www/clahe.html - platform/external/ImageMagick - Git at Google



 <!doctype html>
 <html lang="en">
 <head>
   <meta charset="utf-8"  />
   <meta name="viewport" content="width=device-width, initial-scale=1"  />
   <title>ImageMagick - Contrast Limited Adaptive Histogram Equalization</title>
   <meta name="application-name" content="ImageMagick" />
   <meta name="description" content="Use ImageMagick® to create, edit, compose, and convert digital images. Resize an image, crop it, change its shades and colors, add captions, and more." />
   <meta name="application-url" content="https://imagemagick.org" />
   <meta name="generator" content="PHP" />
   <meta name="keywords" content="contrast, limited, adaptive, histogram, equalization, image processing software" />
   <meta name="rating" content="GENERAL" />
   <meta name="robots" content="INDEX, FOLLOW" />
   <meta name="generator" content="ImageMagick Studio LLC" />
   <meta name="author" content="ImageMagick Studio LLC" />
   <meta name="revisit-after" content="2 DAYS" />
   <meta name="resource-type" content="document" />
   <meta name="copyright" content="Copyright (c) 1999-2020 ImageMagick Studio LLC" />
   <meta name="distribution" content="Global" />
   <meta name="magick-serial" content="P131-S030410-R485315270133-P82224-A6668-G1245-1" />
   <meta property='og:url' content='../' />
   <meta property='og:title' content='ImageMagick' />
   <meta property='og:image' content='../images/logo.png' />
   <meta property='og:type' content='website' />
   <meta property='og:site_name' content='ImageMagick' />
   <meta property='og:description' content="Create, Edit, Compose, or Convert Digital Images" />
   <meta name="google-site-verification" content="_bMOCDpkx9ZAzBwb2kF3PRHbfUUdFj2uO8Jd1AXArz4" />
   <link href="clahe.html" rel="canonical" />
   <link href="../images/wand.png" rel="icon" />
   <link href="../images/wand.ico" rel="shortcut icon" />
   <link href="assets/magick.css" rel="stylesheet" />
 </head>
 <body>
   <nav class="navbar navbar-expand-md navbar-dark bg-dark fixed-top">
   <div class="container-fluid">
     <a class="navbar-brand" href="../"><img class="d-block" id="icon" alt="ImageMagick" width="32" height="32" src="../images/wand.ico"/></a>
     <button class="navbar-toggler" type="button" data-bs-toggle="collapse" data-bs-target="#magick-navbars" aria-controls="magick-navbars" aria-expanded="false" aria-label="Toggle navigation">
       <span class="navbar-toggler-icon"></span>
     </button>

     <div class="collapse navbar-collapse" id="magick-navbars">
       <ul class="navbar-nav me-auto mb-2 mb-md-0">
         <li class="nav-item">
           <a class="nav-link " href="../www/index.html">Home</a>
         </li>
         <li class="nav-item">
           <a class="nav-link " href="../www/download.html">Download</a>
         </li>
         <li class="nav-item">
           <a class="nav-link " href="../www/command-line-tools.html">Tools</a>
         </li>
         <li class="nav-item">
           <a class="nav-link " href="../www/command-line-processing.html">CLI</a>
         </li>
         <li class="nav-item">
           <a class="nav-link " href="../www/develop.html">Develop</a>
         </li>
         <li class="nav-item">
           <a class="nav-link" target="_blank" href="https://github.com/ImageMagick/ImageMagick/discussions">Community</a>
         </li>
         <li class="nav-item">
           <iframe src="https://github.com/sponsors/ImageMagick/button" title="Sponsor ImageMagick" height="35" width="107" style="border: 0;"></iframe>
         </li>
       </ul>
       <form class="d-flex form-inline" action="search.html">
         <input class="form-control me-2" type="text" name="q" placeholder="Search" aria-label="Search">
         <button class="btn btn-outline-success" type="submit" name="sa">Search</button>
       </form>
     </div>
   </div>
   </nav>

   <div class="container">
     <script async="async" src="https://localhost/pagead/js/adsbygoogle.js"></script>
     <ins class="adsbygoogle"
       style="display:block"
       data-ad-client="ca-pub-3129977114552745"
       data-ad-slot="6345125851"
       data-full-width-responsive="true"
       data-ad-format="horizontal"></ins>
     <script>
       (adsbygoogle = window.adsbygoogle || []).push({});
     </script>

   </div>

   <main class="container">
   <div class="magick-template">
 <div class="magick-header">
 <h1 class="text-center">Adaptive Histogram Equalization</h1>
 <p class="lead magick-description">Use contrast limited adaptive histogram equalization (AHE) to improve contrast in images.  Ordinary histogram equalization computes a global equalization whereas an adaptive method computes several histograms, each corresponding to a distinct section of the image, and uses them to redistribute the lightness values of the image.  It is suitable for improving the local contrast and enhancing the definitions of edges in each region of an image.  A variant of adaptive histogram equalization, contrast limited adaptive histogram equalization (CLAHE) limits AHE's tendency to overamplify noise in relatively homogeneous regions of an image.</p>
 <p>CLAHE is supported as of ImageMagick 7.0.8-24 with the <a href="../www/command-line-options.html#clahe">-clahe</a> option:</p>
 <ul>
 <h6><a class="anchor" id="clahe"></a>-clahe <var>width</var>x<var>height</var>{%}{+}<var>number-bins</var>{+}<var>clip-limit</var>{!}</h6>
 </ul>
 <p> The image is divided into tiles of <var>width</var> and <var>height</var> pixels.  Append <code>%</code> to define the width and height as percentages of the image's dimensions. The tile size should be larger than the size of features to be preserved and respects the aspect ratio of the image.  Add <code>!</code> to force an exact tile width and height. <var>number-bins</var> is the number of histogram bins per tile (min 2, max 65536).  The number of histogram bins should be smaller than the number of pixels in a single tile. <var>clip-limit</var> is the contrast limit for localized changes in contrast. A clip-limit of 2 to 3 is a good starting place (e.g. -clahe 50x50%+128+3).  Very large values will let the histogram equalization do whatever it wants to do, that is result in maximal local contrast. The value 1 will result in the original image.  Note, if the number of bins and the clip-limit are omitted, they default to 128 and no clipping respectively.</p>
 <p>To visualize the benefits of CLAHE, we have a low contrast image of mountains:</p>
 <p>
 <ul>
   <a href="../images/mountains.jpg"><img src="../images/mountains.jpg" width="500" height="333" alt="label" /></a>
 </ul>
 <p>We can improve the image with global histogram equalization:</p>
 <ul>
   <a href="../images/mountains.jpg"><img src="../images/mountains-equalize.jpg" width="500" height="333" alt="label" /></a>
 </ul>
 <p>We can further improve the image with the contrast limited adaptive histogram equalization image processing technique:</p>
 <ul>
   <a href="../images/mountains.jpg"><img src="../images/mountains-clahe.jpg" width="500" height="333" alt="label" /></a>
 </ul>
 <p>The latter image was produced with this command:</p>
 <pre class="highlight">
 magick mountains.jpg -clahe 25x25%+128+3 mountains-clahe.jpg
 </pre>
 <p>The <code>25x25%</code> argument divides the image into 16 tiles to perform local contrast enhancement.  The image dimensions are <code>1500x1000</code> so the tiles are exactly <code>375x250</code> pixels each.  Rather than a percentage, you can specify the tile dimensions directly with <code>375x250</code>.</p>
 <p>For tile sizes that do not divide evenly into the image dimensions, CLAHE utilizes virtual pixels, as such the results can vary slightly based on your chosen virtual pixel method.  For example,</p>
 <pre class="highlight">
 magick mountains.jpg -virtual-pixel mirror -clahe 300x300+128+3! mountains-clahe.jpg
 </pre>
 <p>Notice the <code>!</code>.  That forces the tile size to exactly 300x300 pixels, whereas without the <code>!</code>, the tile size respects the aspect ratio of the image and results in tile dimensions of <code>300x200</code>.</p>

 </div>
   </div>
   </main><!-- /.container -->
   <footer class="magick-footer">
     <div class="container-fluid">
       <a href="../www/security-policy.html">Security</a> •
       <a href="../www/news.html">News</a>

       <a href="clahe.html#"><img class="d-inline" id="wand" alt="And Now a Touch of Magick" width="16" height="16" src="../images/wand.ico"/></a>

       <a href="../www/links.html">Related</a> •
       <a href="../www/sitemap.html">Sitemap</a>
    <br/>
      <a href="../www/support.html">Sponsor</a> •
      <a href="../www/cite.html">Cite</a> •
      <a href="http://pgp.mit.edu/pks/lookup?op=get&amp;search=0x89AB63D48277377A">Public Key</a> •
      <a href="../www/https://imagemagick.org/script/contact.php">Contact Us</a>
    <br/>
      <a href="https://github.com/imagemagick/imagemagick" target="_blank" rel="noopener" aria-label="GitHub"><svg xmlns="http://www.w3.org/2000/svg" class="navbar-nav-svg" viewBox="0 0 512 499.36" width="2%" height="2%" role="img" focusable="false"><title>GitHub</title><path fill="currentColor" fill-rule="evenodd" d="M256 0C114.64 0 0 114.61 0 256c0 113.09 73.34 209 175.08 242.9 12.8 2.35 17.47-5.56 17.47-12.34 0-6.08-.22-22.18-.35-43.54-71.2 15.49-86.2-34.34-86.2-34.34-11.64-29.57-28.42-37.45-28.42-37.45-23.27-15.84 1.73-15.55 1.73-15.55 25.69 1.81 39.21 26.38 39.21 26.38 22.84 39.12 59.92 27.82 74.5 21.27 2.33-16.54 8.94-27.82 16.25-34.22-56.84-6.43-116.6-28.43-116.6-126.49 0-27.95 10-50.8 26.35-68.69-2.63-6.48-11.42-32.5 2.51-67.75 0 0 21.49-6.88 70.4 26.24a242.65 242.65 0 0 1 128.18 0c48.87-33.13 70.33-26.24 70.33-26.24 14 35.25 5.18 61.27 2.55 67.75 16.41 17.9 26.31 40.75 26.31 68.69 0 98.35-59.85 120-116.88 126.32 9.19 7.9 17.38 23.53 17.38 47.41 0 34.22-.31 61.83-.31 70.23 0 6.85 4.61 14.81 17.6 12.31C438.72 464.97 512 369.08 512 256.02 512 114.62 397.37 0 256 0z"/></svg></a> •
      <a href="https://twitter.com/imagemagick" target="_blank" rel="noopener" aria-label="Twitter"><svg xmlns="http://www.w3.org/2000/svg" class="navbar-nav-svg" viewBox="0 0 512 416.32" width="2%" height="2%" role="img" focusable="false"><title>Twitter</title><path fill="currentColor" d="M160.83 416.32c193.2 0 298.92-160.22 298.92-298.92 0-4.51 0-9-.2-13.52A214 214 0 0 0 512 49.38a212.93 212.93 0 0 1-60.44 16.6 105.7 105.7 0 0 0 46.3-58.19 209 209 0 0 1-66.79 25.37 105.09 105.09 0 0 0-181.73 71.91 116.12 116.12 0 0 0 2.66 24c-87.28-4.3-164.73-46.3-216.56-109.82A105.48 105.48 0 0 0 68 159.6a106.27 106.27 0 0 1-47.53-13.11v1.43a105.28 105.28 0 0 0 84.21 103.06 105.67 105.67 0 0 1-47.33 1.84 105.06 105.06 0 0 0 98.14 72.94A210.72 210.72 0 0 1 25 370.84a202.17 202.17 0 0 1-25-1.43 298.85 298.85 0 0 0 160.83 46.92"/></svg></a>
     <br/>
     <small>© 1999-2021 ImageMagick Studio LLC</small>
     </div>
   </footer>

   <!-- Javascript assets -->
   <script src="assets/magick.js" ></script>
   </body>
 </html>
 <!-- Magick Cache 13th February 2021 11:37 -->




	<!doctype html>
	<html lang="en">
	<head>
	<meta charset="utf-8" />
	<meta name="viewport" content="width=device-width, initial-scale=1" />
	<title>ImageMagick - Contrast Limited Adaptive Histogram Equalization</title>
	<meta name="application-name" content="ImageMagick" />
	<meta name="description" content="Use ImageMagick® to create, edit, compose, and convert digital images. Resize an image, crop it, change its shades and colors, add captions, and more." />
	<meta name="application-url" content="https://imagemagick.org" />
	<meta name="generator" content="PHP" />
	<meta name="keywords" content="contrast, limited, adaptive, histogram, equalization, image processing software" />
	<meta name="rating" content="GENERAL" />
	<meta name="robots" content="INDEX, FOLLOW" />
	<meta name="generator" content="ImageMagick Studio LLC" />
	<meta name="author" content="ImageMagick Studio LLC" />
	<meta name="revisit-after" content="2 DAYS" />
	<meta name="resource-type" content="document" />
	<meta name="copyright" content="Copyright (c) 1999-2020 ImageMagick Studio LLC" />
	<meta name="distribution" content="Global" />
	<meta name="magick-serial" content="P131-S030410-R485315270133-P82224-A6668-G1245-1" />
	<meta property='og:url' content='../' />
	<meta property='og:title' content='ImageMagick' />
	<meta property='og:image' content='../images/logo.png' />
	<meta property='og:type' content='website' />
	<meta property='og:site_name' content='ImageMagick' />
	<meta property='og:description' content="Create, Edit, Compose, or Convert Digital Images" />
	<meta name="google-site-verification" content="_bMOCDpkx9ZAzBwb2kF3PRHbfUUdFj2uO8Jd1AXArz4" />
	<link href="clahe.html" rel="canonical" />
	<link href="../images/wand.png" rel="icon" />
	<link href="../images/wand.ico" rel="shortcut icon" />
	<link href="assets/magick.css" rel="stylesheet" />
	</head>
	<body>
	<nav class="navbar navbar-expand-md navbar-dark bg-dark fixed-top">
	<div class="container-fluid">
	<a class="navbar-brand" href="../"><img class="d-block" id="icon" alt="ImageMagick" width="32" height="32" src="../images/wand.ico"/></a>
	<button class="navbar-toggler" type="button" data-bs-toggle="collapse" data-bs-target="#magick-navbars" aria-controls="magick-navbars" aria-expanded="false" aria-label="Toggle navigation">
	<span class="navbar-toggler-icon"></span>
	</button>

	<div class="collapse navbar-collapse" id="magick-navbars">
	<ul class="navbar-nav me-auto mb-2 mb-md-0">
	<li class="nav-item">
	<a class="nav-link " href="../www/index.html">Home</a>
	</li>
	<li class="nav-item">
	<a class="nav-link " href="../www/download.html">Download</a>
	</li>
	<li class="nav-item">
	<a class="nav-link " href="../www/command-line-tools.html">Tools</a>
	</li>
	<li class="nav-item">
	<a class="nav-link " href="../www/command-line-processing.html">CLI</a>
	</li>
	<li class="nav-item">
	<a class="nav-link " href="../www/develop.html">Develop</a>
	</li>
	<li class="nav-item">
	<a class="nav-link" target="_blank" href="https://github.com/ImageMagick/ImageMagick/discussions">Community</a>
	</li>
	<li class="nav-item">
	<iframe src="https://github.com/sponsors/ImageMagick/button" title="Sponsor ImageMagick" height="35" width="107" style="border: 0;"></iframe>
	</li>
	</ul>
	<form class="d-flex form-inline" action="search.html">
	<input class="form-control me-2" type="text" name="q" placeholder="Search" aria-label="Search">
	<button class="btn btn-outline-success" type="submit" name="sa">Search</button>
	</form>
	</div>
	</div>
	</nav>

	<div class="container">
	<script async="async" src="https://localhost/pagead/js/adsbygoogle.js"></script>
	<ins class="adsbygoogle"
	style="display:block"
	data-ad-client="ca-pub-3129977114552745"
	data-ad-slot="6345125851"
	data-full-width-responsive="true"
	data-ad-format="horizontal"></ins>
	<script>
	(adsbygoogle = window.adsbygoogle \|\| []).push({});
	</script>

	</div>

	<main class="container">
	<div class="magick-template">
	<div class="magick-header">
	<h1 class="text-center">Adaptive Histogram Equalization</h1>
	<p class="lead magick-description">Use contrast limited adaptive histogram equalization (AHE) to improve contrast in images. Ordinary histogram equalization computes a global equalization whereas an adaptive method computes several histograms, each corresponding to a distinct section of the image, and uses them to redistribute the lightness values of the image. It is suitable for improving the local contrast and enhancing the definitions of edges in each region of an image. A variant of adaptive histogram equalization, contrast limited adaptive histogram equalization (CLAHE) limits AHE's tendency to overamplify noise in relatively homogeneous regions of an image.</p>
	<p>CLAHE is supported as of ImageMagick 7.0.8-24 with the <a href="../www/command-line-options.html#clahe">-clahe</a> option:</p>
	<ul>
	<h6><a class="anchor" id="clahe"></a>-clahe <var>width</var>x<var>height</var>{%}{+}<var>number-bins</var>{+}<var>clip-limit</var>{!}</h6>
	</ul>
	<p> The image is divided into tiles of <var>width</var> and <var>height</var> pixels. Append <code>%</code> to define the width and height as percentages of the image's dimensions. The tile size should be larger than the size of features to be preserved and respects the aspect ratio of the image. Add <code>!</code> to force an exact tile width and height. <var>number-bins</var> is the number of histogram bins per tile (min 2, max 65536). The number of histogram bins should be smaller than the number of pixels in a single tile. <var>clip-limit</var> is the contrast limit for localized changes in contrast. A clip-limit of 2 to 3 is a good starting place (e.g. -clahe 50x50%+128+3). Very large values will let the histogram equalization do whatever it wants to do, that is result in maximal local contrast. The value 1 will result in the original image. Note, if the number of bins and the clip-limit are omitted, they default to 128 and no clipping respectively.</p>
	<p>To visualize the benefits of CLAHE, we have a low contrast image of mountains:</p>
	<p>
	<ul>
	<a href="../images/mountains.jpg"><img src="../images/mountains.jpg" width="500" height="333" alt="label" /></a>
	</ul>
	<p>We can improve the image with global histogram equalization:</p>
	<ul>
	<a href="../images/mountains.jpg"><img src="../images/mountains-equalize.jpg" width="500" height="333" alt="label" /></a>
	</ul>
	<p>We can further improve the image with the contrast limited adaptive histogram equalization image processing technique:</p>
	<ul>
	<a href="../images/mountains.jpg"><img src="../images/mountains-clahe.jpg" width="500" height="333" alt="label" /></a>
	</ul>
	<p>The latter image was produced with this command:</p>
	<pre class="highlight">
	magick mountains.jpg -clahe 25x25%+128+3 mountains-clahe.jpg
	</pre>
	<p>The <code>25x25%</code> argument divides the image into 16 tiles to perform local contrast enhancement. The image dimensions are <code>1500x1000</code> so the tiles are exactly <code>375x250</code> pixels each. Rather than a percentage, you can specify the tile dimensions directly with <code>375x250</code>.</p>
	<p>For tile sizes that do not divide evenly into the image dimensions, CLAHE utilizes virtual pixels, as such the results can vary slightly based on your chosen virtual pixel method. For example,</p>
	<pre class="highlight">
	magick mountains.jpg -virtual-pixel mirror -clahe 300x300+128+3! mountains-clahe.jpg
	</pre>
	<p>Notice the <code>!</code>. That forces the tile size to exactly 300x300 pixels, whereas without the <code>!</code>, the tile size respects the aspect ratio of the image and results in tile dimensions of <code>300x200</code>.</p>

	</div>
	</div>
	</main><!-- /.container -->
	<footer class="magick-footer">
	<div class="container-fluid">
	<a href="../www/security-policy.html">Security</a> •
	<a href="../www/news.html">News</a>

	<a href="clahe.html#"><img class="d-inline" id="wand" alt="And Now a Touch of Magick" width="16" height="16" src="../images/wand.ico"/></a>

	<a href="../www/links.html">Related</a> •
	<a href="../www/sitemap.html">Sitemap</a>
	<br/>
	<a href="../www/support.html">Sponsor</a> •
	<a href="../www/cite.html">Cite</a> •
	<a href="http://pgp.mit.edu/pks/lookup?op=get&search=0x89AB63D48277377A">Public Key</a> •
	<a href="../www/https://imagemagick.org/script/contact.php">Contact Us</a>
	<br/>
	<a href="https://github.com/imagemagick/imagemagick" target="_blank" rel="noopener" aria-label="GitHub"><svg xmlns="http://www.w3.org/2000/svg" class="navbar-nav-svg" viewBox="0 0 512 499.36" width="2%" height="2%" role="img" focusable="false"><title>GitHub</title><path fill="currentColor" fill-rule="evenodd" d="M256 0C114.64 0 0 114.61 0 256c0 113.09 73.34 209 175.08 242.9 12.8 2.35 17.47-5.56 17.47-12.34 0-6.08-.22-22.18-.35-43.54-71.2 15.49-86.2-34.34-86.2-34.34-11.64-29.57-28.42-37.45-28.42-37.45-23.27-15.84 1.73-15.55 1.73-15.55 25.69 1.81 39.21 26.38 39.21 26.38 22.84 39.12 59.92 27.82 74.5 21.27 2.33-16.54 8.94-27.82 16.25-34.22-56.84-6.43-116.6-28.43-116.6-126.49 0-27.95 10-50.8 26.35-68.69-2.63-6.48-11.42-32.5 2.51-67.75 0 0 21.49-6.88 70.4 26.24a242.65 242.65 0 0 1 128.18 0c48.87-33.13 70.33-26.24 70.33-26.24 14 35.25 5.18 61.27 2.55 67.75 16.41 17.9 26.31 40.75 26.31 68.69 0 98.35-59.85 120-116.88 126.32 9.19 7.9 17.38 23.53 17.38 47.41 0 34.22-.31 61.83-.31 70.23 0 6.85 4.61 14.81 17.6 12.31C438.72 464.97 512 369.08 512 256.02 512 114.62 397.37 0 256 0z"/></svg></a> •
	<a href="https://twitter.com/imagemagick" target="_blank" rel="noopener" aria-label="Twitter"><svg xmlns="http://www.w3.org/2000/svg" class="navbar-nav-svg" viewBox="0 0 512 416.32" width="2%" height="2%" role="img" focusable="false"><title>Twitter</title><path fill="currentColor" d="M160.83 416.32c193.2 0 298.92-160.22 298.92-298.92 0-4.51 0-9-.2-13.52A214 214 0 0 0 512 49.38a212.93 212.93 0 0 1-60.44 16.6 105.7 105.7 0 0 0 46.3-58.19 209 209 0 0 1-66.79 25.37 105.09 105.09 0 0 0-181.73 71.91 116.12 116.12 0 0 0 2.66 24c-87.28-4.3-164.73-46.3-216.56-109.82A105.48 105.48 0 0 0 68 159.6a106.27 106.27 0 0 1-47.53-13.11v1.43a105.28 105.28 0 0 0 84.21 103.06 105.67 105.67 0 0 1-47.33 1.84 105.06 105.06 0 0 0 98.14 72.94A210.72 210.72 0 0 1 25 370.84a202.17 202.17 0 0 1-25-1.43 298.85 298.85 0 0 0 160.83 46.92"/></svg></a>
	<br/>
	<small>© 1999-2021 ImageMagick Studio LLC</small>
	</div>
	</footer>

	<!-- Javascript assets -->
	<script src="assets/magick.js" ></script>
	</body>
	</html>
	<!-- Magick Cache 13th February 2021 11:37 -->