1080i VS 1080p The Difference

1080i vs. 1080p: What's the Difference?

Progressive (1080p) video is considered better than interlaced (1080i), but it's not always clear why; here's what's actually happening on your TV screen.

Today's HDTVs can display beautiful, 1,920 X 1,080-pixel video, but the actual quality of what you're viewing depends on the source material. A lot of the time, you're not seeing exactly 1080p. In fact, most TVs today have two modes with similar names: 1080i and 1080p. Both have the same screen resolution, so what's the difference between the two? Here are five things you need to know:

1080i video is "interlaced." 1080i video plays back at 60 frames per second, but that's a bit deceptive, because it's actually broadcast at 30 frames per second. The TV then displays those frames twice, the first pass is 1,920 X 540 for the even scan line field, and the second pass is 1,920 X 540 for the odd scan line field. The process by which this occurs is called interlacing. It contributes to a sense of motion and reduces perceived flicker.

1080p video is called "progressive scan." In this format, 1,920-by-1,080-pixel high-definition movies are progressively drawn line after line, so they're not interlaced. On paper, that may not seem like a huge deal. But in the real world, what you end up seeing looks sharper and more defined than 1080i, particularly during scenes with a lot of fast motion.

Sometimes 1080p is termed "Full HD" or "True HD," to distinguish it from 1080i or 720p video. Blu-ray discs contain 1080p video at 24 Frames Per Second, and then, using a method known as 3:2 pulldown, display it at 30 frames per second on screen.

Data compression can confuse the issue. Sometimes cable companies will deliver a 1080i picture, but then compress the data significantly in order to use up less bandwidth. The result can mean smeared details or pixelated color gradations in certain scenes. It's still technically HD, and still looks better than standard-definition cable, but it's not as good as it could be.

This also happens with 1080p streaming Internet video, but in that case, it's usually dependent on the speed of your data connection. In fact, Blu-ray is currently the only practical format for watching lots of pure 1080p content. Even the latest Apple TV, which supports 1080p streaming, does so in a compressed format that loses a bit of quality (although it still looks quite good).

Both formats look similar on smaller TVs. As a general rule, you need a larger TV to notice the difference between 1080i and 1080p. Depending on your eyesight, you can probably pick up the difference on a 32-inch LCD if you're particular about it. But most consumers don't really see a marked difference until at least a 42-inch screen, if not larger. In fact, many people are perfectly happy with 720p HDTV sets even at higher sizes; we recently named one, the 51" Samsung PN51E490B4F, best Choice for budget large-screen HDTVs.

1080p isn't even the best anymore. Technology never stands still, of course. Five years from now, you'll probably just want Ultra High Definition (aka 4K) video instead. (For a closer look at 4K video, check out What is Ultra HD?) But for now, if you're a videophile who appreciates a sharper picture, 1080p is definitely the way to go—both in HDTV capability and in the source material you're viewing.

Choosing a Frame Rate on CCTV

Movies on film are almost exclusively projected at 24 FPS. Television, however, does not have an internationally accepted frame rate. In Europe and many other countries, PAL and SECAM use 25 FPS, whereas NTSC video in North America and Japan uses 29.97 FPS. Other common frame rates are usually multiples of these.

Note: Converting video formats from one frame rate to another is technically challenging, and there are often unwanted visual side effects. This is especially true when the frame rates do not evenly divide. For example, converting 30 FPS to 60 FPS is fairly easy to do, but converting 29.97 FPS to 25 FPS is much more difficult. Making sure audio stays in sync throughout the conversion is yet another challenge.

Some digital video formats support several frame rates within a single format, allowing variable frame rate video recording and film (24 FPS) compatibility.

Frame rate	Media	Description
24 fps	Film; high definition video	This is the universally accepted film frame rate. Movie theaters worldwide almost always use this frame rate. Many high definition formats can record and play back video at this rate, though 23.98 is usually chosen instead (see below).
23.98 (23.976) fps	Film; high definition video with NTSC compatibility; NTSC	This is 24 fps slowed down by 99.9% (1000/1001) to easily transfer film to NTSC video. Many high definition video formats (and some SD formats) can record at this speed, and it is usually preferred over true 24 fps because of NTSC compatibility.
25FPS	PAL; high definition video	The European video standard. Film is sometimes shot at 25 FPS when destined for editing or distribution on PAL video.
29.97 fps	NTSC; high definition video	This has been the color NTSC video standard since 1953. This number is sometimes inaccurately referred to as 30 fps.
30 fps	High definition video; early black-and-white NTSC video	Some high definition cameras can record at 30 fps, as opposed to 29.97 fps. Before color was added to NTSC video signals, the frame rate was truly 30 fps. However, this format is almost never used today.
50 fps	PAL; high definition video	This refers to the interlaced field rate (double the frame rate) of PAL. Some 1080i high definition cameras can record at this frame rate.
59.94 fps	High definition video with NTSC compatibility	High definition cameras can record at this frame rate, which is compatible with NTSC video. It is also the interlaced field rate of NTSC video. This number is sometimes referred to as 60 fps, but it is best to use 59.94 FPS unless you really mean 60 FPS.
60 fps	High definition video	High definition equipment can often play and record at this frame rate, but 59.94 FPS is much more common because of NTSC compatibility.

Important: Many people round 29.97 FPS to 30 FPS, but this can lead to confusion during post-production. Today, it is still very rare to use a frame rate of 30 FPS, but very common to use 29.97 FPS. When in doubt, ask people to clarify whether they really mean 30 FPS, or if they are simply rounding 29.97 FPS for convenience.