A luminance signal bandwidth expansion method for NTSC system

Bandwidth expansion of the luminance signal is discussed as a method of picture quality improvement in the NTSC television system. By modulating the high-frequency component over a 4.2-MHz luminance signal using a new subcarrier whose phase is field-alternated and multiplexing the aliasing component resulting from that to a low-frequency component, the transmissible bandwidth of the luminance signal can be expanded, with compatibility to NTSC receivers. A method based on this principle is proposed. Expanding the bandwidth as described, the transmissible two-dimensional spatial frequency area is matched with the visual characteristics and an improved image sharpness is achieved. Experiments confirmed that the bandwidth can be expanded while maintaining compatibility with NTSC receivers. In addition, subjective evaluation tests indicated that there is not much deterioration of image sharpness through the method´s deletion of the oblique high spatial frequency component, and that sharpness is improved in pictures including detailed images through the proposed method. A novel phase regeneration circuit is also proposed