Simplified Texture Spectrum

Calculates the "Simplified Texture Spectrum" of an input grayscale image

Calculates the "Simplified Texture Spectrum" of an input image as detailed in the paper "Simplified Texture Spectrum for Texture Analysis" by Dong-Chen He and Li Wang, Journal of Communication and Computer, Aug 2010, Vol 7, No. 8 (Serial No 69) pp. 44-53.
Note: This calculates a Texture Unit Number (N_TU) for all pixels except for the single pixels on the border of the image. Since a 3x3 neighborhood of pixels is used to calculate each N_TU, only the border pixels are ignored.