PBMTOJBG(1) 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 particu-
larly 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 low-
est 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 reso-
lution layer has twice the number of horizontal and verti-
cal 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.
-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 differ-
ent BIEs. Options -l and -h allow to select
the resolution-layer interval that will
appear in the created BIE. The lowest reso-
lution 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 over-
rides 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 a number of neighbour pixels in order
to get statistical a priori knowledge 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 stan-
dard, no higher value than 16 for number is
recommended in order to maintain interoper-
ability with other JBIG1 implementations.
The maximal vertical 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 hori-
zontal 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, lay-
ers, 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 (out-
ermost 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 lay-
ers will be stored before lower layers.
Default order is 3 which writes at first all
planes of the first stripe and then com-
pletes 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 commu-
nication 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 com-
pression result.
-c Determine the adaptive template pixel move-
ment as suggested in annex C of the stan-
dard. 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.
-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 cor-
rect 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 lat-
est possible opportunity to the data stream
to signal the correct final height.
-v After the BIE has been created, a few tech-
nical 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)
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