Okay, it's time for another of my informative posts... If you've seen any of my other posts:
Understanding HDMI cables and why cheap ones work perfectly
Ground loop causing horizontal bars and/or buzzing
You know that I'm a broadcast engineer and live and breath this stuff every day. As part of my trade I have to keep up with TV's, broadcast signals, HD signals, etc. So I've been able to bring some of my knowledge to these boards and help others get informed on various topics.
With that in mind, since I've been seeing a ton of these types of questions asked lately, I thought I should create a post dedicated to giving some answers... So with that said, let's proceed...
"Should I run 720p or 1080i", "What's the difference between 1080i and 1080p", "Should I get 1080p or just 720p", "Will I notice a difference between X and Y", etc...
These are all questions I see asked all the time... The problem is... There is no one fixed answer. It depends on a lot of various factors, and the only way to really be able to answer this question is by understanding what the differences are... So here we go, let's get into the fun stuff...
Section A: Resolution
The first thing you have to understand is the resolution of your TV set. A recent HD set (microdisplay LCD, DLP, LCoS, or Plasma, or directview LCD) can have one of three resolutions.. 480 lines of resolution, 720 lines of resolution, or 1080 lines of resolution.
Now your first thought may be that "bigger is better"... The more resolution, the more detail, and hence, the better the picture. The problem is, that doesn't really apply. Here's why... The smaller your TV set, the smaller a given number of pixels will become... Once they get below a certain size, then it just doesn't make any difference if they get any smaller.
For example... Take a look at this... Let's say you have a massive 350" monitor that your viewing this message on... If we were to walk up to the screen and take a look at . <-- that's a period... We might see that it looked like this for whatever resolution you were running at:
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See... A nice rounded period... Looks good, decent detail.... If we count up the pixels that it's made out of, we see it's made of 20 pixels...
Now let's say on the SAME 350" monitor, we drop down to a resolution that's half of what we were running before... Now if we go up close and look at the SAME period, we might see it looks like this....
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Now it's not so nice and rounded, doesn't have as much detail, and in general just doesn't look as nice... This seems to support the "more resolution is better" theory... But here's the problem... We're looking at this UP CLOSE on a 350" display...
Now let's say your using a nice 19" monitor right now.... Take a look at this . <--- another period...
That period (depending on your resolution) might be made of say 4 pixels... Would it matter if you switched resolutions to 38928282x3892202??? Nope, even if that period was made up of 100 pixels instead of 4, because it's so small to begin with, it's going to look EXACTLY the same... The extra detail might be lost, but it's lost on a level your eyes can't see to begin with...
With that in mind, that's why a set with a maximum 720 lines may be just as good as a set with a maximum of 1080 lines... Depending on it's size... Once the pixels get so small, it doesn't matter if the detail is lost anyway... Of course this varies based on your eyesight, and also the size of the screen vs your viewing distance. In fact, here's a really nice chart that demonstrates how resolution relates to viewing distance and tv size...
So as you can see, let's say your buying a 40" TV... The ONLY way you'll be able to tell the difference between a 1080 lines of resolution and 720 lines of resolution is if your sitting 5ft away or closer... If your buying a 50" TV, it's about 7 ft... 60" makes it about 7.5 to 8ft... So the honest truth is, in most peoples living rooms at normal viewing distances, you won't see the advantage of 1080 lines of resolution anyway.
Now, before we move on to interlaced vs. progressive, there's one other thing I'd like to point out that most people don't realize...
I've heard a lot of people say "I have XXX tv, and when I switch to 1080i I see a big difference in picture quality vs. 720p" Almost 98% of the time you see this statement, it's flat out false... In fact, it's IMPOSSIBLE in most cases for them to see a difference... Here's why...
If you have a microdisplay TV (i.e. DLP, LCD, or LCoS), or MOST plasma's and directview LCD's, and it DOESN'T say that it's 1080p, guess what? The MAXIMUM resolution it will support is 720p... Now I can here some people now, "That's bullcrap! I set my stuff for 1080i all the time"... Sure you do... That's because it WILL accept a 1080i signal, but the problem is, the display chip inside it only has 720 lines of resolution, so that 1080i signal just get's downscaled to 720p before it's displayed anyway... So switching between 1080i and 720p will have NO effect on the picture quality, other then 1080i will introduce motion artifacting which will make it look worse! (we'll get to this in a moment)...
If you have a CRT set, your LUCKY if it get's 720 lines of resolution.. Most don't support even that. They accept the signals, but can't really display anywhere near the level of detail that a microdisplay or plasma or directview lcd can... Now again, there's probably someone barking that their CRT set looks better then xxx set... This is BECAUSE of the loss of detail...
This is the same reason photographers have been shooting portraits with "soft focus" lens and/or filters for years... Because the DETAIL of a persons face RARELY ever looks "good"... The soft focus "blurs" the image, which looks MUCH more pleasing... The same applies with CRT sets... The "blur" or "softening" effect they have on signals often makes BAD signals look MUCH better... However, get a GOOD HD signal and it won't even come close to comparing....
So in other words, just because your set will ACCEPT a 1080i input, doesn't mean it DISPLAYS 1080 lines of resolution, almost CERTAINLY it displays 720 lines...
Now... The next half of what you need to understand is interlaced vs. progressive... So let's move on...