VIR II System

The quality of color reproduction in color television receivers has often suffered due to the misadjustment of chroma level and tint controls by the customer. To give some help to the customer, several schemes have been introduced such as automatic chroma level, automatic tint, and factory preset controls, These systems are widely used, but do not solve the problems caused by chroma level or subcarrier phase differences between stations or control voltage drift during warm-up period. Moreover, factory preset controls are subject to drift from their original setting due to component aging and eventually should be set again, which requires a service call. Therefore, a better system which is not subject to these problems become desirable. In October, 1975, after several years of testing by the broadcasting industry and the EIA, the FCC designated the 19th line of each field of video information as reserved for a specific Vertical Interval Reference (VIR) signal. The signal itself simply consists of a chroma reference, a luminance reference, and a black level reference as shown in Fig. 1. When the chrominance reference and black level reference are equal in amplitude at the receiver's R-Y output, chroma phase (tint) conforms to that of the transmitted reference signal. Likewise, by maintaining proper amplitude relationship between the B-Y output and the luminance signal, chroma level can be matched to the reference signal. The use of this VIR signal has finally provided the color television receivers with the means for truly automatic chroma level and tint reception.