BT.601

Paragraph 2.51 of the BT-601 standard, excerpted below, gives the derivation of the BT.601 digital signal from analog video.

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2.5 Definition of the digital signals Y, CR, CB, from the primary (analogue) signals E'R, E'G and E'B

This paragraph describes, with a view to defining the signals Y, CR, CB, the rules for construction of these signals from the gamma pre-corrected primary analogue signals E'R, E'G and E'B.

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In analog electronics, E is the symbol for electromotive force measured in volts.

BT.601, issued in 1982, was intended to be a bridge between analog and digital video. It was never intended for use with computer video. The IBM PC was released in 1981, just one year prior to the issuance of BT.601. At the time, 4-bit, 16-color CGA graphics were standard.

There is a standard for computer video: sRGB. It was developed in 1996 by Hewlett Packard and Microsoft, and was standardized by the IEC in 1999.

sRGB uses different luma coefficients than BT.601. It uses the same luma coefficients as ITU BT.709, a video standard developed in 1990.