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pbmtojbg - portable bitmap to JBIG1 file converter


pbmtojbg [ options ] [ input-file | - [ output-file ]]


Reads in a portable bitmap (PBM) from a file or standard input, compresses it, and outputs
the image as a JBIG1 bi-level image entity (BIE) file.

JBIG1 is a highly effective lossless compression algorithm for bi-level images (one bit
per pixel), which is particularly suitable for scanned document pages.

A JBIG1 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. JBIG1 files can also store
several bits per pixel as separate bitmap planes, and pbmtojbg can read a PGM file and
transform it into a multi-bitplane BIE.


- A single hyphen instead of an input file name will cause pbmtojbg to read
the data from standard input instead from a file.

-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 chosen automatically such that the lowest layer image
is not larger than 640 × 480 pixels. This is a shortcut for -d 0.

-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 JBIG1 image in
progressive mode into different BIEs. Options -l and -h allow 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
all layers will be written.

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

-b 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 JBIG1 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
JBIG1 encoder uses ten neighbour pixels to estimate the probability of the
next pixel being black or white. It can move one out of these ten pixels.
This is especially useful for dithered images, as long as the distance of
this adaptive pixel can be adjusted to the period of the dither pattern. By
default, the adaptive template pixel is allowed to move up to 8 pixels away
horizontally. This encoder supports distances up to 127 pixels. Annex A of
the standard suggests that decoders should support at least a horizontal
distance of 16 pixels, so using values not higher than 16 for number might
increase the chances of interoperability with other JBIG1 implementations.
On the other hand, the T.85 fax application profile requires decoders to
support horizontal offsets up to 127 pixels, which the maximum value
permitted by the standard. (The maximal vertical offset of the adaptive
template pixel is always zero for this encoder.)

-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 JBIG1 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 JBIG1 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 one to activate or deactivate various optional algorithms
defined in the JBIG1 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 layer 0 typical prediction (TPBON)
16 diff. layer typ. pred. (TPDON)
64 layer 0 two-line template (LRLTWO)

Except for special applications (like communication with JBIG1 subset
implementations) and for debugging purposes you will normally not want to
change anything here. The default is 28, which provides the best compression

-C string Add the string in a comment marker segment to the produced data stream.
(There is no support at present for adding comments that contain the zero

-c Determine the adaptive template pixel movement 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

-r Use the SDRST marker instead of the normal SDNORM marker. The probably only
useful application of this option is to generate test data for checking
whether a JBIG1 decoder has implemented SDRST correctly. In a normal JBIG1
data stream, each stripe data entity (SDE) is terminated by an SDNORM
marker, which preserves the state of the arithmetic encoder (and more) for
the next stripe in the same layer. The alternative SDRST marker resets this
state at the end of the stripe.

-Y number A long time ago, there were fax machines that couldn't even hold a single
page in memory. They had to start transmitting data before the page was
scanned in completely and the length of the image was known. The authors of
the standard added a rather ugly hack to the otherwise beautiful JBIG1
format to support this. The NEWLEN marker segment can override the image
height stated in the BIE header anywhere later in the data stream. Normally
pbmtojbg never generates NEWLEN marker segments, as it knows the correct
image height when it outputs the header. This option is solely intended for
the purpose of generating test files with NEWLEN marker segments. It can be
used to specify a higher initial image height for use in the BIE header, and
pbmtojbg will then add a NEWLEN marker segment at the latest possible
opportunity to the data stream to signal the correct final height.

-f This option makes the output file comply to the "facsimile application
profile" defined in ITU-T Recommendation T.85. It is a shortcut for -q -o 0
-p 8 -s 128 -t 1 -m 127.

-v After the BIE has been created, a few technical details of the created file
will be listed (verbose mode).

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