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.