PBMTOJBG(1)PBMTOJBG(1)NAMEpbmtojbg - portable bitmap to JBIG file converter
SYNOPSISpbmtojbg [ 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 JBIG bi-
level image entity (BIE) file.
JBIG 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 JBIG encoded image can be stored in several resolutions
(progressive mode). These resolution layers can be stored
all in one singe BIE or they can be stored in several sep-
arate 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 reso-
lution layer has twice the number of horizontal and verti-
cal pixels than the next lower layer. JBIG files can also
store several bits per pixel as separate bitmap planes,
however this program stores only one single plane.
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 so 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
JBIG image in progressive mode into differ-
ent BIEs. Options -l and -h allow to select
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the resolution layer intervall 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.
-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 JBIG 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 JBIG encoder
uses a number of neigbour pixels in order to
get statistical a priori knowledge of the
propability, whether the next pixel will be
black or white. One single pixel out of this
template of context neighbour pixels can be
moved around. Especially for dithered images
it can be a significant advantage to have
one neighbour 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 JBIG implementations. The
maximal vertical offset of the adaptive tem-
plate pixel is always zero.
-o number JBIG 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.
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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 JBIG 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
JBIG 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 JBIG 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 The adaptive template pixel movement is
determined as suggested in annex C of the
standard. By default the template change
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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 test suite.
-v After the BIE has been created, a few tech-
nical details of the created file will be
listed (verbose mode).
STANDARDS
This program implements the JBIG 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 beed developed by Markus Kuhn. The most recent
version of this portable JBIG library and tools set is
freely available on the Internet from anonymous ftp server
ftp.informatik.uni-erlangen.de in directory
pub/doc/ISO/JBIG/. Bug reports should be sent to
<mskuhn@cip.informatik.uni-erlangen.de>.
SEE ALSOpbm(5), jbgtopbm(1)
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