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Pnmtojbig User Manual(1) General Commands Manual Pnmtojbig User Manual(1)

NAME
pnmtojbig - PNM to JBIG file converter

SYNOPSIS
pnmtojbig

[options] [input-file [output-file]]

DESCRIPTION
This program is part of Netpbm(1).

pnmtojbig reads a PBM or PGM image, compresses it, and outputs the image as a JBIG bi-level
image entity (BIE) file.

JBIG is a highly effective lossless compression algorithm for bi-level images (one bit per
pixel), which is particularly suitable for scanned document pages.

A JBIG encoded image can be stored in several resolutions (progressive mode). These resolu‐
tion layers can be stored all in one single BIE or they can be stored in several separate BIE
files. All resolution layers except the lowest one are stored merely as differences to the
next lower resolution layer, because this requires less space than encoding the full image
completely every time. Each resolution layer has twice the number of horizontal and vertical
pixels than the next lower layer. JBIG files can also store several bits per pixel as sepa‐
rate bitmap planes, and pnmtojbig can read a PGM file and transform it into a multi-bitplane
BIE.

OPTIONS
In addition to the options common to all programs based on libnetpbm (most notably -quiet,
see ]8;;index.html#commonoptions\ Common Options]8;;\ ), pnmtojbig recognizes the following command line options:

-q Encode the image in one single resolution layer (sequential mode). This is usually the
most efficient compression method. By default, the number of resolution layers is cho‐
sen automatically such that the lowest layer image is not larger than 640 × 480 pix‐
els.

-x number
Specify the maximal horizontal size of the lowest resolution layer. The default is
640 pixels.

-y number
Specify the maximal vertical size of the lowest resolution layer. The default is 480
pixels.

-l number
Select the lowest resolution layer that will be written to the BIE. It is possible to
store the various resolution layers of a JBIG image in progressive mode into different
BIEs. Options -l and -h allow you to select the resolution-layer interval that will
appear in the created BIE. The lowest resolution layer has number 0 and this is also
the default value. By default, pnmtojbig writes all layers.

-h number
Select the highest resolution layer that will be written to the BIE. By default, pnm‐
tojbig writes all layers. See also option -l.

-b Use binary values instead of Gray code words in order to encode pixel values in multi‐
ple bitplanes. This option has only an effect if the input is a PGM file and if more
than one bitplane is produced. Note that the decoder has to make the same selection
but cannot determine from the BIE, whether Gray or binary code words were used by the
encoder.

-d number
Specify the total number of differential resolution layers into which the input image
will be split in addition to the lowest layer. Each additional layer reduces the size
of layer 0 by 50 %. This option overrides options -x and -y, which are usually a more
comfortable way of selecting the number of resolution layers.

-s number
The JBIG algorithm splits each image into a number of horizontal stripes. This option
specifies that each stripe shall have number lines in layer 0. The default value is
selected so that approximately 35 stripes will be used for the whole image.

-m number
Select the maximum horizontal offset of the adaptive template pixel. The JBIG encoder
uses a number of neighbour pixels in order to get statistical a priori knowledge of
the probability, whether the next pixel will be black or white. One single pixel out
of this template of context neighbor pixels can be moved around. Especially for
dithered images it can be a significant advantage to have one neighbor pixel which has
a distance large enough to cover the period of a dither function. By default, the
adaptive template pixel can be moved up to 8 pixels away. This encoder go up to 23
pixels, however as decoders are only required to handle at least a distance of 16 pix‐
els by the standard, no higher value than 16 for number is recommended in order to
maintain interoperability with other JBIG implementations. The maximal vertical off‐
set of the adaptive template pixel is always zero.

-t number
Encode only the specified number of most significant bit planes. This option allows
one to reduce the depth of an input PGM file if not all bits per pixel are needed in
the output.

-o number
JBIG separates an image into several horizontal stripes, resolution layers and planes,
were each plane contains one bit per pixel. One single stripe in one plane and layer
is encoded as a data unit called stripe data entity (SDE) inside the BIE. There are
12 different possible orders in which the SDEs can be stored inside the BIE and number
selects which one shall be used. The order of the SDEs is only relevant for applica‐
tions that want to decode a JBIG file which has not yet completely arrived from e.g. a
slow network connection. For instance some applications prefer that the outermost of
the three loops (stripes, layers, planes) is over all layers so that all data of the
lowest resolution layer is transmitted first.

The following values for number select these loop arrangements for writing the SDEs
(outermost loop first):

0 planes, layers, stripes

2 layers, planes, stripes

3 layers, stripes, planes

4 stripes, planes, layers

5 planes, stripes, layers

6 stripes, layers, planes

All loops count starting with zero, however by adding 8 to the above order code, the
layer loop can be reversed so that it counts down to zero and then higher resolution
layers will be stored before lower layers. Default order is 3 which writes at first
all planes of the first stripe and then completes layer 0 before continuing with the
next layer and so on.

-p number
This option allows you to activate or deactivate various optional algorithms defined
in the JBIG standard. Just add the numbers of the following options which you want to
activate in order to get the number value:

4 deterministic prediction (DPON)

8 typical prediction (TPBON)

16 diff. layer typical prediction (TPDON)

64 layer 0 two-line template (LRLTWO)

Except for special applications (like communication with JBIG subset implementations)
and for debugging purposes you will normally not want to change anything here. The
default is 28, which provides the best compression result.

-c The adaptive template pixel movement is determined as suggested in annex C of the
standard. By default the template change takes place directly in the next line which
is most effective. However a few conformance test examples in the standard require
the adaptive template change to be delayed until the first line of the next stripe.
This option selects this special behavior, which is normally not required except in
order to pass some conformance test suite.

-v After pnmtojbig creates the BIE, it lists a few technical details of the created file
(verbose mode).

FORMATS
Most of the format pnmtojbig creates is defined by the JBIG standard.

The standard, however, does not specify which values in the BIE mean white and which mean
black. It contains a recommendation that for a single plane image zero mean background and
one mean foreground, but the Netpbm formats have no concept of foreground and background.
And the standard says nothing about values for multiple plane BIEs.

pnmtojbig follows Markus Kuhn's implementation of the standard in the pbmtojbg program that
comes with his JBIG library: If the BIE is a single plane BIE, zero means white and one
means black. If it is a multiple plane BIE, zero means black and the maximal value is white.

STANDARDS
This program implements the JBIG image coding algorithm as specified in ISO/IEC 11544:1993
and ITU-T T.82(1993).

AUTHOR
pnmtojbig is based on the JBIG library by Markus Kuhn, part of his JBIG-KIT package. The
pbmtojbg program is part of the JBIG-KIT package. The most recent version of that library
and tools set is freely available on the Internet from anonymous ftp server ]8;;ftp://ftp.informatik.uni-erlangen.de\ftp.infor‐
matik.uni-erlangen.de]8;;\ in directory pub/doc/ISO/JBIG/.

pnmtojbig is part of the Netpbm package of graphics tools.