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https://zunzheng.com/news/wp-content/uploads/mlib/2019/09/23/技术前沿.jpg1200401在CRT显示时代，电子束在扫描图像的时候，并不是从显示器的边缘开始的，为什么呢，因为如果正好100%从边缘开始我们就会看到显示边缘畸变，图像扭曲不正常，为了解决这个问题，就要加大扫描范围，而显示较小的范围，通常国家标准是95%。即实际上我们看到的图像只是真实图像的95%，边缘被切掉了，切掉的图像部分就是畸变的部分。我们称这个现象为过扫描现象即overscan。