--bg-subsample=<1-6>

The bg-subsample option decreases the number of pixels in the image's background layer. Because background objects are generally low-contrast and smooth, you can subsample this layer without affecting their appearance. The background of a 300 dpi image, therefore, can be subsampled to 100 dpi, which corresponds to a value of 3 (300 dpi / 100 dpi = 3). Assigning a value of 3 to the bg-subsample option decreases the size of the output file and ensures that the letters or parts of letters that were not placed in the foreground are still readable.

Because background objects tend to appear blurry below 100 dpi, values 1 and 2 should be used only in the following instances:

• The segmenter places all objects in the appropriate layers and the background does not contain varying colors (for example, colored paper).
• The original resolution of the scanned image is below 100 dpi.

Supporting command:

documenttodjvu

See also Segmentation Process, fg-subsample and subsample-refine.