Sobel Filter / Edge Detector in Image Processing

To filter an image it is filtered using both operators the results of which are added together

The Sobel edge detector is a gradient based method. Sobel filters are typically used for edge detection

Sobel Filter / Edge Detector in Image Processing

  • It works with first order derivatives.
  • It calculates the first derivatives of the image separately for the X and Y axes.
  • The derivatives are only approximations (because the images are not continuous).
  • To approximate them, the following kernels are used for convolution:

The kernel on the left approximates the derivative along the X axis.

The one on the right is for the Y axis. Using this information, you can calculate the following:

  • Magnitude or “strength” of the edge:
  • Approximate strength:
  • The orientation of the edge:

Above, I’ve detected horizontal peaks. You can clearly see the horizontal edges highlighted.

You can then threshold this result to get rid of the grey areas and get solid edges.

Be the first to comment

Leave a Reply

Your email address will not be published.