The marked color contrast between Mars and the bright blue star was easy to discern by eye, but is further enhanced in the picture through the use of a diffusion filter.
火星与明亮的蓝色恒星醒目的颜色对比用肉眼很容易辨认，而这张图用了滤色镜更增强了这种对比。
2
The picture elements across a line are converted to the video signal and low-pass filtered with an electrical filter .
沿着一条直线的图象象素被转换成视频信号，然后由一个电子滤波器进行低通滤波。
3
Digital filter is the basic arithmetic of language, picture processing, model recognition and spectrum analysis.