Feature group	Feature number	Description
Image statistics based features	1–13	Average local value fluctuation of gray level histogram, Mean of gray level histogram values, Standard deviation of gray level histogram values; Statistics based features computed from the pixel value distributions of the ROI (region of interest) including Mean value, Variance, Standard deviation, Skewness, Kurtosis, Energy, Entropy; Statistics based features computed from the local pixel value fluctuation map of the ROI including mean value, Standard deviation, Skewness
Breast tissue composition features	14–17	Fractal dimension estimated with variation method, Fractal dimension estimated with mathematical morphology, Slope estimated by fitting lines using textural edgeness, and Slope estimated by fitting lines using Gaussian subtraction
Texture related image features	18–56
Gray-level co-occurence matrix based features	18–25	Energy, Contrast, Correlation, Homogeneity, Variance, Sum Average, Entropy, and Dissimilarity
Gray-level run-length matrix based features	26–38	Short Run Emphasis (SRE), Long Run Emphasis (LRE), Gray-Level Non-uniformity (GLN), Run-Length Non-uniformity (RLN), Run Percentage (RP), Low Gray-Level Run Emphasis (LGRE), High Gray-Level Run Emphasis (HGRE), Short Run Low Gray-Level Emphasis (SRLGE), Short Run High Gray-Level Emphasis (SRHGE), Long Run Low Gray-Level Emphasis (LRLGE), Long Run High Gray-Level Emphasis (LRHGE), Gray-Level Variance (GLV), and Run-Length Variance (RLV)
Gray-level size zone matrix based features	39–51	Small Zone Emphasis (SZE), Large Zone Emphasis (LZE), Gray-Level Non-uniformity (GLN), Zone-Size Non-uniformity (ZSN), Zone Percentage (ZP), Low Gray-Level Zone Emphasis (LGZE), High Gray-Level Zone Emphasis (HGZE), Small Zone Low Gray-Level Emphasis (SZLGE), Small Zone High Gray-Level Emphasis (SZHGE), Large Zone Low Gray-Level Emphasis (LZLGE), Large Zone High Gray-Level Emphasis (LZHGE), Gray-Level Variance (GLV), and Zone-Size Variance (ZSV)
Neighbourhood gray-tone difference matrix based features	52–56	Coarseness, Contrast, Busyness, Complexity, and Strength
Features for mimicking BIRADS	57–72	Ratio between the number of pixels in the ROI with gray value larger than the average value of all pixels and the total number of pixels in the ROI, Ratio between the number of pixels in the ROI with gray value larger than the average value of all pixels and the total number of pixels in the ROIs of both left and right breasts, Ratio between the number of pixels in the ROI with gray value larger than the median value of all pixels and the total number of pixels in the ROI, Ratio between the number of pixels in the ROI with gray value larger than the median value of all pixels and the total number of pixels in the ROIs of both left and right breasts; Ratio between the average value of pixels under threshold of 25% of the maximum pixel value and the average pixel value of the whole ROI, Ratio between the average value of pixels under threshold of 50% of the maximum pixel value and the average pixel value of the whole ROI, Ratio between the average value of pixels under threshold of 75% of the maximum pixel value and the average pixel value of the whole ROI, Ratio between the number of pixels under 25% threshold and the total number of pixels of the whole ROI, Ratio between the number of pixels under 50% threshold and the total number of pixels of the whole ROI, Ratio between the number of pixels under 75% threshold, and the total number of pixels of the whole ROI; Ratio between the average gray value of the pixels in the ROI whose gray value is under the threshold of 25% of the maximum pixel value and the average gray value of all pixels in the ROIs of both left and right breasts, Ratio between the average gray value of the pixels in the ROI whose gray value is under the threshold of 50% of the maximum pixel value and the average gray value of all pixels in the ROIs of both left and right breasts, Ratio between the average gray value of the pixels in the ROI whose gray value is under the threshold of 75% of the maximum pixel value and the average gray value of all pixels in the ROIs of both left and right breasts, Ratio between the number of the pixels in the ROI with gray values under the threshold of 25% of the maximum pixel value and the total number of pixels in the ROIs of both left and right breasts, Ratio between the number of the pixels in the ROI with gray values under the threshold of 50% of the maximum pixel value and the total number of pixels in the ROIs of both left and right breasts, Ratio between the number of the pixels in the ROI with gray values under the threshold of 75% of the maximum pixel value and the total number of pixels in the ROIs of both left and right breasts
Newly defined features	73–76	Absolute difference of the maximum pixel values in the ROI of the left breast and that of the right breast, Ratio between the absolute difference of the maximum pixel values in the ROI of the left breast and that of the right breast and the number of gray levels in the ROI of left or right breast whose maximum pixel value is higher, The number of the pixels in the ROI of higher maximum pixel value with gray values higher than the maximum pixel value of another ROI, Ratio between the number of the pixels in the ROI of higher maximum pixel value with gray values higher than the maximum pixel value of another ROI and the total number of pixels in the ROI of higher maximum pixel value.