A TechLore "Ask the Experts" Question...

Question:

I own a Hitachi 4:3 HDTV (model # 53UDX10B) and recently acquired a Comcast HDTV receiver. When I view the HDTV channels through the new Comcast receiver, I often get black bars at the top and bottom, as well as the left and right sides of the image. It's like looking in a box within a box. What is wrong, and how can I fix it?

-submitted by chuck's friend

Answer:

4:3 HDTVs are kind of an oddity... compatible with digital signals, but not ideal for HDTV. The explanation of why this is happening can get a bit complicated, so I'll do my best to make it simple.

Old style television signals (NTSC) are broadcast in a 4:3 ratio, meaning that those signals will fill the entire screen when played back on a 4:3 TV like yours. The new HDTV standard dictates that all HDTV signals must be sent in a widescreen shape, which will fit perfectly on a newer 16:9 HDTV. Simple? Good. Here's where the fun begins.

Let's say a broadcaster wants to air an old episode of Seinfeld, which was never produced for HDTV, and has an aspect ratio of 4:3. To air this on their digital station, they have to make some decisions.

The Broadcaster's Dilemma

The first decision is whether or not to air it as an HDTV image. No, they can't magically make Seinfeld HD quality, but they have to upconvert the signal and broadcast it as a 480p, 720p, or 1080i image. Broadcasters cannot air 480i analog programs on their digital stations. If they choose 480p, they can broadcast it in a 4:3 ratio, but most digital stations choose to broadcast it as an HD signal. Which brings us to decision #2.

Bars on the Sides

720p and 1080i signals are inherently widescreen, so they can't broadcast Seinfeld as a 4:3 picture. They have to decide if they want to attach black bars to the sides of the picture, or stretch the image to fill a 16:9 area without bars. Broadcasters all take a different approach, and all of them get yelled at by consumers for whichever they choose.

If the broadcaster chooses to put black bars on the sides, this can cause problems for HDTV owners, and is what's causing your problem. When an HDTV set receives a 1080i or 720p signal, the TV switches to a standard widescreen mode. 4:3 digital TVs like yours leave black bars at the top and bottom of the screen in in order to draw a rectangular widescreen shape in the center. Except, the broadcaster has placed black bars on the sides of the image so they could broadcast it as an HDTV image. On a 16:9 display this would only leave blank space at the sides, but on a 4:3 HDTV, you'll end up with black space all the way around the screen(see image). In essence, a small 4:3 image inside a large black frame.

One reason why consumers don't like this is because many HDTVs (especially the early models) do not allow special formatting when receiving widescreen signals. So if the broadcaster chooses to put bars on the screen, many are forced to watch it that way.

Stretch to Widescreen

On the flip side, stretching the 4:3 signal to fill a widescreen TV also has its problems. Broadcasters don't always do the best job of this, which makes people look fatter than they are. Those who don't enjoy watching TV this way are forced to, since most digital sets have no way to restore the image back to its original shape.

What You Can Do

In your case, they TV you have offers several different formatting options, but the manual is unclear as to which format modes are available for 720p and 1080i signals. Go into the TV's menu and find "picture formats" under the setup heading. Aspect 3 looks like it should do the trick, but I can't verify that this mode will be available when receiving signals of this type. Play with the different options it gives you, and see what you can do to get rid of the bars.

Your cable box may also give you some flexibility. If it's a Motorola box. Hit menu when the box is off, and you should be able to access the setup menu. If there is an option for your display shape, choose 4:3.

One way or another, you could always switch to the analog broadcast of these programs, and only watch the digital channel for shows that are true HDTV programs. Watching the upconverted digital signal will yield little improvement over the analog version anyway.

Matt Whitlock - Editor, TechLore.com