====== 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.).