Historical NTSC standards documents indicate a “precorrection” with a 1⁄2.2-power (approximately 0.45), but in practice the BT.1886 EOCF 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

858 -736 + 0.5(720 -1)

=

858

=321

572

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 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 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 480i content historically used SMPTE primary chromaticities, not BT.709 (see SMPTE RP 145 primaries, Table 26.5 on page 293).

Luma (Y’)

Luma in 480i systems is computed as a weighted sum of nonlinear R’, G’, and B’ primary components, according to the luma coefficients of BT.601, as detailed in BT.601 luma, on page 346:

The luma component Y’, being a weighted sum of nonlinear R’G’B’ components, has no simple relationship with 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 two of the 720 active samples of BT.601, at the fraction 321⁄572 between 0H instants. Concerning the vertical center, see Table 39.1, on page 446.

In 4:3 systems, the aspect ratio is defined to be 4:3 with respect to a clean aperture pixel array, 708 samples wide at a sampling rate of 13.5 MHz, and 480 lines high.

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

30.593 ≈ 63.555 − 732 − 716

213.5

41.259 ≈ 63.555 + 858 − 732 + 2

213.5

In Transition samples, on page 378, I mentioned that it is necessary to avoid, at the start of a line, an instantaneous transition from blanking to picture information. SMPTE standards call for picture information to have a risetime of 140±20 ns. For 480i or 576i video, a blanking transition is best implemented as a threesample sequence where the video signal is limited in turn to 10%, 50%, and 90% of its full excursion.

No studio standard addresses square sampling of 480i video. I recommend using a sample rate of 780fH, that is, 12 3⁄11 MHz (i.e., 12.272727 MHz). I recommend using 648 samples – or, failing that, 644 or 640 – centered as mentioned above.

When MPEG-2 with 480 or 512 image rows is used in the studio, the bottom image row corresponds to line 525 (as indicated in Table 39.1). The bottom lefthand halfline (on line 263) is not among the coded image rows. Unfortunately, 480i DV systems digitize a range one image row up from this.

Halfline blanking

Most component video equipment treats the top and bottom lines of both fields as integral lines; blanking of halflines is assumed to be imposed at the time of conversion to analog. In composite equipment and analog equipment, halfline blanking must be imposed.

In the composite and analog domains, video information at the bottom of the picture, on the left half of line 263, should terminate 30.593 µs after 0H. This timing is comparable to blanking at the end of a full line, but preceding the midpoint between 0H instants instead of preceding the 0H instant itself.

Historically, in the composite and analog domains, a right halfline at the top of the picture – such as picture on line 284 – commenced about 41 µs after 0H. This timing is comparable to blanking at the start of

a full line, but following the midpoint between 0H instants instead of following the 0H instant itself. However, in NTSC broadcast, line 284 must remain available for closed captioning (along with line 21). So, it is now pointless for studio equipment to carry the traditional right-hand halfline of picture on line 284: Picture should be considered to comprise 482 full lines, plus a left-hand halfline on line 263.

SDI was introduced on page 432. Eight-bit SD interfaces between digital ICs are often described as “601” (where horizontal and vertical sync signals are conveyed on dedicated wires) or “656” (where sync is embedded as TRS codes).

Halfline blanking has been abolished from progressive scan video, and from JPEG, MPEG, and HD.

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 are usually conveyed through the serial digital interface (SDI), which I introduced on page 432. R’G’B’ 4:4:4 (or R’G’B’A 4:4:4:4) components can be conveyed across a dual-link interface using two SDI channels; alternatively, the single-link

540 Mb/s SDI interface of SMPTE 344M can be used. In 13.5 MHz sampling of 480i, the sample located 16 sample clock intervals after EAV corresponds to the line sync datum (0H): If digitized, that sample would

take the 50% value of analog sync.

Figure 39.2 above shows a waveform drawing of luma in a 480i component digital 4:2:2 system.

Component analog R’G’B’ interface

A component analog 480i R’G’B’ interface is based on nonlinear R’, G’, and B’ signals. Analog R’,G’, B’ signals are conveyed as voltage, with a range of 1 V from synctip to reference white. (Transient excursions slightly above reference white are permitted.)

SMPTE 253M, Three-Channel RGB

Analog Video Interface.

In studio systems, analog component R’G’B’ signals ideally have zero setup, so zero in Equation 39.2 corresponds to 0 VDC. According to SMPTE 253M, unity corresponds to 700 mV. Sync is added to the green component according to Equation 39.2, where sync and active are taken to be unity when asserted and zero otherwise:

Sadly, the SMPTE R’G’B’ analog interface is unpopular, and “NTSC-related” levels are usually used, either with or without setup.

Some systems, such as 480i studio video in Japan, use a picture-to-sync ratio of 10:4 and zero setup. In this case, unity in Equation 39.3 corresponds to 5⁄7 V, about 714 mV:

Many systems – such as computer framebuffers using the levels of the archaic EIA RS-343-A standard – code component video similarly to composite video, with 10:4 picture-to-sync ratio and 7.5% setup:

The PB and PR scale factors are appropriate only for component analog interfaces. For details concerning scale factors in component digital systems, see CBCR components for SD, on page 361. For details concerning scale factors in composite analog or digital NTSC or PAL, see UV components, in Chapter 5 of Composite NTSC and PAL: Legacy Video Systems.

Component analog Y’PBPR interface, EBU N10

The PB and PR colour difference components of analog video are formed by scaling B’-Y’ and R’-Y’ components, as described in PBPR components for SD on page 359. Wideband PB and PR components are theoretically possible but very rarely used; normally, PB and PR are lowpass filtered to half the bandwidth of luma.

Component Y’PBPR signals in 480i are sometimes interfaced with zero setup, with levels according to the EBU Tech. N10 standard. Zero (reference blanking level) for Y’, PB, and PR corresponds to a level of 0 VDC, and unity corresponds to 700 mV. Sync is added to the luma

EIA/CEA-770.2, Standard Definition

TV Analog Component Video Interface.

CEA/CEDIA-863-B, Connection Color Codes for Home Theater Systems.

component; sync is taken to be unity when asserted and zero otherwise:

Figure 39.3 shows a waveform drawing of luma in a 480i component analog interface according to the EBU Tech. N10 standard. In North America, the levels of EBU N10 mysteriously became known as “SMPTE levels,” or “SMPTE/EBU N10 interface,” even though N10 is solely an EBU standard and SMPTE failed to

standardize a component analog luma/colour difference interface.

CEA has standardized the 700 mV, zero-setup levels for use by consumer electronics devices such as DVD players and set-top boxes, for 480i and 480p formats at 4:3 and 16:9 aspect ratios.

In 2011, about a quarter of a century after the introduction of component analog video interfaces, CEA (with CEDIA, Custom Electronic Design and Installation Association) standardized the colours of the connectors to be used: green for Y’, blue for CB, and red for CR. (In the consumer domain, composite NTSC or PAL video is typically carried on a wire having yellow connectors.)