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Jpeg2ktopam User Manual(0) Jpeg2ktopam User Manual(0)
NAME
jpeg2ktopam - convert JPEG-2000 code stream to PAM/PNM
SYNOPSIS
jpeg2ktopam [-verbose] [-debuglevel=number] filename
OPTION USAGE
Minimum unique abbreviation of option is acceptable. You may use double 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).
jpeg2ktopam converts the named JPEG-2000 file (JP2 or JPC), or Standard Input if no file
is named, to a PBM, PGM, PPM, or PAM 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. A JP2 image contains a JPC stream and metadata describing how
that stream represents a visual image. jpeg2ktopam converts both.
If the color space identified in the image is grayscale (JAS_IMAGE_CS_GRAY), jpeg2ktopam
generates a PGM image, unless the image contains only one bit per pixel, in which case
jpeg2ktopam generates PBM. If the color space is RGB (JAS_IMAGE_CS_RGB), jpeg2ktopam gen-
erates a PPM image. If the input image is anything else, jpeg2ktopam generates a PAM
image with no tuple type identified.
In the PGM and PPM cases, jpeg2ktopam assumes the intensity values in the input image have
the same meaning as for PGM and PPM. One thing that implies is the ITU-R Recommendation
BT.709 color space, which means the assumption is false for JP2 input. JP2 input uses
SRGB color encoding. So if you use jpeg2ktopam to convert a JP2 image to PPM, it changes
the visual image (slightly) -- the colors in the output are not the same as in the input.
In the PAM image, the output samples are numerically identical to the input samples. If
the input samples are signed, they are represented in two's complement form in the output
(because PAM samples are always unsigned). The PAM plane numbers are identical to the JPC
component numbers.
A JPEG-2000 image has a "precision," which is the number of bits used for each code (in
Netpbm lingo, "sample"). Actually, each component has a separate precision. The maxval
of a PGM, PPM, or PAM output is the largest number you can represent in the JPEG-2000 pre-
cision of the JPEG-2000 component with the greatest precision. The samples in all compo-
nents are scaled to that maxval. So if the red component has a precision of 4 bits and
the green component has a precision of 6 bits, the maxval is 63 and the red component
codes from the JPEG-2000 image are multiplied by 63/15 to generate the output samples.
jpeg2ktopam interprets the JPEG-2000 input with the Jasper JPEG-2000 library
<http://www.ece.uvic.ca/~mdadams/jasper/> . See documentation of the library for details
on what jpeg2ktopam handles. Note that the Jasper library contains facilities for writing
PNM images, but jpeg2ktopam does not use those. It uses the Netpbm library instead. Note
that the makers of the Jasper library write it "JasPer," but Netpbm documentation follows
standard American English typography rules, which don't allow that kind of capitalization.
Use pamtojpeg2k 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
-verbose
This option causes jpeg2ktopam to issue informational messages about the conversion
process.
-debuglevel=number
This option controls debug messages from the Jasper library. jpeg2ktopam passes
number as the debug level to the Jasper JPEG-2000 decoder.
EXAMPLES
jpeg2ktopam myimg.jpc >myimg.ppm
ABOUT JPEG-2000
See the pamtojpeg2k manual(1) for general information on JPEG-2000 compression and the
JPEG-2000 formats.
SEE ALSO
pamtojpeg2k(1), jpegtopnm(1), ppm(1), pgm(1), pbm(1), pam(1),
History
jpeg2ktopam was added to Netpbm in Release 10.12 (November 2002).
Before Netpbm 10.49 (December 2009), jpeg2ktopam could not convert a JP2 file -- only JPC.
DOCUMENT SOURCE
This manual page was generated by the Netpbm tool 'makeman' from HTML source. The master
documentation is at
http://netpbm.sourceforge.net/doc/jpeg2ktopam.html
netpbm documentation 08 October 2009 Jpeg2ktopam User Manual(0)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
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