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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "https://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en">
<head>
<meta name="generator" content="HTML Tidy for Linux/x86 (vers 6 November 2007), see www.w3.org" />
<title>RMagick 6.0.1: class Image::Info - Optional method arguments</title>
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<body>
<h6 id="header">RMagick 6.0.1 User's Guide and Reference</h6>
<div class="nav">« <a href="struct.html">Prev</a> | <a href="index.html">Contents</a> | <a href="constants.html">Next</a> »</div>
<h1>class Image::Info - Optional method arguments</h1>
<div id="toc">
<h2>Table of Contents</h2>
<h3>instance methods</h3>
<ul>
<li><a href="#aset">[]=</a></li>
<li><a href="#aref">[]</a></li>
<li><a href="#channel">channel</a></li>
<li><a href="#define">define</a></li>
<li><a href="#undefine">undefine</a></li>
</ul>
<h3>attribute methods</h3>
<div class="toccol">
<ul>
<li><a href="#antialias">antialias</a></li>
<li><a href="#attenuate">attenuate</a></li>
<li><a href="#authenticate">authenticate</a></li>
<li><a href="#background_color">background_color</a></li>
<li><a href="#border_color">border_color</a></li>
<li><a href="#caption">caption</a></li>
<li><a href="#colorspace">colorspace</a></li>
<li><a href="#comment">comment</a></li>
<li><a href="#compression">compression</a></li>
<li><a href="#delay">delay</a></li>
<li><a href="#density">density</a></li>
<li><a href="#depth">depth</a></li>
<li><a href="#dispose">dispose</a></li>
<li><a href="#dither">dither</a></li>
<li><a href="#endian">endian</a></li>
</ul>
</div>
<div class="toccol">
<ul>
<li><a href="#extract">extract</a></li>
<li><a href="#filename">filename</a></li>
<li><a href="#fill">fill</a></li>
<li><a href="#font">font</a></li>
<li><a href="#format">format</a></li>
<li><a href="#fuzz">fuzz</a></li>
<li><a href="#gravity">gravity</a></li>
<li><a href="#image_type">image_type</a></li>
<li><a href="#interlace">interlace</a></li>
<li><a href="#label">label</a></li>
<li><a href="#matte_color">matte_color</a></li>
<li><a href="#monochrome">monochrome</a></li>
<li><a href="#number_scenes">number_scenes</a></li>
<li><a href="#orientation">orientation</a></li>
<li><a href="#origin">origin</a></li>
</ul>
</div>
<div class="toccol">
<ul>
<li><a href="#page">page</a></li>
<li><a href="#pointsize">pointsize</a></li>
<li><a href="#quality">quality</a></li>
<li><a href="#sampling_factor">sampling_factor</a></li>
<li><a href="#scene">scene</a></li>
<li><a href="#server_name">server_name</a></li>
<li><a href="#size">size</a></li>
<li><a href="#stroke">stroke</a></li>
<li><a href="#stroke_width">stroke_width</a></li>
<li><a href="#tile_offset">tile_offset</a></li>
<li><a href="#texture">texture</a></li>
<li><a href="#transparent_color">transparent_color</a></li>
<li><a href="#undercolor">undercolor</a></li>
<li><a href="#units">units</a></li>
<li><a href="#view">view</a></li>
</ul>
</div>
</div>
<div id="intro">
<h2>The Image::Info class</h2>
<p>
Some <code>Image</code> and <code>ImageList</code> methods, such as <code>read</code> and <code>write</code>, accept an "optional arguments" block in
which you can set attributes that modify the method's output. These attributes belong to the <code>Image::Info</code> class. The
<code>Image::Info</code>
class exists only to accept optional arguments for those
<code>Image</code> and <code>ImageList</code> methods.
</p>
<p>
This page explains the methods defined in the
<code>Image::Info</code> class. Generally, each <code>Image</code> or <code>ImageList</code> method that uses the <code>Image::Info</code> class to get
optional arguments will only accept some of the attributes listed on this page, that is, only those attributes that are meaningful for the particular
method. Any other attributes that you set are ignored. Also, some attributes are only used by a subset of the image formats. See the ImageMagick
documentation for more information.
</p>
<p>
Remember, you do not ever need to create an
<code>Image::Info</code> object. The object is created for you before the optional arguments block is entered and destroyed after the block is exited.
</p>
<p>
All the attributes in the <code>Image::Info</code> class are read/write. For simplicity, and because usually you only set these attributes, this page
only describes the setter version of each attribute method.
</p>
</div>
<h2 class="methods">instance methods</h2>
<div class="sig">
<h3 id="aset">[]=</h3>
<p>
<span class="arg">self</span>[<span class="arg">format</span>, <span class="arg">key</span>] = <span class="arg">value</span> ->
<span class="arg">self</span><br />
<span class="arg">self</span>[<span class="arg">key</span>] = <span class="arg">value</span> -> <span class="arg">self</span>
</p>
</div>
<div class="desc">
<h4>Description</h4>
<p>
Define an option. An alternative to <a href="#define">define</a>, below. Use this method to set options for reading or writing certain image formats.
The list of supported options changes from release to release. For a list of the valid image formats, keys, and values, refer to the documentation for
the -define option for the release of ImageMagick installed on your system.
</p>
<h4>Arguments</h4>
<dl>
<dt>format</dt>
<dd>An image format name such as "ps" or "tiff". (Depending on the key, this argument may be omitted.)</dd>
<dt>key</dt>
<dd>A string that identifies the option.</dd>
<dt>value</dt>
<dd>
The value of the option. <span class="arg">Value</span> can be any object that responds to <code>to_s</code>. Use <code>nil</code> to set the key to a
null value.
</dd>
</dl>
<h4 id="user_option">The "user" option</h4>
<p>
The "user" option is unique to RMagick. It may be set to any string. If this option is used when creating an image via one of the methods listed below
then the new image gets the value assigned as a property as if
<code>img["user"]</code> had been used. In addition, the value is displayed in the string returned by <code>Image#inspect</code>. The "user" property
can be used to help distinguish otherwise similar images when debugging.
</p>
<p>For example,</p>
<pre class="language-ruby">
img = Magick::Image.new(10,10) do |options|
options['user'] = __FILE__ + ':' + __LINE__.to_s
end
#=> 10x10 DirectClass 16-bit user:test.rb:3
</pre
>
<p>
These methods propagate the value of the "user" option to new image(s):
<code
>Image.new, ImageList.new, ImageList.new_image, Image.capture, Image.from_blob, ImageList.from_blob, Image.read, ImageList.read, Image.read_inline,
and Image.ping</code
>.
</p>
<h4>Returns</h4>
<p>self</p>
<h4>Example</h4>
<pre class="language-ruby">options["tiff", "bits-per-sample"] = 2</pre>
<h4>Magick API</h4>
<p>SetImageOption</p>
</div>
<div class="sig">
<h3 id="aref">[]</h3>
<p>
<span class="arg">self</span>[<span class="arg">format</span>, <span class="arg">key</span>] -> <em>value</em><br />
<span class="arg">self</span>[<span class="arg">key</span>] ->
<em>value</em>
</p>
</div>
<div class="desc">
<h4>Description</h4>
<p>Returns the value of the specified option for the specified format.</p>
<h4>Arguments</h4>
<dl>
<dt>format</dt>
<dd>An image format name such as "ps" or "tiff". (Depending on the key, this argument may be omitted.)</dd>
<dt>key</dt>
<dd>A string that identifies the option.</dd>
</dl>
<h4>Returns</h4>
<p>The value of the option. Always a string.</p>
<h4>Example</h4>
<pre class="language-ruby">options["tiff", "bits-per-sample"] #=> 2</pre>
<h4>Magick API</h4>
<p>GetImageOption</p>
</div>
<div class="sig">
<h3 id="channel">channel</h3>
<p><span class="arg">self</span>.channel([<span class="arg">channel</span> [, <span class="arg">channel</span>...]])</p>
</div>
<div class="desc">
<h4>Description</h4>
<p>Restrict the method to the specified channel(s). This attribute is set-only.</p>
<h4>Argument</h4>
<p>
The arguments may be any
<a href="constants.html#ChannelType">ChannelType</a> values.
</p>
<h4>Notes</h4>
<p>
If you call <code>channel</code> with no arguments, <em>all</em> channels are included. If you do not call <code>channel</code> at all, the channels
used do not include the alpha channel.
</p>
</div>
<div class="sig">
<h3 id="define">define</h3>
<p><span class="arg">self</span>.define(<span class="arg">format</span>, <span class="arg">key</span>[, <span class="arg">value</span>])</p>
</div>
<div class="desc">
<h4>Description</h4>
<p>Define a format-specific option. See <a href="#aset">[]=</a>, above.</p>
<h4>Arguments</h4>
<dl>
<dt>format</dt>
<dd>An image format name such as "ps" or "tiff".</dd>
<dt>key</dt>
<dd>A string that identifies the option.</dd>
<dt>value</dt>
<dd>
The value of the option. <span class="arg">Value</span> can be any object that responds to <code>to_s</code>. If omitted, the key is simply defined to
an null value.
</dd>
</dl>
<h4>Returns</h4>
<p>self</p>
<h4>Example</h4>
<pre class="language-ruby">options.define("tiff", "bits-per-sample", 2)</pre>
<h4>Magick API</h4>
<p>SetImageOption</p>
</div>
<div class="sig">
<h3 id="undefine">undefine</h3>
<p><span class="arg">self</span>.undefine(<span class="arg">format</span>, <span class="arg">key</span>)</p>
</div>
<div class="desc">
<h4>Description</h4>
<p>
Delete an option definition set by <a href="#aset">[]=</a> or <a href="#define">define</a>. This is not the same as setting the option to a null value.
The <code>undefine</code> method removes the option name from the list of options for the specified format.
</p>
<h4>Arguments</h4>
<dl>
<dt>format</dt>
<dd>An image format name such as "ps" or "tiff".</dd>
<dt>key</dt>
<dd>A string that identifies the option.</dd>
</dl>
<h4>Returns</h4>
<p>self</p>
<h4>Example</h4>
<pre class="language-ruby">options.undefine("tiff", "bits-per-sample")</pre>
</div>
<h2 class="methods">attribute methods</h2>
<div class="sig">
<h3 id="antialias">antialias</h3>
<p>
<span class="arg">self.</span>antialias= <span class="arg"><code>true</code></span> or
<span class="arg"><code>false</code></span>
</p>
</div>
<div class="desc">
<h4>Description</h4>
<p>
<span class="imquote">Control antialiasing of rendered Postscript and Postscript or TrueType fonts.</span>
The default is <code>true</code>.
</p>
</div>
<div class="sig">
<h3 id="attenuate">attenuate</h3>
<p><span class="arg">self</span>.attenuate= <span class="arg">number</span></p>
</div>
<div class="desc">
<h4>Description</h4>
<p class="imquote">Lessen (or intensify) when adding noise to an image.</p>
</div>
<div class="sig">
<h3 id="authenticate">authenticate</h3>
<p>
<span class="arg">self.</span>authenticate=
<span class="arg">string</span>
</p>
</div>
<div class="desc">
<h4>Description</h4>
<p class="imquote">Decrypt an image with this password.</p>
<p>This attribute can be used to specify the password to be used when reading an image or image sequence that is in an encrypted format, such as PDF.</p>
</div>
<div class="sig">
<h3 id="background_color">background_color</h3>
<p><span class="arg">self.</span>background_color= <span class="arg">string</span> or <span class="arg">pixel</span></p>
</div>
<div class="desc">
<h4>Description</h4>
<p>Set the image background color. The default is "white".</p>
<h4>Arguments</h4>
<p>A <a href="imusage.html#color_names">color name</a> or a <a href="struct.html#Pixel">Pixel</a>.</p>
</div>
<div class="sig">
<h3 id="border_color">border_color</h3>
<p><span class="arg">self.</span>border_color= <span class="arg">string</span> or <span class="arg">pixel</span></p>
</div>
<div class="desc">
<h4>Description</h4>
<p>Set the image border color. The default is "#dfdfdf".</p>
<h4>Arguments</h4>
<p>A <a href="imusage.html#color_names">color name</a> or a <a href="struct.html#Pixel">Pixel</a>.</p>
</div>
<div class="sig">
<h3 id="caption">caption</h3>
<p><span class="arg">self.</span>caption= <span class="arg">string</span></p>
</div>
<div class="desc">
<h4>Description</h4>
<p>When used with <a href="image1.html#read">Image.read</a>, assigns a caption to an image. The caption is an image property:</p>
<pre class="language-ruby">
img = Magick::Image.read("xc:white") do |options|
options.caption = "a new caption"
options.size = "20x20"
end
p img.first.properties #=> {"caption"=>"a new caption"}
p img.first['caption'] #=> "a new caption"
</pre
>
<h4>Arguments</h4>
<p>A string.</p>
</div>
<div class="sig">
<h3 id="colorspace">colorspace</h3>
<p>
<span class="arg">self.</span>colorspace=
<span class="arg">colorspace</span>
</p>
</div>
<div class="desc">
<h4>Description</h4>
<p>Specifies the image pixel interpretation.</p>
<h4>Arguments</h4>
A <a href="constants.html#ColorspaceType">ColorspaceType</a> constant.
</div>
<div class="sig">
<h3 id="comment">comment</h3>
<p><span class="arg">self.</span>comment= <span class="arg">string</span></p>
</div>
<div class="desc">
<h4>Description</h4>
<p class="imquote">Use this option to assign a specific comment to the image, when writing to an image format that supports comments.</p>
<h4>Arguments</h4>
<p class="imquote">
You can include the image filename, type, width, height, or other image attribute by embedding special format characters listed under the
<a href="draw.html#annotate">annotate</a> method.
</p>
</div>
<div class="sig">
<h3 id="compression">compression</h3>
<p><span class="arg">self.</span>compression= <span class="arg">type</span></p>
</div>
<div class="desc">
<h4>Description</h4>
<p>
Specifies the type of compression used when writing the image. Only some image formats support compression. For those that do, only some compression
types are supported. If you specify an compression type that is not supported, the default compression type (usually NoCompression) is used instead.
</p>
<p>
Some compression types support varying levels of compression. See the
<a href="#quality"><code>quality</code></a> attribute.
</p>
<p>
The following table shows the image formats that support compression. For each format, the right-hand column shows the supported compression types. The
default compression type is shown in <strong>bold</strong>.
</p>
<table class="simple_table" summary="supported compression types by image format">
<caption>
Supported Compression Types
</caption>
<tr>
<th>Format</th>
<th>Compression Types</th>
</tr>
<tr>
<td>BMP</td>
<td><strong>NoCompression</strong>, RLECompression</td>
</tr>
<tr>
<td>DIB</td>
<td><strong>NoCompression</strong>, RLECompression</td>
</tr>
<tr>
<td>FPX</td>
<td><strong>NoCompression</strong>, JPEGCompression</td>
</tr>
<tr>
<td>GIF</td>
<td><strong>LZWCompression</strong></td>
</tr>
<tr>
<td>JNG</td>
<td><strong>NoCompression</strong>, JPEGCompression</td>
</tr>
<tr>
<td>JP2</td>
<td><strong>JPEGCompression</strong>, LosslessJPEGCompression</td>
</tr>
<tr>
<td>JPG</td>
<td><strong>JPEGCompression</strong>, LosslessJPEGCompression</td>
</tr>
<tr>
<td>MIFF</td>
<td><strong>NoCompression</strong>, RLECompression</td>
</tr>
<tr>
<td>MNG</td>
<td><strong>NoCompression</strong>, JPEGCompression</td>
</tr>
<tr>
<td>PALM</td>
<td><strong>NoCompression</strong>, FaxCompression, RLECompression</td>
</tr>
<tr>
<td>PDB</td>
<td><strong>NoCompression</strong>, RLECompression</td>
</tr>
<tr>
<td>PDF</td>
<td><strong>NoCompression</strong>, JPEGCompression, LZWCompression, ZipCompression</td>
</tr>
<tr>
<td>PICT</td>
<td><strong>NoCompression</strong>, JPEGCompression</td>
</tr>
<tr>
<td>PNG</td>
<td><strong>NoCompression</strong>, ZIPCompression</td>
</tr>
<tr>
<td>PS</td>
<td><strong>NoCompression</strong>, RLECompression</td>
</tr>
<tr>
<td>PS2</td>
<td><strong>RLECompression</strong>, FaxCompression, JPEGCompression, LZWCompression, NoCompression</td>
</tr>
<tr>
<td>PS3</td>
<td><strong>FaxCompression</strong>, JPEGCompression, LZWCompression, NoCompression, RLECompression, ZipCompression</td>
</tr>
<tr>
<td>TIFF</td>
<td><strong>NoCompression</strong>, FaxCompression, Group4Compression, JPEGCompression, LZWCompression, RLECompression, ZipCompression</td>
</tr>
</table>
<h5>Notes</h5>
<ol id="compression_notes">
<li>NoCompression is accepted for all image formats. Except as noted in the table, it is the default.</li>
<li>
This table is based on my examination of the ImageMagick source code. It is not necessarily complete and it may contain mistakes. If you need an
authoritative list, you should consult the ImageMagick developers.
</li>
</ol>
<h4>Arguments</h4>
A <a href="constants.html#CompressionType">CompressionType</a> constant.
</div>
<div class="sig">
<h3 id="density">density</h3>
<p><span class="arg">self.</span>density= <span class="arg">string</span> or <span class="arg">geometry</span></p>
</div>
<div class="desc">
<h4>Description</h4>
<p>
Specifies the vertical and horizontal resolution in pixels. The default density is "72.0x72.0". This attribute can be used when writing JBIG, PCL, PS,
PS2, and PS3 format images.
</p>
<p>This attribute can also be used to specify the width and height of HISTOGRAM format images. For HISTOGRAM, the default is 256x200.</p>
<h4>Arguments</h4>
<p>
The argument can be either a string in the form "XxY" where "X" is the horizontal resolution and "Y" is the vertical resolution, or a
<a href="struct.html#Geometry">Geometry</a> object where <code>width</code> is the horizontal resolution and <code>height</code> is the vertical
resolution.
</p>
</div>
<div class="sig">
<h3 id="delay">delay</h3>
<p><span class="arg">self.</span>delay= <span class="arg">integer</span></p>
</div>
<div class="desc">
<h4>Description</h4>
<p class="imquote">
This attribute is useful for regulating the animation of image sequences. <em>delay</em>/100 seconds must expire before the display of the next image.
The default is no delay between each showing of the image sequence. The maximum delay is 65535.
</p>
</div>
<div class="sig">
<h3 id="depth">depth</h3>
<p><span class="arg">self.</span>depth= <span class="arg">integer</span></p>
</div>
<div class="desc">
<h4>Description</h4>
<p>Specifies the image depth.</p>
<h4>Arguments</h4>
<p>Either 8, 16, or 32. You can specify 16 and 32 only when ImageMagick was compiled with a QuantumDepth that allows these depth values.</p>
<p>
Use <code>depth</code> to specify the depth of CMYK, GRAY, RGB, RGBA, MAP, and XC format images. See also <a href="#size"><code>size</code></a
>.
</p>
</div>
<div class="sig">
<h3 id="dispose">dispose</h3>
<p><span class="arg">self.</span>dispose= <span class="arg">type</span></p>
</div>
<div class="desc">
<h4>Description</h4>
<p class="imquote">The argument indicates the way in which the graphic is to be treated after being displayed.</p>
<h4>Argument</h4>
<p>A <a href="constants.html#DisposeType">DisposeType</a> constant.</p>
</div>
<div class="sig">
<h3 id="dither">dither</h3>
<p>
<span class="arg">self.</span>dither= <span class="arg"><code>true</code></span> or
<span class="arg"><code>false</code></span>
</p>
</div>
<div class="desc">
<h4>Description</h4>
<p>This attribute can be used when writing GIF images.</p>
<p class="imquote">
Apply Floyd/Steinberg error diffusion to the image. The basic strategy of dithering is to trade intensity resolution for spatial resolution by averaging
the intensities of several neighboring pixels. Images which suffer from severe contouring when reducing colors can be improved with this option.
</p>
</div>
<div class="sig">
<h3 id="endian">endian</h3>
<p><span class="arg">self</span>.endian= <span class="arg">type</span></p>
</div>
<div class="desc">
<h4>Description</h4>
<p>Specify the endian of the image when reading the image file.</p>
<h4>Argument</h4>
<p>One of the following Magick::EndianType enum values:</p>
<ul>
<li>MSBEndian</li>
<li>LSBEndian</li>
</ul>
</div>
<div class="sig">
<h3 id="extract">extract</h3>
<p>
<span class="arg"><em>self.</em></span
>extract= <span class="arg">string</span> or
<span class="arg">geometry</span>
</p>
</div>
<div class="desc">
<h4>Description</h4>
<p>
Specifies a portion of an image to be extracted when the image is constituted. This attribute can be used to identify a subset of an image that is
otherwise too large to keep in memory.
</p>
<h4>Arguments</h4>
<p>
Either a geometry string or a
<a href="struct.html#Geometry">Geometry</a> object. For example: <code>options.extract = "200x200+100+100"</code>.
</p>
</div>
<div class="sig">
<h3 id="filename">filename</h3>
<p><span class="arg">self.</span>filename= <span class="arg">string</span></p>
</div>
<div class="desc">
<h4>Description</h4>
<p>See <a href="image1.html#capture">capture</a>.</p>
</div>
<div class="sig">
<h3 id="fill">fill</h3>
<p>
<span class="arg">self.</span>fill= <span class="arg">string</span> or
<span class="arg">pixel</span>
</p>
</div>
<div class="desc">
<h4>Description</h4>
<p>Specifies the fill color to use when creating an image with the "caption:" format..</p>
<h4>Arguments</h4>
<p>A <a href="imusage.html#color_names">color name</a> or a <a href="struct.html#Pixel">pixel</a>.</p>
</div>
<div class="sig">
<h3 id="font">font</h3>
<p><span class="arg">self.</span>font= <span class="arg">string</span></p>
</div>
<div class="desc">
<h4>Description</h4>
<p>Set the text rendering font.</p>
</div>
<div class="sig">
<h3 id="format">format</h3>
<p><span class="arg">self.</span>format= <span class="arg">string</span></p>
</div>
<div class="desc">
<h4>Description</h4>
<p>Set the image format, "GIF" or "JPG" for example.</p>
<h4>Arguments</h4>
<p>
See
<a href="https://www.imagemagick.org/script/formats.php">File Formats</a>.
</p>
</div>
<div class="sig">
<h3 id="fuzz">fuzz</h3>
<p>
<span class="arg">self.</span>fuzz= <span class="arg">number</span> or
<span class="arg">string</span>
</p>
</div>
<div class="desc">
<h4>Description</h4>
<p>
Set the level of "fuzziness" for comparing pixels. By default the pixels must be identical to be considered equal. The larger the
<code>fuzz</code> value the more difference is tolerated. See <a href="imageattrs.html#fuzz">Image#fuzz</a>.
</p>
<h4>Arguments</h4>
<p>
The argument may be a numeric value or a string in the form "NN%". In the second case, the argument is computed as a percentage of
<a href="constants.html#Miscellaneous_constants">QuantumRange</a>. For example, a value of '5%' sets <code>fuzz</code> to 0.05*QuantumRange.
</p>
</div>
<div class="sig">
<h3 id="gravity">gravity</h3>
<p><span class="arg">self.</span>gravity= <span class="arg">gravity</span></p>
</div>
<div class="desc">
<h4>Description</h4>
<p class="imquote">The direction text gravitates to when annotating the image.</p>
<p class="imquote">
The direction you choose specifies where to position the text when annotating the image. For example, a gravity of
<code>CenterGravity</code> forces the text to be centered within the image. By default, the image gravity is <code>NorthWestGravity</code>.
</p>
<p>This attribute can be used to position the text when creating an image with the "caption:" format.</p>
<h4>Arguments</h4>
<p>A <a href="constants.html#GravityType">GravityType</a> constant.</p>
</div>
<div class="sig">
<h3 id="image_type">image_type</h3>
<p>
<span class="arg">self.</span>image_type=
<span class="arg">image_type</span>
</p>
</div>
<div class="desc">
<h4>Description</h4>
<p>
The image type classification. For example, GrayscaleType. Don't confuse this attribute with the <a href="#format">format</a> such as "GIF" or "JPG".
</p>