Eigentransform Texture Measure for region filtering

[CattleProdigy]

This texture measure gives an indication of surface roughness which helps to discriminate text regions where lots of fine changes / detail are expected.

A pixel and a neighborhood around the pixel are chosen. The eigenvalues of this block are found. Large eigenvalues are discarded as they encode course, low-frequency information. The average of the remaining eigenvalues is the Eigen-Transform texture measure. The size of the neighborhood is set based on the size of the region being considered.

This is a relatively costly procedure but is only applied on regions that haven't been filtered out yet. It is also only applied to regularly sampled points.