Contrary to what some may believe, 720p and 1080p are actually both high definition video display formats. In addition, the other characteristic 1080p and 720p share in common is that they are progressive display formats (that is where the "p" comes from). However, this is where the similarity between 720p and 1080p ends.
720p is 1,280 pixels displayed across the screen horizontally and 720 pixels down the screen vertically. This arrangement yields 720 horizontal lines on the screen, which are, in turn, displayed progressively, or each line displayed following another.
1080p represents 1,920 pixels displayed across the screen horizontally and 1,080 pixels down the screen vertically. This arrangement yields 1,080 horizontal lines on the screen, which are, in turn, displayed progressively, or each line of pixels displayed following another. In other words, all lines are displayed progressively, providing the most detailed high definition video image that is currently available to consumers.
The main difference between 720p and 1080p lies in the number of pixels that make up a 720p image and 1080p image. For 720p the number of pixels that make up the image is about 1 million (equivalent to 1 megapixel in a digital still camera) and about 2 million pixels for 1080p. This means that a 1080p image has the potential to display a lot more detail than a 720p image.
However, how does this all translate to what you actually see on a TV screen? Shouldn't it be easy to see the difference between a 720p and 1080p TV? Not necessarily.
Besides pixel density of 1080p vs 720p, there are also the factors of screen size and seating distance from the screen to take into consideration.
Should I Buy a 720p TV?
In answering this question, it must be noted that the large majority of LCD, Plasma, and DLP TVs are now 1080p TVs. However, there are still some inexpensive TVs that are classified as 720p TVs, but mostly in screen sizes below 40-inches. On the other hand, the price difference between 720p and 1080p TVs is so narrow now, that manufacturers are finding it very cost effective to increase the number of 1080p offerings even in smaller screen sizes.
Also, it must be pointed out that most TVs that now labeled as 720p TVs actually have a native pixel resolution of 1366x768, which is technically 768p. However, they are usually advertised as 720p TVs. Don't let this through you off, these sets will all display 720p, 1080i, and 1080p signals. The TV will process and scale any incoming resolution to its native 1366x768 pixel display resolution.
720p, TV Broadcasts, and Cable/Satellite
Television broadcasters and cable/satellite providers send out their programming in several resolutions. For example ABC and FOX (which includes their cable channels, such as ESPN, ABC Family, etc...) use 720p, while most other providers, such as PBS, NBC, CBS, CW, TNT, and most premium services, such as HBO, use 1080i. In addition, there are some cable and satellite feeds that are sent in 1080p. If you have a recent model 720p TV, you will be able to access this content. The TV will scale the input signal according to its own native pixel resolution.
Blu-ray and 720p
Also, when connected via HDMI most Blu-ray Disc players automatically detect the native resolution of the TV they are connected to and will set the output resolution accordingly. In addition, Blu-ray Disc players also provide the ability to set the output resolution manually if you so desire.
In the final analysis, the proof is in the actual viewing - how the image looks to you in the real world with your specific HDTV. You may find that a specific 720p TV can actually look better than a specific 1080p TV. This is because what you see on the screen is the result of many factors, with resolution being just one. Other factors to take into consideration are motion response, color processing, contrast, brightness, and background video, and video scaling. Not all HDTVs and video processors are created equal.
Of course, the quality of the source signal also plays a big part. The TV's video processor can only do so much for compensate for poor quality source signals, especially when you are looking a VHS or analog cable signal. Let your eyes be your guide.
Also, be sure to read my companion articles: