The mask-upsample option increases the number of pixels in an image's mask layer. Because mask objects (text and line drawings) have sharp edges, they must be encoded at a high resolution to maintain their contrast and readability. Documents, therefore, should be scanned at 300–400 dpi so that the mask layer can be encoded at the recommended 300 dpi. If you are encoding an image with a lower resolution, for example, 100 dpi, use this option to upsample the image's mask layer by a value of 3 (3 * 100 dpi = 300 dpi). This new dpi is then delivered to the segmenter during the encoding process.
NOTE: Assigning the upsample option a value of 3 produces the same results but requires additional processing time and memory.
Supporting command:
documenttodjvu
For more information about the mask layer, see Segmentation Process.