The ImageEnhance module contains a number of classes that can be used for image enhancement.
from PIL import ImageEnhance
enhancer = ImageEnhance.Sharpness(image)
for i in range(8):
factor = i / 4.0
enhancer.enhance(factor).show("Sharpness %f" % factor)
Also see the enhancer.py demo program in the Scripts/ directory.
All enhancement classes implement a common interface, containing a single method: