The threshold-level option Interacts with the pix-filter-level and shape-filter-level options to determine which objects in an image belong in the foreground and which belong in the background. A value of 0 indicates that all objects should be placed in the foreground; a value of 100 specifies that all objects should be placed in the background. The default is 75, which is suitable for most documents.
Supporting command:
documenttodjvu
For more information about the foreground and background layers, see Segmentation Process.