Before buying an HD display, read this lowdown on 720p vs. 1080i vs 1080p

Summary:Last week (and just in time for any big holiday buying you plan on doing), David Carnoy who works over at one of ZDNet's sister organizations (within CNET) published what he's calling the final word on 720p vs. 1080p: the two "competing" resolutions for high definition (HD) television.

Last week (and just in time for any big holiday buying you plan on doing), David Carnoy who works over at one of ZDNet's sister organizations (within CNET) published what he's calling the final word on 720p vs. 1080p: the two "competing" resolutions for high definition (HD) television. Carnoy's piece is an absolute must read for anyone considering the purchase of a high definition display because of how well he describes the various technologies and busts the myths around 1080p being better than 720p. Why is this important? Go to just about any electronics store today and you might see two flat panel LCDs that are side-by-side with each other that look identical (same manufacturer, same size, same bezel design, etc.) but that differ in price by several hundred dollars or more. Upon closer inspection of the fine print, you'll notice that one is rated for 720p and the other for 1080p. The big question is, should you pay more? (A question that wrongly answered "Yes" to when I recently bought my 42" HD flat panel). Writes Carnoy:

We still believe that when you're dealing with TVs 50 inches and smaller, the added resolution has only a very minor impact on picture quality. On a regular basis in our HDTV reviews, we put 720p (or 768p) sets next to 1080p sets, then feed them both the same source material, whether it's 1080i or 1080p, from the highest-quality Blu-ray and HD DVD players. We typically watch both sets for a while, with eyes darting back and forth between the two, looking for differences in the most-detailed sections, such as hair, textures of fabric, and grassy plains. Bottom line: It's almost always very difficult to see any difference--especially from farther than 8 feet away on a 50-inch TV....

....The extra sharpness afforded by the 1080p televisions he's seen is noticeable only when watching 1080i or 1080p sources on a larger screens, say 55 inches and bigger, or with projectors that display a wall-size picture. Katzmaier also says that the main real-world advantage of 1080p is not the extra sharpness you'll be seeing, but instead, the smaller, more densely packed pixels. In other words, you can sit closer to a 1080p television and not notice any pixel structure, such as stair-stepping along diagonal lines, or the screen door effect (where you can actually see the space between the pixels). This advantage applies regardless of the quality of the source.

Even though the headline of his story makes it sound as though it's primarily a discussion of 720p vs. 1080p, it's really much more than that.  Carnoy very authoritatively discusses the 1080i as well, describing in most excellent layman's terms what the difference between "i" and "p" are, what it means to you and me, and how many of the displays are capable of resolving differences between the resolution and type of signal being fed into a display and what the display is capable of (for example, feeding a 1080p signal into a 720 display).

What you don't get in this particular story of Carnoy's is a discussion of LCD vs. Plasma (or for that matter, the other display types such as CRT and DLP).  For that, I suggest checking out David Katzmaier's Four styles of HDTV (make sure you click through all the pages and check out the plasma vs. LCD table on the second page).

One rule of thumb that has suprisingly changed this year has been the maximum size of LCD flat panels.  In January, while at CES, we learned that except for Westinghouse which had gone LCD-only and was doing what it could to break the size barrier for LCD, pretty much all the major manufacturers had LCD's that went up to 47" in diagonal size and plasma displays that started at 42" in diagonal size and went up from there (some to more than 100 inches).  Already today though (as evidence of how quickly things are changing), all you need to do is visit your local electronics superstore to see LCDs from many of the majors that are 50-55 inches in size.

Speaking of shopping in superstores for these bad boys, one thing I've learned is that you don't want to eyeball the image quality of these displays in a typical showroom setting where florescent lighting is used.  Chances are that your viewing will involve incandescent lighting which, to the human eye, produces different results than florescent lighting when watching TV.  You're probably better off going to a home theater store that can reproduce the lighting situation you're most likely to use your TV in.

Topics: Hardware


David Berlind was fomerly the executive editor of ZDNet. David holds a BBA in Computer Information Systems. Prior to becoming a tech journalist in 1991, David was an IT manager.

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