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HDV@Work

Feb 27, 1997 4:53 PM


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Just What is 1080? Part 3
By Steve Mullen

In the last HDV@Work newsletter, we learned that “1080i” can have 710 to 1045 TV lines/ph horizontal resolution and 470 to 1040 TVL vertical resolution. The table below summarizes these resolutions.

1280x720

 

1280x720

 

One-CCD

1280x720

 

Three-CCD

1440x1080

Green-shift

One-CMOS

960x1080

Green-shift

Three-CCD

1440x1080

Green-shift

Three-CCD

1920x1080

 

Three-CCD

720p

630x575

694x694

 

 

 

 

1080i

 

 

710x715

590x715

885x715

1045x715

1080 24/30fps

 

 

710x470

590x535

885x535

1045x1040

 

We also learned that 1080i quality is decreased when it is compressed below 19.4Mbps during transmission and storage. The good news is that 1080i quality can be significantly increased by the use of less compression. And that is exactly the path Sony is taking with its new XDCAM HD system. XDCAM HD records up to 35Mbps MPEG-2 to a blue-laser recorder.

Despite the almost 2X increase in bandwidth and thus the dramatic decrease in compression—and hence the elimination of most motion artifacts—XDCAM HD shares one characteristic of HDV. Both use 4:2:0 color sampling.

The following Table displays common MPEG-2 Profiles and Levels.

Profile @ Level


Profile @ Level

Resolution

Maximum Frame-rate

Sampling

Maximum Rate

Comments

MP@ML

MainProfile@MainLevel

720x480

30fps

4:2:0

15Mbps

 

Limited to 9Mbps for DVDs

DVD

MP@H-14

MainProfile@High1440

1080i with 1440 pixels/line

OR

720p with 1280 pixels/line

1080i: 30fps

OR

720p: 30fps

4:2:0

60Mbps

!supportEmptyParas]> 

Limited to 25Mbps for DV tape

HDV:

720p30

1080i

!supportEmptyParas]> 

Potential to move to tape-based at 40Mbps

MP@HL

MainProfile@HighLevel

1080i with 1920 pixels/line

OR

720p with 1280 pixels/line

1080i: 30fps

OR

720p: 60fps

4:2:0

80Mbps

!supportEmptyParas]> 

ATSC: limited to 19Mbps

XDCAM HD at up to

35Mbps

422P@H-14

4:2:2Profile@High1440

1080i with 1440 pixels/line

OR

720p with 1280 pixels/line

1080i: 30fps

OR

720p: 60fps

4:2:2

80Mbps

XDCAM HD at up to

70Mbps

 

When we encode a DVD, we are using MainProfile@MainLevel (MP@ML) MPEG-2. MainProfile@HighLevel (MP@HL) is employed for ATSC broadcasts. Both 720p and 1080i HDV employ MainProfile@High1440 (MP@H-14) MPEG-2.

Sony’s new XDCAM HD uses a MainProfile@HighLevel codec at 18Mbps (120 minutes recording), 25Mbps (90 minutes recording), and 35Mbps (60 minutes recording). Its unlikely 18Mbps will be much used because the actual MPEG-2 data rate is only 14Mbps after PCM audio and Proxy AV data have been subtracted. (These add up to 3.5Mbps.) Recording at 25Mbps (21Mbps video) makes sense when video will be intercut with 1080i HDV.

The real value of XDCAM HD comes with 35Mbps (31Mbps video) where MPEG-2 motion artifacts should be eliminated. Further, the ability of optical disc recording to use VBR rather than CBR encoding increases image quality for difficult scenes.

And although the MainProfile@HighLevel codec supports up to 1920 pixels, the Sony records only 1440 pixels, as does HDCAM.

The next likely step for Sony is 4:2:2 color sampling using the Profile@High1440 (422P@H-14) codec. Naturally, when encoding additional chroma detail, the recorded data rate must increase to avoid MPEG-2 artifacts. Up to 80Mbps is supported by 422P@H-14, which means Sony will be able record at up to 70Mbps. (The maximum recording capability of XDCAM optical system is 72Mbps.)

Sony can be expected to introduce this theoretical XDCAM HD system when double-density blue-laser drives ship. By waiting for these drives, recording times for 4:2:2 XDCAM will remain identical to those of the current XDCAM HD. These camcorders will likely employ 2/3in., 1920x1080 CCDs rather than the 1/2in., 1440x1080 CCDs used by the PDW-F330 (MSRPs of $16,800) and PDW-F350 (MSRPs of $25,800) camcorders. Sony’s MPEG-4-based HDCAM-SR will remain at the top of line with its support of 1920x1080, 4:4:4 video.

“MPEG-2 Long GOP, as an open standard, enables us to be very flexible with existing and future products,” according to Bob Ott, vice president of optical and network systems, Sony Electronics. “The capabilities of the existing XDCAM SD and HD systems, as they relate to customer needs, are keys to addressing the television market both in news and production. The important aspect is we will be shipping the second generation of XDCAM before NAB 2006.”

Looking back at these developments, it is safe to say that the 1080i we are watching now is the worst looking 1080i we will ever see. In the next HDV@Work newletter, well complete our look at “What is 1080i?” by revealing why almost 50 percent of current HDTVs cannot display more than 540 lines of 1080i video.

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