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<h6 id="header">RMagick User's Guide and Reference</h6>
<div class="nav">
« <a href="index.html">Prev</a> | <a href=
"index.html">Contents</a> | <a href=
"imusage.html">Next</a> »
</div>
<h1>How to use RMagick</h1>
<div id="toc">
<h2>Table of Contents</h2>
<ul style="margin-left: 15px; padding-top: 1em">
<li><a href="#basics">Basic concepts</a></li>
<li><a href="#reading">Reading, writing, and creating
images</a></li>
<li><a href="#displaying">Displaying images</a></li>
<li><a href="#modifying">Examining and modifying
images</a></li>
<li><a href="#marshaling">Marshaling images</a></li>
<li><a href="#drawing_on">Drawing on and adding text to
images</a></li>
<li><a href="#more">Where to go from here</a></li>
</ul>
</div>
<h2 id="basics">Basic concepts</h2>
<p>Let's look at the RMagick equivalent of "Hello, world". This
program reads an image file named "Cheetah.jpg" and
displays<sup><a href="#display">1</a></sup> it on your
monitor.</p>
<pre class="example">
1. require 'RMagick'
2. include Magick
3.
4. cat = ImageList.new("Cheetah.jpg")
5. cat.display
6. exit
</pre>
<p class="example_cutline">MS Windows users note: The
<span style="font-style:normal">display</span> method does not
work on native MS Windows. You must use an external viewer to
view the images you create.</p>
<p>Line 1 requires the RMagick.rb file, which defines the
<b>Magick</b> module. The Magick module contains 3 major classes,
<b>ImageList</b>, <b>Image</b>, and <b>Draw</b>. This section -
<em>Basic Comcepts</em> - describes the ImageList and Image
classes. The Draw class is explained in the <em><a href=
"#drawing">Drawing on and adding text to images</a></em> section,
below.</p>
<p>The statement on line 5 creates an <em>imagelist</em> object
and initializes it by reading the <code>Cheetah.jpg</code> file
in the current directory. Line 6 sends the <code>display</code>
method to the object. When you send <code>display</code> to an
imagelist, it causes all the images in the imagelist to be
displayed on the default X Window screen. In this case, the
<code>display</code> method makes a picture of a cheetah appear
on your monitor.</p>
<p>Type this program in and try running it now. The
<code>Cheetah.jpg</code> file is in the <code>ex/images</code>
subdirectory where you installed the RMagick documentation.</p>
<p>The Image and ImageList classes are closely related. An
<em>Image</em> object describes one image or one frame in an
image with multiple frames. (An animated GIF or a Photoshop image
with multiple layers are examples of images with multiple
frames.) You can create a image object from an image file such as
a GIF, PNG, or JPEG. You can create a image from scratch by
specifying its dimensions. You can write an image to disk,
display it on a screen, change its size or orientation, convert
it to another format, or otherwise modify it using one of over
100 methods.</p>
<p>An <em>ImageList</em> object is a <em>list</em> of images. It
contains zero or more images and a <em>scene number</em>. The
scene number indicates the <em>current image</em>. The ImageList
class includes methods that operate on all the images in the
list. Also, with a very few exceptions, any method defined in the
Image class can be used as well. Since Image methods always
operate on a single image, when an Image method is sent to an
imagelist, the ImageList class sends the method to the current
image, that is, the image specified by the scene number.</p>
<p>The ImageList class is a subclass of the Array class, so you
can use most Array methods to change the images in the imagelist.
For example, you can use the <code><<</code> method to add
an image to the list.</p>
<p>Going back to the example, let's make one modification.</p>
<pre class="example">
1. require 'RMagick'
2. include Magick
3.
4. cat = ImageList.new("Cheetah.jpg")
5. smallcat = cat.minify
6. smallcat.display
7. exit
</pre>
<p>The difference is the statement on line 5. This statement
sends the <code>minify</code> method to the imagelist. The
<code>minify</code> method is an Image method that reduces the
size of an image to half its original size. Remember, since
<code>minify</code> is an Image method, the ImageList class sends
<code>minify</code> to the current (and only) image. The return
value is a new image, half the size of the original.</p>
<p>Line 6 demonstrates the Image class's <code>display</code>
method, which displays a single image on the X Window screen.
<code>Image#display</code> makes a picture of a (in this case,
small) cheetah appear on your monitor.</p>
<p>Here's how to write the small cheetah to a file in GIF
format.</p>
<pre class="example">
1. require 'RMagick'
2. include Magick
3.
4. cat = ImageList.new("Cheetah.jpg")
5. smallcat = cat.minify
6. smallcat.display
7. smallcat.write("Small-Cheetah.gif")
8. exit
</pre>
<p>The statement on line 7 writes the image to a file. Notice
that the filename extension is <code>gif</code>. When writing
images, ×Magick uses the filename extension to determine
what image format to write. In this example, the
<code>Small-Cheetah.gif</code> file will be in the GIF format.
Notice how easy it is to covert an image from one format to
another? (For more details, see <a href=
"imusage.html#formats">Image formats and filenames</a>.)</p>
<p>So why, in the previous example, did I create <code>cat</code>
as an ImageList object containing just one image, instead of
creating an Image object? No reason, really. When you only have
one image to deal with, imagelists and images are pretty much
interchangeable.</p>
<p><em><b>Note:</b></em> In most cases, an Image method does not
modify the image to which it is sent. Instead, the method returns
a new image, suitably modified. For example, the <a href=
"image3.html#resize"><code>resize</code></a> method returns a new
image, sized as specified. The receiver image is unaltered.
(Following the Ruby convention, when a method alters the receiver
object, the method name ends with "!". For example, the <a href=
"image3.html#resize_bang"><code>resize!</code></a> method resizes
the receiver in place.)</p>
<h2 id="reading">Reading, writing, and creating images</h2>
<p>You've already seen that you can create an imagelist and
initialize it by specifying the name of an image file as the
argument to <a href=
"ilist.html#new"><code>ImageList.new</code></a>. In fact,
<code>new</code> can take any number of file name arguments. If
the file contains a single image, <code>new</code> reads the
file, creates an image, and adds it to the imagelist. If the file
is a multi-frame image file, <code>new</code> adds an image for
each frame or layer in the file. Lastly, <code>new</code> changes
the scene number to point to the last image in the imagelist. In
the simple case, <code>new</code> reads a single image from a
file and sets the scene number to 0.</p>
<p>You can also create an image from scratch by calling <a href=
"image1.html#new"><code>Image.new</code></a>. This method takes 2
or 3 arguments. The first argument is the number of columns in
the new image (its width). The second argument is the number of
rows (its height). If present, the 3rd argument is a <a href=
"struct.html#fill"><code>Fill</code></a> object. To add a
"scratch" image to an imagelist, call <a href=
"ilist.html#new_image"><code>ImageList#new_image</code></a>. This
method calls <code>Image.new</code>, adds the new image to the
imagelist, and sets the scene number to point to the new image.
Scratch images are good for <a href="#drawing">drawing</a> on or
creating images by <a href=
"image1.html#composite">compositing</a>.</p>
<p>Like many other methods in the Image and ImageList classes,
<code>Image.new</code> accepts an optional block that can be used
to set additional optional parameters. If the block is present,
<code>Image.new</code> creates a <a href="info.html">parameter
object</a> and yields to the block in the scope of that object.
You set the parameters by calling attribute setter methods
defined in the parameter object's class. For example, you can set
the background color of a new image to red with the
<code>background_color=</code> method, as shown here:</p>
<pre class="example">
require 'RMagick'
include Magick
# Create a 100x100 red image.
f = Image.new(100,100) { self.background_color = "red" }
f.display
exit
</pre>
<p>Within the parameter block you must use <code>self</code> so
that Ruby can knows that this statement is a method call, not an
assignment to a variable.</p>
<p>You can create an image by capturing it from the XWindow
screen using <a href=
"image1.html#capture"><code>Image.capture</code></a>. This method
can capture the root window, a window identified by name or ID
number, or perform an interactive capture whereby you designate
the desired window by clicking it or by drawing a rectangle on
the screen with your mouse.</p>
<p>Both the Image class and the ImageList class have
<code>write</code> methods. Both accept a single argument, the
name of the file to be written. <a href=
"image3.html#write"><code>Image#write</code></a> simply writes
the image to a file. Like the <code>Image#read</code> method,
<code>write</code> yields to an optional block that you can use
to set parameters that control how the image is written.</p>
<p>If an ImageList object contains only one image, then <a href=
"ilist.html#write"><code>ImageList#write</code></a> is the same
as <code>Image#write</code>. However, if the imagelist contains
multiple images and the file format (determined by the file name
extension, as I mentioned earlier) supports multi-frame images,
<code>Image#write</code> will automatically create a multi-frame
image file.</p>
<p>For example, the following program reads three GIF files and
then uses <code>ImageList#write</code> to combine all the images
in those files (remember, each input file can contain multiple
images) into one animated GIF file.</p>
<pre class="example">
#! /usr/local/bin/ruby -w
require 'RMagick'
anim = ImageList.new("start.gif", "middle.gif", "finish.gif")
anim.write("animated.gif")
exit
</pre>
<h2 id="displaying">Displaying images</h2>
<p>RMagick defines 3 methods for displaying images and
imagelists. Both the Image class and the ImageList class have a
<code>display</code> method. The <a href=
"image1.html#display"><code>Image#display</code></a> method
displays the image on the default X Window screen. For imagelists
with just one image, <a href=
"ilist.html#display"><code>ImageList#display</code></a> is
identical to <code>Image#display</code>. However, if the
imagelist contains multiple images,
<code>ImageList#display</code> displays each of the images in
turn. With both methods, right-clicking the display window will
produce a menu of other options.</p>
<p>The <a href=
"ilist.html#animate"><code>ImageList#animate</code></a> method
repeatedly cycles through all the images in an imagelist,
displaying each one in turn. You can control the speed of the
animation with the <a href=
"ilist.html#delay_eq"><code>ImageList#delay=</code></a>
method.</p>
<h2 id="modifying">Examining and modifying images</h2>
<p>Once you've created an image or imagelist, what can you do
with it? The Image and ImageList classes define over 100 methods
for examining and modifying images, both individually and in
groups. Remember, unless the ImageList class defines a method
with the same name, you can send any method defined in the Image
class to an instance of the ImageList class. The ImageList class
sends the method to the current image and returns the result.</p>
<p>The methods can be classified into the following broad groups.
ImageList method descriptions look like <span class=
"ilist">this</span>. Some of the listed methods are not available
in some releases of ×Magick. See the method documentation
for details.</p>
<div id="index">
<h4>Utility methods</h4>
<dl>
<dt><a href="image1.html#spaceship"><=></a></dt>
<dd>Compare 2 images</dd>
<dt class="ilist"><a href=
"ilist.html#spaceship"><=></a></dt>
<dd class="ilist">Compare 2 imagelists</dd>
<dt><a href="image1.html#aref">[ ]</a></dt>
<dd>Reference an image property</dd>
<dt><a href="image1.html#aset">[ ]=</a></dt>
<dd>Set an image property</dd>
<dt><a href="image1.html#changed_q">changed?</a></dt>
<dd>Has the image been changed?</dd>
<dt><a href="image1.html#channel">channel</a></dt>
<dd>Extract a color channel from the image</dd>
<dt><a href=
"image1.html#compare_channel">compare_channel</a></dt>
<dd>Compare one or more channels between two images</dd>
<dt><a href=
"image1.html#channel_depth">channel_depth</a></dt>
<dd>Return the depth of the specified channel or
channels</dd>
<dt><a href=
"image1.html#channel_extrema">channel_extrema</a></dt>
<dd>Return the maximum and minimum intensity values for one
or more channels in the image</dd>
<dt><a href="image1.html#clone">clone</a></dt>
<dd>Return a shallow copy of the image</dd>
<dt class="ilist"><a href="ilist.html#clone">clone</a></dt>
<dd class="ilist">Return a shallow copy of the imagelist</dd>
<dt><a href=
"image1.html#color_histogram">color_histogram</a></dt>
<dd>Count the number of times each unique color appears in
the image</dd>
<dt><a href="image1.html#copy">copy</a></dt>
<dd>Return a deep copy of the image</dd>
<dt class="ilist"><a href="ilist.html#copy">copy</a></dt>
<dd class="ilist">Return a deep copy of the imagelist</dd>
<dt><a href="image1.html#difference">difference</a></dt>
<dd>Compute the difference between two images</dd>
<dt><a href="image1.html#dup">dup</a></dt>
<dd>Return a shallow copy of the image</dd>
<dt class="ilist"><a href="ilist.html#dup">dup</a></dt>
<dd class="ilist">Return a shallow copy of the imagelist</dd>
<dt><a href="image1.html#each_profile">each_profile</a></dt>
<dd>Iterate over all the profiles associated with the
image</dd>
<dt><a href=
"image2.html#export_pixels">export_pixels</a></dt>
<dd>Extract pixel data from the image into an array</dd>
<dt><a href=
"image2.html#get_exif_by_entry">get_exif_by_entry</a>,
<a href=
"image2.html#get_exif_by_number">get_exif_by_number</a></dt>
<dd>Get one or more EXIF property values for the image</dd>
<dt><a href="image2.html#get_pixels">get_pixels</a></dt>
<dd>Copy a region of pixels from the image</dd>
<dt><a href="image2.html#gray_q">gray?</a></dt>
<dd>Are all the pixels in the image gray?</dd>
<dt><a href=
"image2.html#import_pixels">import_pixels</a></dt>
<dd>Replace pixels in the image with pixel data from an
array</dd>
<dt><a href="image2.html#monochrome_q">monochrome?</a></dt>
<dd>Are all the pixels in the image either black or
white?</dd>
<dt><a href="image2.html#opaque_q">opaque?</a></dt>
<dd>Are all the pixels in the image opaque?</dd>
<dt><a href="image2.html#palette_q">palette?</a></dt>
<dd>Is the image a PseudoClass type image with 256 colors or
less?</dd>
<dt><a href="image3.html#preview">preview</a></dt>
<dd>Show the effect of a transformation method on the
image</dd>
<dt><a href="image3.html#profile_bang">profile!</a></dt>
<dd>Add or remove an ICM, IPTC, or generic profile from the
image</dd>
<dt><a href="image3.html#properties">properties</a></dt>
<dd>Iterate over all the properties associated with the
image</dd>
<dt><a href=
"image3.html#set_channel_depth">set_channel_depth</a></dt>
<dd>Set the specified channel's depth</dd>
<dt><a href="image3.html#signature">signature</a></dt>
<dd>Compute the 64-byte message signature for the image</dd>
<dt><a href="image3.html#statistics">statistics</a></dt>
<dd>Compute image statistics</dd>
<dt><a href="image3.html#store_pixels">store_pixels</a></dt>
<dd>Replace a region of pixels in the image</dd>
<dt><a href="image3.html#strip_bang">strip!</a></dt>
<dd>Strip the image of all comments and profiles</dd>
<dt><a href="image3.html#view">view</a></dt>
<dd>Access pixels by their coordinates.</dd>
</dl>
<h4>Reduce the number of colors</h4>
<dl>
<dt><a href=
"image1.html#compress_colormap_bang">compress_colormap!</a></dt>
<dd>Remove duplicate or unused entries in the image's
colormap</dd>
<dt><a href=
"image2.html#grayscale_pseudo_class">grayscale_pseudo_class</a></dt>
<dd>Convert the image to a grayscale PseudoClass image.</dd>
<dt><a href="image2.html#map">map</a></dt>
<dd>Replace the colors of the image with the nearest colors
from a reference image</dd>
<dt class="ilist"><a href="ilist.html#map">map</a></dt>
<dd class="ilist">Replace the colors of all the images in the
imagelist with the nearest colors from a reference image</dd>
<dt><a href=
"image2.html#ordered_dither">ordered_dither</a></dt>
<dd>Reduce the image to monochrome using the ordered dither
technique</dd>
<dt><a href="image2.html#posterize">posterize</a></dt>
<dd>Reduce the number of colors for a "poster" effect</dd>
<dt><a href="image3.html#quantize">quantize</a></dt>
<dd>Choose a fixed number of colors to represent the
image</dd>
<dt class="ilist"><a href=
"ilist.html#quantize">quantize</a></dt>
<dd class="ilist">Choose a fixed number of colors to
represent all the images in the imagelist</dd>
</dl>
<h4>Resize</h4>
<dl>
<dt><a href=
"image1.html#change_geometry">change_geometry</a></dt>
<dd>Compute a new constrained size for the image</dd>
<dt><a href="image2.html#magnify">magnify</a></dt>
<dd>Double the size of the image</dd>
<dt><a href="image2.html#minify">minify</a></dt>
<dd>Halve the size of the image</dd>
<dt><a href="image3.html#resize">resize</a></dt>
<dd>Resize the image using a filter</dd>
<dt><a href="image3.html#sample">sample</a></dt>
<dd>Resize the image using pixel sampling</dd>
<dt><a href="image3.html#scale">scale</a></dt>
<dd>Resize the image</dd>
<dt><a href="image3.html#thumbnail">thumbnail</a></dt>
<dd>Quickly create a thumbnail of the image</dd>
</dl>
<h4>Change colors or opacity</h4>
<dl>
<dt><a href=
"image1.html#color_fill_to_border">color_fill_to_border</a></dt>
<dd>Change the color of neighboring pixels. Stop at the
image's border color.</dd>
<dt><a href=
"image1.html#color_floodfill">color_floodfill</a></dt>
<dd>Change the color of neighboring pixels that are the same
color</dd>
<dt><a href="image1.html#colormap">colormap</a></dt>
<dd>Get or set a color in the image's colormap</dd>
<dt><a href="image1.htlm#color_point">color_point</a></dt>
<dd>Change the color of a single pixel in the image</dd>
<dt><a href=
"image1.html#color_reset_bang">color_reset!</a></dt>
<dd>Set the entire image to a single color</dd>
<dt><a href=
"image1.html#cycle_colormap">cycle_colormap</a></dt>
<dd>Displace the image's colormap</dd>
<dt><a href="image1.html#erase_bang">erase!</a></dt>
<dd>Set the entire image to a single color</dd>
<dt><a href=
"image2.html#matte_fill_to_border">matte_fill_to_border</a></dt>
<dd>Make transparent neighboring pixels. Stop at the image's
border color.</dd>
<dt><a href=
"image2.html#matte_floodfill">matte_floodfill</a></dt>
<dd>Make transparent neighboring pixels that are the same
color</dd>
<dt><a href="image2.html#matte_point">matte_point</a></dt>
<dd>Make a single pixel transparent</dd>
<dt><a href=
"image2.html#matte_reset_bang">matte_reset!</a></dt>
<dd>Make the entire image transparent</dd>
<dt><a href="image2.html#opaque">opaque</a></dt>
<dd>Change all pixels from the specified color to a new
color</dd>
<dt><a href="image2.html#pixel_color">pixel_color</a></dt>
<dd>Get or set the color of a single pixel</dd>
<dt><a href="image3.html#splice">splice</a></dt>
<dd>Splice a solid color into the image.</dd>
<dt><a href=
"image3.html#texture_fill_to_border">texture_fill_to_border</a></dt>
<dd>Replace neighbor pixels with pixels from a texture image.
Stop at the image's border color.</dd>
<dt><a href=
"image3.html#texture_floodfill">texture_floodfill</a></dt>
<dd>Replace neighboring pixels that are the same color with
pixels from a texture image</dd>
<dt><a href="image3.html#transparent">transparent</a></dt>
<dd>Change the opacity value of pixels having the specified
color</dd>
</dl>
<h4>Rotate or shear</h4>
<dl>
<dt><a href=
"image1.html#affine_transform">affine_transform</a></dt>
<dd>Transform the image as dictated by an affine matrix</dd>
<dt><a href="image3.html#rotate">rotate</a></dt>
<dd>Rotate the image by the specified angle</dd>
<dt><a href="image3.html#shear">shear</a></dt>
<dd>Shear the image along the X or Y axis, creating a
parallelogram</dd>
</dl>
<h4>Transform</h4>
<dl>
<dt class="ilist"><a href="ilist.html#append">append</a></dt>
<dd class="ilist">Append all the images in the imagelist into
a single image</dd>
<dt class="ilist"><a href=
"ilist.html#average">average</a></dt>
<dd class="ilist">Average all the images in the imagelist
into a single image</dd>
<dt><a href="image1.html#chop">chop</a></dt>
<dd>Chop a region from the image</dd>
<dt class="ilist"><a href=
"ilist.html#coalesce">coalesce</a></dt>
<dd class="ilist">Merge successive images in the imagelist
into a new imagelist</dd>
<dt><a href="image1.html#composite">composite</a></dt>
<dd>Composite the image onto another image</dd>
<dt><a href=
"image1.html#composite_affine">composite_affine</a></dt>
<dd>Composite the image onto another image as dictated by an
affine matrix</dd>
<dt><a href="image1.html#crop">crop</a></dt>
<dd>Extract a region from the image</dd>
<dt class="ilist"><a href=
"ilist.html#deconstruct">deconstruct</a></dt>
<dd class="ilist">Construct a new imagelist containing images
that include only the changed pixels between each image and
its successor</dd>
<dt class="ilist"><a href=
"ilist.html#flatten_images">flatten_images</a></dt>
<dd class="ilist">Merge all the images in the imagelist into
a single image</dd>
<dt><a href="image2.html#flip">flip</a></dt>
<dd>Create a vertical mirror image</dd>
<dt><a href="image2.html#flop">flop</a></dt>
<dd>Create a horizontal mirror image</dd>
<dt class="ilist"><a href="ilist.html#mosaic">mosaic</a></dt>
<dd class="ilist">Inlay all the images in the imagelist into
a single image</dd>
<dt><a href="image3.html#roll">roll</a></dt>
<dd>Offset the image</dd>
<dt><a href="image3.html#shave">shave</a></dt>
<dd>Shave regions from the edges of the image</dd>
<dt><a href="image3.html#trim">trim</a></dt>
<dd>Remove borders from the edges of the image</dd>
</dl>
<h4>Enhance</h4>
<dl>
<dt><a href="image1.html#contrast">contrast</a></dt>
<dd>Enhance the intensity differences between the lighter and
darker elements in the image</dd>
<dt><a href="image1.html#despeckle">despeckle</a></dt>
<dd>Reduce the speckle noise in the image</dd>
<dt><a href="image2.html#enhance">enhance</a></dt>
<dd>Apply a digital filter that improves the quality of a
noisy image</dd>
<dt><a href="image2.html#equalize">equalize</a></dt>
<dd>Apply a histogram equalization to the image</dd>
<dt><a href="image2.html#gamma_correct">gamma_correct</a>,
<a href="image2.html#gamma_channel">gamma_channel</a></dt>
<dd>Gamma correct the image</dd>
<dt><a href="image2.html#level">level</a></dt>
<dd>Adjust the levels of the image</dd>
<dt><a href=
"image2.html#level_channel">level_channel</a></dt>
<dd>Adjust the levels of one or more channels in the
image</dd>
<dt><a href=
"image2.html#median_filter">median_filter</a></dt>
<dd>Apply a digital filter that improves the quality of a
noisy image</dd>
<dt><a href="image2.html#modulate">modulate</a></dt>
<dd>Change the brightness, saturation, or hue of the
image</dd>
<dt><a href="image2.html#negate">negate</a>, <a href=
"image2.html#negate_channel">negate_channel</a></dt>
<dd>Negate the colors of the image</dd>
<dt><a href="image2.html#normalize">normalize</a>, <a href=
"image2.html#normalize_channel">normalize_channel</a></dt>
<dd>Enhance the contrast of the image</dd>
<dt><a href="image3.html#reduce_noise">reduce_noise</a></dt>
<dd>Smooth the contours of an image while still preserving
edge information</dd>
<dt><a href="image3.html#sharpen">sharpen</a>, <a href=
"image3.html#sharpen_channel">sharpen_channel</a>, <a href=
"image3.html#unsharp_mask">unsharp_mask</a>, <a href=
"image3.html#unsharp_mask_channel">unsharp_mask_channel</a></dt>
<dd>Sharpen the image</dd>
<dt><a href=
"image3.html#sigmoidal_contrast_channel">sigmoidal_contrast_channel</a></dt>
<dd>Adjusts the contrast of an image channel with a
non-linear sigmoidal contrast algorithm</dd>
</dl>
<h4>Add effects</h4>
<dl>
<dt><a href=
"image1.html#adaptive_threshold">adaptive_threshold</a></dt>
<dd>Threshold an image whose global intensity histogram
doesn't contain distinctive peaks</dd>
<dt><a href="image1.html#add_noise">add_noise</a></dt>
<dd>Add random noise</dd>
<dt><a href=
"image1.html#bilevel_channel">bilevel_channel</a></dt>
<dd class="imquote">Change the value of individual image
pixels based on the intensity of each pixel channel</dd>
<dt><a href=
"image1.html#black_threshold">black_threshold</a></dt>
<dd>Force all pixels below the threshold into black</dd>
<dt><a href="image1.html#blur_image">blur_image</a>, <a href=
"image1.html#blur_channel">blur_channel</a>, <a href=
"image2.html#gaussian_blur">gaussian_blur</a>, <a href=
"image2.html#gaussian_blur_channel">gaussian_blur_channel</a>,
<a href="image3.html#motion_blur">motion_blur</a>, <a href=
"image3.html#radial_blur">radial_blur</a></dt>
<dd>Blur the image</dd>
<dt><a href="image1.html#colorize">colorize</a></dt>
<dd>Blend the fill color with each pixel in the image</dd>
<dt><a href="image1.html#convolve">convolve</a>, <a href=
"image1.html#convolve_channel">convolve_channel</a></dt>
<dd>Apply a custom convolution kernel to the image</dd>
<dt><a href="image3.html#segment">segment</a></dt>
<dd>Segment an image by analyzing the histograms of the color
components and identifying units that are homogeneous with
the fuzzy c-means technique</dd>
<dt><a href="image3.html#random_threshold_channel">
random_threshold_channel</a></dt>
<dd>Change the value of individual pixels based on the
intensity of each pixel compared to a random threshold.</dd>
<dt><a href="image3.html#threshold">threshold</a></dt>
<dd>Change the value of individual pixels based on the
intensity of each pixel compared to threshold</dd>
<dt><a href=
"image3.html#white_threshold">white_threshold</a></dt>
<dd>Force all pixels above the threshold into white</dd>
</dl>
<h4>Add special effects</h4>
<dl>
<dt><a href="image1.html#charcoal">charcoal</a></dt>
<dd>Add a charcoal effect</dd>
<dt><a href="image1.html#edge">edge</a></dt>
<dd>Find edges in the image</dd>
<dt><a href="image1.html#emboss">emboss</a></dt>
<dd>Add a three-dimensional effect</dd>
<dt><a href="image2.html#implode">implode</a></dt>
<dd>Implode or explode the center pixels in the image</dd>
<dt class="ilist"><a href="ilist.html#morph">morph</a></dt>
<dd class="ilist">Transform each image in the imagelist to
the next in sequence by creating intermediate images</dd>
<dt><a href="image2.html#oil_paint">oil_paint</a></dt>
<dd>Add an oil paint effect</dd>
<dt><a href="image3.html#sepiatone">sepiatone</a></dt>
<dd>Applies an effect similar to the effect achieved in a
photo darkroom by sepia toning.</dd>
<dt><a href="image3.html#shade">shade</a></dt>
<dd>Shine a distant light on an image to create a
three-dimensional effect</dd>
<dt><a href="image3.html#shadow">shadow</a></dt>
<dd>Add a shadow to an image</dd>
<dt><a href="image3.html#solarize">solarize</a></dt>
<dd>Apply a special effect to the image, similar to the
effect achieved in a photo darkroom by selectively exposing
areas of photo sensitive paper to light</dd>
<dt><a href="image3.html#spread">spread</a></dt>
<dd>Randomly displace each pixel in a block</dd>
<dt><a href="image3.html#stegano">stegano</a></dt>
<dd>Hide a digital watermark within the image</dd>
<dt><a href="image3.html#stereo">stereo</a></dt>
<dd>Combine two images into a single image that is the
composite of a left and right image of a stereo pair</dd>
<dt><a href="image3.html#swirl">swirl</a></dt>
<dd>Swirl the pixels about the center of the image</dd>
<dt><a href="image3.html#wave">wave</a></dt>
<dd>Add a ripple effect to the image</dd>
</dl>
<h4>Decorate</h4>
<dl>
<dt><a href="image1.html#border">border</a></dt>
<dd>Surround the image with a solid-colored border</dd>
<dt><a href="image2.html#frame">frame</a></dt>
<dd>Add a simulated three-dimensional border around the
image</dd>
<dt><a href="image3.html#raise">raise</a></dt>
<dd>Create a simulated three-dimensional button-like effect
by lightening and darkening the edges of the image</dd>
</dl>
<h4>Create thumbnail montages</h4>
<dl>
<dt class="ilist"><a href=
"ilist.html#montage">montage</a></dt>
<dd class="ilist">Tile image thumbnails across a canvas</dd>
</dl>
<h4>Create image blobs</h4>
<dl>
<dt><a href="image1.html#from_blob">from_blob</a></dt>
<dd>Create an image from a BLOB</dd>
<dt class="ilist"><a href=
"ilist.html#from_blob">from_blob</a></dt>
<dd class="ilist">Create an imagelist from one or more
BLOBs</dd>
<dt><a href="image3.html#to_blob">to_blob</a></dt>
<dd>Construct a BLOB from an image</dd>
<dt class="ilist"><a href=
"ilist.html#to_blob">to_blob</a></dt>
<dd class="ilist">Construct a BLOB from all the images in the
imagelist</dd>
</dl>
</div>
<h2 id="marshaling">Marshaling images</h2>
<p>Image and ImageList objects can be serialized using Ruby's
<code>Marshal</code> module. Marshaling is supported via
×Magick's Binary Large OBject functions
<code>ImageToBlob</code> (for dumping) and
<code>BlobToImage</code> (for loading).</p>
<h4>Notes</h4>
<ol>
<li>Some image formats cannot be dumped. The only way to be
sure it will work is to try it.</li>
<li>Images in lossy formats, such as JPEG, will have a
different signature after being reconstituted and therefore
will not compare equal (using <a href=
"image1.html#spaceship"><=></a>) to the original
image.</li>
</ol>
<h2 id="drawing_on">Drawing on and adding text to images</h2>
<p>The <strong>Draw</strong> class is the third major class in
the Magick module. This class defines two kinds of methods,
<a href="#drawing">drawing</a> methods and <a href=
"#annotation">annotation</a> methods.</p>
<h3 id="drawing">Drawing</h3>
<p>×Magick supports a set of 2D drawing commands that are
very similar to the commands and elements defined by the W3C's
<a href="http://www.w3.org/TR/SVG/index.html#minitoc">Scalable
Vector Graphics (SVG) 1.1 Specification</a>. In RMagick, each
command (called a <em>primitive</em>) is implemented as a method
in the <code>Draw</code> class. To draw on an image, simply</p>
<ol>
<li>Create an instance of the <code>Draw</code> class.</li>
<li>Call one or more primitive methods with the appropriate
arguments.</li>
<li>Call the <a href="draw.html#draw"><code>draw</code></a>
method.</li>
</ol>
<p>The primitive methods do <em>not</em> draw anything directly.
When you call a primitive method, you are simply adding the
primitive and its arguments to a list of primitives stored in the
<code>Draw</code> object. To "execute" the primitive list, call
<code>draw</code>. Drawing the primitives does not destroy them.
You can draw on another image by calling <code>draw</code> again,
specifying a different image as the "canvas." Of course you can
also draw on an image with multiple <code>Draw</code> objects,
too. The canvas can be any image or imagelist, created by reading
an image file or from scratch using
<code>ImageList#new_image</code> or <code>Image.new</code>. (If
you pass an imagelist object to <code>draw</code>, it draws on
the current image.)</p>
<div id="axes">
<a href="javascript:popup('axes.rb.html')"><img src=
"ex/axes.gif" alt="Drawing coordinate system" title=
"Click to see the example script" /></a>
<div>
<p>Here's an illustration of the default drawing coordinate
system. The origin is in the top left corner. The x axis
extends to the right. The y axis extends downward. The units
are pixels. 0° is at 3 o'clock and rotation is clockwise.
The units of rotation are usually degrees.<sup><a href=
"#degrees">2</a></sup></p>
<p>You can change the default coordinate system by specifying
a <em>scaling</em>, <em>rotation</em>, or
<em>translation</em> transformation.</p>
<p><em>(Click the image to see the Ruby program that created
it.)</em></p>
</div>
</div>
<p>RMagick's primitive methods include methods for drawing
points, lines, Bezier curves, shapes such as ellipses and
rectangles, and text. Shapes and lines have a fill color and a
stroke color. Shapes are filled with the fill color unless the
fill opacity is 0. Similarly, shapes are stroked with the stroke
color unless the stroke opacity is 0. Text is considered a shape
and is stroked and filled. Other rendering properties you can set
include the stroke width, antialiasing, stroke patterns, and fill
patterns.</p>
<p>As an example, here's the section of the Ruby program that
created the circle in the center of the above image.</p>
<pre class="example">
1. !# /usr/local/bin/ruby -w
2. require 'RMagick'
3.
4. canvas = Magick::ImageList.new
5. canvas.new_image(250, 250, Magick::HatchFill.new('white', 'gray90'))
6.
7. circle = Magick::Draw.new
8. circle.stroke('tomato')
9. circle.fill_opacity(0)
10. circle.stroke_opacity(0.75)
11. circle.stroke_width(6)
12. circle.stroke_linecap('round')
13. circle.stroke_linejoin('round')
14. circle.ellipse(canvas.rows/2,canvas.columns/2, 80, 80, 0, 315)
15. circle.polyline(180,70, 173,78, 190,78, 191,62)
16. circle.draw(canvas)
</pre>
<p>The statements on lines 4 and 5 create the drawing canvas with
a single 250x250 image. The <code>HatchFill</code> object fills
the image with light-gray lines 10 pixels apart. The statement on
line 7 creates a Draw object. The method calls on lines 8-15
construct a list of primitives that are "executed" by the
<code>draw</code> method call on line 16.</p>
<p>The <code>stroke</code> method sets the stroke color, as seen
on line 8. Normally, shapes are filled (opacity = 1.0), but the
call to <code>fill_opacity</code> on line 9 sets the opacity to
0, so the background will show through the circle. Similarly, the
stroke lines are normally opaque, but the tomato-colored stroke
line in this example is made slightly transparent by the call to
<code>stroke_opacity</code> on line 10. The method calls on lines
11 through 13 set the stroke width and specify the appearance of
the line ends and corners.</p>
<p>The <code>ellipse</code> method call on line 14 describes an
circle in the center of the canvas with a radius of 80 pixels.
The ellipse occupies 315° of a circle, starting at 0°
(that is, 3 o'clock). The <code>polyline</code> call on line 15
adds the arrowhead to the circle. The arguments (always an even
number) are the x- and y-coordinates of the points the line
passes through.</p>
<p>Finally, the <code>draw</code> method on line 16 identifies
the canvas to be drawn on and executes the stored primitives.</p>
<h3 id="annotation">Annotation</h3>
<p>The <a href="draw.html#annotate"><code>annotate</code></a>
method draws text on an image. In its simplest form,
<code>annotate</code> requires only arguments that describe where
to draw the text and the text string.</p>
<p>Most of the time, you'll want to specify text properties such
as the font, its size, font styles such as italic, font weights
such as bold, the fill and stroke color, etc. The Draw class
defines <a href="draw.html#attribute_writers">attribute
writers</a> for this purpose. You can set the desired text
properties by calling the attribute writers before calling
<code>annotate</code>, or you can call them in an image block
associated with the <code>annotate</code> call.</p>
<p>The following example shows how to use <code>annotate</code>
to produce this image.</p>
<div id="rubyname">
<a href="javascript:popup('rubyname.rb.html')"><img src=
"ex/rubyname.gif" alt="annotate example" title=
"Click to see the example script" /></a>
</div>
<pre class="example">
1. #! /usr/local/bin/ruby -w
2. require 'RMagick'
3.
4. # Demonstrate the annotate method
5.
6. Text = 'RMagick'
7.
8. granite = Magick::ImageList.new('granite:')
9. canvas = Magick::ImageList.new
10. canvas.new_image(300, 100, Magick::TextureFill.new(granite))
11.
12. text = Magick::Draw.new
13. text.font_family = 'helvetica'
14. text.pointsize = 52
15. text.gravity = Magick::CenterGravity
16.
17. text.annotate(canvas, 0,0,2,2, Text) {
18. self.fill = 'gray83'
19. }
20.
21. text.annotate(canvas, 0,0,-1.5,-1.5, Text) {
22. self.fill = 'gray40'
23. }
24.
25. text.annotate(canvas, 0,0,0,0, Text) {
26. self.fill = 'darkred'
27. }
28.
29. canvas.write('rubyname.gif')
30. exit
</pre>
<p>This program uses three calls to <code>annotate</code> to
produce the "etched" appearance. All three calls have some
parameters in common but the fill color and location are
different.</p>
<p>First, the statements in lines 8-10 create the background. See
<a href="struct.html#fill"><code>Fill classes</code></a> for
information about the <code>TextureFill</code> class. The
"granite:" image format is one of ×Magick's built-in image
formats. See <a href="imusage.html#builtin_formats">"Built-in
image formats"</a> for more information. The statement on line 12
creates the Draw object that does the annotation. The next 3
lines set the values of the attributes that are common to all 3
<code>annotate</code> calls.</p>
<p>The first <code>annotate</code> argument is the image on which
the text will be drawn. Arguments 2-5, <code>width</code>,
<code>height</code>, <code>x</code>, and <code>y</code>, describe
a rectangle about which the text is drawn. This rectangle,
combined with the value of <code>gravity</code>, define the
position of the text. When the <code>gravity</code> value is
<a href=
"constants.html#GravityType"><code>CenterGravity</code></a> the
values of <code>width</code> and <code>height</code> are
unused.</p>
<p>The first call to <code>annotate</code>, on lines 17-19, draws
the text 2 pixels to the right and down from the center. The
<code>self.fill = 'gray83'</code> statement sets the text color
to light gray. The second call to <code>annotate</code>, on lines
21-22, draws dark gray text 1.5 pixels to the left and up from
the center. The last call, on lines 25-27, draws the text a third
time, in dark red, exactly in the center of the image.</p>
<h2 id="more">Where to go from here</h2>
<p>The next section, <a href=
"imusage.html">"ImageMagick/GraphicsMagick Conventions,"</a>
describes some conventions that you need to know, such as how
×Magick determines the graphic format of an image file,
etc. The ImageMagick (www.imagemagick.org) and GraphicsMagick
(www.graphicsmagick.org) web sites (from which much of the
information in these pages has been taken) offers a lot of detail
about ×Magick. While these web sites don't describe
RMagick, you can often use the documentation to learn more about
a RMagick method by reading about the Magick API the method
calls. (In the Reference section of this document, most of the
method descriptions include the name of the Magick API that the
method calls.) Check out the example programs. Almost every one
of the methods is demonstrated in one of the examples.</p>
<p>Good luck!</p>
<div>
<h5 id="footnotes">Footnotes</h5>
<p id="display"><sup>1</sup>The <code>display</code> and
<code>animate</code> methods do not work on MS Windows. You
will have to write the image to a file and view it with a
separate image viewer.</p>
<p id="degrees"><sup>2</sup>The rotation attributes
<code>rx</code> and <code>ry</code> in the <a href=
"struct.html#AffineMatrix"><code>AffineMatrix</code></a> class
use radians instead of degrees.</p>
</div>
<p class="spacer"> </p>
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