Pnmtojbig User Manual(0) Pnmtojbig User Manual(0)NAMEpnmtojbig - PNM to JBIG file converter
SYNOPSISpnmtojbig
[options] [input-file [output-file]]
DESCRIPTION
This program is part of Netpbm(1).
pnmtojbig reads a PBM or PGM image, 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 particularly 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 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.
JBIG files can also store several bits per pixel as separate bitmap
planes, and pnmtojbig can read a PGM file and transform it into a
multi-bitplane BIE.
OPTIONS-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.
-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 different BIEs. Options -l
and -h allow you 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, pnmto‐
jbig writes all layers.
-h number
Select the highest resolution layer that will be written to the
BIE. By default, pnmtojbig writes all layers. 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 selec‐
tion 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 lay‐
ers.
-s number
The JBIG algorithm splits each image into a number of horizontal
stripes. This option specifies that each stripe shall have num‐
ber 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 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
standard, no higher value than 16 for number is recommended in
order to maintain interoperability with other JBIG implementa‐
tions. 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
JBIG separates an image into several horizontal stripes, resolu‐
tion 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 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, layers,
planes) is over all layers so that all data of the lowest reso‐
lution 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 you 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 typical prediction (TPBON)
16 diff. layer typical prediction (TPDON)
64 layer 0 two-line template (LRLTWO)
Except for special applications (like communication with JBIG
subset implementations) and for debugging purposes you will nor‐
mally not want to change anything here. The default is 28,
which provides the best compression result.
-c The adaptive template pixel movement is determined 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 con‐
formance test suite.
-v After pnmtojbig creates the BIE, it lists a few technical
details of the created file (verbose mode).
FORMATS
Most of the format pnmtojbig creates is defined by the JBIG standard.
The standard, however, does not specify which values in the BIE mean
white and which mean black. It contains a recommendation that for a
single plane image zero mean background and one mean foreground, but
the Netpbm formats have no concept of foreground and background. And
the standard says nothing about values for multiple plane BIEs.
pnmtojbig follows Markus Kuhn's implementation of the standard in the
pbmtojbg program that comes with his JBIG library: If the BIE is a
single plane BIE, zero means white and one means black. If it is a
multiple plane BIE, zero means black and the maximal value is white.
STANDARDS
This program implements the JBIG image coding algorithm as specified in
ISO/IEC 11544:1993 and ITU-T T.82(1993).
AUTHORpnmtojbig is based on the JBIG library by Markus Kuhn, part of his
JBIG-KIT package. The pbmtojbg program is part of the JBIG-KIT pack‐
age. The most recent version of that library and tools set is freely
available on the Internet from anonymous ftp server ftp.informatik.uni-
erlangen.de ⟨ftp://ftp.informatik.uni-erlangen.de⟩ in directory
pub/doc/ISO/JBIG/.
pnmtojbig is part of the Netpbm package of graphics tools.
SEE ALSOpnm(1), jbigtopnm(1)LICENSE
If you use pnmtojbig, you are using various patents, particularly on
its arithmetic encoding method, and in all probability you do not have
a license from the patent owners to do so.
netpbm documentation 20 May 2000 Pnmtojbig User Manual(0)
