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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 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)
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 gener-
ates PBM. If the color space is RGB (JAS_IMAGE_CS_RGB), jpeg2ktopam
generates 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 precision of the
JPEG-2000 component with the greatest precision. The samples in all
components 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 thepamtojpeg2kmanual(1)
for general information on JPEG-2000 compression and the JPEG-2000 for-
mats.
SEE ALSO
pamtojpeg2k(1) , pnmtopeg(1) , ppm(5) , pgm(5) , pbm(5) , pam(5) ,
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.
netpbm documentation 08 October 2009 Jpeg2ktopam User Manual(0)
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