The more pixels, the merrier?

The number of pixels on a television panel, or its native resolution, determines the amount of detail you'll see on screen. So, it's worth paying more for higher resolutions... or is it?

You're in your local consumer electronics store looking at 42-inch plasma TVs side-by-side, and they're playing the same high-definition demonstration footage that stores typically use to make TVs look good. Cosmetically, the sets appear very similar -- until you examine the little price/information placards. One set costs AU$2,999, one AU$4,999, one AU$6,499 and still another other costs AU$6,999. The pixel resolution on the cheapest set is 852x480, two others are 1024x768 and the other (not the most expensive set) sports 1024x1024 pixel resolution.

When you look a bit closer, you may think that one plasma looks sharper than another, but which set should you buy?

The fix is in
Welcome to the confusing world of fixed-pixel displays. All fixed-pixel TVs -- including every flat-panel LCD and plasma as well as rear-projection televisions that use DLP and LCD technology -- have a certain number of pixels, known as the native resolution, that they use to create the picture. With these types of displays, the native resolution is the absolute limit on the amount of detail you'll see.

In Australia, you may hear of standard definition (SD) broadcasts, which have a resolution of 576i (576 horizontal lines -- interlaced). To qualify as a high definition (HD) broadcast, the minimum picture resolution must be at least 576p (576 lines x 720 pixels per line -- progressive). HD can also be 720p (720 lines x 1280 pixels -- progressive) or 1080i (1080 lines x 1920 pixels -- interlaced). For more on the flavours of digital television see our feature on Digital TV in Australia.

Regardless, fixed-pixel displays follow a few basic rules:

1. No matter the resolution of the source material, whether VHS, DVD, or HDTV, a fixed-pixel display will always convert, or scale, it to fit its native resolution.
2. If the incoming source has more pixels than the display's native resolution, you will lose some visible detail and sharpness, though often what you're left with still looks pretty good.
3. If the incoming source has fewer pixels than the native resolution, you're not getting any benefit from the extra resolution. In almost every case, extra pixels will not make a lower-resolution source look better. All other things being equal, the same DVD shown on an HD and a non-HD plasma will have the same amount of detail.

Here are some examples of how native resolutions interact with DVD and HD sources in the real world:

	32-inch (81cm) analog TV	42-inch (106cm) plasma	42-inch (106cm) HD plasma	50-inch (127cm) or larger plasma; 23-inch (58cm) or larger LCD; 720p DLP or LCD rear projection	1080p flat-panel LCD; 1080p DLP rear projection
What is the native resolution?	No exact number, since it doesn't use pixels, but the amount of detail, for a good analog TV, would be the equivalent of 640 x 480 pixels.	852 x 480 pixels	1,024 x 768 or 1,024 x 1,024 pixels	1,280 x 720, 1,280 x 768, or 1,366 x 768 pixels	1,920 x 1,080 pixels
If you feed it an HD signal, will you see a picture?	No	Yes	Yes	Yes	Yes
Will it display every pixel of wide-screen DVD?	No	Yes	Yes	Yes	Yes
Will it display every pixel of 576p? (ABC, SBS, Seven)	No	No	Yes	Yes	Yes
Will it display every pixel of 720p?	No	No	No	Yes	Yes
Will it display every pixel of 1080i? (Nine, Ten)	No	No	No	No	Yes

1080p
There's another native resolution that's available in flat-panel LCDs and rear-projection televisions: 1080p. These sets have imaging elements with 1,920x1,080 pixels, which should allow them to display every single detail of 1080i high-def TV sources. We say should for a reason: the real onscreen resolution still might be less than all 2 million pixels, for a variety of reasons. With flat-panel LCDs, video processing can soften the visible resolution. With rear-projection sets, the brightness-enhancing screen can also soften resolution, especially in models smaller than 60 inches diagonal. Whether or not these sets can handle every pixel, however, they provide the benefit of smaller, more closely packed pixels, meaning you can sit closer and not notice the pixel grid -- the screen-door effect. And they definitely provide sharper pictures than 720p native-resolution sets, regardless of whether they actually resolve every detail of 1080i.

How much does pixel count matter?
If we go back to the example of the otherwise similar plasmas above, the question remains: Is it worth another AU$2,000-$4000 to get the more pixels, or is 852 x 480 enough? Keep in mind the following:

1. DVD and standard TV will look basically the same on both.
2. Non-HD plasmas generally have better black-level performance and higher contrast ratios than their HD siblings, which lead to better-looking dark scenes.
3. HD plasmas will look significantly more detailed with HD and computer sources, even though they don't show every pixel.
4. HD plasmas have smaller pixels, allowing you to sit closer without discerning the pixel grid.

Here's an estimation of how the same high-def image would look on an HD plasma (top) vs. a non-HD plasma (bottom). Perceived resolution is also affected by factors such as movement in the picture and seating distance.

Ultimately, the choice comes down to whether you believe the increased resolution with high-def or computer sources is worth the price difference and, in some cases, the trade-off in black-level performance. Keep in mind that TVs last a long time and that more and more HD programs and sources (such as Blu-ray and HD-DVD) are becoming available, so you'll have more opportunities to take advantage of extra pixels in the future.

Resolution isn't everything
Before you rush out and buy a plasma purely on the basis of its pixel count, remember that resolution is only part of the story. Performance among fixed-pixel displays still varies widely, and colour accuracy, black levels, video processing and the rest are all important factors in picture quality. What's really the best way to know which fixed-pixel TV to buy? Decide what kind of input you will spend the most time watching, research your purchase using CNET.com.au's TV reviews, and ultimately, go into a store and see for yourself.