The Feng thresholding method is interesting because it can qualitatively outperform the Sauvola thresholding method. However, the Feng method contains many parameters that has to be set. Hence this method was never widely accepted.
The Feng method is described in:
Meng-Ling Feng and Yap-Peng Tan, “Contrast adaptive binarization of low quality document images”, IEICE Electron. Express, Vol. 1, No. 16, pp.501-506, (2004)