Provided by: libjpeg-turbo-progs_2.0.0-0ubuntu2_amd64 bug

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.

       -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 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.

       -perfect
              If  you  are  only  interested in perfect transformations, add the -perfect switch.
              This causes jpegtran to fail 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.

       This version of jpegtran also offers a lossless crop option, which discards  data  outside
       of  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 it doesn't, then it is silently
       moved up and/or left to the nearest iMCU boundary (the lower right corner  is  unchanged.)
       Thus,  the  output image covers at least the requested region, but it 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  the  image to a rectangular region of width W and height H, starting at point
              X,Y.  The lossless crop feature discards data outside of 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 it doesn't, then it is silently
              moved up and/or left to the nearest  iMCU  boundary  (the  lower  right  corner  is
              unchanged.)

       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.)

       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 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.   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:

       -icc file
              Embed ICC color management profile contained in the specified file.  Note that this
              will cause jpegtran to ignore any APP2 markers in the input file, even if -copy all
              is specified.

       -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, an error will
              occur.

       -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.

       -version
              Print version information and exit.

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

       This file was modified by The libjpeg-turbo Project to include only  information  relevant
       to libjpeg-turbo and to wordsmith certain sections.

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.

                                          18 March 2017                               JPEGTRAN(1)