Encoding for Compatibility and Recoverability in the ACTV System

Abstract

This paper describes an advanced compatible television (ACTV) system intended for the single-channel transmission of widescreen EDTV images. Existing NTSC receivers display a selected 4: 3 portion of the widescreen image with standard NTSC resolution. However, a new widescreen receiver, tuned to the same 6-MHz RF channel, displays a widescreen image with a resolution in excess of 400 lines/picture height in both spatial dimensions. To produce the NTSC-compatible signal, the original widescreen high-definition signal is separated into four components: (1) the main NTSC signal with the side panel low frequencies time compressed into the horizontal overscan regions, (2) the time-expanded side panel high frequencies, (3) the extended horizontal-luminance detail, and (4) the extended vertical-temporal luminance detail. Components 2 and 3 are quadrature modulated at low amplitude by a new phase-controlled subcarrier at 3.1 MHz. Component 4 is inserted in quadrature with the RF picture carrier. This paper discusses how the four components are processed to insure full compatibility at the NTSC receiver and complete recoverability at the ACTV receiver.