third_party/libwebp/doc/tools.md - cobalt - Git at Google

 # WebP tools

 ## Encoding tool

 The examples/ directory contains tools for encoding (cwebp) and decoding (dwebp)
 images.

 The easiest use should look like:

 ```shell
 cwebp input.png -q 80 -o output.webp
 ```

 which will convert the input file to a WebP file using a quality factor of 80 on
 a 0->100 scale (0 being the lowest quality, 100 being the best. Default value is
 75).

 You might want to try the `-lossless` flag too, which will compress the source
 (in RGBA format) without any loss. The `-q` quality parameter will in this case
 control the amount of processing time spent trying to make the output file as
 small as possible.

 A longer list of options is available using the `-longhelp` command line flag:

 ```shell
 > cwebp -longhelp
 Usage:
  cwebp [-preset <...>] [options] in_file [-o out_file]
 ```

 If input size (-s) for an image is not specified, it is assumed to be a PNG,
 JPEG, TIFF or WebP file. Note: Animated PNG and WebP files are not supported.

 Options:

 ```
 -h / -help ............. short help
 -H / -longhelp ......... long help
 -q <float> ............. quality factor (0:small..100:big), default=75
 -alpha_q <int> ......... transparency-compression quality (0..100),
                          default=100
 -preset <string> ....... preset setting, one of:
                           default, photo, picture,
                           drawing, icon, text
    -preset must come first, as it overwrites other parameters
 -z <int> ............... activates lossless preset with given
                          level in [0:fast, ..., 9:slowest]

 -m <int> ............... compression method (0=fast, 6=slowest), default=4
 -segments <int> ........ number of segments to use (1..4), default=4
 -size <int> ............ target size (in bytes)
 -psnr <float> .......... target PSNR (in dB. typically: 42)

 -s <int> <int> ......... input size (width x height) for YUV
 -sns <int> ............. spatial noise shaping (0:off, 100:max), default=50
 -f <int> ............... filter strength (0=off..100), default=60
 -sharpness <int> ....... filter sharpness (0:most .. 7:least sharp), default=0
 -strong ................ use strong filter instead of simple (default)
 -nostrong .............. use simple filter instead of strong
 -sharp_yuv ............. use sharper (and slower) RGB->YUV conversion
 -partition_limit <int> . limit quality to fit the 512k limit on
                          the first partition (0=no degradation ... 100=full)
 -pass <int> ............ analysis pass number (1..10)
 -qrange <min> <max> .... specifies the permissible quality range
                          (default: 0 100)
 -crop <x> <y> <w> <h> .. crop picture with the given rectangle
 -resize <w> <h> ........ resize picture (*after* any cropping)
 -mt .................... use multi-threading if available
 -low_memory ............ reduce memory usage (slower encoding)
 -map <int> ............. print map of extra info
 -print_psnr ............ prints averaged PSNR distortion
 -print_ssim ............ prints averaged SSIM distortion
 -print_lsim ............ prints local-similarity distortion
 -d <file.pgm> .......... dump the compressed output (PGM file)
 -alpha_method <int> .... transparency-compression method (0..1), default=1
 -alpha_filter <string> . predictive filtering for alpha plane,
                          one of: none, fast (default) or best
 -exact ................. preserve RGB values in transparent area, default=off
 -blend_alpha <hex> ..... blend colors against background color
                          expressed as RGB values written in
                          hexadecimal, e.g. 0xc0e0d0 for red=0xc0
                          green=0xe0 and blue=0xd0
 -noalpha ............... discard any transparency information
 -lossless .............. encode image losslessly, default=off
 -near_lossless <int> ... use near-lossless image preprocessing
                          (0..100=off), default=100
 -hint <string> ......... specify image characteristics hint,
                          one of: photo, picture or graph

 -metadata <string> ..... comma separated list of metadata to
                          copy from the input to the output if present.
                          Valid values: all, none (default), exif, icc, xmp

 -short ................. condense printed message
 -quiet ................. don't print anything
 -version ............... print version number and exit
 -noasm ................. disable all assembly optimizations
 -v ..................... verbose, e.g. print encoding/decoding times
 -progress .............. report encoding progress
 ```

 Experimental Options:

 ```
 -jpeg_like ............. roughly match expected JPEG size
 -af .................... auto-adjust filter strength
 -pre <int> ............. pre-processing filter
 ```

 The main options you might want to try in order to further tune the visual
 quality are:

 -preset -sns -f -m

 Namely:

 *   `preset` will set up a default encoding configuration targeting a particular
     type of input. It should appear first in the list of options, so that
     subsequent options can take effect on top of this preset. Default value is
     'default'.
 *   `sns` will progressively turn on (when going from 0 to 100) some additional
     visual optimizations (like: segmentation map re-enforcement). This option
     will balance the bit allocation differently. It tries to take bits from the
     "easy" parts of the picture and use them in the "difficult" ones instead.
     Usually, raising the sns value (at fixed -q value) leads to larger files,
     but with better quality. Typical value is around '75'.
 *   `f` option directly links to the filtering strength used by the codec's
     in-loop processing. The higher the value, the smoother the highly-compressed
     area will look. This is particularly useful when aiming at very small files.
     Typical values are around 20-30. Note that using the option
     -strong/-nostrong will change the type of filtering. Use "-f 0" to turn
     filtering off.
 *   `m` controls the trade-off between encoding speed and quality. Default is 4.
     You can try -m 5 or -m 6 to explore more (time-consuming) encoding
     possibilities. A lower value will result in faster encoding at the expense
     of quality.

 ## Decoding tool

 There is a decoding sample in examples/dwebp.c which will take a .webp file and
 decode it to a PNG image file (amongst other formats). This is simply to
 demonstrate the use of the API. You can verify the file test.webp decodes to
 exactly the same as test_ref.ppm by using:

 ```shell
 cd examples
 ./dwebp test.webp -ppm -o test.ppm
 diff test.ppm test_ref.ppm
 ```

 The full list of options is available using -h:

 ```shell
 > dwebp -h
 Usage: dwebp in_file [options] [-o out_file]
 ```

 Decodes the WebP image file to PNG format [Default]. Note: Animated WebP files
 are not supported.

 Use following options to convert into alternate image formats:

 ```
 -pam ......... save the raw RGBA samples as a color PAM
 -ppm ......... save the raw RGB samples as a color PPM
 -bmp ......... save as uncompressed BMP format
 -tiff ........ save as uncompressed TIFF format
 -pgm ......... save the raw YUV samples as a grayscale PGM
                file with IMC4 layout
 -yuv ......... save the raw YUV samples in flat layout
 ```

 Other options are:

 ```
 -version ..... print version number and exit
 -nofancy ..... don't use the fancy YUV420 upscaler
 -nofilter .... disable in-loop filtering
 -nodither .... disable dithering
 -dither <d> .. dithering strength (in 0..100)
 -alpha_dither  use alpha-plane dithering if needed
 -mt .......... use multi-threading
 -crop <x> <y> <w> <h> ... crop output with the given rectangle
 -resize <w> <h> ......... resize output (*after* any cropping)
 -flip ........ flip the output vertically
 -alpha ....... only save the alpha plane
 -incremental . use incremental decoding (useful for tests)
 -h ........... this help message
 -v ........... verbose (e.g. print encoding/decoding times)
 -quiet ....... quiet mode, don't print anything
 -noasm ....... disable all assembly optimizations
 ```

 ## WebP file analysis tool

 `webpinfo` can be used to print out the chunk level structure and bitstream
 header information of WebP files. It can also check if the files are of valid
 WebP format.

 Usage:

 ```shell
 webpinfo [options] in_files
 ```

 Note: there could be multiple input files; options must come before input files.

 Options:

 ```
 -version ........... Print version number and exit.
 -quiet ............. Do not show chunk parsing information.
 -diag .............. Show parsing error diagnosis.
 -summary ........... Show chunk stats summary.
 -bitstream_info .... Parse bitstream header.
 ```

 ## Visualization tool

 There's a little self-serve visualization tool called 'vwebp' under the
 examples/ directory. It uses OpenGL to open a simple drawing window and show a
 decoded WebP file. It's not yet integrated in the automake build system, but you
 can try to manually compile it using the recommendations below.

 Usage:

 ```shell
 vwebp in_file [options]
 ```

 Decodes the WebP image file and visualize it using OpenGL

 Options are:

 ```
 -version ..... print version number and exit
 -noicc ....... don't use the icc profile if present
 -nofancy ..... don't use the fancy YUV420 upscaler
 -nofilter .... disable in-loop filtering
 -dither <int>  dithering strength (0..100), default=50
 -noalphadither disable alpha plane dithering
 -usebgcolor .. display background color
 -mt .......... use multi-threading
 -info ........ print info
 -h ........... this help message
 ```

 Keyboard shortcuts:

 ```
 'c' ................ toggle use of color profile
 'b' ................ toggle background color display
 'i' ................ overlay file information
 'd' ................ disable blending & disposal (debug)
 'q' / 'Q' / ESC .... quit
 ```

 ### Building

 Prerequisites:

 1.  OpenGL & OpenGL Utility Toolkit (GLUT)

     Linux: `sudo apt-get install freeglut3-dev mesa-common-dev`

     Mac + Xcode: These libraries should be available in the OpenGL / GLUT
     frameworks.

     Windows: http://freeglut.sourceforge.net/index.php#download

 2.  (Optional) qcms (Quick Color Management System)

     1.  Download qcms from Mozilla / Chromium:
         https://hg.mozilla.org/mozilla-central/file/0e7639e3bdfb/gfx/qcms
         https://source.chromium.org/chromium/chromium/src/+/main:third_party/qcms/;drc=d4a2f8e1ed461d8fc05ed88d1ae2dc94c9773825
     2.  Build and archive the source files as libqcms.a / qcms.lib
     3.  Update makefile.unix / Makefile.vc
         1.  Define WEBP_HAVE_QCMS
         2.  Update include / library paths to reference the qcms directory.

 Build using makefile.unix / Makefile.vc:

 ```shell
 $ make -f makefile.unix examples/vwebp
 > nmake /f Makefile.vc CFG=release-static \
     ../obj/x64/release-static/bin/vwebp.exe
 ```

 ## Animation creation tool

 The utility `img2webp` can turn a sequence of input images (PNG, JPEG, ...) into
 an animated WebP file. It offers fine control over duration, encoding modes,
 etc.

 Usage:

 ```shell
 img2webp [file_options] [[frame_options] frame_file]... [-o webp_file]
 ```

 File-level options (only used at the start of compression):

 ```
 -min_size ............ minimize size
 -kmax <int> .......... maximum number of frame between key-frames
                         (0=only keyframes)
 -kmin <int> .......... minimum number of frame between key-frames
                         (0=disable key-frames altogether)
 -mixed ............... use mixed lossy/lossless automatic mode
 -near_lossless <int> . use near-lossless image preprocessing
                        (0..100=off), default=100
 -sharp_yuv ........... use sharper (and slower) RGB->YUV conversion
                        (lossy only)
 -loop <int> .......... loop count (default: 0, = infinite loop)
 -v ................... verbose mode
 -h ................... this help
 -version ............. print version number and exit
 ```

 Per-frame options (only used for subsequent images input):

 ```
 -d <int> ............. frame duration in ms (default: 100)
 -lossless  ........... use lossless mode (default)
 -lossy ... ........... use lossy mode
 -q <float> ........... quality
 -m <int> ............. method to use
 ```

 example: `img2webp -loop 2 in0.png -lossy in1.jpg -d 80 in2.tiff -o out.webp`

 Note: if a single file name is passed as the argument, the arguments will be
 tokenized from this file. The file name must not start with the character '-'.

 ## Animated GIF conversion

 Animated GIF files can be converted to WebP files with animation using the
 gif2webp utility available under examples/. The files can then be viewed using
 vwebp.

 Usage:

 ```shell
 gif2webp [options] gif_file -o webp_file
 ```

 Options:

 ```
 -h / -help ............. this help
 -lossy ................. encode image using lossy compression
 -mixed ................. for each frame in the image, pick lossy
                          or lossless compression heuristically
 -q <float> ............. quality factor (0:small..100:big)
 -m <int> ............... compression method (0=fast, 6=slowest)
 -min_size .............. minimize output size (default:off)
                          lossless compression by default; can be
                          combined with -q, -m, -lossy or -mixed
                          options
 -kmin <int> ............ min distance between key frames
 -kmax <int> ............ max distance between key frames
 -f <int> ............... filter strength (0=off..100)
 -metadata <string> ..... comma separated list of metadata to
                          copy from the input to the output if present
                          Valid values: all, none, icc, xmp (default)
 -loop_compatibility .... use compatibility mode for Chrome
                          version prior to M62 (inclusive)
 -mt .................... use multi-threading if available

 -version ............... print version number and exit
 -v ..................... verbose
 -quiet ................. don't print anything
 ```

 ### Building

 With the libgif development files installed, gif2webp can be built using
 makefile.unix:

 ```shell
 $ make -f makefile.unix examples/gif2webp
 ```

 or using autoconf:

 ```shell
 $ ./configure --enable-everything
 $ make
 ```

 ## Comparison of animated images

 Test utility anim_diff under examples/ can be used to compare two animated
 images (each can be GIF or WebP).

 Usage:

 ```shell
 anim_diff <image1> <image2> [options]
 ```

 Options:

 ```
 -dump_frames <folder> dump decoded frames in PAM format
 -min_psnr <float> ... minimum per-frame PSNR
 -raw_comparison ..... if this flag is not used, RGB is
                       premultiplied before comparison
 -max_diff <int> ..... maximum allowed difference per channel
                       between corresponding pixels in subsequent
                       frames
 -h .................. this help
 -version ............ print version number and exit
 ```

 ### Building

 With the libgif development files installed, anim_diff can be built using
 makefile.unix:

 ```shell
 $ make -f makefile.unix examples/anim_diff
 ```

 or using autoconf:

 ```shell
 $ ./configure --enable-everything
 $ make
 ```

 ## WebP Mux tool

 The examples/ directory contains a tool (webpmux) for manipulating WebP files.
 The webpmux tool can be used to create an extended format WebP file and also to
 extract or strip relevant data from such a file.

 A list of options is available using the -help command line flag:

 ```shell
 > webpmux -help
 Usage: webpmux -get GET_OPTIONS INPUT -o OUTPUT
        webpmux -set SET_OPTIONS INPUT -o OUTPUT
        webpmux -duration DURATION_OPTIONS [-duration ...]
                INPUT -o OUTPUT
        webpmux -strip STRIP_OPTIONS INPUT -o OUTPUT
        webpmux -frame FRAME_OPTIONS [-frame...] [-loop LOOP_COUNT]
                [-bgcolor BACKGROUND_COLOR] -o OUTPUT
        webpmux -info INPUT
        webpmux [-h|-help]
        webpmux -version
        webpmux argument_file_name

 GET_OPTIONS:
  Extract relevant data:
    icc       get ICC profile
    exif      get EXIF metadata
    xmp       get XMP metadata
    frame n   get nth frame

 SET_OPTIONS:
  Set color profile/metadata/parameters:
    loop LOOP_COUNT            set the loop count
    bgcolor BACKGROUND_COLOR   set the animation background color
    icc  file.icc              set ICC profile
    exif file.exif             set EXIF metadata
    xmp  file.xmp              set XMP metadata
    where:    'file.icc' contains the ICC profile to be set,
              'file.exif' contains the EXIF metadata to be set
              'file.xmp' contains the XMP metadata to be set

 DURATION_OPTIONS:
  Set duration of selected frames:
    duration            set duration for all frames
    duration,frame      set duration of a particular frame
    duration,start,end  set duration of frames in the
                         interval [start,end])
    where: 'duration' is the duration in milliseconds
           'start' is the start frame index
           'end' is the inclusive end frame index
            The special 'end' value '0' means: last frame.

 STRIP_OPTIONS:
  Strip color profile/metadata:
    icc       strip ICC profile
    exif      strip EXIF metadata
    xmp       strip XMP metadata

 FRAME_OPTIONS(i):
  Create animation:
    file_i +di[+xi+yi[+mi[bi]]]
    where:    'file_i' is the i'th animation frame (WebP format),
              'di' is the pause duration before next frame,
              'xi','yi' specify the image offset for this frame,
              'mi' is the dispose method for this frame (0 or 1),
              'bi' is the blending method for this frame (+b or -b)

 LOOP_COUNT:
  Number of times to repeat the animation.
  Valid range is 0 to 65535 [Default: 0 (infinite)].

 BACKGROUND_COLOR:
  Background color of the canvas.
   A,R,G,B
   where:    'A', 'R', 'G' and 'B' are integers in the range 0 to 255 specifying
             the Alpha, Red, Green and Blue component values respectively
             [Default: 255,255,255,255]

 INPUT & OUTPUT are in WebP format.

 Note: The nature of EXIF, XMP and ICC data is not checked and is assumed to be
 valid.

 Note: if a single file name is passed as the argument, the arguments will be
 tokenized from this file. The file name must not start with the character '-'.
 ```
	# WebP tools

	## Encoding tool

	The examples/ directory contains tools for encoding (cwebp) and decoding (dwebp)
	images.

	The easiest use should look like:

	```shell
	cwebp input.png -q 80 -o output.webp
	```

	which will convert the input file to a WebP file using a quality factor of 80 on
	a 0->100 scale (0 being the lowest quality, 100 being the best. Default value is
	75).

	You might want to try the `-lossless` flag too, which will compress the source
	(in RGBA format) without any loss. The `-q` quality parameter will in this case
	control the amount of processing time spent trying to make the output file as
	small as possible.

	A longer list of options is available using the `-longhelp` command line flag:

	```shell
	> cwebp -longhelp
	Usage:
	cwebp [-preset <...>] [options] in_file [-o out_file]
	```

	If input size (-s) for an image is not specified, it is assumed to be a PNG,
	JPEG, TIFF or WebP file. Note: Animated PNG and WebP files are not supported.

	Options:

	```
	-h / -help ............. short help
	-H / -longhelp ......... long help
	-q <float> ............. quality factor (0:small..100:big), default=75
	-alpha_q <int> ......... transparency-compression quality (0..100),
	default=100
	-preset <string> ....... preset setting, one of:
	default, photo, picture,
	drawing, icon, text
	-preset must come first, as it overwrites other parameters
	-z <int> ............... activates lossless preset with given
	level in [0:fast, ..., 9:slowest]

	-m <int> ............... compression method (0=fast, 6=slowest), default=4
	-segments <int> ........ number of segments to use (1..4), default=4
	-size <int> ............ target size (in bytes)
	-psnr <float> .......... target PSNR (in dB. typically: 42)

	-s <int> <int> ......... input size (width x height) for YUV
	-sns <int> ............. spatial noise shaping (0:off, 100:max), default=50
	-f <int> ............... filter strength (0=off..100), default=60
	-sharpness <int> ....... filter sharpness (0:most .. 7:least sharp), default=0
	-strong ................ use strong filter instead of simple (default)
	-nostrong .............. use simple filter instead of strong
	-sharp_yuv ............. use sharper (and slower) RGB->YUV conversion
	-partition_limit <int> . limit quality to fit the 512k limit on
	the first partition (0=no degradation ... 100=full)
	-pass <int> ............ analysis pass number (1..10)
	-qrange <min> <max> .... specifies the permissible quality range
	(default: 0 100)
	-crop <x> <y> <w> <h> .. crop picture with the given rectangle
	-resize <w> <h> ........ resize picture (after any cropping)
	-mt .................... use multi-threading if available
	-low_memory ............ reduce memory usage (slower encoding)
	-map <int> ............. print map of extra info
	-print_psnr ............ prints averaged PSNR distortion
	-print_ssim ............ prints averaged SSIM distortion
	-print_lsim ............ prints local-similarity distortion
	-d <file.pgm> .......... dump the compressed output (PGM file)
	-alpha_method <int> .... transparency-compression method (0..1), default=1
	-alpha_filter <string> . predictive filtering for alpha plane,
	one of: none, fast (default) or best
	-exact ................. preserve RGB values in transparent area, default=off
	-blend_alpha <hex> ..... blend colors against background color
	expressed as RGB values written in
	hexadecimal, e.g. 0xc0e0d0 for red=0xc0
	green=0xe0 and blue=0xd0
	-noalpha ............... discard any transparency information
	-lossless .............. encode image losslessly, default=off
	-near_lossless <int> ... use near-lossless image preprocessing
	(0..100=off), default=100
	-hint <string> ......... specify image characteristics hint,
	one of: photo, picture or graph

	-metadata <string> ..... comma separated list of metadata to
	copy from the input to the output if present.
	Valid values: all, none (default), exif, icc, xmp

	-short ................. condense printed message
	-quiet ................. don't print anything
	-version ............... print version number and exit
	-noasm ................. disable all assembly optimizations
	-v ..................... verbose, e.g. print encoding/decoding times
	-progress .............. report encoding progress
	```

	Experimental Options:

	```
	-jpeg_like ............. roughly match expected JPEG size
	-af .................... auto-adjust filter strength
	-pre <int> ............. pre-processing filter
	```

	The main options you might want to try in order to further tune the visual
	quality are:

	-preset -sns -f -m

	Namely:

	* `preset` will set up a default encoding configuration targeting a particular
	type of input. It should appear first in the list of options, so that
	subsequent options can take effect on top of this preset. Default value is
	'default'.
	* `sns` will progressively turn on (when going from 0 to 100) some additional
	visual optimizations (like: segmentation map re-enforcement). This option
	will balance the bit allocation differently. It tries to take bits from the
	"easy" parts of the picture and use them in the "difficult" ones instead.
	Usually, raising the sns value (at fixed -q value) leads to larger files,
	but with better quality. Typical value is around '75'.
	* `f` option directly links to the filtering strength used by the codec's
	in-loop processing. The higher the value, the smoother the highly-compressed
	area will look. This is particularly useful when aiming at very small files.
	Typical values are around 20-30. Note that using the option
	-strong/-nostrong will change the type of filtering. Use "-f 0" to turn
	filtering off.
	* `m` controls the trade-off between encoding speed and quality. Default is 4.
	You can try -m 5 or -m 6 to explore more (time-consuming) encoding
	possibilities. A lower value will result in faster encoding at the expense
	of quality.

	## Decoding tool

	There is a decoding sample in examples/dwebp.c which will take a .webp file and
	decode it to a PNG image file (amongst other formats). This is simply to
	demonstrate the use of the API. You can verify the file test.webp decodes to
	exactly the same as test_ref.ppm by using:

	```shell
	cd examples
	./dwebp test.webp -ppm -o test.ppm
	diff test.ppm test_ref.ppm
	```

	The full list of options is available using -h:

	```shell
	> dwebp -h
	Usage: dwebp in_file [options] [-o out_file]
	```

	Decodes the WebP image file to PNG format [Default]. Note: Animated WebP files
	are not supported.

	Use following options to convert into alternate image formats:

	```
	-pam ......... save the raw RGBA samples as a color PAM
	-ppm ......... save the raw RGB samples as a color PPM
	-bmp ......... save as uncompressed BMP format
	-tiff ........ save as uncompressed TIFF format
	-pgm ......... save the raw YUV samples as a grayscale PGM
	file with IMC4 layout
	-yuv ......... save the raw YUV samples in flat layout
	```

	Other options are:

	```
	-version ..... print version number and exit
	-nofancy ..... don't use the fancy YUV420 upscaler
	-nofilter .... disable in-loop filtering
	-nodither .... disable dithering
	-dither <d> .. dithering strength (in 0..100)
	-alpha_dither use alpha-plane dithering if needed
	-mt .......... use multi-threading
	-crop <x> <y> <w> <h> ... crop output with the given rectangle
	-resize <w> <h> ......... resize output (after any cropping)
	-flip ........ flip the output vertically
	-alpha ....... only save the alpha plane
	-incremental . use incremental decoding (useful for tests)
	-h ........... this help message
	-v ........... verbose (e.g. print encoding/decoding times)
	-quiet ....... quiet mode, don't print anything
	-noasm ....... disable all assembly optimizations
	```

	## WebP file analysis tool

	`webpinfo` can be used to print out the chunk level structure and bitstream
	header information of WebP files. It can also check if the files are of valid
	WebP format.

	Usage:

	```shell
	webpinfo [options] in_files
	```

	Note: there could be multiple input files; options must come before input files.

	Options:

	```
	-version ........... Print version number and exit.
	-quiet ............. Do not show chunk parsing information.
	-diag .............. Show parsing error diagnosis.
	-summary ........... Show chunk stats summary.
	-bitstream_info .... Parse bitstream header.
	```

	## Visualization tool

	There's a little self-serve visualization tool called 'vwebp' under the
	examples/ directory. It uses OpenGL to open a simple drawing window and show a
	decoded WebP file. It's not yet integrated in the automake build system, but you
	can try to manually compile it using the recommendations below.

	Usage:

	```shell
	vwebp in_file [options]
	```

	Decodes the WebP image file and visualize it using OpenGL

	Options are:

	```
	-version ..... print version number and exit
	-noicc ....... don't use the icc profile if present
	-nofancy ..... don't use the fancy YUV420 upscaler
	-nofilter .... disable in-loop filtering
	-dither <int> dithering strength (0..100), default=50
	-noalphadither disable alpha plane dithering
	-usebgcolor .. display background color
	-mt .......... use multi-threading
	-info ........ print info
	-h ........... this help message
	```

	Keyboard shortcuts:

	```
	'c' ................ toggle use of color profile
	'b' ................ toggle background color display
	'i' ................ overlay file information
	'd' ................ disable blending & disposal (debug)
	'q' / 'Q' / ESC .... quit
	```

	### Building

	Prerequisites:

	1. OpenGL & OpenGL Utility Toolkit (GLUT)

	Linux: `sudo apt-get install freeglut3-dev mesa-common-dev`

	Mac + Xcode: These libraries should be available in the OpenGL / GLUT
	frameworks.

	Windows: http://freeglut.sourceforge.net/index.php#download

	2. (Optional) qcms (Quick Color Management System)

	1. Download qcms from Mozilla / Chromium:
	https://hg.mozilla.org/mozilla-central/file/0e7639e3bdfb/gfx/qcms
	https://source.chromium.org/chromium/chromium/src/+/main:third_party/qcms/;drc=d4a2f8e1ed461d8fc05ed88d1ae2dc94c9773825
	2. Build and archive the source files as libqcms.a / qcms.lib
	3. Update makefile.unix / Makefile.vc
	1. Define WEBP_HAVE_QCMS
	2. Update include / library paths to reference the qcms directory.

	Build using makefile.unix / Makefile.vc:

	```shell
	$ make -f makefile.unix examples/vwebp
	> nmake /f Makefile.vc CFG=release-static \
	../obj/x64/release-static/bin/vwebp.exe
	```

	## Animation creation tool

	The utility `img2webp` can turn a sequence of input images (PNG, JPEG, ...) into
	an animated WebP file. It offers fine control over duration, encoding modes,
	etc.

	Usage:

	```shell
	img2webp [file_options] [[frame_options] frame_file]... [-o webp_file]
	```

	File-level options (only used at the start of compression):

	```
	-min_size ............ minimize size
	-kmax <int> .......... maximum number of frame between key-frames
	(0=only keyframes)
	-kmin <int> .......... minimum number of frame between key-frames
	(0=disable key-frames altogether)
	-mixed ............... use mixed lossy/lossless automatic mode
	-near_lossless <int> . use near-lossless image preprocessing
	(0..100=off), default=100
	-sharp_yuv ........... use sharper (and slower) RGB->YUV conversion
	(lossy only)
	-loop <int> .......... loop count (default: 0, = infinite loop)
	-v ................... verbose mode
	-h ................... this help
	-version ............. print version number and exit
	```

	Per-frame options (only used for subsequent images input):

	```
	-d <int> ............. frame duration in ms (default: 100)
	-lossless ........... use lossless mode (default)
	-lossy ... ........... use lossy mode
	-q <float> ........... quality
	-m <int> ............. method to use
	```

	example: `img2webp -loop 2 in0.png -lossy in1.jpg -d 80 in2.tiff -o out.webp`

	Note: if a single file name is passed as the argument, the arguments will be
	tokenized from this file. The file name must not start with the character '-'.

	## Animated GIF conversion

	Animated GIF files can be converted to WebP files with animation using the
	gif2webp utility available under examples/. The files can then be viewed using
	vwebp.

	Usage:

	```shell
	gif2webp [options] gif_file -o webp_file
	```

	Options:

	```
	-h / -help ............. this help
	-lossy ................. encode image using lossy compression
	-mixed ................. for each frame in the image, pick lossy
	or lossless compression heuristically
	-q <float> ............. quality factor (0:small..100:big)
	-m <int> ............... compression method (0=fast, 6=slowest)
	-min_size .............. minimize output size (default:off)
	lossless compression by default; can be
	combined with -q, -m, -lossy or -mixed
	options
	-kmin <int> ............ min distance between key frames
	-kmax <int> ............ max distance between key frames
	-f <int> ............... filter strength (0=off..100)
	-metadata <string> ..... comma separated list of metadata to
	copy from the input to the output if present
	Valid values: all, none, icc, xmp (default)
	-loop_compatibility .... use compatibility mode for Chrome
	version prior to M62 (inclusive)
	-mt .................... use multi-threading if available

	-version ............... print version number and exit
	-v ..................... verbose
	-quiet ................. don't print anything
	```

	### Building

	With the libgif development files installed, gif2webp can be built using
	makefile.unix:

	```shell
	$ make -f makefile.unix examples/gif2webp
	```

	or using autoconf:

	```shell
	$ ./configure --enable-everything
	$ make
	```

	## Comparison of animated images

	Test utility anim_diff under examples/ can be used to compare two animated
	images (each can be GIF or WebP).

	Usage:

	```shell
	anim_diff <image1> <image2> [options]
	```

	Options:

	```
	-dump_frames <folder> dump decoded frames in PAM format
	-min_psnr <float> ... minimum per-frame PSNR
	-raw_comparison ..... if this flag is not used, RGB is
	premultiplied before comparison
	-max_diff <int> ..... maximum allowed difference per channel
	between corresponding pixels in subsequent
	frames
	-h .................. this help
	-version ............ print version number and exit
	```

	### Building

	With the libgif development files installed, anim_diff can be built using
	makefile.unix:

	```shell
	$ make -f makefile.unix examples/anim_diff
	```

	or using autoconf:

	```shell
	$ ./configure --enable-everything
	$ make
	```

	## WebP Mux tool

	The examples/ directory contains a tool (webpmux) for manipulating WebP files.
	The webpmux tool can be used to create an extended format WebP file and also to
	extract or strip relevant data from such a file.

	A list of options is available using the -help command line flag:

	```shell
	> webpmux -help
	Usage: webpmux -get GET_OPTIONS INPUT -o OUTPUT
	webpmux -set SET_OPTIONS INPUT -o OUTPUT
	webpmux -duration DURATION_OPTIONS [-duration ...]
	INPUT -o OUTPUT
	webpmux -strip STRIP_OPTIONS INPUT -o OUTPUT
	webpmux -frame FRAME_OPTIONS [-frame...] [-loop LOOP_COUNT]
	[-bgcolor BACKGROUND_COLOR] -o OUTPUT
	webpmux -info INPUT
	webpmux [-h\|-help]
	webpmux -version
	webpmux argument_file_name

	GET_OPTIONS:
	Extract relevant data:
	icc get ICC profile
	exif get EXIF metadata
	xmp get XMP metadata
	frame n get nth frame

	SET_OPTIONS:
	Set color profile/metadata/parameters:
	loop LOOP_COUNT set the loop count
	bgcolor BACKGROUND_COLOR set the animation background color
	icc file.icc set ICC profile
	exif file.exif set EXIF metadata
	xmp file.xmp set XMP metadata
	where: 'file.icc' contains the ICC profile to be set,
	'file.exif' contains the EXIF metadata to be set
	'file.xmp' contains the XMP metadata to be set

	DURATION_OPTIONS:
	Set duration of selected frames:
	duration set duration for all frames
	duration,frame set duration of a particular frame
	duration,start,end set duration of frames in the
	interval [start,end])
	where: 'duration' is the duration in milliseconds
	'start' is the start frame index
	'end' is the inclusive end frame index
	The special 'end' value '0' means: last frame.

	STRIP_OPTIONS:
	Strip color profile/metadata:
	icc strip ICC profile
	exif strip EXIF metadata
	xmp strip XMP metadata

	FRAME_OPTIONS(i):
	Create animation:
	file_i +di[+xi+yi[+mi[bi]]]
	where: 'file_i' is the i'th animation frame (WebP format),
	'di' is the pause duration before next frame,
	'xi','yi' specify the image offset for this frame,
	'mi' is the dispose method for this frame (0 or 1),
	'bi' is the blending method for this frame (+b or -b)

	LOOP_COUNT:
	Number of times to repeat the animation.
	Valid range is 0 to 65535 [Default: 0 (infinite)].

	BACKGROUND_COLOR:
	Background color of the canvas.
	A,R,G,B
	where: 'A', 'R', 'G' and 'B' are integers in the range 0 to 255 specifying
	the Alpha, Red, Green and Blue component values respectively
	[Default: 255,255,255,255]

	INPUT & OUTPUT are in WebP format.

	Note: The nature of EXIF, XMP and ICC data is not checked and is assumed to be
	valid.

	Note: if a single file name is passed as the argument, the arguments will be
	tokenized from this file. The file name must not start with the character '-'.
	```