Historical PAL standards documents indicate a “precorrection” (OECF) with a 1⁄2.8-power (approximately 0.36); however, that value is unrealistic. In practice, the BT.1886 EOCF value of 1⁄2.4 is used. See Gamma in video on page 318.

SMPTE RP 187, Center, Aspect Ratio and Blanking of Video Images.

STL - SEAV-0H + 0.5(SAL -1)

STL

864 -732 + 0.5(720 -1)

=

864

= 983 1728

Three nonlinear primary components R’, G’, and B’ are computed such that the intended image appearance is obtained on the reference display in the reference viewing conditions (see Reference display and viewing conditions, on page 427).

In the default power-up state of a camera, the nonlinear primary components are computed from the camera’s RGB tristimulus estimates according to the opto-electronic conversion function of the BT.709 OECF, described on page 320; this process is loosely called gamma correction.

The colorimetric properties of the display primaries are supposed to conform to the BT.709 primaries described on page 290: DTV transmission standards call for BT.709, and modern consumer displays use BT.709. However, production and mastering of 576i content historically used EBU primary chromaticities, not BT.709 (see EBU Tech. 3213 primaries, Table 26.4 on page 293).

Luma (Y’)

Luma in 576i systems is computed as a weighted sum of nonlinear R’, G’, and B’ primary components according to the luma coefficients of BT.601:

The luma component Y’, being a weighted sum of nonlinear R’G’B’ components, has no simple relationship with the CIE relative luminance (Y) used in colour science. Video encoding specifications typically place no upper bound on luma bandwidth (though transmission standards may).

Picture center, aspect ratio, and blanking

The center of the picture is located midway between the central pair of the 720 active samples of BT.601, at the fraction 983⁄1728 between 0H instants. Concerning the vertical center, see Table 40.1, on page 458.

Aspect ratio is defined as 4:3 with respect to a clean aperture pixel array, 690 samples wide at a sampling rate of 13.5 MHz, and 566 lines high. Blanking transitions should not intrude into the clean aperture.

In the composite and analog domains, video information on the left-hand halfline of line 623 terminates 30.350±0.1 µs after 0H. Video information on the right-

SMPTE RP 202, Video Alignment for MPEG-2 Coding.

SDI was introduced on page 432. Mechanical and electrical details were presented on page 439.

hand halfline of line 23 commences 42.500±0.1 µs after

0H.

No studio standard addresses square sampling of 576i video. I recommend using a sample rate of 944fH, that is, 14.75 MHz. I recommend using 768 active samples, centered as mentioned above.

When MPEG-2 with 576 or 608 image rows is used in the studio, the bottom image row corresponds to line 623 (as indicated in Table 40.1). The bottom lefthand halfline (on line 623) is among the coded image rows. The right-hand half of this line will be blank when presented to the MPEG encoder; upon decoding, it may contain artifacts. Unfortunately, 576i DV systems digitize a range one image row up from this.

Component digital 4:2:2 interface

The CB and CR colour difference components of digital video are formed by scaling B’-Y’ and R’-Y’ components, as described in CBCR components for SD on page 361. Y’CBCR signals were once conveyed through the parallel digital interface specified in Rec. 656 and EBU Tech. 3246; nowadays, the serial digital interface (SDI) is used.

In 13.5 MHz sampling of 576i, sample 732 corresponds to the line sync datum, 0H. If digitized, that sample would take the 50% value of analog sync.

SMPTE RP 187 specifies that samples 8 and 710 correspond to the 50%-points of picture width. For flatpanel displays, EBU suggests that the central

702 samples contain active video.

The choice of 720 active samples for BT.601 accommodates the blanking requirements of both 480i and 576i analog video: 720 samples are sufficient to accommodate the necessary transition samples for either system; see page 378.

Unfortunately, the blanking tolerances between 480i and 576i do not permit a single choice of blanking transition samples: The narrowest possible picture width in 480i is several samples too wide to meet 576i tolerances.

Figure 40.2 overleaf shows a waveform drawing of luma in a 576i component digital 4:2:2 system.

EBU Tech. N20, Parallel interface for analogue component video signals in GRB form.

EBU Tech. N10, Parallel interface for analogue component video signals.

A component analog 576i R’G’B’ interface is based on nonlinear R’, G’, and B’ signals conveyed as voltage, with a range of 1 VPP from synctip to reference white. Transient excursions slightly outside the reference black-to-white range are permitted. A video signal of zero – blanking level, equal to reference black – corresponds to a level of 0 VDC. A video signal of unity corresponds to 700 mV.

Sync is added to the green component according to Equation 40.2, where sync and active are taken to be unity when asserted and zero otherwise:

The excursion of the G’ signal from synctip to reference white is 1 VPP . Levels in 576i systems are usually specified in millivolts, not the IRE units common in 480i systems. If IRE units were used, 1 IRE would equal 7 mV.

Analog luma (Y’) is carried as a voltage ranging 1 VPP from synctip to reference white. Luma signal of zero – blanking level, equal to reference black – corresponds to a level of 0 VDC. Luma signal of unity corresponds to