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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta name="generator" content=
"HTML Tidy for Linux/x86 (vers 6 November 2007), see www.w3.org" />
<title>RMagick 0.0.0: class Image::Info - Optional method
arguments</title>
<meta http-equiv="Content-Type" content=
"text/html; charset=us-ascii" />
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<meta name="Copyright" content=
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<body>
<h6 id="header">RMagick 0.0.0 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="#monitor">monitor</a></li>
<li><a href="#monochrome">monochrome</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>
img = Magick::Image.new(10,10) do
self['user'] = __FILE__ + ':' + __LINE__.to_s
end » 10x10 DirectClass 16-bit user:test.rb:3
</pre>
<p>These methods propogate 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>
self["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>
self["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>
self.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>
self.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>
img = Magick::Image.read("xc:white") do
self.caption = "a new caption"
self.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 endianess 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>self.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=
"http://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=