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PBMTOJBG(1) DragonFly General Commands Manual PBMTOJBG(1)
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 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
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.
-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).
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)
2003-06-04 PBMTOJBG(1)