NAME

minidjvu - encode/decode black-and-white DjVu pages

SYNOPSIS

minidjvu [options] input_file output_file

There is a similar syntax for multipage compression:

minidjvu [options] input_files output_file

See MULTIPAGE ENCODING section below for more details.

DESCRIPTION

minidjvu encodes and decodes single-page black-and-white DjVu files.

minidjvu is derived from DjVuLibre, which is the primary support library for DjVu.

Besides bitonal DjVu, minidjvu understands Windows BMP, PBM and TIFF (through libtiff) formats. Both inputfile and outputfile may be BMP, PBM, TIFF or DjVu. The file type is determined by extension. Input and output may coincide.

When given a DjVu-to-DjVu job, minidjvu decodes, then re-encodes the image. DjVu layers other than bitonal picture are lost.

Specifying a bitmap-to-bitmap job is possible, but relatively useful only with --smooth option.

All options preceded by two hyphens can be used with one hyphen. This is done to make minidjvu interface more familiar for DjVuLibre users.

MULTIPAGE ENCODING

To activate the multipage mode either specify in your command line more than just one input file, or pass to minidjvu a single multipage tiff document. By default (if --indirect is not specified) the compressed pages are stored into a single bundled document under the name provided in the command line.

There are several options referring to the multipage encoding process, namely --pages-per-dict, --indirect and --report.

OPTIONS

-A

--Averaging

Compute "average" representatives for shapes matching a pattern.

-a n

--aggression n

Sets aggression for pattern matching. The more the aggression, the less the file size, but the more likely substitution errors will occur. The default is 100. Usually you can raise it to about 110 more or less safely. Probably even 200 will work fine, but don't rely on that.

Consistent aggression levels between versions is not guaranteed. The default, however, will always be 100.

This option turns on --match automatically.

-c

--clean

Remove small black marks that are probably noise. This algorithm can really devastate halftone patterns, so use with caution.

This option is turned on by --lossy.

-d n

--dpi n

Specify the resolution of an image, measured in dots per inch. The resolution affects some algorithms and it's recorded in DjVu and BMP files (TIFF should join someday).

-e

--erosion

Sacrifice image quality to gain about 5-10% in file size. One erosion is almost invisible, but 10 erosions in a row spoil an image badly (and they won't give you 50-100% of file size, alas). Erosion bonus stacks with pattern matching.

Erosion makes no sense when the output is not DjVu.

This option is turned on by --lossy.

-i

--indirect

Specifying this option in multipage mode causes minidjvu to generate an indirect multipage document, consisting from a single index file, several single-page DjVu files (one per each image passed to the encoder) and several shared dictionary files. Note that the index file is created under the name specified for the output file in the command line, while for each page the original input file name is preserved, with the extension being changed to ".djvu".

This mode is useful for placing a large document to a Web server, or if you are going to postprocess the generated files (e. g. by adding a color background). In the later case you may then want to convert your indirect document to DjVu bundled, using the djvmcvt utility, supplied with DjVuLibre.

-l

--lossy

Turn on all lossy options. Is equivalent to --clean --erosion --match --smooth.

-m

--match

Run pattern matching. This is the main method of shrinking the file size, but it can also bring trouble with substitution errors. Use --aggression option to maintain balance between file size and error probability.

This option is turned on by --lossy or --aggression.

-n

--no-prototypes

Disable prototype searching. This makes lossless compression faster, but produced files become much bigger.

-p

--pages-per-dict

Specify how many pages to compress in one pass. The default is 10. If -p 0 is specified, minidjvu will attempt to process all pages at once, but be aware that this can take a lot of memory, especially on large books.

-r

--report

Print verbose messages about what's done on which page. Works only with multipage encoding. Useful only to survive boredom while compressing a book.

-s

--smooth

Flip some pixels that appear to be noise. The gain in file size is about 5%. Visually the image is slightly improved, but it's hardly noticeable.

Current filter is dumb and only removes black pixels with at least 3 white neighbors (of 4). You probably won't notice the effects.

This option is turned on by --lossy.

-v

--verbose

Print messages about various stages of the process. It's not very useful, but interesting to examine.

-X

--Xtension

Specifies an extension for shared dictionary files (without a leading period). The default is "iff".

-w

--warnings

Do not disable libtiff warnings. By default, TIFF warnings are suppressed. Under Windows default TIFF warning handler creates a message box. This is unacceptable in a batch processing script, for instance. So the minidjvu default behavior is a workaround for libtiff default behavior.

BUGS

Multipage encoder does not work properly if pages have different resolution.