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JPEGTRAN(1)							   JPEGTRAN(1)

NAME
       jpegtran - lossless transformation of JPEG files

SYNOPSIS
       jpegtran [ options ] [ filename ]

DESCRIPTION
       jpegtran performs various useful transformations of JPEG files.	It can
       translate the coded representation from one variant of JPEG to another,
       for  example  from baseline JPEG to progressive JPEG or vice versa.  It
       can also perform some rearrangements of the  image  data,  for  example
       turning an image from landscape to portrait format by rotation.

       jpegtran	 works	by rearranging the compressed data (DCT coefficients),
       without ever fully decoding the image.  Therefore, its  transformations
       are  lossless: there is no image degradation at all, which would not be
       true if you used djpeg followed by cjpeg to accomplish the same conver‐
       sion.   But by the same token, jpegtran cannot perform lossy operations
       such as changing the image quality.

       jpegtran reads the named JPEG/JFIF file, or the standard	 input	if  no
       file is named, and produces a JPEG/JFIF file on the standard output.

OPTIONS
       All  switch  names  may	be  abbreviated; for example, -optimize may be
       written -opt or -o.  Upper and  lower  case  are	 equivalent.   British
       spellings are also accepted (e.g., -optimise), though for brevity these
       are not mentioned below.

       To specify the coded JPEG representation used in the output file, jpeg‐
       tran accepts a subset of the switches recognized by cjpeg:

       -optimize
	      Perform optimization of entropy encoding parameters.

       -progressive
	      Create progressive JPEG file.

       -restart N
	      Emit  a  JPEG  restart  marker  every N MCU rows, or every N MCU
	      blocks if "B" is attached to the number.

       -arithmetic
	      Use arithmetic coding.

       -scans file
	      Use the scan script given in the specified text file.

       See cjpeg(1) for more details about these  switches.   If  you  specify
       none of these switches, you get a plain baseline-JPEG output file.  The
       quality setting and so forth are determined by the input file.

       The image  can  be  losslessly  transformed  by	giving	one  of	 these
       switches:

       -flip horizontal
	      Mirror image horizontally (left-right).

       -flip vertical
	      Mirror image vertically (top-bottom).

       -rotate 90
	      Rotate image 90 degrees clockwise.

       -rotate 180
	      Rotate image 180 degrees.

       -rotate 270
	      Rotate image 270 degrees clockwise (or 90 ccw).

       -transpose
	      Transpose image (across UL-to-LR axis).

       -transverse
	      Transverse transpose (across UR-to-LL axis).

	      The transpose transformation has no restrictions regarding image
	      dimensions.  The other transformations operate rather  oddly  if
	      the  image  dimensions are not a multiple of the iMCU size (usu‐
	      ally 8 or 16 pixels), because they can only  transform  complete
	      blocks of DCT coefficient data in the desired way.

	      jpegtran's  default behavior when transforming an odd-size image
	      is designed to preserve  exact  reversibility  and  mathematical
	      consistency  of the transformation set.  As stated, transpose is
	      able to flip the entire image area.  Horizontal mirroring leaves
	      any partial iMCU column at the right edge untouched, but is able
	      to flip all rows of the image.   Similarly,  vertical  mirroring
	      leaves any partial iMCU row at the bottom edge untouched, but is
	      able to flip all columns.	 The other transforms can be built  up
	      as  sequences of transpose and flip operations; for consistency,
	      their actions on edge pixels are defined to be the same  as  the
	      end result of the corresponding transpose-and-flip sequence.

	      For practical use, you may prefer to discard any untransformable
	      edge pixels rather than having a strange-looking strip along the
	      right  and/or  bottom edges of a transformed image.  To do this,
	      add the -trim switch:

       -trim  Drop non-transformable edge blocks.

	      Obviously, a transformation with -trim  is  not  reversible,  so
	      strictly	speaking  jpegtran  with  this switch is not lossless.
	      Also, the expected mathematical equivalences between the	trans‐
	      formations  no  longer  hold.  For example, -rot 270 -trim trims
	      only the bottom edge, but -rot 90 -trim  followed	 by  -rot  180
	      -trim trims both edges.

	      If  you  are  only interested in perfect transformation, add the
	      -perfect switch:

       -perfect
	      Fails with an error if the transformation is not perfect.

	      For example you may want to do

	      (jpegtran -rot 90 -perfect foo.jpg || djpeg  foo.jpg  |  pnmflip
	      -r90 | cjpeg)

	      to  do a perfect rotation if available or an approximated one if
	      not.

       We also offer a lossless-crop option, which  discards  data  outside  a
       given  image  region but losslessly preserves what is inside.  Like the
       rotate and flip transforms, lossless crop is restricted by the  current
       JPEG  format: the upper left corner of the selected region must fall on
       an iMCU boundary.  If this does not hold for the given crop parameters,
       we  silently  move  the upper left corner up and/or left to make it so,
       simultaneously increasing the region dimensions to keep the lower right
       crop  corner  unchanged.	  (Thus,  the output image covers at least the
       requested region, but may cover more.)

       The image can be losslessly cropped by giving the switch:

       -crop WxH+X+Y
	      Crop to a rectangular subarea of width W, height H  starting  at
	      point X,Y.

       Other not-strictly-lossless transformation switches are:

       -grayscale
	      Force grayscale output.

	      This option discards the chrominance channels if the input image
	      is YCbCr (ie, a standard color JPEG), resulting in  a  grayscale
	      JPEG  file.  The luminance channel is preserved exactly, so this
	      is a better method of reducing to grayscale than	decompression,
	      conversion,  and	recompression.	 This  switch  is particularly
	      handy for	 fixing	 a  monochrome	picture	 that  was  mistakenly
	      encoded  as  a  color  JPEG.  (In such a case, the space savings
	      from getting rid of the  near-empty  chroma  channels  won't  be
	      large;  but  the	decoding time for a grayscale JPEG is substan‐
	      tially less than that for a color JPEG.)

       -scale M/N
	      Scale the output image by a factor M/N.

	      Currently supported scale factors are M/N with all M from	 1  to
	      16,  where  N  is	 the  source DCT size, which is 8 for baseline
	      JPEG.  If the /N part is	omitted,  then	M  specifies  the  DCT
	      scaled size to be applied on the given input.  For baseline JPEG
	      this is equivalent to M/8 scaling, since the source DCT size for
	      baseline	JPEG  is  8.   Caution:	 An implementation of the JPEG
	      SmartScale extension is required for this	 feature.   SmartScale
	      enabled  JPEG  is	 not  yet widely implemented, so many decoders
	      will be unable to view a SmartScale extended JPEG file at all.

       jpegtran also recognizes these switches that control what  to  do  with
       "extra" markers, such as comment blocks:

       -copy none
	      Copy no extra markers from source file.  This setting suppresses
	      all comments and other excess  baggage  present  in  the	source
	      file.

       -copy comments
	      Copy  only  comment  markers.  This setting copies comments from
	      the source file, but discards any other inessential  (for	 image
	      display) data.

       -copy all
	      Copy  all	 extra	markers.  This setting preserves miscellaneous
	      markers found in the source file, such as JFIF thumbnails,  Exif
	      data, and Photoshop settings.  In some files these extra markers
	      can be sizable.  See 'EXIF FILES' for special tratement of  EXIF
	      markers.

       -copy exif
	      This  setting  preserves the EXIF marker, commonly found in JPEG
	      files produced by digital cameras, in addition  to  any  comment
	      markers.	 If  there is an EXIF marker it is copied and the JFIF
	      marker (incompatible with EXIF) is omitted. If there is no  EXIF
	      marker  a	 JFIF  one  is emitted as usual.  See 'EXIF FILES' for
	      special tratement of EXIF markers.

	      The default behavior is -copy comments.  (Note: in IJG  releases
	      v6 and v6a, jpegtran always did the equivalent of -copy none.)

       Additional switches recognized by jpegtran are:

       -maxmemory N
	      Set  limit  for  amount  of  memory  to  use in processing large
	      images.  Value is in thousands of bytes, or millions of bytes if
	      "M"  is  attached	 to  the number.  For example, -max 4m selects
	      4000000 bytes.  If more space is needed, temporary files will be
	      used.

       -outfile name
	      Send output image to the named file, not to standard output.

       -verbose
	      Enable  debug printout.  More -v's give more output.  Also, ver‐
	      sion information is printed at startup.

       -debug Same as -verbose.

EXIF FILES
       The EXIF variety of JPEG files, which are  often	 produced  by  digital
       cameras,	 are  recognized  by jpegtran as EXIF files (i.e. not as JFIF,
       the usual variety of JPEG files). If the input file  is	recognized  as
       EXIF  (i.e.,  there  is	an  EXIF marker and no JFIF marker) the '-copy
       exif' option is automatically turned on	if  '-copy  comments',	or  no
       '-copy'	option,	 was specified. Thus, unless '-copy none' is specified
       an EXIF file is kept as EXIF and not converted to JFIF.

       If a geometrical transformation is applied  (e.g.,  rotate,  transpose)
       the EXIF width and height fields are set to the width and height of the
       output image. Furthermore, the orientation field is reset to one, mean‐
       ing tha the orientation of the output image is upright (i.e. normal).

       Note  that an explicitely given '-copy exif' option will output an EXIF
       file if the input is an EXIF file that was saved as JFIF, and that  the
       EXIF marker is still present. This option is useful for recovering EXIF
       files that where converted to JFIF by a non EXIF-aware  software.  Note
       however,	 that  the  data in the EXIF marker is not validated, unless a
       geometrical transformation is applied.

EXAMPLES
       This example converts a baseline JPEG file to progressive form:

	      jpegtran -progressive foo.jpg > fooprog.jpg

       This example rotates an image  90  degrees  clockwise,  discarding  any
       unrotatable edge pixels:

	      jpegtran -rot 90 -trim foo.jpg > foo90.jpg

ENVIRONMENT
       JPEGMEM
	      If  this	environment  variable is set, its value is the default
	      memory limit.  The value	is  specified  as  described  for  the
	      -maxmemory  switch.   JPEGMEM overrides the default value speci‐
	      fied when the program was compiled, and itself is overridden  by
	      an explicit -maxmemory.

SEE ALSO
       cjpeg(1), djpeg(1), rdjpgcom(1), wrjpgcom(1)
       Wallace,	 Gregory  K.   "The  JPEG Still Picture Compression Standard",
       Communications of the ACM, April 1991 (vol. 34, no. 4), pp. 30-44.

AUTHOR
       Independent JPEG Group

BUGS
       The transform options can't transform odd-size images  perfectly.   Use
       -trim or -perfect if you don't like the results.

       The  entire  image is read into memory and then written out again, even
       in cases where this isn't really necessary.  Expect swapping  on	 large
       images, especially when using the more complex transform options.

			       28 December 2009			   JPEGTRAN(1)
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