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 JPEGTRAN(1)                                                     JPEGTRAN(1)
                              20 September 2015



 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.

      For EXIF files and JPEG files containing Exif data, you may prefer to
      use exiftran instead.

      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
      conversion.  But by the same token, jpegtran cannot perform lossy
      operations such as changing the image quality.  However, while the
      image data is losslessly transformed, metadata can be removed.  See
      the -copy option for specifics.

      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,
      jpegtran 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.




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 JPEGTRAN(1)                                                     JPEGTRAN(1)
                              20 September 2015



      -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 (usually
           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



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 JPEGTRAN(1)                                                     JPEGTRAN(1)
                              20 September 2015



           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
           transformations 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 adjustment of
      the region dimensions may be optionally disabled by attaching an 'f'
      character ("force") to the width or height number.

      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.

      A complementary lossless-wipe option is provided to discard (gray out)
      data inside a given image region while losslessly preserving what is
      outside:

      -wipe WxH+X+Y
           Wipe (gray out) a rectangular subarea of width W, height H



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 JPEGTRAN(1)                                                     JPEGTRAN(1)
                              20 September 2015



           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 substantially 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 metadata in the source file.

      -copy comments
           Copy only comment markers.  This setting copies comments from the
           source file, but discards any other metadata.

      -copy all
           Copy all extra markers.  This setting preserves metadata found in
           the source file, such as JFIF thumbnails, Exif data, and
           Photoshop settings.  In some files these extra markers can be
           sizable.  Note that this option will copy thumbnails as-is; they
           will not be transformed.

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



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 JPEGTRAN(1)                                                     JPEGTRAN(1)
                              20 September 2015



      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,
           version information is printed at startup.

      -debug
           Same as -verbose.

 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 specified
           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.



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