“…During preprocessing, the input images might be converted to the frequency domain using methods such as discrete cosine transform (DCT) [4], [78], [79] or discrete wavelet transform (DWT) [27], or they may be converted to another color space, such as YC b C r . Various types of image features, such as scale-invariant feature transform (SIFT) [1], [2], [12], [80], speeded-up robust features (SURF) [81], [82], [83], local binary pattern (LBP) [4], [84], and Zenike moments [2], were extracted in block-based or keypoint-based methods. Usually, the final stages are feature matching and filtering to generate detected heatmaps.…”