Updated: 20 May 2000
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pnmtojbig - PNM to JBIG file converter
This program is part of Netpbm.
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 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 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 separate bitmap planes, and pnmtojbig
can read a PGM file and transform it into a multi-bitplane BIE.
- 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 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 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, pnmtojbig writes all layers. See also option
- Use binary values instead of Gray code words in order to encode
pixel values in multiple 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 supports up to 23 pixels,
however as decoders are only required to support 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 template pixel is always zero.
- -t number
- Encode only the specified number of most significant bit planes.
This option allows 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 applications 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):
- planes, layers, stripes
- layers, planes, stripes
- layers, stripes, planes
- stripes, planes, layers
- planes, stripes, layers
- 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
- deterministic prediction (DPON)
- typical prediction (TPBON)
- diff. layer typical prediction (TPDON)
- 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.
- 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.
- After pnmtojbig creates the BIE, it lists a few technical
details of the created file (verbose mode).
Most of the format pnmtojbig creates is defined by the
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.
This program implements the JBIG image coding algorithm as
specified in ISO/IEC 11544:1993 and ITU-T T.82(1993).
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
in directory pub/doc/ISO/JBIG/.
pnmtojbig is part of the Netpbm package of graphics tools.
If you use pnmtojbig, you are using various patents,
particularly on its arithmetic encoding method, and in all probability
you do not have a license from the patent owners to do so.
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