Friday, June 11, 2010

The 1080p Full HD format: A simple explanation

The 1080p standard for video has been around for quite some time now. But still, there are a lot of people who don't know the real idea about this breakthrough. Specifically, the meaning of the mysterious letter "p".

Most of the web people (beginners and average users) defines "p" as PIXEL. This statement is wrong, but somehow is accepted by the web community. They accepted this, because a 1080p video does have 1080 vertical pixels. A full HD video has a resolution of 1920x1080 pixels. So defining the "p" as pixel, is not a bad idea.

If the letter "p" don't stand for pixel, then what does it really mean?...

The real meaning of "p" on 1080p (same as on 720p) HD video is PROGRESSIVE. It is derived from a TV technique called Progressive Scanning. To fully understand the significance of the word PROGRESSIVE in HD technology, I think it is better if we would briefly discuss the idea of standard definition TV (SDTV).

Our old TV sets (SDTV) uses a technique called INTERLACING to display images. It has 480 horizontal active scan lines and another 45 horizontal scan lines which serves as buffer. Interlacing is a system where the TV displays the odd number scan lines first (1 - 479. It will take 1/60 seconds to be done), before it displays the even number scan lines (2 - 480. It will also take 1/60 seconds to be done). If you notice, the total time it takes for SDTV to display an image is 1/30 seconds. Therefore, it has a framerate of 30 frames per second.

On a full HD TV, as stated above, uses Progressive Scanning. This technique displays all the 1080 horizontal scan lines progressively. Meaning it start with the number 1 scan line then followed by 2,3,4....1080. And it only takes 1/60 seconds to display all of the 1080 horizontal scan lines. Having twice the speed of a SDTV. So how does this speed improve the quality of the image being displayed?...

The answer is very simple. It makes the image brighter and more stable. The standard frame rate of a video, HD or SD, is 30 frames per second. Since HDTV can display all the scan lines in just 1/60 seconds, and we only have 30 frames to show every second, the HDTV displays the same image twice to occupy 1/30 second period. And this process helps the stability and brightness of the video.

Now we already knew what does ”p” means on the term 1080p, we will now discuss the characteristics of a full HD video.

The amount of scan lines that a full HDTV has, 1080, helps solve another issue of the SDTV - poor video quality on huge screens. Try to watch a video on a 21" SDTV and a 42" SDTV. You can notice that the video displayed on the 21" screen looks great. So clean and clear. But on the 42" screen, the image looks dull and somewhat rough (you can see disturbing small squares on the image). This is because of the huge scan lines and slow scan rate.

Another characteristic of a full HD video is its 16:9 aspect ratio. It gives the viewer a more theatrical look for the video and adds more dimension to the viewing experience of the audience.

So we’re almost done discussing the full HD format. There’s one thing left, just a little clarification. On the second paragraph, I mentioned the line “1080 vertical pixels”. While on the latter part of our discussion, I also mentioned the line “1080 horizontal scan lines”. You might be confuse with this contradicting statements. But this two statements are both true! Look at the picture below for the explanation:

HDTV scan lines explanation

Did you get it?


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