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<a name="Displaying-Images"></a>
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<p>
Next: <a href="Representing-Images.html#Representing-Images" accesskey="n" rel="next">Representing Images</a>, Previous: <a href="Loading-and-Saving-Images.html#Loading-and-Saving-Images" accesskey="p" rel="prev">Loading and Saving Images</a>, Up: <a href="Image-Processing.html#Image-Processing" accesskey="u" rel="up">Image Processing</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="Displaying-Images-1"></a>
<h3 class="section">32.2 Displaying Images</h3>
<p>A natural part of image processing is visualization of an image.
The most basic function for this is the <code>imshow</code> function that
shows the image given in the first input argument.
</p>
<a name="XREFimshow"></a><dl>
<dt><a name="index-imshow"></a>Function File: <em></em> <strong>imshow</strong> <em>(<var>im</var>)</em></dt>
<dt><a name="index-imshow-1"></a>Function File: <em></em> <strong>imshow</strong> <em>(<var>im</var>, <var>limits</var>)</em></dt>
<dt><a name="index-imshow-2"></a>Function File: <em></em> <strong>imshow</strong> <em>(<var>im</var>, <var>map</var>)</em></dt>
<dt><a name="index-imshow-3"></a>Function File: <em></em> <strong>imshow</strong> <em>(<var>rgb</var>, …)</em></dt>
<dt><a name="index-imshow-4"></a>Function File: <em></em> <strong>imshow</strong> <em>(<var>filename</var>)</em></dt>
<dt><a name="index-imshow-5"></a>Function File: <em></em> <strong>imshow</strong> <em>(…, <var>string_param1</var>, <var>value1</var>, …)</em></dt>
<dt><a name="index-imshow-6"></a>Function File: <em><var>h</var> =</em> <strong>imshow</strong> <em>(…)</em></dt>
<dd><p>Display the image <var>im</var>, where <var>im</var> can be a 2-dimensional
(grayscale image) or a 3-dimensional (RGB image) matrix.
</p>
<p>If <var>limits</var> is a 2-element vector <code>[<var>low</var>, <var>high</var>]</code>,
the image is shown using a display range between <var>low</var> and
<var>high</var>. If an empty matrix is passed for <var>limits</var>, the
display range is computed as the range between the minimal and the
maximal value in the image.
</p>
<p>If <var>map</var> is a valid color map, the image will be shown as an indexed
image using the supplied color map.
</p>
<p>If a file name is given instead of an image, the file will be read and
shown.
</p>
<p>If given, the parameter <var>string_param1</var> has value
<var>value1</var>. <var>string_param1</var> can be any of the following:
</p>
<dl compact="compact">
<dt><code>"displayrange"</code></dt>
<dd><p><var>value1</var> is the display range as described above.
</p>
</dd>
<dt><code>"xdata"</code></dt>
<dd><p>If <var>value1</var> is a two element vector, it must contain horizontal axis
limits in the form [xmin xmax]; Otherwise <var>value1</var> must be a
vector and only the first and last elements will be used for xmin and
xmax respectively.
</p>
</dd>
<dt><code>"ydata"</code></dt>
<dd><p>If <var>value1</var> is a two element vector, it must contain vertical axis
limits in the form [ymin ymax]; Otherwise <var>value1</var> must be a
vector and only the first and last elements will be used for ymin and
ymax respectively.
</p>
</dd>
</dl>
<p>The optional return value <var>h</var> is a graphics handle to the image.
</p>
<p><strong>See also:</strong> <a href="#XREFimage">image</a>, <a href="#XREFimagesc">imagesc</a>, <a href="Representing-Images.html#XREFcolormap">colormap</a>, <a href="Representing-Images.html#XREFgray2ind">gray2ind</a>, <a href="Representing-Images.html#XREFrgb2ind">rgb2ind</a>.
</p></dd></dl>
<a name="XREFimage"></a><dl>
<dt><a name="index-image"></a>Function File: <em></em> <strong>image</strong> <em>(<var>img</var>)</em></dt>
<dt><a name="index-image-1"></a>Function File: <em></em> <strong>image</strong> <em>(<var>x</var>, <var>y</var>, <var>img</var>)</em></dt>
<dt><a name="index-image-2"></a>Function File: <em></em> <strong>image</strong> <em>(…, "<var>prop</var>", <var>val</var>, …)</em></dt>
<dt><a name="index-image-3"></a>Function File: <em></em> <strong>image</strong> <em>("<var>prop1</var>", <var>val1</var>, …)</em></dt>
<dt><a name="index-image-4"></a>Function File: <em><var>h</var> =</em> <strong>image</strong> <em>(…)</em></dt>
<dd><p>Display a matrix as an indexed color image.
</p>
<p>The elements of <var>img</var> are indices into the current colormap.
<var>x</var> and <var>y</var> are optional 2-element vectors, <code>[min, max]</code><!-- /@w -->,
which specify the range for the axis labels. If a range is specified as
<code>[max, min]</code><!-- /@w --> then the image will be reversed along that axis. For
convenience, <var>x</var> and <var>y</var> may be specified as N-element vectors
matching the length of the data in <var>img</var>. However, only the first and
last elements will be used to determine the axis limits.
<strong>Warning:</strong> <var>x</var> and <var>y</var> are ignored when using gnuplot 4.0
or earlier.
</p>
<p>Multiple property/value pairs may be specified for the image object, but
they must appear in pairs.
</p>
<p>The optional return value <var>h</var> is a graphics handle to the image.
</p>
<p>Implementation Note: The origin (0, 0) for images is located in the
upper left. For ordinary plots, the origin is located in the lower
left. Octave handles this inversion by plotting the data normally,
and then reversing the direction of the y-axis by setting the
<code>ydir</code> property to <code>"reverse"</code>. This has implications whenever
an image and an ordinary plot need to be overlaid. The recommended
solution is to display the image and then plot the reversed ydata
using, for example, <code>flipud (ydata)</code>.
</p>
<p>Calling Forms: The <code>image</code> function can be called in two forms:
High-Level and Low-Level. When invoked with normal options, the High-Level
form is used which first calls <code>newplot</code> to prepare the graphic figure
and axes. When the only inputs to <code>image</code> are property/value pairs
the Low-Level form is used which creates a new instance of an image object
and inserts it in the current axes.
</p>
<p><strong>See also:</strong> <a href="#XREFimshow">imshow</a>, <a href="#XREFimagesc">imagesc</a>, <a href="Representing-Images.html#XREFcolormap">colormap</a>.
</p></dd></dl>
<a name="XREFimagesc"></a><dl>
<dt><a name="index-imagesc"></a>Function File: <em></em> <strong>imagesc</strong> <em>(<var>img</var>)</em></dt>
<dt><a name="index-imagesc-1"></a>Function File: <em></em> <strong>imagesc</strong> <em>(<var>x</var>, <var>y</var>, <var>img</var>)</em></dt>
<dt><a name="index-imagesc-2"></a>Function File: <em></em> <strong>imagesc</strong> <em>(…, <var>climits</var>)</em></dt>
<dt><a name="index-imagesc-3"></a>Function File: <em></em> <strong>imagesc</strong> <em>(…, "<var>prop</var>", <var>val</var>, …)</em></dt>
<dt><a name="index-imagesc-4"></a>Function File: <em></em> <strong>imagesc</strong> <em>("<var>prop1</var>", <var>val1</var>, …)</em></dt>
<dt><a name="index-imagesc-5"></a>Function File: <em></em> <strong>imagesc</strong> <em>(<var>hax</var>, …)</em></dt>
<dt><a name="index-imagesc-6"></a>Function File: <em><var>h</var> =</em> <strong>imagesc</strong> <em>(…)</em></dt>
<dd><p>Display a scaled version of the matrix <var>img</var> as a color image. The
colormap is scaled so that the entries of the matrix occupy the entire
colormap. If <code><var>climits</var> = [<var>lo</var>, <var>hi</var>]</code> is given, then that
range is set to the <code>"clim"</code> of the current axes.
</p>
<p>The axis values corresponding to the matrix elements are specified in
<var>x</var> and <var>y</var>, either as pairs giving the minimum and maximum
values for the respective axes, or as values for each row and column
of the matrix <var>img</var>.
</p>
<p>The optional return value <var>h</var> is a graphics handle to the image.
</p>
<p>Calling Forms: The <code>imagesc</code> function can be called in two forms:
High-Level and Low-Level. When invoked with normal options, the High-Level
form is used which first calls <code>newplot</code> to prepare the graphic figure
and axes. When the only inputs to <code>image</code> are property/value pairs
the Low-Level form is used which creates a new instance of an image object
and inserts it in the current axes.
</p>
<p><strong>See also:</strong> <a href="#XREFimage">image</a>, <a href="#XREFimshow">imshow</a>, <a href="Axis-Configuration.html#XREFcaxis">caxis</a>.
</p></dd></dl>
<hr>
<div class="header">
<p>
Next: <a href="Representing-Images.html#Representing-Images" accesskey="n" rel="next">Representing Images</a>, Previous: <a href="Loading-and-Saving-Images.html#Loading-and-Saving-Images" accesskey="p" rel="prev">Loading and Saving Images</a>, Up: <a href="Image-Processing.html#Image-Processing" accesskey="u" rel="up">Image Processing</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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