PBMTOJBG(1) PBMTOJBG(1)
2003-06-04
NAME
pbmtojbg - portable bitmap to JBIG1 file converter
SYNOPSIS
pbmtojbg [ options ] [ input-file | - [ output-file ]]
DESCRIPTION
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.
OPTIONS
- 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 x 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
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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 to reduce the depth of an
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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 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
result.
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-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 byte.)
-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 tests.
-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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BUGS
Using standard input and standard output for binary data works only on
systems where there is no difference between binary and text streams
(e.g., Unix). On other systems (e.g., MS-DOS), using standard input or
standard output may cause control characters like CR or LF to be
inserted or deleted and this will damage the binary data.
STANDARDS
This program implements the JBIG1 image coding algorithm as specified
in ISO/IEC 11544:1993 and ITU-T T.82(1993).
AUTHOR
The pbmtojbg program is part of the JBIG-KIT package, which has been
developed by Markus Kuhn. The most recent version of this portable
JBIG1 library and tools set is available from
<http://www.cl.cam.ac.uk/~mgk25/jbigkit/>.
SEE ALSO
pbm(5), pgm(5), jbgtopbm(1)
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