You are here: Home Page » HDTV » 1080 60p and beyond …

1080 60p and beyond …

Nov 18, 2006 8:00 AM, By Philip Cianci

Beyond 1080 60p

Some professional and consumer equipment manufacturers believe the ultimate resolution of home DTV displays in 10 years will be 2K. This is the 2K, 2048x1536 format now being used for digital cinema.

Comparing the number of display pixels:

1920 x 1080 => 2,073,600

2048 x 1536 => 3,145,728

This shows that 2K has about 50 percent more pixels than a 1080 display. Let’s look at the number of pixels for a 2K image at 24p using three different color sampling structures:

4:4:4 => 1,811,939,328 pixels

4:2:2 => 1,207,859,552 pixels

4:2:0 => 905,969,664 pixels

So, 2K at 24p 4:2:0 is about 21 percent larger than 1080i. Therefore, it may just be possible to compress 2K, 24p, 4:2:0, while maintaining acceptable image quality so it can be delivered in a 6MHz channel. This becomes even more realistic as advanced codecs (AVC & VC-1) are used in the broadcast chain.

2K by the numbers

Looking at the numbers in a little more detail, the 2K display format results in:

2048 x 1536 = 3,145,728 pixels per “frame.”

Comparing the data rates for 24p, 30p and 60p:

Pix/sec RGB Pel/sec 8 bit RGB/sec 24 HZ P => 75,497,472 226,492,416 1,811,939,328 30 Hz P => 94,371,840 283,115,520 2,264,924,160 60 Hz P => 188,743,680 566,231,040 4,529,848,320

An advantage of 24p is that if a 48Hz or 72Hz refresh rate is used, mapping onto the display is simplified, 2:1 or 3:1. This minimizes temporal artifacts that may be produced by frame interpolation. It’s possible that the loss of detail in a rapidly changing scene with current frame rates might be eliminated.

What about the audio?

If all this engineering energy has been successfully expended to deliver a much higher video resolution to consumers, will AC-3 audio suffice? Data rates for compressed Dolby Digital multichannel sound top out at 640kb/s and present virtually no additional challenge for the transport stream.

E-AC-3, Dolby Digital Plus, extends audio channel numbers up to 13.1 at data rates up to 6.144Mb/s. Dolby E can handle eight audio channels as an AES-3 pair with a data rate of 1.536Mb/s at 48KHz and 16 bits. This would allow up to 7.1 channels of surround sound.

A hybrid solution

Although it appears quite possible to deliver 2K format video over a 19.39Mb/s MPEG-2 transport stream, the stumbling block is finding an adequate audio format. Or is it? Dolby Digital (AC-3) is still in its authoring infancy while speaker technology continues to improve. Unless you have a gigantic home theatre, 5.1 audio is completely adequate for a 2K video experience. The difference between uncompressed and Dolby Digital barely is perceptible, even to golden ears.

Granted, moving up to large 2K displays will take some time. Today, QXGA computer monitors operate at 2K resolution with a 72Hz refresh rate. IBM offers a 22.2in 3840 x 2400 pixel model, so availability of 2K displays is really not an issue. And who knows what will be possible 10 years from now in display technology?

Content production is the issue for broadcasters. Most are still struggling with conversion to HD-capable infrastructures and workflows. Only the movie industry is working in 2K and 4K Digital Intermediary (DI). The DI process occurs after film acquisition and digitalization. Content is edited, composited, conformed and effects added in the digital domain. The finished piece is then used to produce release prints on film, or can be presented in digital cinemas. This may represent an opportunity for Hollywood to attain parity with the TV industry by virtue of being the sole content creator capable of providing 2K material for transmission.