Authors(Kumar J, et al.) present a very intuitive and simple measure which works on grayscale image, is comparable to state-of-art solution and takes far less time to compute as it doesn't require expensive FFT, canny-edge detection or SVD. It is effective in detecting motion-blur, de-focused images or inherent properties of imaging system.The paper claims to work better than any other perceptually-based, no-reference sharpness measures on LIVE Dataset.
https://github.com/umang-singhal/pydom
See also #184