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JPEGTOPNM(1)							  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]	[-ver‐
       bose] [-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  han‐
       dles 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 accu‐
	      rate 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 ver‐
	      sion, 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 identi‐
	      cal 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.	 -ver‐
	      bose 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 signifi‐
       cant in practice.

       Another program, djpeg, is similar.  djpeg is maintained by  the	 Inde‐
       pendent	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  com‐
       monly 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 Hender‐
       son on March 19, 2000.

				 19 March 2000			  JPEGTOPNM(1)
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