众所周知,PAL制电视接收机有一种特有的失真称为“爬行”.这种失真看上去是一些行结构很粗的水平条纹,在整个屏幕上自下而上的蠕动,影响图象的质量,就是因为爬行效应致使简单的PAL解码方式未被人们所采用,而代之以更复杂的PAL-D解码方式.一部调整精良的PAL-D接收机是看不出爬行的,但如果解码器失调(元件老化、变质、电路参数发生变化等原因所致),就有可能出现明显的爬行. It is well-known that PAL television receivers have a peculiar distortion called “crawling.” Such distortion appears to be horizontal stripes with thick lines and bottom-up motions throughout the screen, affecting the quality of the picture, Because of the creeping effect, a simple PAL decoding method has not been adopted by people and has been replaced by a more complex PAL-D decoding method. A well-tuned PAL-D receiver can not see a crawl, but if the decoder Dislocation (aging components, deterioration, changes in circuit parameters and other reasons), there may be significant crawling.