jpegtopnm(1)
NAME
jpegtopnm - convert JPEG/JFIF file to portable pixmap or graymap
SYNOPSIS
jpegtopnm [-dct {int|fast|float}] [-nosmooth] [-maxmemory N]
[{-adobe|-notadobe}] [-comments] [-dumpexif] [-exif=filespec]
[-verbose] [-tracelevel N] [ filename ]
All options may be abbreviated to their shortest unique prefix.
DESCRIPTION
jpegtopnm converts the named JFIF file, or the standard input if no file is named to a PPM or PGM image file on the standard output. If the JFIF file is of the grayscale variety, jpegtopnm generates a PGM (Portable Graymap) file. Otherwise, it generates a PPM (Portable Pixmap) file. jpegtopnm uses the Independent JPEG Group's JPEG library to interpret the input file. See http://www.ijg.org for information on the library. "JFIF" is the correct name for the image format commonly known as "JPEG." Strictly speaking, JPEG is a method of compression. The image format using JPEG compression that is by far the most common is JFIF. There is also a subformat of TIFF that uses JPEG compression. EXIF is an image format that is a subformat of JFIF (to wit, a JFIF file that contains an EXIF header as an APP1 marker). jpegtopnm handles EXIF. JFIF files can have either 8 bits per sample or 12 bits per sample. The 8 bit variety is by far the most common. There are two versions of the IJG JPEG library. One reads only 8 bit files and the other reads only 12 bit files. You must link the appropriate one of these libraries with jpegtopnm. Ordinarily, this means the library is in your shared library search path when you run jpegtopnm. jpegtopnm generates output with either one byte or two bytes per sample depending on whether the JFIF input has either 8 bits or 12 bits per sample. You can use pnmdepth to reduce a two-byte-per-sample file to a one-byte-per-sample file if you need to. If the JFIF file uses the CMYK or YCCK color space, the input does not actually contain enough information to know what color each pixel is. To know what color a pixel is, one would have to know the properties of the inks to which the color space refers. jpegtopnm interprets the colors using the common transformation which assumes all the inks are simply subtractive and linear.
OPTIONS
The options are only for advanced users:
-dct int
Use integer DCT method (default).
-dct fast
Use fast integer DCT (less accurate).
-dct float
Use floating-point DCT method. The float method is very
slightly more accurate than the int method, but is much slower
unless your machine has very fast floating-point hardware. Also
note that results of the floating-point method may vary slightly
across machines, while the integer methods should give the same
results everywhere. The fast integer method is much less
accurate than the other two.
-nosmooth
Use a faster, lower-quality upsampling routine.
-maxmemory N
Set limit on the amount of memory jpegtopnm uses in processing
large images. Value is in thousands of bytes, or millions of
bytes if "M" is suffixed to the number. For example, -maxmemory
4m selects 4000000 bytes. If jpegtopnm needs more space, it
uses temporary files.
-adobe
-notadobe
There are two variations on the CMYK (and likewise YCCK) color
space that may be used in the JFIF input. In the normal one, a
zero value for a color components indicates absence of ink. In
the other, a zero value means the maximum ink coverage. The
latter is used by Adobe Photoshop when it creates a bare JFIF
output file (but not when it creates JFIF output as part of
Encapsulated Postscript output).
These options tell jpegtopnm which version of the CMYK or YCCK
color space the image uses. If you specify neither, jpegtopnm
tries to figure it out on its own. In the present version, it
doesn't try very hard at all: It just assumes the Photoshop
version, since Photoshop and its emulators seem to be the main
source of CMYK and YCCK images. But with experience of use,
future versions might be more sophisticated.
If the JFIF image does not indicate that it is CMYK or YCCK,
these options have no effect.
If you don't use the right one of these options, the symptom is
output that looks like a negative.
-dumpexif
Print the interpreted contents of any Exif header in the input
file to the Standard Error file. Similar to the program jhead
(not part of the Netpbm package).
-exif=filespec
Extract the contents of the EXIF header from the input image and
write it to the file filespec. filespec = - means write it to
Standard Output. In this case, jpegtopnm does not output the
converted image at all.
jpegtopnm writes the contents of the EXIF header byte-for-byte,
starting with the two byte length field (which length includes
those two bytes).
You can use this file as input to ppmtojpeg to insert an
identical EXIF header into a new JFIF image.
If there is no EXIF header, jpegtopnm writes two bytes of binary
zero and nothing else.
An EXIF header takes the form of a JFIF APP1 marker. Only the
first such marker within the JFIF header counts.
-comments
Print any comments in the input file to the Standard Error file.
-verbose
Print details about the conversion to the Standard Error file.
-tracelevel n
Turn on the JPEG library's trace messages to the Standard Error
file. A higher value of n gets more trace information.
-verbose implies a trace level of at least 1.
EXAMPLES
This example converts the color JFIF file foo.jpg to a PPM file named
foo.ppm:
jpegtopnm foo.jpg >foo.ppm
HINTS
You can use ppmquant to color quantize the result, i.e. to reduce the
number of distinct colors in the image. In fact, you may have to if
you want to convert the PPM file to certain other formats. ppmdither
Does a more sophisticated quantization.
Use pnmscale to change the dimensions of the resulting image.
Use ppmtopgm to convert a color JFIF file to a grayscale PGM file.
You can easily use these converters together. E.g.:
jpegtopnm foo.jpg | ppmtopgm | pnmscale .25
>foo.pgm
-dct fast and/or -nosmooth gain speed at a small sacrifice in quality.
If you are fortunate enough to have very fast floating point hardware,
-dct float may be even faster than -dct fast. But on most machines
-dct float is slower than -dct int; in this case it is not worth using,
because its theoretical accuracy advantage is too small to be
significant in practice.
Another program, djpeg, is similar. djpeg is maintained by the
Independent JPEG Group and packaged with the JPEG library which
jpegtopnm uses for all its JPEG work. Because of that, you may expect
it to exploit more current JPEG features. Also, since you have to have
the library to run jpegtopnm, but not vice versa, cjpeg may be more
commonly available.
On the other hand, djpeg does not use the NetPBM libraries to generate
its output, as all the NetPBM tools such as jpegtopnm do. This means
it is less likely to be consistent with all the other programs that
deal with the NetPBM formats. Also, the command syntax of jpegtopnm is
consistent with that of the other Netpbm tools, unlike djpeg.
ENVIRONMENT
JPEGMEM
If this environment variable is set, its value is the default
memory limit. The value is specified as described for the
-maxmemory option. An explicit -maxmemory option overrides any
JPEGMEM.
SEE ALSO
ppm(5), pgm(5), ppmtojpeg(1), ppmquant(1), pnmscale(1), ppmtopgm(1), ppmdither(1), pnmdepth(1), djpeg(1), cjpeg(1), jpegtran(1), rdjpgcom(1), wrjpgcom(1), jhead(1) Wallace, Gregory K. "The JPEG Still Picture Compression Standard", Communications of the ACM, April 1991 (vol. 34, no. 4), pp. 30-44.
LIMITATIONS
Arithmetic coding is not supported for legal reasons. The program could be much faster.
AUTHOR
jpegtopnm and this man page were derived in large part from djpeg, by
the Independent JPEG Group. The program is otherwise by Bryan
Henderson on March 19, 2000.
19 March 2000 JPEGTOPNM(1)
Opportunity
Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.
Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.
Free Software
Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.
Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.
Free Books
The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.
Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.
Education
Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.
Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.
