详细分析了多级误差扩散（MED）半色调数字图像中出现伪轮廓现象的原因，提出了一种二级多次半色调图像叠合成多级半色调图像的方法，并利用其结果图像对多级半色调图像进行修正补偿，最终获得的半色调图像基本消除了伪轮廓现象，并且保留了多级误差扩散的原有优点。

The major causes of pseudo-contour in multi-level error diffusion (MED) halftone digital images were analyzed. A new method for producing multi-level halftone images by superposition of two level halftone images was put forward. The new multi-level halftone images were used to modify the images produced by traditional MED algorithm. The modified halftone images were basically free of pseudo-contour phenomena and kept the advantages of multi-level error diffusion.