but is also freely distributable.
The IJG distribution formerly included code to read and write GIF files.
- To avoid entanglement with the Unisys LZW patent, GIF reading support has
- been removed altogether, and the GIF writer has been simplified to produce
- "uncompressed GIFs". This technique does not use the LZW algorithm; the
- resulting GIF files are larger than usual, but are readable by all standard
- GIF decoders.
+ To avoid entanglement with the Unisys LZW patent (now expired), GIF reading
+ support has been removed altogether, and the GIF writer has been simplified
+ to produce "uncompressed GIFs". This technique does not use the LZW
+ algorithm; the resulting GIF files are larger than usual, but are readable
+ by all standard GIF decoders.
+We are required to state that
+ "The Graphics Interchange Format(c) is the Copyright property of
+ CompuServe Incorporated. GIF(sm) is a Service Mark property of
+ CompuServe Incorporated."
+
REFERENCES
==========
The "official" archive site for this software is www.ijg.org.
The most recent released version can always be found there in
--directory "files". This particular version will be archived as
- http://www.ijg.org/files/jpegsrc.v8d.tar.gz, and in Windows-compatible
- "zip" archive format as http://www.ijg.org/files/jpegsr8d.zip.
-http://www.ijg.org/files/jpegsrc.v9b.tar.gz, and in Windows-compatible
-"zip" archive format as http://www.ijg.org/files/jpegsr9b.zip.
++directory "files".
The JPEG FAQ (Frequently Asked Questions) article is a source of some
general information about JPEG.
CHANGE LOG for Independent JPEG Group's JPEG software
-Improvements and optimizations in DCT and color calculations.
-Normalize range limit array composition and access pattern.
-Thank to Sia Furler and Maddie Ziegler for inspiration.
-
-Use merged upsample with scaled DCT sizes larger than 8.
-Thank to Taylor Hatala for inspiration.
-
-Check for excessive comment lengths in argument parsing in wrjpgcom.c.
-Thank to Julian Cohen for hint.
-
-Add makefile.b32 for use with Borland C++ 32-bit (bcc32).
-Thank to Joe Slater for contribution.
-
+ Version 9b 17-Jan-2016
+ -----------------------
+
-Use defined value from header instead of hardwired number in rdswitch.c.
-Thank to Robert Sprowson for hint.
-
-
-Version 9a 19-Jan-2014
------------------------
-
-Add support for wide gamut color spaces (JFIF version 2).
-Improve clarity and accuracy in color conversion modules.
-Note: Requires rebuild of test images.
-
-Extend the bit depth support to all values from 8 to 12
-(BITS_IN_JSAMPLE configuration option in jmorecfg.h).
-jpegtran now supports N bits sample data precision with all N from 8 to 12
-in a single instance. Thank to Roland Fassauer for inspiration.
-
-Try to resolve issues with new boolean type definition.
-Thank also to v4hn for suggestion.
-
-Enable option to use default Huffman tables for lossless compression
-(for hardware solution), and in this case improve lossless RGB compression
-with reversible color transform. Thank to Benny Alexandar for hint.
-
-Extend the entropy decoding structure, so that extraneous bytes between
-compressed scan data and following marker can be reported correctly.
-Thank to Nigel Tao for hint.
-
-Add jpegtran -wipe option and extension for -crop.
-Thank to Andrew Senior, David Clunie, and Josef Schmid for suggestion.
-
+ Document 'f' specifier for jpegtran -crop specification.
+ Thank to Michele Martone for suggestion.
+
-Add cjpeg -rgb1 option to create an RGB JPEG file, and insert
-a simple reversible color transform into the processing which
-significantly improves the compression.
-The recommended command for lossless coding of RGB images is now
-cjpeg -rgb1 -block 1 -arithmetic.
-As said, this option improves the compression significantly, but
-the files are not compatible with JPEG decoders prior to IJG v9
-due to the included color transform.
-The used color transform and marker signaling is compatible with
-other JPEG standards (e.g., JPEG-LS part 2).
-
-Remove the automatic de-ANSI-fication support (Automake 1.12).
-Thank also to Nitin A Kamble for suggestion.
-
+
+ Version 9 13-Jan-2013
+ ----------------------
+
-Support files with invalid component identifiers (created
-by Adobe PDF). Thank to Robin Watts for the suggestion.
-
-Adapt full buffer case in jcmainct.c for use with scaled DCT.
-Thank to Sergii Biloshytskyi for the suggestion.
-
-Add type identifier for declaration of noreturn functions.
-Thank to Brett L. Moore for the suggestion.
-
+ Add remark for jpeg_mem_dest() in jdatadst.c.
+ Thank to Elie-Gregoire Khoury for the hint.
+
-Add missing #include directives in configuration checks, avoid
-configuration errors. Thank to John Spencer for the hint.
-
+ Correct argument type in format string, avoid compiler warnings.
+ Thank to Vincent Torri for hint.
+
+
Version 8d 15-Jan-2012
-----------------------
/*
* djpeg.c
*
+ * This file was part of the Independent JPEG Group's software:
* Copyright (C) 1991-1997, Thomas G. Lane.
- * Modified 2009-2015 by Guido Vollbeding.
- * This file is part of the Independent JPEG Group's software.
- * For conditions of distribution and use, see the accompanying README file.
++ * Modified 2013 by Guido Vollbeding.
+ * libjpeg-turbo Modifications:
+ * Copyright (C) 2010-2011, 2013-2015, D. R. Commander.
+ * Copyright (C) 2015, Google, Inc.
+ * For conditions of distribution and use, see the accompanying README.ijg
+ * file.
*
* This file contains a command-line user interface for the JPEG decompressor.
* It should work on any system with Unix- or MS-DOS-style command lines.
/* RLE output format. */
requested_fmt = FMT_RLE;
- } else if (keymatch(arg, "scale", 1)) {
+ } else if (keymatch(arg, "scale", 2)) {
/* Scale the output image by a fraction M/N. */
- if (++argn >= argc) /* advance to next argument */
- usage();
+ if (++argn >= argc) /* advance to next argument */
+ usage();
- if (sscanf(argv[argn], "%d/%d",
+ if (sscanf(argv[argn], "%u/%u",
- &cinfo->scale_num, &cinfo->scale_denom) < 1)
- usage();
+ &cinfo->scale_num, &cinfo->scale_denom) != 2)
+ usage();
+
+ } else if (keymatch(arg, "strip", 2)) {
+ if (++argn >= argc)
+ usage();
+ if (sscanf(argv[argn], "%d,%d", &startY, &endY) != 2 || startY > endY)
+ usage();
+ strip = TRUE;
+
+
+ } else if (keymatch(arg, "skip", 2)) {
+ if (++argn >= argc)
+ usage();
+ if (sscanf(argv[argn], "%d,%d", &startY, &endY) != 2 || startY > endY)
+ usage();
+ skip = TRUE;
} else if (keymatch(arg, "targa", 1)) {
/* Targa output format. */
/*
* jdarith.c
*
- * Developed 1997-2009 by Guido Vollbeding.
+ * This file was part of the Independent JPEG Group's software:
- * This file is part of the Independent JPEG Group's software.
- * For conditions of distribution and use, see the accompanying README file.
+ * Developed 1997-2015 by Guido Vollbeding.
+ * libjpeg-turbo Modifications:
+ * Copyright (C) 2015, D. R. Commander.
+ * For conditions of distribution and use, see the accompanying README.ijg
+ * file.
*
* This file contains portable arithmetic entropy decoding routines for JPEG
* (implementing the ISO/IEC IS 10918-1 and CCITT Recommendation ITU-T T.81).
- .TH JPEGTRAN 1 "21 November 2014"
-.TH JPEGTRAN 1 "20 September 2015"
++.TH JPEGTRAN 1 "18 February 2016"
.SH NAME
jpegtran \- lossless transformation of JPEG files
.SH SYNOPSIS
.I foo.jpg
.B | pnmflip \-r90 | cjpeg)
.IP
-to do a perfect rotation if available or an approximated one if not.
+to do a perfect rotation, if available, or an approximated one if not.
+ .PP
-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.
++This version of \fBjpegtran\fR 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:
.TP
.B \-crop WxH+X+Y
-Crop to a rectangular subarea of width W, height H starting at point X,Y.
-.PP
-A complementary lossless-wipe option is provided to discard (gray out) data
-inside a given image region while losslessly preserving what is outside:
-.TP
-.B \-wipe WxH+X+Y
-Wipe (gray out) a rectangular subarea of width W, height H starting at point
-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.)
.PP
Other not-strictly-lossless transformation switches are:
.TP
.TP
.B \-copy none
Copy no extra markers from source file. This setting suppresses all
- comments and other excess baggage present in the source file.
+ comments and other metadata in the source file.
.TP
.B \-copy comments
-Copy only comment markers. This setting copies comments from the source file,
+Copy only comment markers. This setting copies comments from the source file
- but discards any other data that is inessential for image display.
+ but discards any other metadata.
.TP
.B \-copy all
-Copy all extra markers. This setting preserves metadata
+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.
-settings. In some files these extra markers can be sizable. Note that this
++settings. In some files, these extra markers can be sizable. Note that this
+ option will copy thumbnails as-is; they will not be transformed.
-.IP
-The default behavior is
-.BR "\-copy comments" .
-(Note: in IJG releases v6 and v6a,
-.B jpegtran
-always did the equivalent of
-.BR "\-copy none" .)
+.PP
+The default behavior is \fB-copy comments\fR. (Note: in IJG releases v6 and
+v6a, \fBjpegtran\fR always did the equivalent of \fB-copy none\fR.)
.PP
Additional switches recognized by jpegtran are:
.TP
*/
-#define JVERSION "9b 17-Jan-2016"
+#if JPEG_LIB_VERSION >= 80
-#define JCOPYRIGHT "Copyright (C) 2016, Thomas G. Lane, Guido Vollbeding"
+#define JVERSION "8d 15-Jan-2012"
+
+#elif JPEG_LIB_VERSION >= 70
+
+#define JVERSION "7 27-Jun-2009"
+
+#else
+
+#define JVERSION "6b 27-Mar-1998"
+
+#endif
+
- #define JCOPYRIGHT "Copyright (C) 1991-2012 Thomas G. Lane, Guido Vollbeding\n" \
++#define JCOPYRIGHT "Copyright (C) 1991-2016 Thomas G. Lane, Guido Vollbeding\n" \
+ "Copyright (C) 1999-2006 MIYASAKA Masaru\n" \
+ "Copyright (C) 2009 Pierre Ossman for Cendio AB\n" \
+ "Copyright (C) 2009-2016 D. R. Commander\n" \
+ "Copyright (C) 2009-2011 Nokia Corporation and/or its subsidiary(-ies)\n" \
+ "Copyright (C) 2013-2014 MIPS Technologies, Inc.\n" \
+ "Copyright (C) 2013 Linaro Limited\n" \
+ "Copyright (C) 2015 Matthieu Darbois"
+
+#define JCOPYRIGHT_SHORT "Copyright (C) 1991-2016 The libjpeg-turbo Project and many others"
USING THE IJG JPEG LIBRARY
- Copyright (C) 1994-2011, Thomas G. Lane, Guido Vollbeding.
+This file was part of the Independent JPEG Group's software:
-This file is part of the Independent JPEG Group's software.
-For conditions of distribution and use, see the accompanying README file.
+ Copyright (C) 1994-2013, Thomas G. Lane, Guido Vollbeding.
+libjpeg-turbo Modifications:
+Copyright (C) 2010, 2014, 2015, D. R. Commander.
+Copyright (C) 2015, Google, Inc.
+For conditions of distribution and use, see the accompanying README.ijg file.
This file describes how to use the IJG JPEG library within an application
Compression parameters (cinfo fields) include:
-int block_size
- Set DCT block size. All N from 1 to 16 are possible.
- Default is 8 (baseline format).
- Larger values produce higher compression,
- smaller values produce higher quality.
- An exact DCT stage is possible with 1 or 2.
- With the default quality of 75 and default Luminance qtable
- the DCT+Quantization stage is lossless for value 1.
- Note that values other than 8 require a SmartScale capable decoder,
- introduced with IJG JPEG 8. Setting the block_size parameter for
- compression works with version 8c and later.
-
+ boolean arith_code
+ If TRUE, use arithmetic coding.
+ If FALSE, use Huffman coding.
+
J_DCT_METHOD dct_method
- Selects the algorithm used for the DCT step. Choices are:
- JDCT_ISLOW: slow but accurate integer algorithm
- JDCT_IFAST: faster, less accurate integer method
- JDCT_FLOAT: floating-point method
- JDCT_DEFAULT: default method (normally JDCT_ISLOW)
- JDCT_FASTEST: fastest method (normally JDCT_IFAST)
- The FLOAT method is very slightly more accurate than the ISLOW method,
- but may give different results on different machines due to varying
- roundoff behavior. The integer methods should give the same results
- on all machines. On machines with sufficiently fast FP hardware, the
- floating-point method may also be the fastest. The IFAST method is
- considerably less accurate than the other two; its use is not
- recommended if high quality is a concern. JDCT_DEFAULT and
- JDCT_FASTEST are macros configurable by each installation.
-
-unsigned int scale_num, scale_denom
- Scale the image by the fraction scale_num/scale_denom. Default is
- 1/1, or no scaling. Currently, the supported scaling ratios are
- M/N with all N from 1 to 16, where M is the destination DCT size,
- which is 8 by default (see block_size parameter above).
- (The library design allows for arbitrary scaling ratios but this
- is not likely to be implemented any time soon.)
+ Selects the algorithm used for the DCT step. Choices are:
+ JDCT_ISLOW: slow but accurate integer algorithm
+ JDCT_IFAST: faster, less accurate integer method
+ JDCT_FLOAT: floating-point method
+ JDCT_DEFAULT: default method (normally JDCT_ISLOW)
+ JDCT_FASTEST: fastest method (normally JDCT_IFAST)
+ In libjpeg-turbo, JDCT_IFAST is generally about 5-15% faster than
+ JDCT_ISLOW when using the x86/x86-64 SIMD extensions (results may vary
+ with other SIMD implementations, or when using libjpeg-turbo without
+ SIMD extensions.) For quality levels of 90 and below, there should be
+ little or no perceptible difference between the two algorithms. For
+ quality levels above 90, however, the difference between JDCT_IFAST and
+ JDCT_ISLOW becomes more pronounced. With quality=97, for instance,
+ JDCT_IFAST incurs generally about a 1-3 dB loss (in PSNR) relative to
+ JDCT_ISLOW, but this can be larger for some images. Do not use
+ JDCT_IFAST with quality levels above 97. The algorithm often
+ degenerates at quality=98 and above and can actually produce a more
+ lossy image than if lower quality levels had been used. Also, in
+ libjpeg-turbo, JDCT_IFAST is not fully accelerated for quality levels
+ above 97, so it will be slower than JDCT_ISLOW. JDCT_FLOAT is mainly a
+ legacy feature. It does not produce significantly more accurate
+ results than the ISLOW method, and it is much slower. The FLOAT method
+ may also give different results on different machines due to varying
+ roundoff behavior, whereas the integer methods should give the same
+ results on all machines.
J_COLOR_SPACE jpeg_color_space
int num_components
The currently supported image file formats are: PPM (PBMPLUS color format),
PGM (PBMPLUS grayscale format), BMP, Targa, and RLE (Utah Raster Toolkit
- format). (RLE is supported only if the URT library is available.)
- cjpeg recognizes the input image format automatically, with the exception
- of some Targa-format files. You have to tell djpeg which format to generate.
+ format). (RLE is supported only if the URT library is available, which it
+ isn't on most non-Unix systems.) cjpeg recognizes the input image format
-automatically, with the exception of some Targa-format files. You have to
-tell djpeg which format to generate.
++automatically, with the exception of some Targa files.
-JPEG files are in the standard JFIF file format. There are other,
+JPEG files are in the defacto standard JFIF file format. There are other,
less widely used JPEG-based file formats, but we don't support them.
All switch names may be abbreviated; for example, -grayscale may be written
The basic command line switches for djpeg are:
- -colors N Reduce image to at most N colors. This reduces the
- or -quantize N number of colors used in the output image, so that it
- can be displayed on a colormapped display or stored in
- a colormapped file format. For example, if you have
- an 8-bit display, you'd need to reduce to 256 or fewer
- colors. (-colors is the recommended name, -quantize
- is provided only for backwards compatibility.)
-
- -fast Select recommended processing options for fast, low
- quality output. (The default options are chosen for
- highest quality output.) Currently, this is equivalent
- to "-dct fast -nosmooth -onepass -dither ordered".
-
- -grayscale Force grayscale output even if JPEG file is color.
- Useful for viewing on monochrome displays; also,
- djpeg runs noticeably faster in this mode.
-
- -rgb Force RGB output even if JPEG file is grayscale.
- This is provided to support applications that don't
- want to cope with grayscale as a separate case.
-
- -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. Scaling is handy if the image is larger
- than your screen; also, djpeg runs much faster when
- scaling down the output.
-
- -bmp Select BMP output format (Windows flavor). 8-bit
- colormapped format is emitted if -colors or -grayscale
- is specified, or if the JPEG file is grayscale;
- otherwise, 24-bit full-color format is emitted.
-
- -gif Select GIF output format. Since GIF does not support
- more than 256 colors, -colors 256 is assumed (unless
- you specify a smaller number of colors). If you
- specify -fast, the default number of colors is 216.
-
- -os2 Select BMP output format (OS/2 1.x flavor). 8-bit
- colormapped format is emitted if -colors or -grayscale
- is specified, or if the JPEG file is grayscale;
- otherwise, 24-bit full-color format is emitted.
-
- -pnm Select PBMPLUS (PPM/PGM) output format (this is the
- default format). PGM is emitted if the JPEG file is
- grayscale or if -grayscale is specified; otherwise
- PPM is emitted.
-
- -rle Select RLE output format. (Requires URT library.)
-
- -targa Select Targa output format. Grayscale format is
- emitted if the JPEG file is grayscale or if
- -grayscale is specified; otherwise, colormapped format
- is emitted if -colors is specified; otherwise, 24-bit
- full-color format is emitted.
+ -colors N Reduce image to at most N colors. This reduces the
+ or -quantize N number of colors used in the output image, so that it
+ can be displayed on a colormapped display or stored in
+ a colormapped file format. For example, if you have
+ an 8-bit display, you'd need to reduce to 256 or fewer
+ colors. (-colors is the recommended name, -quantize
+ is provided only for backwards compatibility.)
+
+ -fast Select recommended processing options for fast, low
+ quality output. (The default options are chosen for
+ highest quality output.) Currently, this is equivalent
+ to "-dct fast -nosmooth -onepass -dither ordered".
+
+ -grayscale Force grayscale output even if JPEG file is color.
+ Useful for viewing on monochrome displays; also,
+ djpeg runs noticeably faster in this mode.
+
++ -rgb Force RGB output even if JPEG file is grayscale.
++
+ -scale M/N Scale the output image by a factor M/N. Currently
+ the scale factor must be M/8, where M is an integer
+ between 1 and 16 inclusive, or any reduced fraction
+ thereof (such as 1/2, 3/4, etc. Scaling is handy if
+ the image is larger than your screen; also, djpeg runs
+ much faster when scaling down the output.
+
+ -bmp Select BMP output format (Windows flavor). 8-bit
+ colormapped format is emitted if -colors or -grayscale
+ is specified, or if the JPEG file is grayscale;
+ otherwise, 24-bit full-color format is emitted.
+
+ -gif Select GIF output format. Since GIF does not support
+ more than 256 colors, -colors 256 is assumed (unless
+ you specify a smaller number of colors). If you
+ specify -fast, the default number of colors is 216.
+
+ -os2 Select BMP output format (OS/2 1.x flavor). 8-bit
+ colormapped format is emitted if -colors or -grayscale
+ is specified, or if the JPEG file is grayscale;
+ otherwise, 24-bit full-color format is emitted.
+
+ -pnm Select PBMPLUS (PPM/PGM) output format (this is the
+ default format). PGM is emitted if the JPEG file is
+ grayscale or if -grayscale is specified; otherwise
+ PPM is emitted.
+
+ -rle Select RLE output format. (Requires URT library.)
+
+ -targa Select Targa output format. Grayscale format is
+ emitted if the JPEG file is grayscale or if
+ -grayscale is specified; otherwise, colormapped format
+ is emitted if -colors is specified; otherwise, 24-bit
+ full-color format is emitted.
Switches for advanced users:
"-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
+If you are only interested in perfect transformations, add the -perfect switch:
+ -perfect 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.
-
-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.
+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.)
++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 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.
+ -crop WxH+X+Y Crop to a rectangular region of width W and height H,
+ starting at point X,Y.
Other not-strictly-lossless transformation switches are:
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.
+ -copy none Copy no extra markers from source file. This setting
- suppresses all comments and other excess baggage
- present in the source file.
++ 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 data that is inessential for image display.
++ 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.)
projects / libjpeg-turbo / commitdiff