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| <p class="lead magick-description">Connected-component labeling (alternatively connected-component analysis, blob extraction, region labeling, blob discovery, or region extraction) uniquely labels connected components in an image. The labeling process scans the image, pixel-by-pixel from top-left to bottom-right, in order to identify connected pixel regions, i.e. regions of adjacent pixels which share the same set of intensity values. For example, let's find the objects in this image:</p> |
| <ul> |
| <a href="../images/objects.gif"><img src="../images/objects.gif" width="256" height="171" class="image-slices" alt="purse"></a> |
| </ul> |
| <p>To identify the objects in this image, use this command:</p> |
| <pre> |
| convert objects.gif -connected-components 4 -auto-level -depth 8 objects.png |
| </pre> |
| <p>The detected objects are uniquely labeled starting with 1. Use auto leveling to visualize the detected objects:</p> |
| <ul> |
| <a href="../images/objects.png"><img src="../images/objects.png" width="256" height="171" class="image-slices" alt="Objects"></a> |
| </ul> |
| <p>Note, the <code>-connected-components</code> option requires ImageMagick version 6.8.9-10 or later.</p> |
| <p>Object statistics is useful to review. To display them, use this command:</p> |
| <pre> |
| convert objects.gif -define connected-components:verbose=true -connected-components 4 objects.png |
| </pre> |
| <p>Five objects were detected with these statistics:</p> |
| <pre> |
| Objects (id: bounding-box centroid area mean-color): |
| 0: 256x171+0+0 +119.2,+80.8 33117 gray(0) |
| 2: 120x135+104+18 +159.5,+106.5 8690 gray(255) |
| 3: 50x36+129+44 +154.2,+63.4 1529 gray(0) |
| 4: 21x23+0+45 +8.8,+55.9 409 gray(255) |
| 1: 4x10+252+0 +253.9,+4.1 31 gray(255) |
| </pre> |
| <p>Use <code>-connected-components 8</code> to visit 8 neighbors rather than 4. By default, neighbor colors must be exact to be part of a unique object. Use <a href="command-line-options.html#fuzz">-fuzz</a> to include pixels that are <var>close</var> in color.</p> |
| <p>You might want to eliminate small objects by merging them with their larger neighbors. If so, use this command:</p> |
| <pre> |
| convert objects.gif -define connected-components:area-threshold=410 -connected-components 4 \ |
| -auto-level objects.jpg |
| </pre> |
| <p>Here are the expected results. Notice, how the small objects are now merged with the background.</p> |
| <p class="img-responsive center-block"> |
| <a href="../images/objects.jpg"><img src="../images/objects.jpg" width="256" height="171" class="image-slices" alt="Objects"></a> |
| </p> |
| <p>Use the <a href="command-line-options.html#fuzz">-fuzz</a> option to identify objects that are made up of pixels similiar in color (e.g. <code>-fuzz 3%</code>).</p> |
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