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copied!<p>I'm thinking in a solution based on ImageMagick. We would need the following steps:</p> <ol> <li>Find the color used to draw in the scanned document (for now on, called <strong>target color</strong>);</li> <li>Find its <code>x</code> and <code>y</code> coordinates in the image;</li> <li>Pass this position as a seed to Flood Fill algorithm.</li> </ol> <p>We could use the following script based on functions of ImageMagick:</p> <ol> <li><p>Output all the unique colors in the picture. This will be used to find out which are the RGB components of the target color (<a href="http://www.imagemagick.org/discourse-server/viewtopic.php?f=1&t=13493" rel="nofollow">command source</a>). </p> <pre><code>convert <image> -unique-colors -depth 8 txt:- > output.txt </code></pre></li> <li><p>Output the coordinates of each color in a text file:</p> <pre><code>convert <image> txt:- > coord.txt </code></pre></li> <li><p>Find the <code>x</code> and <code>y</code> coordinates of the target color (<a href="http://www.imagemagick.org/discourse-server/viewtopic.php?f=1&t=20900" rel="nofollow">command source</a>). Suppose the target color obtained by step 1 was red:</p> <pre><code>grep red coord.txt </code></pre></li> <li><p>Finally, use <code>x</code> and <code>y</code> as a seed to <code>floodfill</code> to replace the circle region by your desired color (<a href="http://www.imagemagick.org/discourse-server/viewtopic.php?f=1&t=17659" rel="nofollow">command source</a>). In this case, I've used <code>white</code> to erase the region:</p> <pre><code>convert <image> -fill white -fuzz 13% \ -draw 'color <x>,<y> floodfill' <image_floodfill_output> </code></pre></li> </ol> <p>The <code>-fuzz</code> parameter will avoid that colors which were originally <code>red</code> and became corrupted due to noise also gets replaced.</p> <p>This <a href="http://www.imagemagick.org/discourse-server/viewtopic.php?f=1&t=17659" rel="nofollow">tutorial</a> gives more information about <code>floodfill</code> function, such as how to replace the edge colors.</p>

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