Detect edges (2)

Edge detection can be performed along multiple axes, then combined into a single edge value. For 2D images, the horizontal and vertical "edge maps" can be combined using the Pythagorean theorem:

$$z = \sqrt{x^2 + y^2}$$

One popular edge detector is the Sobel filter. The Sobel filter provides extra weight to the center pixels of the detector:

weights = [[ 1,  2,  1], 
           [ 0,  0,  0],
           [-1, -2, -1]]

For this exercise, improve upon your previous detection effort by merging the results of two Sobel-filtered images into a composite edge map.

Apply ndi.sobel() to im along the first and second axes.
Calculate the overall edge magnitude using the Pythagorean theorem. Use np.sqrt() and np.square().
Display the magnitude image. Use a grayscale colormap and set vmax to 75.

Exercise

Detect edges (2)

Instructions