HDTV Update!

If you have been to your local electronics retailer lately, you likely noticed the explosion of HDTVs (High Definition Televisions). You might already own your own HDTV. With the FCC mandated conversion well under way, we felt it might be useful to re-visit this issue and discuss how it will affect AV presentation needs.

In a previous blog post we have discussed:

– The history of broadcast standards. The NTSC standard used throughout North America, Japan, and other various nations has 525 horizontal lines of information updated 60 times per second. The PAL standard used in Europe, most of Asia, Africa, and South America has 625 lines of information updated 50 times per second.

– Why the FCC was mandating a change to Digital Television. Digital broadcasts take up a fraction of the airspace as analog broadcasts – not to mention improved quality of both video and audio with digital.

– The change in aspect ratio. Standard television broadcasts are in a ratio of 4 wide to 3 high. HDTV is broadcast in a ratio of 16 wide to 9 high. This change in aspect ratio more closely matches motion pictures, commonly shot in a 1.85 to 1 format.

The FCC mandated conversion from analog to digital broadcasts (but not necessarily high definition) is scheduled for completion by January 2007. At that time all 1500+ pubic and non-profit TV stations should be broadcasting digital signals. Four years ago, the feeling in the Industry was that the conversion “could not be physically completed by 2007.” There would not be enough bodies and equipment to do the actual work. Well, the Industry was wrong. According to the National Association of Broadcasters, 1175 stations are already broadcasting digital information.

So how will all of this impact audiovisual presentation needs and system designs?

First, lets look at the equipment components. Eventually you will need to replace the television with one that supports digital signals. In the meantime, you can get a conversion box (such as a Sony’s SATHD200 HDTV & DirecTV Receivers / Decoders) that will convert a digital TV signal to the analog NTSC standard, then display that signal on your existing TV. Most audiovisual manufacturers have already begun manufacturing equipment (projectors, switchers, and other video routing products) that support HDTV signals as well as traditional NTSC and computer signals. The conversion process will take time, with most analog components being replaced through obsolescence as old equipment is replaced and new equipment (that supports both formats) is installed.

Next, lets look at the issue of aspect ratios. As mentioned above, until now, video signals (NTSC) and most computer signals typically used the same aspect ratio of 4 to 3. So a video or computer image on a projection screen or TV monitor in a 4 to 3 ratio will “fill” the screen without any distortion or stretching. Of course when motion picture films (which use a wide screen format – typically 1.85 to 1) are converted to NTSC, they are compressed horizontally or each side is cut off in a “pan and scan” conversion process.

With the advent of HDTV screens, in the 16 to 9 format, there is a closer correlation between HDTV images and motion picture images. The issue is that there is less of a correlation between HDTV/Motion picture and Computer images. One solution is to size the screen or display device for the largest dimension in both directions then leave blank “bars” on the top and bottom of the display or blank “pillars” on each side of the image, thus maintaining the correct aspect ratio of the original image.

Alternatively, the image can be electronically expanded or compressed to fill the screen. Unfortunately this distorts the image. While not a significant problem for video images, this is noticeable when text or computer images with text are displayed. The best solution may be found in solving another problem with mixing various aspect ratios through the video input/display process. A drawback with current video projectors is that very few, to date, use an HDTV native resolution or wide screen aspect ratio LCD chip inside the projector. They still use a 4 to 3 aspect ratio display chip.

Pixel based displays (e.g. LCD chips) provide the best image when they use the same resolution from signal input to signal display. On the consumer side where most projectors only display video data (but this is quickly changing!) there are already a number of projectors that have LCD chips in wide screen resolutions. These projectors display the image at its native resolution and do not distort or manipulate the image to fit a particular aspect ratio. Unfortunately they don’t display computer resolutions very well nor are these chips found in higher brightness projectors needed for larger AV presentation spaces. It is only a matter of time before this consumer trend is pushed into professional AV projectors with native wide screen aspect ratio chips. These projectors will fill an HDTV format projection screen when displaying HDTV signals and show pillars on each side when displaying lower resolution 4 by 3 aspect ratio images.

A simple way to think about it is that it all comes down to geometry. Traditional televisions and computers use a smaller, almost square, rectangle compared to an HDTV display. Like an IQ test where you must fit the correct block in the proper hole, we have dissimilar shapes that must fit together. Until we all agree to use the same shape rectangle to watch video and computer images, it’s going to be a challenge to put it all together and make it look good. No matter how you address these issues, what is certain is that the quality of video and computer images is on the way up.