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144 lines
5.0 KiB
Groff
144 lines
5.0 KiB
Groff
.\" Hey, EMACS: -*- nroff -*-
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.TH CWEBP 1 "March 1, 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 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 \-q float
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Specify the compression factor between 0 and 100. Small factor
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produce 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 parameter's 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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(x_position, y_position) and size width x height. This cropping area must
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be fully contained within the source rectangle.
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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 \-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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