Pulse Coupled Neural Network (PCNN) model has been widely used in digital image processing

but most of the study and the improvement of the model are based on the external characteristic of PCNN

ignoring the shortage resulted from the discretization of the neuron firing time.For both the non-linking PCNN and coupled linking PCNN

this paper analyzed the firing mechanism of neurons from the point of PCNN iterative equations

and the modified formulas of the neuron firing time are proposed.The phenomenon that the mathematics coupled characteristic of model itself has an overwritten effect on its biological characteristics is revealed.On that basis

the method of eliminating the mathematics coupled characteristic is proposed and the automatic parameters determination of PCNN is implemented.Then

a new modified PCNN model is proposed

and it is used in image segmentation and a good result is obtained.