3.4. Preprocessing

At the time the original image is input to the model, the normalization operation needs to be completed. Before training, to avoid excessive order of magnitude differences in the variables of each input, which influence the effect of subsequent algorithms, the data will generally be normalized to a decimal number between [0, 1] first [35]. The mathematical expression of the normalization is as in Equation (4):

where x is the original data and xnorm is the normalized data. After normalization, the value of the input data is between [0, 1] and contributes to the convergence of the model, avoiding the polarization of weights, thus causing numerical problems.