Manual: pnmtojbig

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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 particu‐
larly suitable for scanned document pages.

A JBIG encoded image can be stored in several resolutions (progressive mode). These resolution 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 encod‐
ing the full image completely every time. Each resolution layer has twice the number of horizontal and vertical pix‐
els than the next lower layer. JBIG files can also store several bits per pixel as separate bitmap planes, and pnm‐
tojbig 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 Common Options ), pn‐
mtojbig recognizes the following command line options:

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

-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 reso‐
lution 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, pnmtojbig writes all layers.
See also option -l.

-b Use binary values instead of Gray code words in order to encode pixel values in multiple bitplanes. This op‐
tion 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 addi‐
tion 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 neigh‐
bour 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. Espe‐
cially 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 pixels by the standard, no higher value than 16 for number is recommended in order to
maintain interoperability with other JBIG implementations. The maximal vertical offset of the adaptive tem‐
plate 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 con‐
tains 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 in‐
side 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 connec‐
tion. 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 re‐
versed 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 con‐
tinuing 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 pur‐
poses you will normally not want to change anything here. The default is 28, which provides the best compres‐
sion 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 rec‐
ommendation 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 li‐
brary: 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 ftp.informatik.uni-erlangen.de in directory pub/doc/ISO/JBIG/.

pnmtojbig is part of the Netpbm package of graphics tools.

Manual: pnmtojbig

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