What is the Difference Between a 1080p and 1080i HDTV?

High definition television (HDTV) is a welcome change from the old standard analog TVs, but there is no shortage of confusion when it comes to choosing a unit. One of the most asked questions is what is the difference between a 1080i and 1080p HDTV? The question itself mixes apples and oranges but marketing has led to much of the confusion.

There are two types of HD broadcasts: 720p and 1080i. Broadcasts in 720p utilize a resolution of 1280 x 720, or a picture composed of 1280 pixels across and 720 pixels high. The “p” in 720p stands for progressive scan, meaning the picture is painted from top to bottom in a single pass, refreshed (repainted) 60 times per second.

Broadcasts in 1080i utilize a higher resolution of 1920 x 1080, theoretically resulting in better quality picture. However, the “i” stands for interlaced. Interlaced images are painted in a two-pass process. The first pass paints every other line, the second pass paints the skipped lines. Painting all lines takes 1/30th of a second, or twice as long as a progressive scan signal. So while resolution is higher, interlacing can create flicker and can also make fast moving objects appear slightly blurred. For this reason, networks that broadcast high-definition sports typically use 720p, while nature channels will tend towards 1080i for the richer resolution.

Any HDTV can display both 720p and 1080i broadcasts, but will convert signals to the native resolution of the set. For example, a 720p HDTV will take a 1080i signal and use an internal processing chip to downconvert the picture to the 720p resolution. This is called scaling. It will also de-interlace the 1080i signal and display it in progressive scan mode. Manufacturers sometimes market the 720p HDTV as a 1080i HDTV, simply because it supports 1080i, albeit by scaling down the resolution.

A 1080p HDTV doesn’t reduce the resolution of a 1080i signal. It only has to de-interlace it. Therefore a 1080i picture should look slightly better on a 1080p HDTV, particularly when comparing large screens. When watching a 720p broadcast on a 1080p HDTV, the signal is upconverted to the higher 1080p resolution. While this upconversion arguably makes a negligible difference in modest sized TVs, it does reduce pixel-related artifacts which can be appreciated on larger displays.

There are no broadcasts in 1080p, (1920 x 1080 in progressive scan mode), and none expected anytime soon. However, there are digital formats that can produce a true 1080p signal including Blu-ray™ players. Only a 1080p HDTV can display Blu-ray™ in its native, full resolution format. Among 1080p HDTVs, there are also various models with different support modes. The newer models support 1080p/60, 1080p/30 and 1080p/24, with the latter number being frames per second. The 1080p is also preferable for gaming and PC use.

Hence, 1080i is a video or broadcast mode. There is technically no such thing as a “1080i HDTV” because all HDTVs are progressive scan, not interlaced. This includes LCD and plasma flat screens, and LCD, LCoS and DLP rear projection TVs. Only cathode ray tube (CRT) televisions are interlaced, and though there were CRT rear projection HDTVs, they have been phased out.

Some might ask why some manufacturers promote 720p HDTV as 1080i? The answer is marketing. When 1080p HDTVs came along, renaming 720p HDTV to “1080i HDTV” was a shrewd move. The 1080i was priced much lower than a comparable 1080p model, with many if not most consumers not realizing the difference. Some industry sites now refer to “720p/1080i HDTV” to make it clearer.

In the end, if a consumer be happy with a 720p HDTV, he or she shouldn’t pay extra for a model promoted as “1080i." But if it’s a 1080p HDTV that he or she wants, he or she will have to cough up the extra cash or buy a smaller display for the same price tag.