pnmtojbig(1) - phpMan

Pnmtojbig User Manual(0) Pnmtojbig User Manual(0)

NAME
pnmtojbig - PNM to JBIG file converter

SYNOPSIS
pnmtojbig

[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 reso-
lution layers can be stored all in one single BIE or they can be stored in several sepa-
rate BIE files. All resolution layers except the lowest one are stored merely as differ-
ences 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 hori-
zontal 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 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
different BIEs. Options -l and -h allow you to select the resolution-layer inter-
val that will appear in the created BIE. The lowest resolution layer has number 0
and this is also the default value. By default, pnmtojbig 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
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 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 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 neigh-
bor pixel which has a distance large enough to cover the period of a dither func-
tion. 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
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
JBIG 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 rel-
evant 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 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 reso-
lution 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 continu-
ing 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 implementa-
tions) and for debugging purposes you will normally 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 conformance 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 back-
ground. 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).

AUTHOR
pnmtojbig is based on the JBIG library by Markus Kuhn, part of his JBIG-KIT package. The
pbmtojbg program is part of the JBIG-KIT package. 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.