Drawing contour lines for an image

A contour line for an image is a curve connecting all of the pixels where they have the same particular value. The following code block shows how to draw the contour lines and filled contours for a grayscale image of Einstein:

im = rgb2gray(imread("../images/einstein.jpg")) # read the image from disk as a numpy ndarray
plt.figure(figsize=(20,8))
plt.subplot(131), plt.imshow(im, cmap='gray'), plt.title('Original Image', size=20) 
plt.subplot(132), plt.contour(np.flipud(im), colors='k', levels=np.logspace(-15, 15, 100))
plt.title('Image Contour Lines', size=20)
plt.subplot(133), plt.title('Image Filled Contour', size=20), plt.contourf(np.flipud(im), cmap='inferno')
plt.show()