| 摘要 |
Method and device for eliminating the background brightness variation of a video signal, in which the background brightness in each line of the frame of a video signal has its low frequency brightness signal a(t) limited, as well as being limited by its deviation from the limited brightness of the preceding line of frame. This can be expressed mathematically by stating that ¦V(t)-a(t)¦ is minimized by means of a(t) on the marginal conditions ¦a(t)-a(t-T)¦</= epsilon and ¦a(t)-a(t- DELTA )¦</= epsilon , in which V(t)=the video signal V at the moment t; a(t)=an estimation of the background brightness variation a(t); T=the duration of a line; DELTA =h/b T/k, in which h/b=the height/width ratio of the image and k=the number of lines per frame, and epsilon =the maximum value of the derivative of a(t) multiplied by DELTA . Thus the method of this invention comprises means for limiting the rate of the build-up of the video signal current during each line by means of a slope limiter comprising a current limiter and condensor connected to the video signal, means for delaying the resulting limited current for the duration of one line of the frame comprising a delay and a one-to-one amplifier so that the difference between the limited variation can be limited with respect to the preceding line in the frame, and then means for subtracting this difference from that of each line of the original video signal. Since the first line of each frame has no preceding line by which to be limited, a separate prolongation device is provided responsive to the frame synchronization pulse for inactivating the difference limiting device for the first line of each frame. |
