Rec. 709

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Rec. 709

ITU-R
ITU-R

The ITU Radiocommunication Sector is one of the three sectors of the International Telecommunication Union and is responsible for radio communication....
Recommendation BT.709, more commonly known by the abbreviations Rec. 709 or BT.709, standardizes the format of High-definition television

High-definition television

High-definition television is a digital television broadcasting system with higher than traditional television systems . HDTV is digitally broadcast; the earliest implementations used analog broadcasting, but today digital television signals are used, requiring less Bandwidth due to digital video compression....
, having 16:9 (widescreen

Widescreen

A widescreen image is a film, computer or television image with a wider and shorter aspect ratio than the standard Academy frame developed during the classical Hollywood cinema era....
) aspect ratio

Aspect ratio

The aspect ratio of a shape is the ratio of its longer dimension to its shorter dimension. It may be applied to two characteristic dimensions of a three-dimensional shape, such as the ratio of the longest and shortest axis, or for symmetrical objects that are described by just two measurements, such as the length and diameter of a rod....
.

Pixel count
Rec. 709 refers to HDTV systems having roughly two million luma samples per frame. Rec. 709 has two parts: Part 1 codifies what are now referred to as 1035i30 and 1152i25 HDTV systems. The 1035i30 system is now obsolete, having been superseded by 1080i and 1080p square-sampled (“square-pixel”) systems. The 1152i25 system was used for experimental equipment in Europe and was never commercially deployed.

Part 2 codifies current and prospective 1080i and 1080p systems with square sampling.

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Encyclopedia

High-definition television

Widescreen

Aspect ratio

Technical details

Pixel count

Rec. 709 refers to HDTV systems having roughly two million luma samples per frame. Rec. 709 has two parts: Part 1 codifies what are now referred to as 1035i30 and 1152i25 HDTV systems. The 1035i30 system is now obsolete, having been superseded by 1080i and 1080p square-sampled (“square-pixel”) systems. The 1152i25 system was used for experimental equipment in Europe and was never commercially deployed.

Part 2 codifies current and prospective 1080i and 1080p systems with square sampling. In attempt to unify 1080-line HDTV standards, part 2 defines a common image format (CIF) with picture parameters independent of the picture rate.

Frame rate

Rec. 709 specifies the following picture rates: 60 Hz, 50 Hz, 30 Hz, 25 Hz and 24 Hz. "Fractional" rates having the above values divided by 1.001 are also permitted.

Initial acquisition is possible in either progressive or interlaced form. Video captured as progressive can be transported with either progressive transport or progressive segmented frame

Progressive segmented Frame

Progressive segmented Frame is a High-definition_television mastering video format designed to acquire, store, modify and distribute progressive scan content using interlaced equipment and media....
(PsF) transport. Video captures as interlaced can be transported with interlace transport. In cases where a progressive captured image is transported as a segmented frame, segment/field frequency must be twice higher than frame rate.

In practice, the above results in following frame rates ("fractional" rates specified in commonly used "decimal" form): 25i, 25PsF, 25p, 50p for 50 Hz systems; 23.976p, 23.976PsF, 24p, 24PsF, 29.97i, 29.97PsF, 29.97p, 30p, 30PsF, 59.94p, 60p for 60 Hz systems.

Digital representation

Rec. 709 coding uses “studio-swing” levels where reference black is defined as 8-bit interface code 16 and reference white is defined as 8-bit interface code 235. Interface codes 0 and 255 are used for synchronization, and are prohibited from video data. Eight-bit codes between 1 and 15 provide footroom, and can be used to accommodate transient signal content such as filter undershoots. Eight-bit interface codes 236 through 254 provide headroom, and can be used to accommodate transient signal content such as filter overshoots and specular highlights. Bit-depths deeper than 8 bits are obtained by appending least-significant bits. Ten-bit systems are commonplace in studios. (Desktop computer graphic systems ordinarily use “full-swing” encoding that places reference black at code 0 and reference white at code 255, and provide no footroom or headroom.) The 16..235 limits (for luma; 16..240 for chroma) originated with ITU Rec. 601

CCIR 601

ITU-R Recommendation BT.601, more commonly known by the abbreviations Rec. 601 or BT.601 is a standard published by ITU-R for encoding interlaced analogue video signals in digital form....
.

Primary chromaticities

**RGB color space parameters**
Color space Color space A color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components ....	White point White point A white point is a set of tristimulus or chromaticity coordinates that serve to define the color "white" in image capture, encoding, or reproduction....		Primaries Primary color Primary colors are sets of colors that can be combined to make a useful range of colors. For human applications, three are often used; for additive combination of colors, as in overlapping projected lights or in cathode ray tube displays, the primary colors normally used are red, green, and blue....
	x_W	y_W	x_R	y_R	x_G	y_G	x_B	y_B
ITU-R BT.709	0.3127	0.3290	0.64	0.33	0.30	0.60	0.15	0.06

Note that red and blue are the same as the EBU primaries while green is halfway between EBU and SMPTE C.

Standards Conversion

When converting between the various HD and SD formats, it would be correct to compensate for the differences in the primaries (e.g. between the Rec. 709, EBU, and SMPTE C primaries). In practice, this conversion is rarely performed and such a conversion would create a liability for post production facilities as they would need to ensure that the color bars on all the new masters are redone. Correcting for differences in the primaries would cause the resulting color bars on the converted tape to be inaccurate. Incorrect color bars will cause a (sub)master to be rejected by quality control checks.

Luma coefficients

HDTV according to Rec. 709 forms luma (Y’) using R’G’B’ coefficients 0.2126, 0.7152, and 0.0722. These coefficients are different from those of Rec.601 (for no good reason, according to some experts ). Although worldwide agreement on a single R’G’B’ system was achieved upon the adoption of Rec. 709, adoption of different luma coefficients created a second flavour of Y’C_BC_R. Whenever SDTV is upconverted to HDTV, or HDTV is downconverted to SDTV, at the studio or at the consumers’ premises, luma-chroma matrixing is required.

Transfer characteristics

Rec. 709 is written as if it specifies the capture and transfer characteristics of HDTV encoding - that is, as if it were scene-referred. However, in practice it is output (display) referred with respect to a 2.4-power function display. (Rec. 709 and sRGB share the same primary chromaticities and white point chromaticity; however, sRGB is explicitly output (display) referred.)

Rec. 709

Technical details

Pixel count

Frame rate

Digital representation

Primary chromaticities

Standards Conversion

Luma coefficients

Transfer characteristics

See also