“…The filters used to retrieve features from images include CLAHE (contrast limited adaptive histogram equalization) [24], Gabor filter [25], Gamma Correction [26], Gaussian filter [27], Hessian [8], Laplacian operator [28], Median filter [29], Mean filter [30], Minimum filter [31], Bilateral filter [32], Sobel operator [33], Canny edge detector [34], as well as the ten filters predefined in the imageFilter module of Pillow [35], which are BLUR, CONTOUR, DE-TAIL, EDGE ENHANCE, EDGE ENHANCE MORE, EMBOSS, FIND EDGES, SMOOTH, SMOOTH MORE and SHARPEN. The mathematical definitions of these filters/operators are shown in Table 4.…”