“…(1) Image preprocessing : when fingerprint recognition device collects fingerprint image information, the image will have interference because of the noise and differences in human skin state or pressing force, so it needs preprocessing: the calculation formula of image enhancement 7 is as follows: where ( i , j ) is the coordinates of an image pixel, G ( i , j ) is the gray value of the original image, G ′ ( i , j ) is the gray value of the enhanced image, and max( i , j ) and min( i , j ) are the upper and lower limits of gray levels of an image. Binarization is to convert an image into a black‐and‐white image.…”