PBMTOJBG(1)PBMTOJBG(1)NAMEpbmtojbg - portable bitmap to JBIG1 file converter
SYNOPSISpbmtojbg [ options ] [ input-file | - [ output-file ]]
DESCRIPTION
Reads in a portable bitmap (PBM) from a file or standard input, com‐
presses 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 lay‐
ers 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 (sequen‐
tial mode). This is usually the most efficient compres‐
sion 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 resolu‐
tion layer. The default is 640 pixels.
-y number Specify the maximal vertical size of the lowest resolu‐
tion 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 resolu‐
tion 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 lay‐
ers 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 tem‐
plate pixel. The JBIG1 encoder uses a number of neigh‐
bour pixels in order to get statistical a priori knowl‐
edge 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 interoperabil‐
ity with other JBIG1 implementations. The maximal verti‐
cal 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 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 Determine the adaptive template pixel movement as sug‐
gested in annex C of the standard. By default the tem‐
plate change takes place directly in the next line, which
is most effective. However, a few conformance test exam‐
ples 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 nor‐
mally not required except in order to pass some confor‐
mance tests.
-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 com‐
pletely 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.
-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 ALSOpbm(5), pgm(5), jbgtopbm(1)
2003-06-04 PBMTOJBG(1)
