The histograms of big target and small target images are analyzed.It is pointed out that they are made up of peaks from background and tails from target.

• 分析了大目标图像和小目标图像的直方图，指出其均由一个背景的尖峰和目标的拖尾组成，理想的分割阈值点应为尖峰和拖尾的临界点。