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 × 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)