1080p and 1080i: a practical guide
Most newer models of Full HD TVs (and some models that call themselves HD Ready) have 1080p resolution, but there are still some 1080i models around and still, it seems, quite a bit of confusion between the two resolutions. So what’s the difference between 1080p and 1080i?
The short answer is that 1080p gives a higher quality picture, while 1080i can suffer from problems with blurry motion. The full explanation is a little more complicated.
The key difference between the two resolutions can be found in the letter at the end, which represents the format of the display:
1080p - progressive
1080i - interlaced
These two kinds of display method determine the way the image on screen is refreshed. How often the image is refreshed (reloaded from the TV signal) is determined by the frequency of the TV: on a 50hz (hertz) TV, the image is refreshed 50 times a second.
The ‘1080′ refers to the number of pixels the screen displays vertically. A resolution of 1080 pixels means the image on the screen is 1080 pixels high.
For 1080i (interlaced) displays, the image is divided into 1080 horizontal lines, only half of which are refreshed at a time. So, in the first 1/50th of a second, the first, third, fifth, seventh and all the other odd numbered lines will be refreshed. In the second 1/50th of a second, all the even numbered lines will be refreshed. This works fine for static or slow-moving images, but for faster images (like the movement of a football or a fight scene) this can lead to blurry or jagged images.
In 1080p format, all the ‘lines’ are refreshed at the same time, and so has none of these jagging or blurring problems.
This animation shows the blurry/jagged effect I’m talking about. It comes from a great article at Secrets of Home Theater and High Fidelity which gives a much more complex, technical explanation of 1080i/1080p (although it is a couple of years out of date).
So why have 1080i at all? HD TV is broadcast in 1080i format. Old fashioned cathode ray tube TVs (ie, non-flat screen TVs) naturally display in interlaced format, refreshing alternate lines of the picture. Modern LCD, plasma and LED TVs convert interlaced format signal into progressive format signal by deinterlacing.
With a good quality de-interlacer, 1080i signal should display brilliantly, even when showing high-speed motion. With a bad deinterlacer, the jagging and blurring problems persist. Checking the reviews of the TVs you’re thinking of buying will quickly tell you what their deinterlacers are like. The image below shows the difference between good and bad deinterlacers.
While broadcast TV is (for the moment) still 1080i, Blu-Ray discs are 1080p.
And that is it - all you need to know about the difference between 1080i and 1080p.
Tags: 1080i, 1080i vs 1080p, 1080p, Add new tag, difference between 1080i and 1080p, Full HD, HD TV, home entertainment, Televisions, tv
Blog posted on Friday, August 7th, 2009 at 4:44 pm under Televisions. Leave a comment, or trackback from your own site.
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Eric Says:
August 18th, 2009 at 2:19 am
Are you saying that if I buy a 1080p television, I can’t watch hd television on it?