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<html>
<head>
<title>
IMAGE_EDGE - Edge Detection in Images
</title>
</head>
<body bgcolor="#eeeeee" link="#cc0000" alink="#ff3300" vlink="#000055">
<h1 align = "center">
IMAGE_EDGE <br> Edge Detection in Images
</h1>
<hr>
<p>
<b>IMAGE_EDGE</b>
is a MATLAB library which
demonstrates the detection of edges in an image.
</p>
<p>
NEWS is a particularly simple edge detection scheme, which compares
the North, East, West, and South neighbors of a pixel to determine
if the pixel lies along an edge.
</p>
<p>
There are many sophisticated edge detection algorithms, and MATLAB
has many of them built into its image processing toolbox. The purpose
of these examples is simply to demonstrate how a simple version of
such edge detection schemes works.
</p>
<h3 align = "center">
Licensing:
</h3>
<p>
The computer code and data files described and made available on this web page
are distributed under
<a href = "../../txt/gnu_lgpl.txt">the GNU LGPL license.</a>
</p>
<h3 align = "center">
Languages:
</h3>
<p>
<b>IMAGE_EDGE</b> is available in
<a href = "../../c_src/image_edge/image_edge.html">a C version<a> and
<a href = "../../cpp_src/image_edge/image_edge.html">a C++ version<a> and
<a href = "../../f77_src/image_edge/image_edge.html">a FORTRAN77 version<a> and
<a href = "../../f_src/image_edge/image_edge.html">a FORTRAN90 version<a> and
<a href = "../../m_src/image_edge/image_edge.html">a MATLAB version<a>.
</p>
<h3 align = "center">
Related Data and Programs:
</h3>
<p>
<a href = "../../m_src/cell_detection_tasks/cell_detection_tasks.html">
CELL_DETECTION_TASKS</a>,
a MATLAB program which
creates modified versions of a sequence of gray-scale TIF files containing
images of cells; the process of each file is carried out independently,
using the "task" feature of MATLAB's parallel computing toolbox.
</p>
<p>
<a href = "../../m_src/color_remote/color_remote.html">
COLOR_REMOTE</a>,
a MATLAB program which
carries out the color segmentation of an image in parallel,
via SPMD commands; this includes instructions on how to run the job,
via MATLAB's BATCH facility,
on a remote system such as Virginia Tech's ITHACA cluster.
</p>
<p>
<a href = "../../m_src/contrast_spmd/contrast_spmd.html">
CONTRAST_SPMD</a>,
a MATLAB program which
demonstrates the SPMD parallel programming feature for image operations;
the client reads an image, the workers increase contrast over separate portions, and
the client assembles and displays the results.
</p>
<p>
<a href = "../../m_src/contrast2_spmd/contrast2_spmd.html">
CONTRAST2_SPMD</a>,
a MATLAB program which
demonstrates the SPMD parallel programming feature for image operations;
this improves the contrast_spmd program by allowing the workers to share some
data; this makes it possible to eliminate artificial "seams" in the processed
image.
</p>
<p>
<a href = "../../m_src/edge/edge.html">
EDGE</a>,
a MATLAB library which
defines some test functions in 1D, 2D and 3D for the detection of edges.
</p>
<p>
<a href = "../../m_src/image_components/image_components.html">
IMAGE_COMPONENTS</a>,
a MATLAB library which
seeks the connected "nonzero" or "nonblack" components of an image or integer vector,
array or 3D block.
</p>
<p>
<a href = "../../m_src/image_contrast/image_contrast.html">
IMAGE_CONTRAST</a>,
a MATLAB program which
applies image processing techniques to increase the contrast in an image.
</p>
<p>
<a href = "../../m_src/image_denoise/image_denoise.html">
IMAGE_DENOISE</a>,
a MATLAB program which
applies image processing techniques to remove noise from an image.
</p>
<p>
<a href = "../../m_src/image_diffuse/image_diffuse.html">
IMAGE_DIFFUSE</a>,
a MATLAB library which
uses diffusion to smooth out an image.
</p>
<p>
<a href = "../../m_src/image_match_genetic/image_match_genetic.html">
IMAGE_MATCH_GENETIC</a>,
a MATLAB program which
tries to match a 256x256 JPEG image by blending 32 colored rectangles,
using ideas from genetic algorithms,
based on an example by Nick Berry.
</p>
<p>
<a href = "../../m_src/image_noise/image_noise.html">
IMAGE_NOISE</a>,
MATLAB programs which
add noise to an image.
</p>
<p>
<a href = "../../m_src/image_quantization/image_quantization.html">
IMAGE_QUANTIZATION</a>,
a MATLAB library which
demonstrates how the KMEANS algorithm can be used to reduce the number
of colors or shades of gray in an image.
</p>
<p>
<a href = "../../m_src/image_rgb_to_gray/image_rgb_to_gray.html">
IMAGE_RGB_TO_GRAY</a>,
MATLAB programs which
makes a grayscale version of an RGB image.
</p>
<p>
<a href = "../../m_src/image_threshold/image_threshold.html">
IMAGE_THRESHOLD</a>,
a MATLAB library which
makes a black and white version of a grayscale image by setting all pixels
below or above a threshold value to black or white.
</p>
<p>
<a href = "../../m_src/pgma_io/pgma_io.html">
PGMA_IO<a>,
a MATLAB library which
handles the ASCII Portable Gray Map (PGM) format.
</p>
<h3 align = "center">
Reference:
</h3>
<p>
<ol>
<li>
Jonas Gomes, Luiz Velho,<br>
Image Processing for Computer Graphics,<br>
Springer, 1997,<br>
ISBN: 0387948546,<br>
LC: T385.G65.
</li>
</ol>
</p>
<p>
MathWorks documentation for the Image Processing Toolbox is available at
<a href = "http://www.mathworks.com/access/helpdesk/help/pdf_doc/images/images_tb.pdf">
http://www.mathworks.com/access/helpdesk/help/pdf_doc/images/images_tb.pdf</a>.
</p>
<h3 align = "center">
Source Code:
</h3>
<p>
<ul>
<li>
<a href = "news.m">news.m</a>,
demonstrates the NEWS stencil.
</li>
<li>
<a href = "pgma_read.m">pgma_read.m</a>,
reads an ASCII PGM file. This can be used if MATLAB's
image processing toolbox is not available.
</li>
</ul>
</p>
<h3 align = "center">
Examples and Tests:
</h3>
<p>
<b>COINS</b> is an image of several coins. These are displayed
against a uniform gray background, so the edges are easy to spot.
<ul>
<li>
<a href = "coins.pgm">coins.pgm</a>,
a binary PGM file containing a grayscale image of coins.
</li>
<li>
<a href = "coins.ascii.pgm">coins.ascii.pgm</a>,
an ASCII PGM file containing a grayscale image of coins.
</li>
<li>
<a href = "coins.png">coins.png</a>,
a PNG version of the image.
</li>
<li>
<a href = "coins_news1.png">coins_news1.png</a>,
image 1 produced by NEWS shows the input data.
</li>
<li>
<a href = "coins_news2.png">coins_news2.png</a>,
image 2 produced by NEWS shows the data after a
1 pixel boundary has been added.
</li>
<li>
<a href = "coins_news3.png">coins_news3.png</a>,
image 3 shows the E data measuring the "edginess" of each pixel.
</li>
<li>
<a href = "coins_news4.png">coins_news4.png</a>,
image4 uses a threshold. Values below the threshold are set to
0 (black), and values above are set to the maximum (white).
</li>
<li>
<a href = "coins_news5.png">coins_news5.png</a>,
is the same as image 4, but in "reverse video". It is easier
to "read" the image with black lines and a white background.
</li>
<li>
<a href = "coins_news6.png">coins_news6.png</a>,
image 6 is actually an RGB color image. It combines the original
grayscale image of the coins with the edges marked in red.
</li>
</ul>
</p>
<p>
You can go up one level to <a href = "../m_src.html">
the MATLAB source codes</a>.
</p>
<hr>
<i>
Last modified on 26 February 2011.
</i>
<!-- John Burkardt -->
</body>
</html>