Enhancement of degraded documents is one of the significant and challenging research areas. In recent years, several binarization methods are proposed and presented for the improvement of degraded documents, but, most of them are not appropriate for all kinds of degradation. In this paper, we have described some state-of-the-art binarization techniques and compared their performances using DIBCO 2016 to DIBCO 2018 databases. In addition, we briefly discussed about the challenges and possible future works of image binarization.