.\"                                      Hey, EMACS: -*- nroff -*-
.TH DWEBP 1 "June 23, 2016"
.SH NAME
dwebp \- decompress a WebP file to an image file
.SH SYNOPSIS
.B dwebp
.RI [ options ] " input_file.webp
.br
.SH DESCRIPTION
This manual page documents the
.B dwebp
command.
.PP
\fBdwebp\fP decompresses WebP files into PNG, PAM, PPM or PGM images.
.SH OPTIONS
The basic options are:
.TP
.B \-h
Print usage summary.
.TP
.B \-version
Print the version number (as major.minor.revision) and exit.
.TP
.BI \-o " string
Specify the name of the output file (as PNG format by default).
Using "-" as output name will direct output to 'stdout'.
.TP
.BI \-\- " string
Explicitly specify the input file. This option is useful if the input
file starts with an '\-' for instance. This option must appear \fBlast\fP.
Any other options afterward will be ignored. If the input file is "\-",
the data will be read from \fIstdin\fP instead of a file.
.TP
.B \-bmp
Change the output format to uncompressed BMP.
.TP
.B \-tiff
Change the output format to uncompressed TIFF.
.TP
.B \-pam
Change the output format to PAM (retains alpha).
.TP
.B \-ppm
Change the output format to PPM (discards alpha).
.TP
.B \-pgm
Change the output format to PGM. The output consists of luma/chroma
samples instead of RGB, using the IMC4 layout. This option is mainly
for verification and debugging purposes.
.TP
.B \-yuv
Change the output format to raw YUV. The output consists of
luma/chroma-U/chroma-V samples instead of RGB, saved sequentially as
individual planes. This option is mainly for verification and debugging
purposes.
.TP
.B \-nofancy
Don't use the fancy upscaler for YUV420. This may lead to jaggy
edges (especially the red ones), but should be faster.
.TP
.B \-nofilter
Don't use the in-loop filtering process even if it is required by
the bitstream. This may produce visible blocks on the non-compliant output,
but it will make the decoding faster.
.TP
.BI \-dither " strength
Specify a dithering \fBstrength\fP between 0 and 100. Dithering is a
post-processing effect applied to chroma components in lossy compression.
It helps by smoothing gradients and avoiding banding artifacts.
.TP
.BI \-alpha_dither
If the compressed file contains a transparency plane that was quantized
during compression, this flag will allow dithering the reconstructed plane
in order to generate smoother transparency gradients.
.TP
.B \-nodither
Disable all dithering (default).
.TP
.B \-mt
Use multi-threading for decoding, if possible.
.TP
.BI \-crop " x_position y_position width height
Crop the decoded picture to a rectangle with top-left corner at coordinates
(\fBx_position\fP, \fBy_position\fP) and size \fBwidth\fP x \fBheight\fP.
This cropping area must be fully contained within the source rectangle.
The top-left corner will be snapped to even coordinates if needed.
This option is meant to reduce the memory needed for cropping large images.
Note: the cropping is applied \fIbefore\fP any scaling.
.TP
.B \-flip
Flip decoded image vertically (can be useful for OpenGL textures for instance).
.TP
\fB\-resize\fR, \fB\-scale\fI width height\fR
Rescale the decoded picture to dimension \fBwidth\fP x \fBheight\fP. This
option is mostly intended to reducing the memory needed to decode large images,
when only a small version is needed (thumbnail, preview, etc.). Note: scaling
is applied \fIafter\fP cropping.
If either (but not both) of the \fBwidth\fP or \fBheight\fP parameters is 0,
the value will be calculated preserving the aspect-ratio.
.TP
.B \-quiet
Do not print anything.
.TP
.B \-v
Print extra information (decoding time in particular).
.TP
.B \-noasm
Disable all assembly optimizations.

.SH BUGS
Please report all bugs to the issue tracker:
https://bugs.chromium.org/p/webp
.br
Patches welcome! See this page to get started:
http://www.webmproject.org/code/contribute/submitting-patches/

.SH EXAMPLES
dwebp picture.webp \-o output.png
.br
dwebp picture.webp \-ppm \-o output.ppm
.br
dwebp \-o output.ppm \-\- \-\-\-picture.webp
.br
cat picture.webp | dwebp \-o \- \-\- \- > output.ppm

.SH AUTHORS
\fBdwebp\fP is a part of libwebp and was written by the WebP team.
.br
The latest source tree is available at
https://chromium.googlesource.com/webm/libwebp
.PP
This manual page was written by Pascal Massimino <pascal.massimino@gmail.com>,
for the Debian project (and may be used by others).

.SH SEE ALSO
.BR cwebp (1),
.BR gif2webp (1),
.BR webpmux (1)
.br
Please refer to http://developers.google.com/speed/webp/ for additional
information.
.SS Output file format details
PAM: http://netpbm.sourceforge.net/doc/pam.html
.br
PGM: http://netpbm.sourceforge.net/doc/pgm.html
.br
PPM: http://netpbm.sourceforge.net/doc/ppm.html
.br
PNG: http://www.libpng.org/pub/png/png-sitemap.html#info