These signals can evolve in the processing of encoding or decoding between RGB and composite video. They occur in pairs and are forms of R - Y and B - Y. I and Q are the band limited, reduced amplitude color difference signals used in transmitting color information in NTSC. Most of the component video systems now handle three video channels: Y, R - Y, & B - Y. The D1 digital recorder stores the digital equivalent of luminance and the pair of color difference signals. There are any number of designations for component video. In the digital domain, the SMPTE spelled out component as Y Cb Cr. Even the order has changed from Y R-Y B-Y where Cb represents B-Y and Cr represents R-Y. The designation has since evolved to Y Pb Pr. While this designation is most often associated with an analog signal, we’ve seen it applied to the digital world.