up: