Twenty years after the drafting of RS-170, the EIA video signal standards committee proposed the RS-170A color video standard, which evolved into what is known today as the NTSC composite video signal standard. In this standard, color images are produced on a video display by mixing different intensities of red, green, and blue light which have been encoded onto 1, 2, 3, or 4 wires. The earliest version of the RS-170A standard was the single-wire composite video format known as the basic NTSC video standard. Based the original RS-170 monochrome video standard, the NTSC color video signal contains intensity, color, and timing information on the same line. The basic intensity and timing information conforms to the RS-170 monochrome standard, while the color information is superimposed on the intensity waveform. Information contained in a ‘color burst’ located in the back porch of each horizontal scan signal is used to decode the color information. This color information is combined with the analog intensity signal to reconstruct the three primary colors needed to generate a colorized image. The encoding scheme was designed such that, with the proper filtering, a RS-170 monochrome monitor will produce an acceptable black and white image when fed an NTSC color video signal. The two-wire version of the RS-170A color standard is known as “S-Video”. In this format, one pair of coax wires carries the Y channel, which contains the combined intensity and timing signals in accordance with the RS-170 monochrome standard. A second wire pair, the ‘chroma’ or C channel, carries a separate color signal which transmits the color information. S-video is usually transmitted over a single cable with a special 4-pin connector on either end. The four-wire format is known as RGBS for Red, Green, Blue, and Sync. RGBS video is a “component video” format, meaning the various components of information required to reproduce a video display are enclosed by the three separate video signals as well as a separate composite sync signal. In this case the color signal is broken into three separate and equal channels, each carrying high-resolution information. Timing information is provided on a separate wire – the synch channel. Timing information is sometimes also present on the green channel, but more often not. This video format is called RS-170 RGB.