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faq:technical:what_is_the_algorithm_used_in_find_edges

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faq:technical:what_is_the_algorithm_used_in_find_edges [2019/04/12 13:13] (current)
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 +====== FAQ: What is the algorithm used in Find Edges? ======
  
 +It is the 3x3 [[http://​homepages.inf.ed.ac.uk/​rbf/​HIPR2/​sobel.htm|Sobel edge filter]].
 +
 +The source is in the //​filter()//​ method of the// ij/​process/​ByteProcessor.java //class.
 +
 +  ...
 +  case FIND_EDGES: // 3x3 Sobel filter
 +  sum1 = p1 + 2*p2 + p3 - p7 - 2*p8 - p9;
 +  sum2 = p1  + 2*p4 + p7 - p3 - 2*p6 - p9;
 +  sum = (int)Math.sqrt(sum1*sum1 + sum2*sum2); ​
 +  if (sum> 255) sum = 255;
 +  break;
 +  ...
 +
 +p1...p9 hold the grey value of the pixels in the 3x3 kernel (the central pixel is p5).
 +
 +There are many other edge detecting algorithms (such as Canny, Roberts, Marr's Laplacian-of-Gaussian or LoG, difference-of-boxes or DoB, Frei-Chen, etc.).
faq/technical/what_is_the_algorithm_used_in_find_edges.txt ยท Last modified: 2019/04/12 13:13 (external edit)