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d260310511
You can now use WebPDecBuffer, WebPBitstreamFeatures and WebPDecoderOptions to have better control over the decoding process (and the speed/quality tradeoff). WebPDecoderOptions allow to: - turn fancy upsampler on/off - turn in-loop filter on/off - perform on-the-fly cropping - perform on the-fly rescale (and more to come. Not all features are implemented yet). On-the-fly cropping and scaling allow to save quite some memory (as the decoding operation will now scale with the output's size, not the input's one). It saves some CPU too (since for instance, in-loop filtering is partially turned off where it doesn't matter, and some YUV->RGB conversion operations are ommitted too). The scaler uses summed area, so is mainly meant to be used for downscaling (like: for generating thumbnails or previews). Incremental decoding works with these new options. More doc to come soon. dwebp is now using the new decoding interface, with the new flags: -nofancy -nofilter -crop top left width height -scale width height Change-Id: I08baf2fa291941686f4ef70a9cc2e4137874e85e
151 lines
5.2 KiB
Groff
151 lines
5.2 KiB
Groff
.\" Hey, EMACS: -*- nroff -*-
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.TH CWEBP 1 "June 20, 2011"
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.SH NAME
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cwebp \- compress an image file to a WebP file
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.SH SYNOPSIS
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.B cwebp
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.RI [ options ] " input_file -o output_file.webp
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.br
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.SH DESCRIPTION
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This manual page documents the
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.B cwebp
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command.
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.PP
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\fBcwebp\fP compresses an image using the WebP format.
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Input format can be either PNG, JPEG, or raw Y'CbCr samples.
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When using PNG, the transparency information (alpha channel) is currently
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discarded.
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.SH OPTIONS
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The basic options are:
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.TP
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.B \-o string
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Specify the name of the output WebP file. If omitted, \fBcwebp\fP will
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perform compression but only report statistics.
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.TP
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.B \-h, \-help
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A short usage summary.
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.TP
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.B \-H, \-longhelp
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A summary of all the possible options.
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.TP
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.B \-version
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Print the version number (as major.minor.revision) and exit.
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.TP
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.B \-q float
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Specify the compression factor between 0 and 100. A small factor
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produces a smaller file with lower quality. Best quality is achieved
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using a value of 100. The default is 75.
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.TP
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.B \-f int
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Specify the strength of the deblocking filter, between 0 (no filtering)
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and 100 (maximum filtering). A value of 0 will turn off any filtering.
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Higher value will increase the strength of the filtering process applied
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after decoding the picture. The higher the smoother the picture will
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appear. Typical values are usually in the range of 20 to 50.
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.TP
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.B \-preset string
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Specify a set of pre-defined parameters to suit a particular type of
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source material. Possible values are: \fBdefault\fP, \fBphoto\fP,
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\fBpicture\fP, \fBdrawing\fP, \fBicon\fP, \fBtext\fP. Since
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\fB\-preset\fP overwrites the other parameters' values (except the
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\fB\-q\fP one), this option should preferably appear first in the
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order of the arguments.
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.TP
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.B \-sns int
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Specify the amplitude of the spatial noise shaping. Spatial noise shaping
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(or \fBsns\fP for short) refers to a general collection of built-in algorithms
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used to decide which area of the picture should use relatively less bits,
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and where else to better transfer these bits. The possible range goes from
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0 (algorithm is off) to 100 (the maximal effect). The default value is 80.
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.TP
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.B \-m int
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Specify the compression method to use. This parameter controls the
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tradeoff between encoding speed and the compressed file size and quality.
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Possible values range from 0 to 6. Default value is 4.
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When higher values are used, the encoder will spend more time inspecting
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additional encoding possibilities and decide on the quality gain.
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Lower value can result is faster processing time at the expense of
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larger filesize and lower compression quality.
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.TP
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.B \-af
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Turns auto-filter on. This algorithm will spend additional time optimizing
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the filtering strength to reach a well-balanced quality.
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.SH ADDITIONAL OPTIONS
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More advanced options are:
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.TP
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.B \-sharpness int
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Specify the sharpness of the filtering (if used).
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Range is 0 (sharpest) to 7 (least sharp). Default is 0.
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.TP
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.B \-strong
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Use a stronger filtering than the default one (if filtering is being
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used thanks to the \fB\-f\fP option). Strong filtering is off by default.
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.TP
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.B \-segments int
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Change the number of partitions to use during the segmentation of the
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sns algorithm. Segments should be in range 1 to 4. Default value is 4.
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.TP
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.B \-size int
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Specify a target size (in bytes) to try and reach for the compressed output.
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Compressor will make several pass of partial encoding in order to get as
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close as possible to this target.
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.TP
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.B \-psnr float
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Specify a target PSNR (in dB) to try and reach for the compressed output.
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Compressor will make several pass of partial encoding in order to get as
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close as possible to this target.
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.TP
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.B \-pass int
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Set a maximum number of pass to use during the dichotomy used by
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options \fB\-size\fP or \fB\-psnr\fP. Maximum value is 10.
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.TP
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.B \-crop x_position y_position width height
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Crop the source to a rectangle with top-left corner at coordinates
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(\fBx_position\fP, \fBy_position\fP) and size \fBwidth\fP x \fBheight\fP.
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This cropping area must be fully contained within the source rectangle.
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.TP
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.B \-s width height
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Specify that the input file actually consists of raw Y'CbCr samples following
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the ITU-R BT.601 recommendation, in 4:2:0 linear format.
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The luma plane has size \fBwidth\fP x \fBheight\fP.
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.TP
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.B \-map int
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Output additional ASCII-map of encoding information. Possible map values
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range from 1 to 6. This is only meant to help debugging.
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.TP
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.B \-pre int
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Specify a pre-processing filter. This option is a placeholder
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and has currently no effect.
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.TP
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.B \-noasm
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Disable all assembly optimizations.
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.TP
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.B \-v
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Print extra information (encoding time in particular).
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.TP
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.B \-quiet
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Do not print anything.
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.TP
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.B \-short
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Only print brief information (output file size and PSNR) for testing purpose.
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.SH Examples:
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cwebp -q 70 picture.png -o picture.webp
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.br
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cwebp -sns 70 -f 50 -strong -af -size 60000 picture.png -o picture.webp
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.SH
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.SH SEE ALSO
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.BR dwebp (1).
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.br
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Please refer to http://code.google.com/speed/webp/ for additional
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information.
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.SH AUTHOR
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\fBcwebp\fP was written by the WebP team.
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.br
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The latest source tree is available at http://www.webmproject.org/code
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.PP
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This manual page was written by Pascal Massimino <pascal.massimino@gmail.com>,
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for the Debian project (and may be used by others).
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