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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
82 lines
2.4 KiB
Groff
82 lines
2.4 KiB
Groff
.\" Hey, EMACS: -*- nroff -*-
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.TH DWEBP 1 "June 20, 2011"
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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, 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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.B \-o string
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Specify the name of the output file (as PNG format by default).
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.TP
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.B \-ppm
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Change the output format to PPM.
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.TP
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.B \-pgm
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Change the output format to PGM. The output consist of luma/chroma
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samples instead of RGB, using the ICM4 layout. This option is mainly
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for verification and debugging purpose.
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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 will make the decoding faster.
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.TP
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.B \-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 \-scale width height
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Rescale the decoded picture to dimension \fBwidth\fP x \fBheight\fP. This option is
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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.).
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Note: scaling 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 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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.SH
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.SH SEE ALSO
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.BR cwebp (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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\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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