.\" 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