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PO3 classes (0, 1, 4) on Boost graph cut
 

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    <p>I obtain strange results when I use the BGL boykov_kolmogorov_max_flow() function. I though I would see 2 classes (0-1 or anything else, but only 2!) but I often see three classes: 0, 1 and 4.</p> <p>For example, using the image below with</p> <ul> <li>source: middle pixel on left border</li> <li>sink: middle pixel on right border</li> <li>horizontal edge cost = 10 * e^(rightPixel / 50)</li> <li>vertical edge code = 0.1.</li> </ul> <p><img src="https://i.stack.imgur.com/L6VMa.png" alt="8 bits image"></p> <p>I obtain the following results:</p> <pre><code>444444444444400000000000000000 444444444444440000000000000000 444444444444440000000000000000 444444444444440000000000000000 444444444444444000000000000000 444444444444444000000000000000 444444444444444000000000000000 444444444444444000000000000000 444444444444444000000000000000 444444444444444000000000000000 444444444444444411000000000000 444444444444444444000000000000 444444444444444444000000000000 444444444444444444000000000000 444444444441111111000000000000 444444444440000000000000000000 444444444440000000000000000000 444444444440000000000000000000 444444444440000000000000000000 444444444444000000000000000000 444444444444000000000000000000 444444444444100000000000000000 444444444444110000000000000000 444444444444110000000000000000 444444444444411000000000000000 444444444444444400000000000000 444444444444444400000000000000 444444444444444400000000000000 444444444444444400000000000000 444444444444444400000000000000 </code></pre> <p>Can someone explain the real meaning of these classes? I'm quite sure 4 is the source class and 0 is the sink class, but what about 1? I found nothing in the documentation about that. I think it means a "not sure" horizontal zone, but why would it means that?!?</p> <p>Second question. Are the 1 reliable? Would it be possible to use them to find a smoother border like in the image below? The goal would be to choose one of the green pixel instead of the red one who are too far to the right. I mean, I know that I could use the 1 in this case to do it, but can I trust them to be there when I need them? :)</p> <p><img src="https://i.stack.imgur.com/osNQO.png" alt="Colored border"></p> <p>Thanks for your time.</p>
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    1. COWhats the output you show (0, 1, 4)? Is this the vertex_color?
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      1. USJan Rüegg
    2. CONo, it's not color values. The goal of a maxflow/mincut is to divide the graph in two classes, so those number are actual class of each pixel. It's obtained by one of the out parameters of boost::boykov_kolmogorov_max_flow(), as you can see in this question http://stackoverflow.com/questions/16178978/boost-grid-graph-and-graph-cut-on-image.
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