1. A binary image downsampling method, comprising: generating a gray-scale image from a binary image having a background and one or more foreground portions; locating skeleton pixels of the gray-scale image, which are pixels corresponding to skeletons of the binary image in the one or more foreground portions; manipulating values of certain foreground pixels in the gray-scale image including at least the skeleton pixels, by changing their original pixel values to new pixel values wherein differences between the new pixel values and background pixel value is greater than differences between the original pixel values and the background pixel value; downsampling the gray-scale image after manipulating the values of the certain foreground pixels; and generating a downsampled binary image from the downsampled gray-scale image.