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Pamtojpeg2k User Manual(0) Pamtojpeg2k User Manual(0)
NAME
pamtojpeg2k - convert PAM/PNM image to a JPEG-2000 code stream
SYNOPSIS
pamtojpeg2k [-imgareatlx=column] [-imgareatly=row] [-tilegrdtlx=column]
[-tilegrdtly=row] [-tilewidth=columns] [-tileheight=rows]
[-prcwidth=columns] [-prcheight=rows] [-cblkwidth=columns]
[-cblkheight=rows] [-mode={integer|int|real}] [-compression=ratio]
[-ilyrrates=ratestring] [-numrlvls=number] [-progres-
sion={lrcp|rlcp|rpcl|pcrl|cprl}] [-numgbits=number] [-nomct] [-sop]
[-eph] [-lazy] [-termall] [-segsym] [-vcausal] [-pterm] [-resetprob]
[-verbose] [-debuglevel=number] filename
Minimum unique abbreviation of option is acceptable. You may use dou-
ble hyphens instead of single hyphen to denote options. You may use
white space in place of the equals sign to separate an option name from
its value.
DESCRIPTION
This program is part of Netpbm(1)
pamtojpeg2k converts the named PBM, PGM, PPM, or PAM file, or Standard
Input if no file is named, to a JPEG-2000 code stream (JPC) file on
Standard Output.
The JPEG-2000 specification specifies two different formats: JP2 and
JPEG-2000 code stream (JPC). JP2 represents a visual image quite
specifically, whereas JPC is a more or less arbitrary array of codes.
pamtojpeg2k can't produce a JP2, but the JPC image that pamtojpeg2k
produces is very similar to a JP2 if the input is a PBM, PGM, or PPM
image or equivalent PAM image. One difference is that the RGB inten-
sity values in a JP2 are SRGB values, while pamtojpeg2k produces ITU-R
Recommendation BT.709 values. Those are very similar, but not identi-
cal. Another difference is that a JP2 can contain extra information
about an image that JPC cannot.
When the input is a PAM image other than a PBM, PGM, or PPM equivalent,
the JPC raster produced contains whatever the PAM raster does. It can
have any number of planes with any meanings; the planes are in the same
order in the JPC output as in the PAM input.
A JPC image has a "precision," which is the number of bits used for
each code (in Netpbm lingo, "sample"). Actually, it has a separate
precision for each component. pamtojpeg2k uses for the precision of
every component the least number of bits that can represent the maxval
of the input image. A JPC image does not have an independent concept
of maxval; the maxval of a JPC sample is the maximum value that the
number of bits specified by the precision can represent in pure binary
code. E.g. if the precision is 4, the maxval is 15. pamtojpeg2k does
of course scale the sample values from the input maxval to the output
maxval. Example: The input maxval is 99. This means JPC precision is
7 bits and the JPC maxval is 127. A sample value of 33 in the input
becomes a sample value of 43 in the output.
pamtojpeg2k generates the JPC output with the Jasper JPEG-2000 library
<http://www.ece.uvic.ca/~mdadams/jasper/> . See documentation of the
library for details on what pamtojpeg2k produces. Note that the Jasper
library contains facilities for reading PNM images, but pamtojpeg2k
does not use those. It uses the Netpbm library instead. Note that the
makers of the Jasper library write it "JasPer," but Netpbm documenta-
tion follows standard American English typography rules, which don't
allow that kind of capitalization.
Use jpeg2ktopam to convert in the other direction.
The program jasper, which is packaged with the Jasper JPEG-2000
library, also converts between JPEG-2000 and PNM formats. Because it's
packaged with the library, it may exploit it better, especially
recently added features. However, since it does not use the Netpbm
library to read and write the Netpbm formats, it doesn't do as good a
job on that side.
OPTIONS
Most of the options are identical in name and function to options that
the Jasper library JPC encoder subroutine takes. See Jasper
documentation <http://www.ece.uvic.ca/~mdadams/jasper/> for details.
Here, we document only options that are not direct analogs of Jasper
options.
-compression=ratio
ratio is a floating point number that specifies the compression
ratio. pamtojpeg2k will adjust quality as necessary to ensure
that you get this compression ratio. E.g. 4 means the output
will be about one fourth the size in bytes of the input file.
The ratio concerns just the raster part of the image, with the
denominator being what the raster would take if it were encoded
the most naive way possible (e.g. 3 bytes per pixel in 8-bit-
per-sample RGB). It does, however, include metadata that is
part of the compressed raster. Because of that, it may not be
possible to give you your requested compression ratio at any
quality. If it isn't, pamtojpeg2k fails with a message saying
so.
If you don't specify this option, pamtojpeg2k gives you the best
compression it can without losing any quality. Because of the
metadata issue described above, this may mean, for a small
image, the image actually expands.
Note that though the Jasper library takes a compression factor,
this option specifies a compression ratio. The compression fac-
tor is the multiplicative inverse of (1 divided by) the compres-
sion ratio.
Before Netpbm 10.61 (December 2012), the default was a compres-
sion ratio of 1, and if pamtojpeg2k could not make the output
that small, it just made it as small as it could, with zero
quality. You know this is happening when you see the warning
message, 'empty layer generated.'
-verbose
This option causes pamtojpeg2k to issue informational messages
about the conversion process.
-debuglevel=number
This option controls debug messages from the Jasper library.
pamtojpeg2k passes number as the debug level to the Jasper JPC
encoder.
EXAMPLES
This example compresses losslessly.
pamtojpeg2k myimg.ppm >myimg.jpc
jpeg2ktopam will recreate myimg.ppm exactly.
This example compresses the file to one tenth its original size, throw-
ing away information as necessary.
pamtojpeg2k -compression=10 myimg.pgm >myimg.jpc
ABOUT JPEG-2000
JPEG-2000 is a format that compresses a visual image (or a similar set
of data) into a minimal number of bytes for storage or transmission.
In that, its goal is similar to JPEG. It has two main differences from
JPEG.
One difference is that it does a much better job on most images of
throwing out information in order to achieve a smaller output. That
means when you reconstruct the image from the resulting compressed
file, it looks a lot closer to the image you started with JPEG-2000
than with JPEG, for the same compressed file size. Or, looked at
another way, with JPEG-2000 you get a much smaller file than with JPEG
for the same image quality.
The second difference is that with JPEG-2000, you decide how much com-
pression you want and the compressor adjusts the quality to meet your
requirement, whereas with JPEG, you decide how much quality you want
and the compressor adjusts the size of the output to meet your require-
ment. I.e. with JPEG-2000, the quality of the result depends on the
compressibility of the input, but with JPEG, the size of the result
depends on the compressibility of the input.
With JPEG-2000, you can specify lossless compression, thus making it
compete with GIF and PNG. With standard JPEG, you always lose some-
thing. (There are rumored to be variations of JPEG around that are
lossless, though).
JPEG is much older than JPEG-2000 and far more popular. JPEG is one of
the half dozen most popular graphics formats and virtually all graphics
facilities understand it. JPEG-2000 is virtually unknown.
There is no compatibility between JPEG and JPEG-2000. Programs that
read JPEG do not automatically read JPEG-2000 and vice versa.
SEE ALSO
jpeg2ktopam(1) , pnmtopeg(1) , ppm(5) , pgm(5) , pbm(5) , pam(5) ,
History
pamtojpeg2k was added to Netpbm in Release 10.12 (November 2002).
netpbm documentation 27 October 2002 Pamtojpeg2k User Manual(0)
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