Robust measure of image focus in the wavelet domain

In this paper we propose a robust technique for image focus measure based on discrete wavelet transform (DWT). We suggest the absolute sum of the second-level detailed image of DWT as focus measure. In the experiment the absolute-sum based measure shows equally well performance as the energy-based measure while enhancing computation efficiency. Comparison to other benchmarking measures is also discussed. Our measure exhibits more robustness to Gaussian noise. Moreover, we show that setting a threshold on the wavelet coefficients can dramatically increase the discriminative power of the focus measure in noisy condition.