| 摘要 |
Additional information may be transmitted in the active picture period of a video signal by providing the lines of the signal which carry the additional information with a black reference at a higher level than usual (4) thus avoiding visual disturbances on the receiver display (black is displayed at these locations). New, or modified, types of receiver can detect this transmission of data in the active picture period and extract the data for use. This enables high definition images and wide screen images to be transmitted in a form compatible with conventional receivers (the data here being transmitted during lines above and below a letterbox image to be produced on conventional receivers and being the extra information needed to convert the letterbox image to the enhanced image). It also enables control signals to be transmitted (as the data) to new types of receiver, or modified receivers, so as to cause these receivers to alter their operation. |
