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Is your HDTV underperforming? Here' s a really quick fix

HDTV

Every TV has one: a button that zooms in on the picture, or changes the aspect ratio. Sometimes called View Mode, Format, Size, Zoom, or something similar, these modes have a variety of names, but all have the same purpose.

In reality, most of the time there is only one “correct” mode, the other modes offering less resolution, possible artifacts, and in a few limited cases, a better picture.

Overscan
One of the primary reasons why these controls exist is a “feature” called Overscan. In the olden days, TV makers had a lot of wiggle room in defining the edges of the image. So two TVs, of the same size, might show slightly more or less of the broadcast image. At the edges of the image, there was frequently a lot of noise (some of which was part of the image, some not).

Even in the early days of HD, many stations broadcast a few pixels of noise, so a TV was better off showing, let’s say, 1900 x 1060 of the original signal, than blowing it up to fill the 1920 x 1080 screen.

And that “blowing up” is the problem.

Scaling
Every pixel on your TV is active, regardless of the resolution of the source. With DVDs, the TV upconverts (aka scales) the image to fill the screen. It is creating information that is not in the original source, in order to have data for every pixel.

To a lesser extent, the same is happening when you view an HDTV with any amount of overscan active, or when in one of the modes listed earlier. The TV is zooming in slightly on the original image, which requires it to modify every pixel in the image to fit. Look at it this way, if you’re watching a Blu-ray, or a 1080i image from cable/satellite, that image has a specific pixel for every one of the actual pixels on your TV. A 1:1 map, if you will. If the TV has overscan active, or is zooming in slightly, now it’s more like a 1:0.9 map. The TV has to scale the image.

Regardless of how good the scaler is in the TV, this is going to increase noise and artifacts, and potentially reduce resolution (if it can’t scale the image well).

Find this control on your TV, and for the best picture, set it to Just Scan, 1:1, Full, Native, Dot-by-Dot and so on. You’ll be able to tell which is the right one, as when you’re watching a 1080i or 1080p image, it will appear to zoom out slightly, and you’ll see more of the picture’s edges.

A few exceptions
Occasionally, you’ll find a channel or program that has some weird, non-picture data on the edge of the screen, usually only a few pixels wide. If this bothers you, well, now you know where the control is to zoom in and clip it off. But this is pretty rare these days.

One other use for this control is zooming in on a 16x9 image that resides in a 4x3 window. For example, on my AT&T U-verse, BBC America is available only in standard definition (thanks a lot AT&T). So if I want to watch the 16x9 "Top Gear" it’s only viewable with black bars on the sides (SD is 4x3) and on the top and bottom (because it’s 16x9 within the 4x3). Obviously I don’t, I buy the show in HD on iTunes, but you get my point. In this case, you could zoom in on the image, to better fill the screen with the tiny program. Keep in mind, this will likely look like crap.

However, and this is a HUGE deal, you should only be doing this rarely and for the few channels not available in HD. If you are doing this a lot, especially with network shows, you are likely not set up correctly for HD. (Check out my article on How to Set Aspect Ratio on Your TV.)

If you’re black-bar-ophobic, there are often modes that stretch the entire 4x3 standard definition image to fill the screen, or the more, uh, clever of these modes that keep the center of the image at the correct aspect ratio, and only stretch the edges. It’s worth noting that using either of these modes is quite possibly the worst your TV will ever look, and should be avoided if at all possible.

This is almost always the default setting for TVs in hotels, which is one of the main reasons hotel TVs look so terrible.

Source boxes
All cable/satellite boxes and Blu-ray players have aspect ratio settings, too. The wrong setting will provide a distorted, lower resolution image. Most on-screen menus ask you to select your TV aspect ratio. For all current HDTVs this would be 16:9. If set to 4:3, the image will be badly distorted. Make sure your source box is set to the 16:9 image setting.

Most boxes also will ask for an output resolution setting. Choices will include 480i, 480p, 720p and 1080i. With 1080p TVs (most current models), this control should be set to 1080i (some cable/satellite boxes also allow 1080p output, but it only applies to pay per view movies).

Blu-ray players should be set to 1080p. Many offer a 1080p/24 setting, though not all TVs can do anything with this frame rate. Most Blu-ray players will have a test mode to verify that your TV can accept the resolution prior to making the final setting.

If you have a 720p TV, you can set the cablebox to either 720p or 1080i, though the latter is probably better. If you choose 720p, the signal will be ideal for 720p content such as ABC and Fox but 1080i content (used by CBS, NBC, HBO and others) will be down converted in the box. It’s likely your TV will do a better job de-interlacing and downconverting 1080i content than your cablebox, so choosing 1080i output is likely better. Also, most non-1080p TVs these days are actually 1,024 x 768, slightly more vertical resolution than 720p. So you may squeeze a few extra lines of resolution when watching 1080i content by choosing the 1080i output.

Conclusion
The short version? Ideally you’d watch all HD content set to fill the screen, with no overscan. Check your settings, there may be aspect ratio controls, and separate overscan controls.

While most Blu-ray players will auto-detect the correct aspect ratio (nearly always 16x9), DVD players and cable/satellite boxes do not. Check the settings of these as well to make sure they’re sending your TV the correct aspect ratio (and resolution!). I always watch TV with the overscan off and in a 1:1 pixel mapping mode, and it has been years since I’ve seen noise on the edges of the screen. Check both controls, your TV may look better … for free!

Reach Geoff Morrison on Twitter at @TechWriterGeoff. Have a question for the HD Guru? Send an email.

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