.TH PBMTOJBG 1 "2003-06-04"
.SH NAME
pbmtojbg \- portable bitmap to JBIG1 file converter
.SH SYNOPSIS
.B pbmtojbg
[
.I options
]
[
.I input-file
| \-  [
.I output-file
]]
.br
.SH DESCRIPTION
Reads in a portable bitmap (PBM)
from a file or standard
input, compresses it, and outputs the image as a
.I JBIG1
bi-level image entity (BIE) file.

.I 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
.I 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 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.
.I JBIG1
files can also store several bits per pixel as separate bitmap planes,
and
.I pbmtojbg
can read a PGM file and transform it into a multi-bitplane BIE.

.SH OPTIONS
.TP 14
.BI \-
A single hyphen instead of an input file name will cause 
.I pbmtojbg
to read the data from standard input instead from a file.
.TP
.BI \-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 \(mu 480 pixels.
.TP
.BI \-x " number"
Specify the maximal horizontal size of the lowest resolution layer.
The default is 640 pixels.
.TP
.BI \-y " number"
Specify the maximal vertical size of the lowest resolution layer.
The default is 480 pixels.
.TP
.BI \-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 
.I JBIG1
image in progressive mode into different BIEs. Options
.BI \-l
and
.BI \-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.
.TP
.BI \-h " number"
Select the highest resolution layer that will be written to the
BIE. By default all layers will be written. See also option
.BI \-l.
.TP
.BI \-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.
.TP
.BI \-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
.BI \-x
and
.BI \-y
which are usually a more comfortable way of selecting the number of
resolution layers.
.TP
.BI \-s " number"
The
.I JBIG1
algorithm splits each image into a number of horizontal stripes. This
option specifies that each stripe shall have
.I number
lines in layer 0. The default value is selected so that approximately
35 stripes will be used for the whole image.
.TP
.BI \-m " number"
Select the maximum horizontal offset of the adaptive template pixel.
The
.I 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 standard, no higher value
than 16 for
.I number
is recommended in order to maintain interoperability with other
.I JBIG1
implementations. The maximal vertical offset of the adaptive
template pixel is always zero.
.TP
.BI \-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.
.TP
.BI \-o " number"
.I 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
.I number
selects which one shall be used. The order of the SDEs is only relevant
for applications that want to decode a
.I 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.
.br
The following values for
.I number
select these loop arrangements for writing the SDEs (outermost
loop first):

   0  	planes, layers, stripes
.br
   2  	layers, planes, stripes
.br
   3  	layers, stripes, planes
.br
   4  	stripes, planes, layers
.br
   5  	planes, stripes, layers
.br
   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. 
.TP
.BI \-p " number"
This option allows to activate or deactivate various optional algorithms
defined in the
.I JBIG1
standard. Just add the numbers of the following options which you want to
activate in
order to get the
.I number
value:

   4 	deterministic prediction (DPON)
.br
   8 	layer 0 typical prediction (TPBON)
.br
  16 	diff. layer typ. pred. (TPDON)
.br
  64 	layer 0 two-line template (LRLTWO)

Except for special applications (like communication with
.I 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.
.TP
.BI \-c
Determine the adaptive template pixel movement 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 tests.
.TP
.BI \-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
.I 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
.I pbmtojbg
will then add a NEWLEN marker segment at the latest possible
opportunity to the data stream to signal the correct final height.
.TP
.BI \-v
After the BIE has been created, a few technical details of the created
file will be listed (verbose mode).
.SH 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.
.SH STANDARDS
This program implements the
.I JBIG1
image coding algorithm as specified in ISO/IEC 11544:1993 and
ITU-T T.82(1993).
.SH AUTHOR
The
.I pbmtojbg
program is part of the 
.I JBIG-KIT
package, which has been developed by Markus Kuhn.
The most recent version of this
portable
.I JBIG1
library and tools set is available from
<http://www.cl.cam.ac.uk/~mgk25/jbigkit/>.
.SH SEE ALSO
pbm(5), pgm(5), jbgtopbm(1)