1 .TH JPEGTRAN 1 "20 September 2015"
3 jpegtran \- lossless transformation of JPEG files
16 performs various useful transformations of JPEG files.
17 It can translate the coded representation from one variant of JPEG to another,
18 for example from baseline JPEG to progressive JPEG or vice versa. It can also
19 perform some rearrangements of the image data, for example turning an image
20 from landscape to portrait format by rotation.
22 For EXIF files and JPEG files containing Exif data, you may prefer to use
27 works by rearranging the compressed data (DCT coefficients), without
28 ever fully decoding the image. Therefore, its transformations are lossless:
29 there is no image degradation at all, which would not be true if you used
33 to accomplish the same conversion. But by the same token,
35 cannot perform lossy operations such as changing the image quality. However,
36 while the image data is losslessly transformed, metadata can be removed. See
42 reads the named JPEG/JFIF file, or the standard input if no file is
43 named, and produces a JPEG/JFIF file on the standard output.
45 All switch names may be abbreviated; for example,
51 Upper and lower case are equivalent.
52 British spellings are also accepted (e.g.,
54 though for brevity these are not mentioned below.
56 To specify the coded JPEG representation used in the output file,
58 accepts a subset of the switches recognized by
62 Perform optimization of entropy encoding parameters.
65 Create progressive JPEG file.
68 Emit a JPEG restart marker every N MCU rows, or every N MCU blocks if "B" is
69 attached to the number.
72 Use arithmetic coding.
75 Use the scan script given in the specified text file.
79 for more details about these switches.
80 If you specify none of these switches, you get a plain baseline-JPEG output
81 file. The quality setting and so forth are determined by the input file.
83 The image can be losslessly transformed by giving one of these switches:
86 Mirror image horizontally (left-right).
89 Mirror image vertically (top-bottom).
92 Rotate image 90 degrees clockwise.
95 Rotate image 180 degrees.
98 Rotate image 270 degrees clockwise (or 90 ccw).
101 Transpose image (across UL-to-LR axis).
104 Transverse transpose (across UR-to-LL axis).
106 The transpose transformation has no restrictions regarding image dimensions.
107 The other transformations operate rather oddly if the image dimensions are not
108 a multiple of the iMCU size (usually 8 or 16 pixels), because they can only
109 transform complete blocks of DCT coefficient data in the desired way.
112 default behavior when transforming an odd-size image is designed
113 to preserve exact reversibility and mathematical consistency of the
114 transformation set. As stated, transpose is able to flip the entire image
115 area. Horizontal mirroring leaves any partial iMCU column at the right edge
116 untouched, but is able to flip all rows of the image. Similarly, vertical
117 mirroring leaves any partial iMCU row at the bottom edge untouched, but is
118 able to flip all columns. The other transforms can be built up as sequences
119 of transpose and flip operations; for consistency, their actions on edge
120 pixels are defined to be the same as the end result of the corresponding
121 transpose-and-flip sequence.
123 For practical use, you may prefer to discard any untransformable edge pixels
124 rather than having a strange-looking strip along the right and/or bottom edges
125 of a transformed image. To do this, add the
130 Drop non-transformable edge blocks.
132 Obviously, a transformation with
134 is not reversible, so strictly speaking
136 with this switch is not lossless. Also, the expected mathematical
137 equivalences between the transformations no longer hold. For example,
139 trims only the bottom edge, but
145 If you are only interested in perfect transformation, add the
150 Fails with an error if the transformation is not perfect.
152 For example you may want to do
154 .B (jpegtran \-rot 90 -perfect
158 .B | pnmflip \-r90 | cjpeg)
160 to do a perfect rotation if available or an approximated one if not.
162 We also offer a lossless-crop option, which discards data outside a given
163 image region but losslessly preserves what is inside. Like the rotate and
164 flip transforms, lossless crop is restricted by the current JPEG format: the
165 upper left corner of the selected region must fall on an iMCU boundary. If
166 this does not hold for the given crop parameters, we silently move the upper
167 left corner up and/or left to make it so, simultaneously increasing the
168 region dimensions to keep the lower right crop corner unchanged. (Thus, the
169 output image covers at least the requested region, but may cover more.)
170 The adjustment of the region dimensions may be optionally disabled by
171 attaching an 'f' character ("force") to the width or height number.
173 The image can be losslessly cropped by giving the switch:
176 Crop to a rectangular subarea of width W, height H starting at point X,Y.
178 A complementary lossless-wipe option is provided to discard (gray out) data
179 inside a given image region while losslessly preserving what is outside:
182 Wipe (gray out) a rectangular subarea of width W, height H starting at point
185 Other not-strictly-lossless transformation switches are:
188 Force grayscale output.
190 This option discards the chrominance channels if the input image is YCbCr
191 (ie, a standard color JPEG), resulting in a grayscale JPEG file. The
192 luminance channel is preserved exactly, so this is a better method of reducing
193 to grayscale than decompression, conversion, and recompression. This switch
194 is particularly handy for fixing a monochrome picture that was mistakenly
195 encoded as a color JPEG. (In such a case, the space savings from getting rid
196 of the near-empty chroma channels won't be large; but the decoding time for
197 a grayscale JPEG is substantially less than that for a color JPEG.)
200 Scale the output image by a factor M/N.
202 Currently supported scale factors are M/N with all M from 1 to 16, where N is
203 the source DCT size, which is 8 for baseline JPEG. If the /N part is omitted,
204 then M specifies the DCT scaled size to be applied on the given input. For
205 baseline JPEG this is equivalent to M/8 scaling, since the source DCT size
206 for baseline JPEG is 8.
208 An implementation of the JPEG SmartScale extension is required for this
209 feature. SmartScale enabled JPEG is not yet widely implemented, so many
210 decoders will be unable to view a SmartScale extended JPEG file at all.
213 also recognizes these switches that control what to do with "extra" markers,
214 such as comment blocks:
217 Copy no extra markers from source file. This setting suppresses all
218 comments and other metadata in the source file.
221 Copy only comment markers. This setting copies comments from the source file,
222 but discards any other metadata.
225 Copy all extra markers. This setting preserves metadata
226 found in the source file, such as JFIF thumbnails, Exif data, and Photoshop
227 settings. In some files these extra markers can be sizable. Note that this
228 option will copy thumbnails as-is; they will not be transformed.
230 The default behavior is
231 .BR "\-copy comments" .
232 (Note: in IJG releases v6 and v6a,
234 always did the equivalent of
237 Additional switches recognized by jpegtran are:
240 Set limit for amount of memory to use in processing large images. Value is
241 in thousands of bytes, or millions of bytes if "M" is attached to the
244 selects 4000000 bytes. If more space is needed, temporary files will be used.
246 .BI \-outfile " name"
247 Send output image to the named file, not to standard output.
250 Enable debug printout. More
252 give more output. Also, version information is printed at startup.
259 This example converts a baseline JPEG file to progressive form:
261 .B jpegtran \-progressive
266 This example rotates an image 90 degrees clockwise, discarding any
267 unrotatable edge pixels:
269 .B jpegtran \-rot 90 -trim
276 If this environment variable is set, its value is the default memory limit.
277 The value is specified as described for the
281 overrides the default value specified when the program was compiled, and
282 itself is overridden by an explicit
290 Wallace, Gregory K. "The JPEG Still Picture Compression Standard",
291 Communications of the ACM, April 1991 (vol. 34, no. 4), pp. 30-44.
293 Independent JPEG Group
295 The transform options can't transform odd-size images perfectly. Use
299 if you don't like the results.
301 The entire image is read into memory and then written out again, even in
302 cases where this isn't really necessary. Expect swapping on large images,
303 especially when using the more complex transform options.