on (EBU) became mask most of the quantizing distortion. However, if the interested in a standard for digital component video due video source is virtually noise-free, the quantizing dis- to the difficulties of exchanging video material between tortion is noticeable as contouring in areas where the the 576i PAL and SECAM systems. The format held signal brightness gradually changes. In addition, at least the promise that the digital video signals would be two additional bits of fractional YCbCr or R'G'B' data identical whether sourced in a PAL or SECAM country, were desirable to reduce rounding effects when trans- allowing subsequent encoding to the appropriate com- mitting between equipment in the studio editing envi- posite form for broadcasting. Consultations with the ronment. For these reasons, most pro-video equipment Society of Motion Picture and Television Engineers uses 10-bit YCbCr or R'G'B', allowing 2 bits of fractional (SMPTE) resulted in the development of an approach to YCbCr or R'G'B' data to be maintained. support international program exchange, including 480i Initial proposals had equal coding ranges for all three systems. YCbCr components. However, this was changed SO that A series of demonstrations were carried out to de- Y had a greater margin for overloads at the white levels, termine the quality and suitability for signal processing of as white level limiting is more visible than black. Thus, various methods. From these investigations, the main the nominal 8-bit Y levels are 16-235, while the parameters of the digital component coding, filtering, nominal 8-bit CbCr levels are 16-240 (with 128 and timing were chosen and incorporated into ITU-R corresponding to no color). Occasional excursions into BT.601. BT.601 has since served as the starting point for the other levels are permissible, but never at the 0 and other digital component video standards. 255 levels. Communications Engineering Desk Reference; ISBN: 9780123746481 Copyright © 2007 Elsevier Inc. All rights reserved CHAPTER 7.3 Video si