NAME

       jpegtopnm - convert JPEG/JFIF file to PPM or PGM image

SYNOPSIS

       jpegtopnm [-dct {int|fast|float}] [-nosmooth] [-maxmemory N] [{-adobe|-notadobe}] [-comments] [-dumpexif]
       [-exif=filespec] [-multiple] [-repair] [-verbose] [-tracelevel N] [-traceexif] [filename]

       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).

       jpegtopnm converts JFIF images to PPM or PGM images.

       By default, jpegtopnm expects the input stream to contain one JFIF image and  produces  one  PGM  or  PPM
       image as output.  It fails if the input stream is empty.

       But  with the -multiple option, jpegtopnm reads JFIF images sequentially from the input stream and writes
       one PPM or PGM image to the output stream for each JFIF input.  If the input stream is empty, so  is  the
       output.

       The  input  stream  is  the  filename you specify or, if you don't specify filename, Standard Input.  The
       output stream is Standard Output.

       If a JFIF input image is of the grayscale variety,  jpegtopnm  generates  a  PGM  image.   Otherwise,  it
       generates a PPM image.

       Before  Netpbm  10.11  (October 2002), jpegtopnm did not have the multiple image stream capability.  From
       10.11 through 10.22, Netpbm always behaved as if you specified -multiple.   Starting  with  Netpbm  10.23
       (July  2004),  Netpbm's default behavior went back to the pre-10.11 behavior and the new -multiple option
       selected the 10.12 behavior.  The reason for the reversion was that there were discovered  in  the  world
       files  that  contain  JFIF  images followed by something other than another JFIF image.  The producers of
       these files expect them to work with any JFIF  interpreter  because  most  JFIF  interpreters  just  stop
       reading the file after the first JFIF image.

       jpegtopnm   uses   the  Independent  JPEG  Group's  JPEG  library  to  interpret  the  input  file.   See
       http://www.ijg.org ⟨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 pamdepth 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.

       See the jpegtopnm manual(1) for information on how images lose quality when you convert to and from JFIF.

OPTIONS

       In addition to the options common to all programs based on libnetpbm (most notably -quiet, see
        Common Options ⟨index.html#commonoptions⟩ ), jpegtopnm recognizes the following command line 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).

              This option was added in Netpbm 9.19 (September 2001).

       -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.  When you write the EXIF header to Standard Output,
              jpegtopnm does not output the converted image (which is what normally would go to Standard Output)
              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 pnmtojpeg 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.

              This option was added in Netpbm 9.19 (September 2001).

       -multiple
              Read  multiple  JFIF  images  sequentially  from  the  input  stream.   See  Description   section
              ⟨#description⟩  for details.

              This option was new in Netpbm 10.23 (July 2004).

       -repair
              If the JFIF input is invalid, try to salvage whatever information is there and produce a valid PNM
              image as output.

              Without this option, some invalid input causes jpegtopnm to fail, and what output it  produces  is
              undefined.  With -repair such invalid input causes jpegtopnm to succeed instead.

              But note that there are some forms of invalid input that always cause jpegtopnm to fail and others
              that always cause it to salvage image information and succeed.

              One particular case where -repair makes a difference is the common case that the file is truncated
              somewhere  after  the JFIF header.  Without -repair, that always causes a failure; with -repair it
              always causes success.  Because the image information is laid out generally top to bottom  in  the
              JFIF  stream,  the image jpegtopnm produces in this case has the proper image contents at the top,
              but the bottom is padded with gray.

              This option was new in Netpbm 10.38.0 (March 2007).  Before that, jpegtopnm always  fails  in  the
              cases in question.

       -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.

       -traceexif
              Print trace information about the processing of EXIF header information.

              This option was new in Netpbm 11.02 (March 2023).

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 pnmquant 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 pamscale 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 | pamscale .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(1), pgm(1), pnmtojpeg(1), pnmquant(1), pamscale(1), ppmtopgm(1), ppmdither(1), pamdepth(1),

       djpeg man page, cjpeg man page, jpegtran man page, rdjpgcom man page, wrjpgcom man page, jhead man page

       Wallace, Gregory K.  "The JPEG Still Picture Compression Standard", Communications of the ACM, April 1991
       (vol. 34, no. 4), pp. 30-44.

AUTHOR

       jpegtopnm  and  this  manual  were  derived in large part from djpeg, by the Independent JPEG Group.  The
       program is otherwise by Bryan Henderson on March 19, 2000.

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/jpegtopnm.html