1 2 3 4 5<!doctype html> 6<html lang="en"> 7<head> 8 <meta charset="utf-8" /> 9 <meta name="viewport" content="width=device-width, initial-scale=1" /> 10 <title>ImageMagick - Convex Hull</title> 11 <meta name="application-name" content="ImageMagick" /> 12 <meta name="description" content="Use ImageMagick® to create, edit, compose, and convert digital images. 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The convex hull may be visualized as the shape enclosed by a rubber band stretched around the set of points.</p> 98 99<p>The convex-hull string format returns a list of x,y coordinates of the vertices of the convex-hull polygon containing all the non-black pixels within it.</p> 100 101<ul><pre class="code"> 102magick [-fuzz <var>value</var>%] [-background <var>background-color</var>] -format "%[convex-hull]" info: 103</pre></ul> 104 105<p>where the string format is sensitive to an optional <code>-fuzz</code> value and to an optional background color specified by the define. The command above will find the background color automatically according to the fuzz value unless the background color is defined. The fuzz value defaults to 0 when not specified.</p> 106 107<p>For example, consider the following white rectangle on a black background:</p> 108 109<ul><img class="img-fluid d-block" src="../images/convex-hull.png" alt="[Convex Hull]" width="250" height="250" name="convert-hull" /></ul> 110 111<p>The convex hull set of points may be computed as:</p> 112 113<ul><pre class="code">magick rect.png -format "%[convex-hull]" info: 114190,121 193,122 281,154 377,189 378,190 377,193 345,281 310,377 309,378 306,377 218,345 122,310 121,309 122,306 154,218 189,122 190,121 115</pre></ul> 116 117<p>The convex hull may also be drawn as a polygon (filled or unfilled) using <code>-draw</code> as follows:</p> 118 119<ul><pre class="code">magick rect.png -set option:hull "%[convex-hull]" -fill none -stroke red -strokewidth 1 -draw "polygon %[hull]" blocks_hull.png</pre></ul> 120 121<p>Here is an example using a non-convex shaped image on a black background:</p> 122 123<ul><img class="img-fluid d-block" src="../images/convex-hull-blocks.png" alt="[Convex Hull Blocks]" width="128" height="128" name="convert-hull-blocks" /></ul> 124 125<ul><pre class="code">magick blocks_black.png -set option:hull "%[convex-hull]" -fill none -stroke red -strokewidth 1 -draw "polygon %[hull]" blocks_hull.png</pre></ul> 126 127<ul><img class="img-fluid d-block" src="../images/convex-hull-blocks-closure.png" alt="[Convex Hull Blocks Closure]" width="128" height="128" name="convert-hull" /></ul> 128 129<p>Finally, here is an example with a non-constant, non-black background using -fuzz to determine the background color:</p> 130 131<ul><img class="img-fluid d-block" src="../images/convex-hull-barn.jpg" alt="[Convex Hull Barn]" width="250" height="250" name="convert-hull-barn" /></ul> 132 133<p>Now let's highlight the convex hull of the image foreground object:</p> 134<ul><pre class="code">magick barn_rot20.png -fuzz 10% -set hull "%[convex-hull]" -fill none -stroke red -strokewidth 1 -draw "polygon %[hull]" barn_rot20_hull.png</pre></ul> 135 136<ul><img class="img-fluid d-block" src="../images/convex-hull-barn-closure.jpg" alt="[Convex Hull Barn Closure]" width="250" height="250" name="convert-hull-barn-closure" /></ul> 137 138<h2><a class="anchor" id="box"></a>Minimum Bounding Box</h2> 139<p>Similar to the convex hull of the image foreground object(s), is the minimum bounding box. Use <code>%[minimum-bounding-box]</code> to return the points that make up the bounding box. In addition, these properties are set: <code>minimum-bounding-box:area</code>, <code>minimum-bounding-box:width</code>, <code>minimum-bounding-box:height</code>, and <code>minimum-bounding-box:angle</code>. 140 141<ul><pre class="code">magick barn_rot20.png -fuzz 10% -background black -set MBR "%[minimum-bounding-box]" -fill none -stroke red -strokewidth 1 -draw "polygon %[MBR]" barn-mbr.png</pre></ul> 142 143<h2><a class="anchor" id="unrotate"></a>Unrotate an Image</h2> 144<p>Use <code>%[minimum-bounding-box:unrotate]</code> to correct for any rotation the image may exhibit. Unless you specify the image orientation, the unrotate angle should properly align the image to the correct coordinate axis for angles <= 45. For angles > 45, the image will align with the wrong coordinate axis. Set the correct image orientation to ensure the proper unrotate angle is returned. Use <code>-define minimum-bounding-box:orientation=<em>{landscape,portrait}</em></code> to set the image orientation. Note, that like convex-hull, the string format is sensitive to an optional <a href="../www/command-line-options.html#fuzz">-fuzz</a> value and an optional <a href="../www/command-line-options.html#background">-background</a> color.</p> 145 146<p>The barn image above is rotated by 20 degrees. Here is how we can automatically correct for the rotation and return it to its original landscape orientation: 147 148<ul><pre class="code">magick barn_rotate20.jpg -fuzz 15% -set option:angle "%[minimum-bounding-box:unrotate]" -background gray -rotate "%[angle]" -trim barn_unrotate.jpg</pre></ul> 149</p> 150 151</div> 152 </div> 153 </main><!-- /.container --> 154 <footer class="magick-footer"> 155 <div class="container-fluid"> 156 <a href="../www/security-policy.html">Security</a> • 157 <a href="../www/news.html">News</a> 158 159 <a href="convex-hull.html#"><img class="d-inline" id="wand" alt="And Now a Touch of Magick" width="16" height="16" src="../images/wand.ico"/></a> 160 161 <a href="../www/links.html">Related</a> • 162 <a href="../www/sitemap.html">Sitemap</a> 163 <br/> 164 <a href="../www/support.html">Sponsor</a> • 165 <a href="../www/cite.html">Cite</a> • 166 <a href="http://pgp.mit.edu/pks/lookup?op=get&search=0x89AB63D48277377A">Public Key</a> • 167 <a href="../www/https://imagemagick.org/script/contact.php">Contact Us</a> 168 <br/> 169 <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> • 170 <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> 171 <br/> 172 <small>© 1999-2021 ImageMagick Studio LLC</small> 173 </div> 174 </footer> 175 176 <!-- Javascript assets --> 177 <script src="assets/magick.js" ></script> 178 </body> 179</html> 180<!-- Magick Cache 13th February 2021 13:09 -->
