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Next: <a rel="next" accesskey="n" href="Displaying-Images.html#Displaying-Images">Displaying Images</a>,
Up: <a rel="up" accesskey="u" href="Image-Processing.html#Image-Processing">Image Processing</a>
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<h3 class="section">32.1 Loading and Saving Images</h3>
<p>The first step in most image processing tasks is to load an image
into Octave. This is done using the <code>imread</code> function, which uses the
<code>GraphicsMagick</code> library for reading. This means a vast number of image
formats is supported. The <code>imwrite</code> function is the corresponding function
for writing images to the disk.
<p>In summary, most image processing code will follow the structure of this code
<pre class="example"> I = imread ("my_input_image.img");
J = process_my_image (I);
imwrite ("my_output_image.img", J);
</pre>
<!-- imread scripts/image/imread.m -->
<p><a name="doc_002dimread"></a>
<div class="defun">
— Function File: [<var>img</var>, <var>map</var>, <var>alpha</var>] = <b>imread</b> (<var>filename</var>)<var><a name="index-imread-2887"></a></var><br>
<blockquote><p>Read images from various file formats.
<p>The size and numeric class of the output depends on the
format of the image. A color image is returned as an
MxNx3 matrix. Gray-level and black-and-white images are
of size MxN.
The color depth of the image determines the numeric
class of the output: "uint8" or "uint16" for gray
and color, and "logical" for black and white.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dimwrite.html#doc_002dimwrite">imwrite</a>, <a href="doc_002dimfinfo.html#doc_002dimfinfo">imfinfo</a>.
</p></blockquote></div>
<!-- imwrite scripts/image/imwrite.m -->
<p><a name="doc_002dimwrite"></a>
<div class="defun">
— Function File: <b>imwrite</b> (<var>img, filename</var>)<var><a name="index-imwrite-2888"></a></var><br>
— Function File: <b>imwrite</b> (<var>img, filename, fmt</var>)<var><a name="index-imwrite-2889"></a></var><br>
— Function File: <b>imwrite</b> (<var>img, filename, fmt, p1, v1, <small class="dots">...</small></var>)<var><a name="index-imwrite-2890"></a></var><br>
— Function File: <b>imwrite</b> (<var>img, map, filename, <small class="dots">...</small></var>)<var><a name="index-imwrite-2891"></a></var><br>
<blockquote><p>Write images in various file formats.
<p>If <var>fmt</var> is not supplied, the file extension of <var>filename</var> is used
to determine the format.
<p>The parameter-value pairs (<var>p1</var>, <var>v1</var>, <small class="dots">...</small>) are optional.
Currently the following options are supported for <tt>JPEG</tt> images:
<dl>
<dt>‘<samp><span class="samp">Quality</span></samp>’<dd>Set the quality of the compression. The value should be an
integer between 0 and 100, with larger values indicating higher visual
quality and lower compression.
</dl>
<p><strong>Supported Formats</strong>
<p><table summary=""><tr align="left"><th valign="top" width="33%">Extension </th><th valign="top" width="66%">Format
<br></th></tr><tr align="left"><td valign="top" width="33%">bmp </td><td valign="top" width="66%">Windows Bitmap
<br></td></tr><tr align="left"><td valign="top" width="33%">gif </td><td valign="top" width="66%">Graphics Interchange Format
<br></td></tr><tr align="left"><td valign="top" width="33%">jpg and jpeg </td><td valign="top" width="66%">Joint Photographic Experts Group
<br></td></tr><tr align="left"><td valign="top" width="33%">pbm </td><td valign="top" width="66%">Portable Bitmap
<br></td></tr><tr align="left"><td valign="top" width="33%">pcx </td><td valign="top" width="66%">
<br></td></tr><tr align="left"><td valign="top" width="33%">pgm </td><td valign="top" width="66%">Portable Graymap
<br></td></tr><tr align="left"><td valign="top" width="33%">png </td><td valign="top" width="66%">Portable Network Graphics
<br></td></tr><tr align="left"><td valign="top" width="33%">pnm </td><td valign="top" width="66%">Portable Anymap
<br></td></tr><tr align="left"><td valign="top" width="33%">ppm </td><td valign="top" width="66%">Portable Pixmap
<br></td></tr><tr align="left"><td valign="top" width="33%">ras </td><td valign="top" width="66%">Sun Raster
<br></td></tr><tr align="left"><td valign="top" width="33%">tif and tiff </td><td valign="top" width="66%">Tagged Image File Format
<br></td></tr><tr align="left"><td valign="top" width="33%">xwd </td><td valign="top" width="66%">X11 Dump
<br></td></tr></table>
<p><strong>Unsupported Formats</strong>
<p><table summary=""><tr align="left"><th valign="top" width="33%">Extension </th><th valign="top" width="66%">Format
<br></th></tr><tr align="left"><td valign="top" width="33%">hdf </td><td valign="top" width="66%">Hierarchical Data Format V4
<br></td></tr><tr align="left"><td valign="top" width="33%">jp2 and jpx </td><td valign="top" width="66%">Joint Photographic Experts Group 2000
<br></td></tr></table>
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dimread.html#doc_002dimread">imread</a>, <a href="doc_002dimfinfo.html#doc_002dimfinfo">imfinfo</a>.
</p></blockquote></div>
<!-- IMAGE_PATH src/defaults.cc -->
<p><a name="doc_002dIMAGE_005fPATH"></a>
<div class="defun">
— Built-in Function: <var>val</var> = <b>IMAGE_PATH</b> ()<var><a name="index-IMAGE_005fPATH-2892"></a></var><br>
— Built-in Function: <var>old_val</var> = <b>IMAGE_PATH</b> (<var>new_val</var>)<var><a name="index-IMAGE_005fPATH-2893"></a></var><br>
— Built-in Function: <b>IMAGE_PATH</b> (<var>new_val, "local"</var>)<var><a name="index-IMAGE_005fPATH-2894"></a></var><br>
<blockquote><p>Query or set the internal variable that specifies a colon separated
list of directories in which to search for image files.
<p>When called from inside a function with the "local" option, the variable is
changed locally for the function and any subroutines it calls. The original
variable value is restored when exiting the function.
</p></blockquote></div>
<p>It is possible to get information about an image file on disk, without actually
reading it into Octave. This is done using the <code>imfinfo</code> function which
provides read access to many of the parameters stored in the header of the image
file.
<!-- imfinfo scripts/image/imfinfo.m -->
<p><a name="doc_002dimfinfo"></a>
<div class="defun">
— Function File: <var>info</var> = <b>imfinfo</b> (<var>filename</var>)<var><a name="index-imfinfo-2895"></a></var><br>
— Function File: <var>info</var> = <b>imfinfo</b> (<var>url</var>)<var><a name="index-imfinfo-2896"></a></var><br>
<blockquote><p>Read image information from a file.
<p><code>imfinfo</code> returns a structure containing information about the image
stored in the file <var>filename</var>. The output structure contains the
following fields.
<dl>
<dt>‘<samp><span class="samp">Filename</span></samp>’<dd>The full name of the image file.
<br><dt>‘<samp><span class="samp">FileSize</span></samp>’<dd>Number of bytes of the image on disk
<br><dt>‘<samp><span class="samp">FileModDate</span></samp>’<dd>Date of last modification to the file.
<br><dt>‘<samp><span class="samp">Height</span></samp>’<dd>Image height in pixels.
<br><dt>‘<samp><span class="samp">Width</span></samp>’<dd>Image Width in pixels.
<br><dt>‘<samp><span class="samp">BitDepth</span></samp>’<dd>Number of bits per channel per pixel.
<br><dt>‘<samp><span class="samp">Format</span></samp>’<dd>Image format (e.g., <code>"jpeg"</code>).
<br><dt>‘<samp><span class="samp">LongFormat</span></samp>’<dd>Long form image format description.
<br><dt>‘<samp><span class="samp">XResolution</span></samp>’<dd>X resolution of the image.
<br><dt>‘<samp><span class="samp">YResolution</span></samp>’<dd>Y resolution of the image.
<br><dt>‘<samp><span class="samp">TotalColors</span></samp>’<dd>Number of unique colors in the image.
<br><dt>‘<samp><span class="samp">TileName</span></samp>’<dd>Tile name.
<br><dt>‘<samp><span class="samp">AnimationDelay</span></samp>’<dd>Time in 1/100ths of a second (0 to 65535) which must expire before displaying
the next image in an animated sequence.
<br><dt>‘<samp><span class="samp">AnimationIterations</span></samp>’<dd>Number of iterations to loop an animation (e.g., Netscape loop extension)
for.
<br><dt>‘<samp><span class="samp">ByteOrder</span></samp>’<dd>Endian option for formats that support it. Is either <code>"little-endian"</code>,
<code>"big-endian"</code>, or <code>"undefined"</code>.
<br><dt>‘<samp><span class="samp">Gamma</span></samp>’<dd>Gamma level of the image. The same color image displayed on two different
workstations may look different due to differences in the display monitor.
<br><dt>‘<samp><span class="samp">Matte</span></samp>’<dd><code>true</code> if the image has transparency.
<br><dt>‘<samp><span class="samp">ModulusDepth</span></samp>’<dd>Image modulus depth (minimum number of bits required to support
red/green/blue
components without loss of accuracy).
<br><dt>‘<samp><span class="samp">Quality</span></samp>’<dd>JPEG/MIFF/PNG compression level.
<br><dt>‘<samp><span class="samp">QuantizeColors</span></samp>’<dd>Preferred number of colors in the image.
<br><dt>‘<samp><span class="samp">ResolutionUnits</span></samp>’<dd>Units of image resolution. Is either <code>"pixels per inch"</code>,
<code>"pixels per centimeter"</code>, or <code>"undefined"</code>.
<br><dt>‘<samp><span class="samp">ColorType</span></samp>’<dd>Image type. Is either <code>"grayscale"</code>, <code>"indexed"</code>,
<code>"truecolor"</code>,
or <code>"undefined"</code>.
<br><dt>‘<samp><span class="samp">View</span></samp>’<dd>FlashPix viewing parameters.
</dl>
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dimread.html#doc_002dimread">imread</a>, <a href="doc_002dimwrite.html#doc_002dimwrite">imwrite</a>.
</p></blockquote></div>
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