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Jpegtopnm User Manual(0)						 Jpegtopnm User Manual(0)

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

SYNOPSIS
       jpegtopnm  [-dct  {int|fast|float}] [-nosmooth] [-maxmemory N] [{-adobe|-notadobe}] [-com-
       ments] [-dumpexif]  [-exif=filespec]  [-multiple]  [-repair]  [-verbose]  [-tracelevel  N]
       [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.  Oth-
       erwise, it generates a PPM image.

       Before Netpbm 10.11 (October 2002), jpegtopnm did not have the multiple image stream capa-
       bility.	 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  speak-
       ing,  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  compres-
       sion.

       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 sim-
       ply subtractive and linear.

       See the jpegtopnmmanual(1)

       for information on how images lose quality when you convert to and from JFIF.

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 cover-
	      age.  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 Photo-
	      shop 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 sophis-
	      ticated.

	      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 pro-
	      duce 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 suc-
	      ceed instead.

	      But note that there are some forms of invalid input that always cause jpegtopnm  to
	      fail and other than 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 infor-
	      mation 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.

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 cer-
       tain 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 avail-
       able.

       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.

netpbm documentation			 13 October 2002		 Jpegtopnm User Manual(0)
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