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Next: <a rel="next" accesskey="n" href="Representing-Images.html#Representing-Images">Representing Images</a>,
Previous: <a rel="previous" accesskey="p" href="Loading-and-Saving-Images.html#Loading-and-Saving-Images">Loading and Saving Images</a>,
Up: <a rel="up" accesskey="u" href="Image-Processing.html#Image-Processing">Image Processing</a>
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<h3 class="section">31.2 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. This function uses
an external program to show the image. If gnuplot 4.2 or later is
available it will be used to display the image, otherwise the
<code>display</code>, <code>xv</code>, or <code>xloadimage</code> program is used. The
actual program can be selected with the <code>image_viewer</code> function.
<!-- ./image/imshow.m -->
<p><a name="doc_002dimshow"></a>
<div class="defun">
— Function File: <b>imshow</b> (<var>im</var>)<var><a name="index-imshow-2189"></a></var><br>
— Function File: <b>imshow</b> (<var>im, limits</var>)<var><a name="index-imshow-2190"></a></var><br>
— Function File: <b>imshow</b> (<var>im, map</var>)<var><a name="index-imshow-2191"></a></var><br>
— Function File: <b>imshow</b> (<var>rgb, <small class="dots">...</small></var>)<var><a name="index-imshow-2192"></a></var><br>
— Function File: <b>imshow</b> (<var>filename</var>)<var><a name="index-imshow-2193"></a></var><br>
— Function File: <b>imshow</b> (<var><small class="dots">...</small>, string_param1, value1, <small class="dots">...</small></var>)<var><a name="index-imshow-2194"></a></var><br>
<blockquote><p>Display the image <var>im</var>, where <var>im</var> can be a 2-dimensional
(gray-scale image) or a 3-dimensional (RGB image) matrix.
<p>If <var>limits</var> is a 2-element vector <code>[</code><var>low</var><code>, </code><var>high</var><code>]</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>If <var>map</var> is a valid color map, the image will be shown as an indexed
image using the supplied color map.
<p>If a file name is given instead of an image, the file will be read and
shown.
<p>If given, the parameter <var>string_param1</var> has value
<var>value1</var>. <var>string_param1</var> can be any of the following:
<dl>
<dt>‘<samp><span class="samp">"displayrange"</span></samp>’<dd><var>value1</var> is the display range as described above.
</dl>
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dimage.html#doc_002dimage">image</a>, <a href="doc_002dimagesc.html#doc_002dimagesc">imagesc</a>, <a href="doc_002dcolormap.html#doc_002dcolormap">colormap</a>, <a href="doc_002dgray2ind.html#doc_002dgray2ind">gray2ind</a>, <a href="doc_002drgb2ind.html#doc_002drgb2ind">rgb2ind</a>.
</p></blockquote></div>
<!-- ./image/image.m -->
<p><a name="doc_002dimage"></a>
<div class="defun">
— Function File: <b>image</b> (<var>img</var>)<var><a name="index-image-2195"></a></var><br>
— Function File: <b>image</b> (<var>x, y, img</var>)<var><a name="index-image-2196"></a></var><br>
<blockquote><p>Display a matrix as a color image. The elements of <var>x</var> are indices
into the current colormap, and the colormap will be scaled so that the
extremes of <var>x</var> are mapped to the extremes of the colormap.
<p>It first tries to use <code>gnuplot</code>, then <code>display</code> from
<code>ImageMagick</code>, then <code>xv</code>, and then <code>xloadimage</code>.
The actual program used can be changed using the <code>image_viewer</code>
function.
<p>The axis values corresponding to the matrix elements are specified in
<var>x</var> and <var>y</var>. If you're not using gnuplot 4.2 or later, these
variables are ignored.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dimshow.html#doc_002dimshow">imshow</a>, <a href="doc_002dimagesc.html#doc_002dimagesc">imagesc</a>, <a href="doc_002dcolormap.html#doc_002dcolormap">colormap</a>, <a href="doc_002dimage_005fviewer.html#doc_002dimage_005fviewer">image_viewer</a>.
</p></blockquote></div>
<!-- ./image/imagesc.m -->
<p><a name="doc_002dimagesc"></a>
<div class="defun">
— Function File: <b>imagesc</b> (<var>a</var>)<var><a name="index-imagesc-2197"></a></var><br>
— Function File: <b>imagesc</b> (<var>x, y, a</var>)<var><a name="index-imagesc-2198"></a></var><br>
— Function File: <b>imagesc</b> (<var><small class="dots">...</small>, limits</var>)<var><a name="index-imagesc-2199"></a></var><br>
— Function File: <b>imagesc</b> (<var>h, <small class="dots">...</small></var>)<var><a name="index-imagesc-2200"></a></var><br>
— Function File: <var>h</var> = <b>imagesc</b> (<var><small class="dots">...</small></var>)<var><a name="index-imagesc-2201"></a></var><br>
<blockquote><p>Display a scaled version of the matrix <var>a</var> as a color image. The
colormap is scaled so that the entries of the matrix occupy the entire
colormap. If <var>limits</var> = [<var>lo</var>, <var>hi</var>] are given, then that
range is set to the 'clim' of the current axes.
<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>a</var>.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dimage.html#doc_002dimage">image</a>, <a href="doc_002dimshow.html#doc_002dimshow">imshow</a>, <a href="doc_002dcaxis.html#doc_002dcaxis">caxis</a>.
</p></blockquote></div>
<!-- ./image/image_viewer.m -->
<p><a name="doc_002dimage_005fviewer"></a>
<div class="defun">
— Function File: [<var>fcn</var>, <var>default_zoom</var>] = <b>image_viewer</b> (<var>fcn, default_zoom</var>)<var><a name="index-image_005fviewer-2202"></a></var><br>
<blockquote><p>Change the program or function used for viewing images and return the
previous values.
<p>When the <code>image</code> or <code>imshow</code> function is called it will
launch an external program to display the image. The default behavior
is to use gnuplot if the installed version supports image viewing,
and otherwise try the programs <code>display</code>, <code>xv</code>, and
<code>xloadimage</code>. Using this function it is possible to change that
behavior.
<p>When called with one input argument images will be displayed by saving
the image to a file and the system command <var>command</var> will be called
to view the image. The <var>command</var> must be a string containing
<code>%s</code> and possibly <code>%f</code>. The <code>%s</code> will be replaced by
the filename of the image, and the <code>%f</code> will (if present) be
replaced by the zoom factor given to the <code>image</code> function.
For example,
<pre class="example"> image_viewer ("eog %s");
</pre>
<p>changes the image viewer to the <code>eog</code> program.
<p>With two input arguments, images will be displayed by calling
the function <var>function_handle</var>. For example,
<pre class="example"> image_viewer (data, @my_image_viewer);
</pre>
<p>sets the image viewer function to <code>my_image_viewer</code>. The image
viewer function is called with
<pre class="example"> my_image_viewer (<var>x</var>, <var>y</var>, <var>im</var>, <var>zoom</var>, <var>data</var>)
</pre>
<p>where <var>x</var> and <var>y</var> are the axis of the image, <var>im</var> is the image
variable, and <var>data</var> is extra user-supplied data to be passed to
the viewer function.
<p>With three input arguments it is possible to change the zooming.
Some programs (like <code>xloadimage</code>) require the zoom factor to be
between 0 and 100, and not 0 and 1 like Octave assumes. This is
solved by setting the third argument to 100.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dimage.html#doc_002dimage">image</a>, <a href="doc_002dimshow.html#doc_002dimshow">imshow</a>.
</p></blockquote></div>
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