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Originally Posted by Sinister Angel  I've never quite got the difference between 1080i and 1080p |
I don't know what you know, so excuse me if I sound like I'm talking down. I'm no real expert, but I do know some stuff.
Start out with the native resolution of your monitor or TV. The maximum resolution you can display from any source is limited by the native resolution of your monitor. Let's assume you have a newer widescreen. It may be a big (say, 42 inches or bigger) plasma or LCD or DLP that is 1,920 pixels wide by 1,080 pixels high; if so, these days the manufacturer would call it a '1080p' monitor because its native resolution is capable of displaying all the pixels from a 1080p source. Or it may be smaller (or just as big, but cheaper) and have fewer pixels (e.g. 1,280 x 720, 1,366 x 768, 1,024 x 768). Monitors with these native resolutions are lumped into the '720p' category, because that's max they can handle.
In the good old days of CRT, the screen was divided up into horizontal lines of virtual dot targets that a really fast electron beam would hit like a tommy gun, spraying left to right, then skipping down two lines and spraying left to right again, then skipping down two lines and spraying left to right again, etc. until every other line on the screen from top to bottom was illuminated. Then the beam would jump back up to the top of the screen and start shooting again left to right, left to right, hitting all the lines that it skipped the first time. When every virtual dot target that needed to be hit HAD been hit on the entire screen (e.g. two passes of the electron beam from the top of the screen to the bottom of the screen), the screen displayed one complete still image in a film or video sequence. (That's not 100% accurate when talking about film, but that's a different discussion.) This process of displaying video by hitting every other line of pixels is called 'interlacing.' Good old 480i NTSC analog broadcasts received on an analog CRT monitor is how us old farts watched our Bugs Bunny cartoons when we were kids.
Skip ahead to today. Let's assume that you have a non-CRT monitor, meaning a plasma or LCD panel, a DLP set (or some other type of rear projection set), or a DLP projector. These are all digital display technologies. Unlike the analog CRT, they cannot display interlaced video signals. In fact two things about digital displays are all you really need to remember (at least in this area of discussion):
- They can ONLY display images in the monitor's native resolution
- The can ONLY display progressive video signals
#1 means that if you've got a 1366 x 768 pixel monitor, and you're watching an incoming 1080p signal from your BlueRay DVD (e.g. 1920 x 1080 pixels to display), then your monitor doesn't have enough pixels in its native resolution to display it and the signal has to be 'scaled' (in this case, downconverted) to match your monitor's native resolution. Similarly, if you're watching a non-HD digital cable channel on your 1920 x 1080 monitor, the signal has to be upconverted to display on your monitor.
#2 means that if you're watching an interlaced video signal (say, the 1080i signal from NBC Sunday Night Football HD), it first has to be "deinterlaced" before it can be displayed on your digital monitor. Although 1080i uses just as many pixels as 1080p, it paints every other 'line' of pixels instead of painting them 'progressively,' which is what your progressive digital monitor needs to display.
Let's say that you have a 50" Panasonic plasma like mine, with a native 1,920 x 1,080 resolution, which is "true HD" 1080p resolution. The very best case is if you're feeding it with a 1080p signal, meaning at the monitor's native resolution and progressively scanned, so zero conversion is required. Unfortunately, ALMOST every signal out there from broadcast, satellite, cable, DVDs, VCRs, etc. is lower resolution and requires scaling and possibly deinterlacing before it hits your screen.
It's possible that your cable box, your video switching audio receiver, or something else is doing some or all of the scaling and deinterlacing for you; it's also possible that your monitor is doing some or all if the conversion. I like to know that my monitor is capable of doing it all, so I won't buy one until I'm sure that it scales and deinterlaces without serious artifacts that I can see. (There's a lot of other stuff to look for but once again that's a different discussion.)