Abstract: A blackener for letter box lines associated with a HDTV/conventional-analog hybrid television transmission where the blackener counts horizontal sync pulses contained in the HDTV/conventional-analog hybrid television transmission and determines when the HDTV/conventional-analog hybrid television transmission is in letter-box lines: if it is, then the blackener sends substitute black signal to an output; and if it is not, then the blackener sends the HDTV/conventional-analog hybrid television transmission to the output.

Abstract: HDTV and NTSC compatible image communication is done in a single NTSC channel bandwidth. Luminance and chrominance image data of a scene to be transmitted is obtained. The image data is quantized and digitally encoded to form digital image data in HDTV transmission format having low-resolution terms and high-resolution terms. The low-resolution digital image data terms are transformed to a voltage signal corresponding to NTSC color subcarrier modulation with retrace blanking and color bursts to form a NTSC video signal. The NTSC video signal and the high-resolution digital image data terms are then transmitted in a composite NTSC video transmission. In a NTSC receiver, the NTSC video signal is processed directly to display the scene. In a HDTV receiver, the NTSC video signal is processed to invert the color subcarrier modulation to recover the low-resolution terms, where the recovered low-resolution terms are combined with the high-resolution terms to reconstruct the scene in a high definition format.