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       jpegtran - lossless transformation of JPEG files


       jpegtran [ options ] [ filename ]


       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

       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.


       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:

              Perform optimization of entropy encoding parameters.

              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.

              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 image (across UL-to-LR axis).

              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  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:

              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 starting at point X,Y.

       Other not-strictly-lossless transformation switches are:

              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.)

       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.

              Enable debug printout.  More -v's give more output.  Also, version  information  is
              printed at startup.

       -debug Same as -verbose.


       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

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


              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.


       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.


       Independent JPEG Group


       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.

                                        20 September 2015                             JPEGTRAN(1)