In the process of video scan conversion, data sampling rate (Nyquist) problems are presented in many different ways. One of the most visually objectionable problems presented by the sampling rate is that of field flicker. Field flicker occurs, for example, when a progressively scanned image is converted into an interlaced scan image. When progressive-to-interlace scan conversion occurs within an NTSC television system, the flicker occurs at the 30 Hz frame rate. When progressive-to-interlace scan conversion occurs within a PAL television system, the flicker rate is 25 Hz.
One prior approach to flicker reduction has been to provide vertical low pass filtering of the scan converted video stream. While vertical low pass filtering is effective to remove the flicker artifacts from the displayed picture image, the tradeoff has been significant, perceptible loss of vertical resolution in the resultant picture display.
The present inventor has proposed a solution to the problem of flicker reduction in single bit computer graphics systems in which light transitions are between black and white, i.e. wherein there is no gray scale range. That solution is to be found in copending U.S. patent application Ser. No. 07/445,369, filed on Dec. 4, 1989, and entitled "Scan Converter with Adaptive Vertical Filter for Single Bit Computer Graphics Systems", the disclosure of which is hereby incorporated herein by reference.
Heretofore, there has been no satisfactory method to remove flicker artifacts from a scan converted television image signal stream without constantly degrading the vertical resolution.