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JPEGTRAN(1)		    General Commands Manual		   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.

       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 conver-
       sion.  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, 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	dimen-
       sions.  The other transformations operate rather	oddly if the image di-
       mensions	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  de-
       signed  to preserve exact reversibility and mathematical	consistency of
       the transformation set.	As stated, transpose is	able to	flip  the  en-
       tire  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 con-
       sistency, 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.

       -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 dis-
       cards 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 se-
       lected 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  en-
	      coded  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 mark-
	      ers 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  im-
	      ages.   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.

       -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 un-
       rotatable 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

       This file was modified by The libjpeg-turbo Project to include only in-
       formation 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 February 2016			   JPEGTRAN(1)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXAMPLES | ENVIRONMENT | SEE ALSO | AUTHOR | BUGS

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