664 lines
21 KiB
HTML
664 lines
21 KiB
HTML
<!-- Creator : groff version 1.19.2 -->
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<!-- CreationDate: Fri Aug 5 18:48:54 2022 -->
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
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"http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<head>
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<meta name="generator" content="groff -Thtml, see www.gnu.org">
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<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
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<meta name="Content-Style" content="text/css">
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<style type="text/css">
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p { margin-top: 0; margin-bottom: 0; }
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pre { margin-top: 0; margin-bottom: 0; }
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table { margin-top: 0; margin-bottom: 0; }
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</style>
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<title>CWEBP</title>
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</head>
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<body>
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<h1 align=center>CWEBP</h1>
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<a href="#NAME">NAME</a><br>
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<a href="#SYNOPSIS">SYNOPSIS</a><br>
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<a href="#DESCRIPTION">DESCRIPTION</a><br>
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<a href="#OPTIONS">OPTIONS</a><br>
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<a href="#BUGS">BUGS</a><br>
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<a href="#EXAMPLES">EXAMPLES</a><br>
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<a href="#AUTHORS">AUTHORS</a><br>
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<a href="#SEE ALSO">SEE ALSO</a><br>
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<hr>
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<a name="NAME"></a>
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<h2>NAME</h2>
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<p style="margin-left:11%; margin-top: 1em">cwebp −
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compress an image file to a WebP file</p>
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<a name="SYNOPSIS"></a>
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<h2>SYNOPSIS</h2>
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<p style="margin-left:11%; margin-top: 1em"><b>cwebp</b>
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[<i>options</i>] <i>input_file −o
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output_file.webp</i></p>
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<a name="DESCRIPTION"></a>
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<h2>DESCRIPTION</h2>
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<p style="margin-left:11%; margin-top: 1em">This manual
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page documents the <b>cwebp</b> command.</p>
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<p style="margin-left:11%; margin-top: 1em"><b>cwebp</b>
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compresses an image using the WebP format. Input format can
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be either PNG, JPEG, TIFF, WebP or raw Y’CbCr samples.
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Note: Animated PNG and WebP files are not supported.</p>
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<a name="OPTIONS"></a>
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<h2>OPTIONS</h2>
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<p style="margin-left:11%; margin-top: 1em">The basic
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options are: <b><br>
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−o</b> <i>string</i></p>
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<p style="margin-left:22%;">Specify the name of the output
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WebP file. If omitted, <b>cwebp</b> will perform compression
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but only report statistics. Using "−" as
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output name will direct output to ’stdout’.</p>
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<p style="margin-left:11%;"><b>−−</b>
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<i>string</i></p>
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<p style="margin-left:22%;">Explicitly specify the input
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file. This option is useful if the input file starts with a
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’−’ for instance. This option must appear
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<b>last</b>. Any other options afterward will be
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ignored.</p>
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<p style="margin-left:11%;"><b>−h,
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−help</b></p>
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<p style="margin-left:22%;">A short usage summary.</p>
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<p style="margin-left:11%;"><b>−H,
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−longhelp</b></p>
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<p style="margin-left:22%;">A summary of all the possible
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options.</p>
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<p style="margin-left:11%;"><b>−version</b></p>
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<p style="margin-left:22%;">Print the version number (as
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major.minor.revision) and exit.</p>
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<p style="margin-left:11%;"><b>−lossless</b></p>
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<p style="margin-left:22%;">Encode the image without any
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loss. For images with fully transparent area, the invisible
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pixel values (R/G/B or Y/U/V) will be preserved only if the
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−exact option is used.</p>
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<p style="margin-left:11%;"><b>−near_lossless</b>
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<i>int</i></p>
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<p style="margin-left:22%;">Specify the level of
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near−lossless image preprocessing. This option adjusts
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pixel values to help compressibility, but has minimal impact
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on the visual quality. It triggers lossless compression mode
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automatically. The range is 0 (maximum preprocessing) to 100
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(no preprocessing, the default). The typical value is around
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60. Note that lossy with <b>−q 100</b> can at times
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yield better results.</p>
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<p style="margin-left:11%;"><b>−q</b>
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<i>float</i></p>
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<p style="margin-left:22%;">Specify the compression factor
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for RGB channels between 0 and 100. The default is 75. <br>
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In case of lossy compression (default), a small factor
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produces a smaller file with lower quality. Best quality is
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achieved by using a value of 100. <br>
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In case of lossless compression (specified by the
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<b>−lossless</b> option), a small factor enables
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faster compression speed, but produces a larger file.
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Maximum compression is achieved by using a value of 100.</p>
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<table width="100%" border=0 rules="none" frame="void"
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cellspacing="0" cellpadding="0">
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<tr valign="top" align="left">
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<td width="11%"></td>
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<td width="9%">
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<p style="margin-top: 1em" valign="top"><b>−z</b>
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<i>int</i></p> </td>
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<td width="2%"></td>
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<td width="78%">
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<p style="margin-top: 1em" valign="top">Switch on
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<b>lossless</b> compression mode with the specified level
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between 0 and 9, with level 0 being the fastest, 9 being the
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slowest. Fast mode produces larger file size than slower
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ones. A good default is <b>−z 6</b>. This option is
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actually a shortcut for some predefined settings for quality
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and method. If options <b>−q</b> or <b>−m</b>
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are subsequently used, they will invalidate the effect of
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this option.</p></td>
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</table>
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<p style="margin-left:11%;"><b>−alpha_q</b>
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<i>int</i></p>
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<p style="margin-left:22%;">Specify the compression factor
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for alpha compression between 0 and 100. Lossless
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compression of alpha is achieved using a value of 100, while
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the lower values result in a lossy compression. The default
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is 100.</p>
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<p style="margin-left:11%;"><b>−preset</b>
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<i>string</i></p>
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<p style="margin-left:22%;">Specify a set of
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pre−defined parameters to suit a particular type of
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source material. Possible values are: <b>default</b>,
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<b>photo</b>, <b>picture</b>, <b>drawing</b>, <b>icon</b>,
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<b>text</b>. Since <b>−preset</b> overwrites the other
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parameters’ values (except the <b>−q</b> one),
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this option should preferably appear first in the order of
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the arguments.</p>
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<table width="100%" border=0 rules="none" frame="void"
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cellspacing="0" cellpadding="0">
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<tr valign="top" align="left">
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<td width="11%"></td>
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<td width="9%">
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<p style="margin-top: 1em" valign="top"><b>−m</b>
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<i>int</i></p> </td>
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<td width="2%"></td>
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<td width="78%">
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<p style="margin-top: 1em" valign="top">Specify the
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compression method to use. This parameter controls the trade
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off between encoding speed and the compressed file size and
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quality. Possible values range from 0 to 6. Default value is
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4. When higher values are used, the encoder will spend more
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time inspecting additional encoding possibilities and decide
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on the quality gain. Lower value can result in faster
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processing time at the expense of larger file size and lower
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compression quality.</p></td>
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</table>
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<p style="margin-left:11%;"><b>−crop</b>
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<i>x_position y_position width height</i></p>
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<p style="margin-left:22%;">Crop the source to a rectangle
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with top−left corner at coordinates
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(<b>x_position</b>, <b>y_position</b>) and size <b>width</b>
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x <b>height</b>. This cropping area must be fully contained
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within the source rectangle. Note: the cropping is applied
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<i>before</i> any scaling.</p>
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<p style="margin-left:11%;"><b>−resize</b> <i>width
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height</i></p>
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<p style="margin-left:22%;">Resize the source to a
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rectangle with size <b>width</b> x <b>height</b>. If either
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(but not both) of the <b>width</b> or <b>height</b>
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parameters is 0, the value will be calculated preserving the
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aspect−ratio. Note: scaling is applied <i>after</i>
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cropping.</p>
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<table width="100%" border=0 rules="none" frame="void"
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cellspacing="0" cellpadding="0">
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<tr valign="top" align="left">
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<td width="11%"></td>
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<td width="4%">
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<p style="margin-top: 1em" valign="top"><b>−mt</b></p> </td>
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<td width="7%"></td>
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<td width="70%">
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<p style="margin-top: 1em" valign="top">Use
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multi−threading for encoding, if possible.</p></td>
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<td width="8%">
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</td>
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</table>
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<p style="margin-left:11%;"><b>−low_memory</b></p>
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<p style="margin-left:22%;">Reduce memory usage of lossy
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encoding by saving four times the compressed size
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(typically). This will make the encoding slower and the
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output slightly different in size and distortion. This flag
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is only effective for methods 3 and up, and is off by
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default. Note that leaving this flag off will have some side
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effects on the bitstream: it forces certain bitstream
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features like number of partitions (forced to 1). Note that
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a more detailed report of bitstream size is printed by
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<b>cwebp</b> when using this option.</p>
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<p style="margin-left:11%; margin-top: 1em"><b>LOSSY
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OPTIONS</b> <br>
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These options are only effective when doing lossy encoding
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(the default, with or without alpha). <b><br>
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−size</b> <i>int</i></p>
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<p style="margin-left:22%;">Specify a target size (in
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bytes) to try and reach for the compressed output. The
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compressor will make several passes of partial encoding in
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order to get as close as possible to this target. If both
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<b>−size</b> and <b>−psnr</b> are used,
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<b>−size</b> value will prevail.</p>
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<p style="margin-left:11%;"><b>−psnr</b>
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<i>float</i></p>
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<p style="margin-left:22%;">Specify a target PSNR (in dB)
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to try and reach for the compressed output. The compressor
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will make several passes of partial encoding in order to get
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as close as possible to this target. If both
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<b>−size</b> and <b>−psnr</b> are used,
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<b>−size</b> value will prevail.</p>
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<p style="margin-left:11%;"><b>−pass</b>
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<i>int</i></p>
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<p style="margin-left:22%;">Set a maximum number of passes
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to use during the dichotomy used by options
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<b>−size</b> or <b>−psnr</b>. Maximum value is
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10, default is 1. If options <b>−size</b> or
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<b>−psnr</b> were used, but <b>−pass</b>
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wasn’t specified, a default value of ’6’
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passes will be used.</p>
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<p style="margin-left:11%;"><b>−qrange</b> <i>int
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int</i></p>
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<p style="margin-left:22%;">Specifies the permissible
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interval for the quality factor. This is particularly useful
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when using multi-pass (<b>−size</b> or
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<b>−psnr</b> options). Default is 0 100. If the
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quality factor is outside this range, it will be clamped. If
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the minimum value must be less or equal to the maximum
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one.</p>
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<table width="100%" border=0 rules="none" frame="void"
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cellspacing="0" cellpadding="0">
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<tr valign="top" align="left">
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<td width="11%"></td>
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<td width="4%">
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<p style="margin-top: 1em" valign="top"><b>−af</b></p> </td>
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<td width="7%"></td>
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<td width="78%">
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<p style="margin-top: 1em" valign="top">Turns
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auto−filter on. This algorithm will spend additional
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time optimizing the filtering strength to reach a
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well−balanced quality.</p></td>
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</table>
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<p style="margin-left:11%;"><b>−jpeg_like</b></p>
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<p style="margin-left:22%;">Change the internal parameter
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mapping to better match the expected size of JPEG
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compression. This flag will generally produce an output file
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of similar size to its JPEG equivalent (for the same
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<b>−q</b> setting), but with less visual
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distortion.</p>
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<p style="margin-left:11%;">Advanced options:</p>
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<table width="100%" border=0 rules="none" frame="void"
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cellspacing="0" cellpadding="0">
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<tr valign="top" align="left">
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<td width="11%"></td>
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<td width="9%">
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<p style="margin-top: 1em" valign="top"><b>−f</b>
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<i>int</i></p> </td>
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<td width="2%"></td>
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<td width="78%">
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<p style="margin-top: 1em" valign="top">Specify the
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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
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filtering. Higher value will increase the strength of the
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filtering process applied after decoding the picture. The
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higher the value the smoother the picture will appear.
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Typical values are usually in the range of 20 to 50.</p></td>
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</table>
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<p style="margin-left:11%;"><b>−sharpness</b>
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<i>int</i></p>
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<p style="margin-left:22%;">Specify the sharpness of the
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filtering (if used). Range is 0 (sharpest) to 7 (least
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sharp). Default is 0.</p>
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<p style="margin-left:11%;"><b>−strong</b></p>
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<p style="margin-left:22%;">Use strong filtering (if
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filtering is being used thanks to the <b>−f</b>
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option). Strong filtering is on by default.</p>
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<p style="margin-left:11%;"><b>−nostrong</b></p>
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<p style="margin-left:22%;">Disable strong filtering (if
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filtering is being used thanks to the <b>−f</b>
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option) and use simple filtering instead.</p>
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<p style="margin-left:11%;"><b>−sharp_yuv</b></p>
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<p style="margin-left:22%;">Use more accurate and sharper
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RGB->YUV conversion if needed. Note that this process is
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slower than the default ’fast’ RGB->YUV
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conversion.</p>
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<p style="margin-left:11%;"><b>−sns</b>
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<i>int</i></p>
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<p style="margin-left:22%;">Specify the amplitude of the
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spatial noise shaping. Spatial noise shaping (or <b>sns</b>
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for short) refers to a general collection of built−in
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algorithms used to decide which area of the picture should
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use relatively less bits, and where else to better transfer
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these bits. The possible range goes from 0 (algorithm is
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off) to 100 (the maximal effect). The default value is
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50.</p>
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<p style="margin-left:11%;"><b>−segments</b>
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<i>int</i></p>
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<p style="margin-left:22%;">Change the number of partitions
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to use during the segmentation of the sns algorithm.
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Segments should be in range 1 to 4. Default value is 4. This
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option has no effect for methods 3 and up, unless
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<b>−low_memory</b> is used.</p>
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<p style="margin-left:11%;"><b>−partition_limit</b>
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<i>int</i></p>
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<p style="margin-left:22%;">Degrade quality by limiting the
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number of bits used by some macroblocks. Range is 0 (no
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degradation, the default) to 100 (full degradation). Useful
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values are usually around 30−70 for moderately large
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images. In the VP8 format, the so−called control
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partition has a limit of 512k and is used to store the
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following information: whether the macroblock is skipped,
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which segment it belongs to, whether it is coded as intra
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4x4 or intra 16x16 mode, and finally the prediction modes to
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use for each of the sub−blocks. For a very large
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image, 512k only leaves room to few bits per 16x16
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macroblock. The absolute minimum is 4 bits per macroblock.
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Skip, segment, and mode information can use up almost all
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these 4 bits (although the case is unlikely), which is
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problematic for very large images. The partition_limit
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factor controls how frequently the most bit−costly
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mode (intra 4x4) will be used. This is useful in case the
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512k limit is reached and the following message is
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displayed: <i>Error code: 6 (PARTITION0_OVERFLOW: Partition
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#0 is too big to fit 512k)</i>. If using
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<b>−partition_limit</b> is not enough to meet the 512k
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constraint, one should use less segments in order to save
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more header bits per macroblock. See the
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<b>−segments</b> option.</p>
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<p style="margin-left:11%; margin-top: 1em"><b>LOGGING
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OPTIONS</b> <br>
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These options control the level of output:</p>
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<table width="100%" border=0 rules="none" frame="void"
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cellspacing="0" cellpadding="0">
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<tr valign="top" align="left">
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<td width="11%"></td>
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<td width="3%">
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<p style="margin-top: 1em" valign="top"><b>−v</b></p> </td>
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<td width="8%"></td>
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<td width="78%">
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<p style="margin-top: 1em" valign="top">Print extra
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information (encoding time in particular).</p></td>
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</table>
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<p style="margin-left:11%;"><b>−print_psnr</b></p>
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<p style="margin-left:22%;">Compute and report average PSNR
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(Peak−Signal−To−Noise ratio).</p>
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<p style="margin-left:11%;"><b>−print_ssim</b></p>
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<p style="margin-left:22%;">Compute and report average SSIM
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(structural similarity metric, see
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https://en.wikipedia.org/wiki/SSIM for additional
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details).</p>
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<p style="margin-left:11%;"><b>−print_lsim</b></p>
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<p style="margin-left:22%;">Compute and report local
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similarity metric (sum of lowest error amongst the
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collocated pixel neighbors).</p>
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<p style="margin-left:11%;"><b>−progress</b></p>
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|
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<p style="margin-left:22%;">Report encoding progress in
|
|
percent.</p>
|
|
|
|
<table width="100%" border=0 rules="none" frame="void"
|
|
cellspacing="0" cellpadding="0">
|
|
<tr valign="top" align="left">
|
|
<td width="11%"></td>
|
|
<td width="9%">
|
|
|
|
|
|
|
|
<p style="margin-top: 1em" valign="top"><b>−quiet</b></p> </td>
|
|
<td width="2%"></td>
|
|
<td width="78%">
|
|
|
|
|
|
<p style="margin-top: 1em" valign="top">Do not print
|
|
anything.</p> </td>
|
|
<tr valign="top" align="left">
|
|
<td width="11%"></td>
|
|
<td width="9%">
|
|
|
|
|
|
|
|
<p style="margin-top: 1em" valign="top"><b>−short</b></p> </td>
|
|
<td width="2%"></td>
|
|
<td width="78%">
|
|
|
|
|
|
<p style="margin-top: 1em" valign="top">Only print brief
|
|
information (output file size and PSNR) for testing
|
|
purposes.</p> </td>
|
|
</table>
|
|
|
|
<p style="margin-left:11%;"><b>−map</b>
|
|
<i>int</i></p>
|
|
|
|
<p style="margin-left:22%;">Output additional
|
|
ASCII−map of encoding information. Possible map values
|
|
range from 1 to 6. This is only meant to help debugging.</p>
|
|
|
|
<p style="margin-left:11%; margin-top: 1em"><b>ADDITIONAL
|
|
OPTIONS</b> <br>
|
|
More advanced options are: <b><br>
|
|
−s</b> <i>width height</i></p>
|
|
|
|
<p style="margin-left:22%;">Specify that the input file
|
|
actually consists of raw Y’CbCr samples following the
|
|
ITU−R BT.601 recommendation, in 4:2:0 linear format.
|
|
The luma plane has size <b>width</b> x <b>height</b>.</p>
|
|
|
|
<p style="margin-left:11%;"><b>−pre</b>
|
|
<i>int</i></p>
|
|
|
|
<p style="margin-left:22%;">Specify some preprocessing
|
|
steps. Using a value of ’2’ will trigger
|
|
quality−dependent pseudo−random dithering during
|
|
RGBA−>YUVA conversion (lossy compression only).</p>
|
|
|
|
<p style="margin-left:11%;"><b>−alpha_filter</b>
|
|
<i>string</i></p>
|
|
|
|
<p style="margin-left:22%;">Specify the predictive
|
|
filtering method for the alpha plane. One of
|
|
’none’, ’fast’ or
|
|
’best’, in increasing complexity and slowness
|
|
order. Default is ’fast’. Internally, alpha
|
|
filtering is performed using four possible predictions
|
|
(none, horizontal, vertical, gradient). The
|
|
’best’ mode will try each mode in turn and pick
|
|
the one which gives the smaller size. The ’fast’
|
|
mode will just try to form an a priori guess without testing
|
|
all modes.</p>
|
|
|
|
<p style="margin-left:11%;"><b>−alpha_method</b>
|
|
<i>int</i></p>
|
|
|
|
<p style="margin-left:22%;">Specify the algorithm used for
|
|
alpha compression: 0 or 1. Algorithm 0 denotes no
|
|
compression, 1 uses WebP lossless format for compression.
|
|
The default is 1.</p>
|
|
|
|
<table width="100%" border=0 rules="none" frame="void"
|
|
cellspacing="0" cellpadding="0">
|
|
<tr valign="top" align="left">
|
|
<td width="11%"></td>
|
|
<td width="9%">
|
|
|
|
|
|
|
|
<p style="margin-top: 1em" valign="top"><b>−exact</b></p> </td>
|
|
<td width="2%"></td>
|
|
<td width="78%">
|
|
|
|
|
|
<p style="margin-top: 1em" valign="top">Preserve RGB values
|
|
in transparent area. The default is off, to help
|
|
compressibility.</p> </td>
|
|
</table>
|
|
|
|
<p style="margin-left:11%;"><b>−blend_alpha</b>
|
|
<i>int</i></p>
|
|
|
|
<p style="margin-left:22%;">This option blends the alpha
|
|
channel (if present) with the source using the background
|
|
color specified in hexadecimal as 0xrrggbb. The alpha
|
|
channel is afterward reset to the opaque value 255.</p>
|
|
|
|
<p style="margin-left:11%;"><b>−noalpha</b></p>
|
|
|
|
<p style="margin-left:22%;">Using this option will discard
|
|
the alpha channel.</p>
|
|
|
|
<p style="margin-left:11%;"><b>−hint</b>
|
|
<i>string</i></p>
|
|
|
|
<p style="margin-left:22%;">Specify the hint about input
|
|
image type. Possible values are: <b>photo</b>,
|
|
<b>picture</b> or <b>graph</b>.</p>
|
|
|
|
<p style="margin-left:11%;"><b>−metadata</b>
|
|
<i>string</i></p>
|
|
|
|
<p style="margin-left:22%;">A comma separated list of
|
|
metadata to copy from the input to the output if present.
|
|
Valid values: <b>all</b>, <b>none</b>, <b>exif</b>,
|
|
<b>icc</b>, <b>xmp</b>. The default is <b>none</b>.</p>
|
|
|
|
<p style="margin-left:22%; margin-top: 1em">Note: each
|
|
input format may not support all combinations.</p>
|
|
|
|
<table width="100%" border=0 rules="none" frame="void"
|
|
cellspacing="0" cellpadding="0">
|
|
<tr valign="top" align="left">
|
|
<td width="11%"></td>
|
|
<td width="9%">
|
|
|
|
|
|
|
|
<p style="margin-top: 1em" valign="top"><b>−noasm</b></p> </td>
|
|
<td width="2%"></td>
|
|
<td width="53%">
|
|
|
|
|
|
<p style="margin-top: 1em" valign="top">Disable all
|
|
assembly optimizations.</p></td>
|
|
<td width="25%">
|
|
</td>
|
|
</table>
|
|
|
|
<a name="BUGS"></a>
|
|
<h2>BUGS</h2>
|
|
|
|
|
|
<p style="margin-left:11%; margin-top: 1em">Please report
|
|
all bugs to the issue tracker:
|
|
https://bugs.chromium.org/p/webp <br>
|
|
Patches welcome! See this page to get started:
|
|
https://www.webmproject.org/code/contribute/submitting−patches/</p>
|
|
|
|
<a name="EXAMPLES"></a>
|
|
<h2>EXAMPLES</h2>
|
|
|
|
|
|
<p style="margin-left:11%; margin-top: 1em">cwebp −q
|
|
50 -lossless picture.png −o picture_lossless.webp <br>
|
|
cwebp −q 70 picture_with_alpha.png −o
|
|
picture_with_alpha.webp <br>
|
|
cwebp −sns 70 −f 50 −size 60000
|
|
picture.png −o picture.webp <br>
|
|
cwebp −o picture.webp −−
|
|
−−−picture.png</p>
|
|
|
|
<a name="AUTHORS"></a>
|
|
<h2>AUTHORS</h2>
|
|
|
|
|
|
<p style="margin-left:11%; margin-top: 1em"><b>cwebp</b> 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</p>
|
|
|
|
<p style="margin-left:11%; margin-top: 1em">This manual
|
|
page was written by Pascal Massimino
|
|
<pascal.massimino@gmail.com>, for the Debian project
|
|
(and may be used by others).</p>
|
|
|
|
<a name="SEE ALSO"></a>
|
|
<h2>SEE ALSO</h2>
|
|
|
|
|
|
|
|
<p style="margin-left:11%; margin-top: 1em"><b>dwebp</b>(1),
|
|
<b>gif2webp</b>(1) <br>
|
|
Please refer to https://developers.google.com/speed/webp/
|
|
for additional information.</p>
|
|
<hr>
|
|
</body>
|
|
</html>
|