1080 60p and beyond …
Nov 18, 2006 8:00 AM, By Philip Cianci
High-grade DTV promises to deliver a home theatre experience and might impact movie theatre attendance. Large home screens and surround audio can create the theatre experience right at home. Why go to the movies and pay a lot of money, when you can stay home and enjoy content from a DVD or VoD just a few months after its release?
TV has always been a threat to the movie industry. In 1950, movie theatre attendance was more than 3 billion yearly (80 million weekly). Heavily affected by TV, the number dropped to 1 billion (20 million weekly) by 1968. Can the movie production industry find a way to exploit the limit of DTV compression and transmission?
Only the most extravagant home theatres, can match the ambiance and massive sensual stimulus, as well as the group experience, of a small multiplex theatre. And there is something to be said for the sensation of a group scream or sigh that cannot be duplicated at home.
One-upmanship
HDTV broadcasting was launched (in part) with the goal of delivering a unique viewing experience, over the air, to homes for free. Cable operators showed little interest in HD, so terrestrial broadcasters envisioned HD as a means to gain an advantage and reclaim audience.
With the proliferation of new 1080 60p native displays, an opportunity may exist for theatrical content producers to deliver a differentiating experience and regain some of the revenue lost with declines in movie audiences.
Broadcasters will be hard pressed to deliver a true 1080 60p video format as it requires twice the bandwidth of 1080 30i or 720 60p. Source material does not exist in a native 1080 60p format. DVD’s store HD content as 1080 30i or 1080 24p. Scaling up to 1080 60p is done either at the source DVD player or at the display.
By the numbers
If the numbers are examined, use of the 1080 60p video format is not beyond the reach of broadcasters constrained to a 6MHz delivery channel. First, compare the data rate for uncompressed 1080 formats:
1080 60p, 4:2:2 => 1920*1080*60*2*8= 1,990,656,000; 102:1 compression ratio 1080 30i, 4:2:2 => 1920*1080*30*2*8 = 995,328,000; 50:1
As can be seen, 1080 60p doesn’t fit in SMPTE 292 SDI channel. Even with the adoption of the 3Gb/s serial interface, SMPTE 424, the 1080 60p bandwidth requirement will present content distribution challenges in a production infrastructure.
However, 1080 24p isn’t as bad as one might think. 1080 24p, 4:2:2 => 1920*1080*24*2*8 = 796,262,400 which does fit in an HD-SDI stream and is already being delivered by some broadcasters. 3:2 pulldown and scaling converts the 24fps format to the display’s native resolution.
To further reduce the data rate, conversion from RGB to YUV color space is required. Because of the limited ability of the human visual system to perceive color detail, this conversion may be unperceivable. Taking this concept one step further, because ATSC broadcasts use a 4:2:0 color sampling structure, the data rate can be reduced even more.
1080 24p, 4:2:0 => 1920*1080*24*1.5*8= 597,196,800
Which is less than
1080 30i, 4:2:0 => 1920*1080*30*1.5*8= 746,496,000
So, 1080 24p actually has less data than 1080 30i. Subsequently, an argument can be made that there is a lot of free space in a transport stream that can be exploited.| Want to use this article? Click here for options! |  |
