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POHow to remove convexity defects in a Sudoku square?
 

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  1. POHow to remove convexity defects in a Sudoku square?
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    <p>I was doing a fun project: Solving a Sudoku from an input image using OpenCV (as in Google goggles etc). And I have completed the task, but at the end I found a little problem for which I came here.</p> <p>I did the programming using Python API of OpenCV 2.3.1.</p> <p>Below is what I did :</p> <ol> <li>Read the image</li> <li>Find the contours </li> <li>Select the one with maximum area, ( and also somewhat equivalent to square).</li> <li><p>Find the corner points.</p> <p>e.g. given below:</p> <p><img src="https://i.stack.imgur.com/h1yKg.png" alt="enter image description here"></p> <p>(<strong>Notice here that the green line correctly coincides with the true boundary of the Sudoku, so the Sudoku can be correctly warped</strong>. Check next image)</p></li> <li><p>warp the image to a perfect square</p> <p>eg image:</p> <p><img src="https://i.stack.imgur.com/i4D9o.png" alt="enter image description here"></p></li> <li><p>Perform OCR ( for which I used the method I have given in <a href="https://stackoverflow.com/questions/9413216/simple-digit-recognition-ocr-in-opencv-python">Simple Digit Recognition OCR in OpenCV-Python</a> )</p></li> </ol> <p>And the method worked well.</p> <p><strong>Problem:</strong></p> <p>Check out <a href="http://web.archive.org/web/20140601100441/http://davemark.com/images/sudoku.jpg" rel="noreferrer">this image.</a></p> <p>Performing the step 4 on this image gives the result below:</p> <p><img src="https://i.stack.imgur.com/YTiOC.jpg" alt="enter image description here"></p> <p>The red line drawn is the original contour which is the true outline of sudoku boundary.</p> <p>The green line drawn is approximated contour which will be the outline of warped image.</p> <p>Which of course, there is difference between green line and red line at the top edge of sudoku. So while warping, I am not getting the original boundary of the Sudoku.</p> <p><strong>My Question :</strong> </p> <p>How can I warp the image on the correct boundary of the Sudoku, i.e. the red line OR how can I remove the difference between red line and green line? Is there any method for this in OpenCV?</p>
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    1. USAbid Rahman K
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      1. POHow to remove convexity defects in a Sudoku square?
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    1. COYou're doing your detection based on corner points, which the red and green lines agree on. I don't know OpenCV, but presumably you'll want to detect the lines between those corner points and warp based on that.
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      1. POHow to remove convexity defects in a Sudoku square?
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    2. COPerhaps force the lines that connect the corner points to coincide with heavy black pixels in the image. That is, instead of letting the green lines just find a straight line between corner points, force them to traverse heavy black pixels. This will make your problem substantially more difficult, I think, and I don't know of any OpenCV built-ins that will be immediately useful for you.
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      1. POHow to remove convexity defects in a Sudoku square?
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    3. CO@ Dougal : I think the green line drawn is the approximated straight line of red line. so it is the line between those corner points. When i warp according to green line, i get curved red line at the top of warped image. ( i hope you understand, my explanation seems a little bad)
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      1. POHow to remove convexity defects in a Sudoku square?
      1. USAbid Rahman K
 

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