Before revision:  However, previous detection methods of the viscous and gravitational fingers are based on density thresholding, which is susceptible to the user-specified threshold value. Also, the geometric structures of fingers and their evolution are little studied .
After revision:  However, previous detection methods of the viscous and gravitational fingers are based on density thresholding, which provides limited geometric information of the fingers. The geometric structures of fingers and their evolution are little studied .