The varying pitch helixes were constructed on the parameter equation,and were selected as sweep trajectory;the surface of the screw was enveloped on the generating method.

• 运用傅立叶分析的方法说明了加网和扫描的过程,对扫描半色调印刷品时所产生的龟纹进行了理论的解释,并提出了抑制此类龟纹的方法。