Because of digital technologies, high-definition television (HDTV) has become a common video system. Commercial 4K TV broadcasting has started in Japan in 2015. 8K is also under developing, and the 8K TV broadcasting service is planned in 2020. 4K/8K are prospective media, and their
high-resolution video has various possibilities for broadcasting, medical, publishing, and others. With regard to the video system equipment, cameras are very important because they determine the image quality, particularly resolution. However, a fine focus is more important than the capability
of a camera. Professional HD/4K/8K cameras are not equipped with auto-focus systems because the focus areas should be controlled manually due to production-making requirements. The image is blurry if the focus is not fine. Because of operability, small and light-weight cameras are preferred.
The size of the viewfinders is similar with that of the HDTV cameras. It is extremely difficult to adjust the focus with a small viewfinder even for a professional video camera person. Large bulky LCDs are used to adjust the focus even for outside broadcasting. They reduce the performance
and obstruct mobility. Focus aid systems are proposed to cope with the focus issues. They are based on the linear signal processing method. However, these do not have tolerance against noise. Noise always appears if the lighting condition is not sufficient. In this paper, a nonlinear signal
processing is proposed to fix the noise issue. The nonlinear focus assist method also shows a more accurate focus and smaller areas than the current systems.