Abstract: Based on the channel width theory,a method of defining electronic zooming in direct-view photo-electronic imaging is given,showing that there exists an optimal value of electronic zooming in the efficacy of photo-electronic imaging.Appropriate electronic zooming may get better in visual effects imaging.Both excessive or insufficient electronic zooming may lead to defective visual efficacy.Gives the quantitative determination method for optimal electronic zooming value under "optimal" conditions of channel width.The computational result agrees basically with that observed in actual photo-electronic imaging systems.