SD Digital Video Standards

Printer-friendly version

Moviola's Resource Center: 

  Tips, Tutorials, Articles & More »

Standard Definition Digital Video Standards

With the evolution toward the superior nature of digital video, international standards were developed for digitizing analog standard definition video compatible with both 525 line video standards (NTSC) and 625 line standards (PAL).

ITU-R 601: (Formerly CCIR 601). Properly expressed as ITU-R BT.601. The ITU stands for the International Telecommunications Union and sets international standards (called "recommendations") for radio and other telecommunications. Rec. 601 defines standard definition encoding. Although called a recommendation in reality it is treated more like a standard.

Basic recommendations:

 
Video encoded in YCbCr sampled at 4:2:2 (See Color Spaces for more info on this)
720 luma and 360 chroma samples per line
Allows for 8-bit or 10-bit recording (See Bit Depth)

For simplicity, we'll just look at 8-bit video coding, on which the above scale is based. An interesting and important side note: 16 for black is the same for both 525 and 625 standards. Although NTSC (U.S.) and PAL have different standards for analog black levels (7.5 IRE and 0 IRE respectively), when they are recorded to a digital (601) format, these analog black levels are completely irrelevant. Since it is a digital recording, analog values do not come into play at all- both standards use code 16 for digital video black (for 8-bit video). 10-bit video, although it uses a different scale, corresponds to the same black and white levels.

Analog black levels are only a concern at the stage when the digital video is converted to analog video- for display, transmission, dubs, connecting to analog video scopes. This conversion to analog can happen during output from a digital video deck or output from a digital editing system through an analog output.