bbe32df1e3
new options: dwebp -alpha_dither vwebp -noalphadither When the source was marked as quantized, we use a threshold-averaging filter to smooth the decoded alpha plane. Note: this option forces the decoding of alpha data in one pass, and might slow the decoding a bit. The new field in WebPDecoderOptions struct is 'alpha_dithering_strength' (0 by default, means: off). Max strength value is '100'. Change-Id: I218e21af96360d4781587fede95f8ea4e2b7287a
144 lines
4.4 KiB
Groff
144 lines
4.4 KiB
Groff
.\" Hey, EMACS: -*- nroff -*-
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.TH DWEBP 1 "June 13, 2014"
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.SH NAME
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dwebp \- decompress a WebP file to an image file
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.SH SYNOPSIS
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.B dwebp
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.RI [ options ] " input_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 dwebp
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command.
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.PP
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\fBdwebp\fP decompresses WebP files into PNG, PAM, PPM or PGM images.
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.SH OPTIONS
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The basic options are:
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.TP
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.B \-h
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Print usage summary.
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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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.BI \-o " string
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Specify the name of the output file (as PNG format by default).
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Using "-" as output name will direct output to 'stdout'.
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.TP
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.BI \-\- " string
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Explicitly specify the input file. This option is useful if the input
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file starts with an '\-' for instance. This option must appear \fBlast\fP.
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Any other options afterward will be ignored. If the input file is "\-",
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the data will be read from \fIstdin\fP instead of a file.
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.TP
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.B \-bmp
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Change the output format to uncompressed BMP.
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.TP
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.B \-tiff
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Change the output format to uncompressed TIFF.
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.TP
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.B \-pam
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Change the output format to PAM (retains alpha).
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.TP
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.B \-ppm
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Change the output format to PPM (discards alpha).
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.TP
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.B \-pgm
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Change the output format to PGM. The output consists of luma/chroma
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samples instead of RGB, using the IMC4 layout. This option is mainly
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for verification and debugging purposes.
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.TP
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.B \-yuv
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Change the output format to raw YUV. The output consists of
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luma/chroma-U/chroma-V samples instead of RGB, saved sequentially as
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individual planes. This option is mainly for verification and debugging
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purposes.
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.TP
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.B \-nofancy
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Don't use the fancy upscaler for YUV420. This may lead to jaggy
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edges (especially the red ones), but should be faster.
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.TP
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.B \-nofilter
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Don't use the in-loop filtering process even if it is required by
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the bitstream. This may produce visible blocks on the non-compliant output,
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but it will make the decoding faster.
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.TP
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.BI \-dither " strength
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Specify a dithering \fBstrength\fP between 0 and 100. Dithering is a
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post-processing effect applied to chroma components in lossy compression.
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It helps by smoothing gradients and avoiding banding artifacts.
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.TP
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.BI \-alpha_dither
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If the compressed file contains a transparency plane that was quantized
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during compression, this flag will allow dithering the reconstructed plane
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in order to generate smoother transparency gradients.
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.TP
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.B \-nodither
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Disable all dithering (default).
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.TP
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.B \-mt
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Use multi-threading for decoding, if possible.
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.TP
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.BI \-crop " x_position y_position width height
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Crop the decoded picture 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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The top-left corner will be snapped to even coordinates if needed.
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This option is meant to reduce the memory needed for cropping large images.
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Note: the cropping is applied \fIbefore\fP any scaling.
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.TP
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.B \-flip
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Flip decoded image vertically (can be useful for OpenGL textures for instance).
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.TP
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.BI \-scale " width height
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Rescale the decoded picture to dimension \fBwidth\fP x \fBheight\fP. This
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option is mostly intended to reducing the memory needed to decode large images,
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when only a small version is needed (thumbnail, preview, etc.). Note: scaling
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is applied \fIafter\fP cropping.
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.TP
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.B \-v
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Print extra information (decoding time in particular).
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.TP
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.B \-noasm
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Disable all assembly optimizations.
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.SH BUGS
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Please report all bugs to our issue tracker:
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http://code.google.com/p/webp/issues
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.br
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Patches welcome! See this page to get started:
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http://www.webmproject.org/code/contribute/submitting-patches/
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.SH EXAMPLES
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dwebp picture.webp \-o output.png
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.br
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dwebp picture.webp \-ppm \-o output.ppm
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.br
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dwebp \-o output.ppm \-\- \-\-\-picture.webp
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.br
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cat picture.webp | dwebp \-o \- \-\- \- > output.ppm
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.SH AUTHORS
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\fBdwebp\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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.SH SEE ALSO
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.BR cwebp (1),
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.BR gif2webp (1),
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.BR webpmux (1)
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.br
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Please refer to http://developers.google.com/speed/webp/ for additional
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information.
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.SS Output file format details
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PAM: http://netpbm.sourceforge.net/doc/pam.html
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.br
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PGM: http://netpbm.sourceforge.net/doc/pgm.html
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.br
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PPM: http://netpbm.sourceforge.net/doc/ppm.html
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.br
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PNG: http://www.libpng.org/pub/png/png-sitemap.html#info
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