The fg-subsample option decreases the number of pixels in the image's foreground layer. Because foreground objects vary little in color, you can subsample this layer without affecting their appearance. The foreground of a 300 dpi image, therefore, can be subsampled to 25 dpi, which corresponds to a value of 12 (300 dpi / 25 dpi = 12). Assigning a value of 12 to the fg-subsample option usually ensures that each letter in a word is the correct color.
Supporting command:
documenttodjvu
See also Segmentation Process, bg-subsample and subsample-refine.