The ImageEnhance module can also be used for contrast stretching. The following code block shows how to use the enhance() method from the contrast object to enhance the contrast of the same input image:

contrast = ImageEnhance.Contrast(im)
im1 = np.reshape(np.array(contrast.enhance(2).getdata()).astype(np.uint8), (im.height, im.width, 4)) 
pylab.style.use('ggplot')
pylab.figure(figsize=(15,5))
pylab.subplot(121), plot_image(im1)
pylab.subplot(122), plot_hist(im1[...,0], im1[...,1], im1[...,2]), pylab.yscale('log',basey=10)
pylab.show()

The following shows the output of the code. As can be seen, the contrast of the input image has been enhanced and the color channel histograms are stretched towards the endpoints: