This is a homework assignment I had for my Film/Video Materials & Technology class. In case you are interested in some of the stuff I am learning, this is a snapshot.
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Over the past decade, especially in recent years, HD television sets have became increasingly more popular. With the increase of popularity have come new display resolutions that have brought confusion and debate among consumers and broadcasters alike. The two most popular displays, 720p and 1080i have perhaps brought the most confusion. Many are confused as to the difference between these two displays. In this brief article I hope to explain the difference as well as explain the newer 1080p resolution and its future.
The differences between 720p and 1080i are not too difficult to understand. 720p is a signal that consists of 720 horizontal lines. It then displays each frame in its entirety on the screen for 1/60th of a second. When each frame is displayed in its entirety like this it is called progressive scan (which is why there is a p after 720). 1080i on the other hand consists of 1080 horizontal lines. However each frame is not all displayed at once. First the odd lines are displayed and then the even lines. Each set of lines is displayed at 1/60th of a second making the total frame rate 30fps. This is called interlacing (which is why there is an i after 1080). Even though not all the lines are not displayed at one time, because they are flashing so fast your brain is able to connect them for you.
So what makes one better than the other? Well, it really depends what you use it for. As a consumer, it really isn’t something that you need to pay attention to because all HDTV’s are required to be compatible with both. However when it comes to the broadcasting companies, some choose 720p and some choose 1080i. It really depends on their content as each resolution works better with different things. 720p is usually considered better for showing sports. One of the reasons for this is that most sports are shot in 60fps and therefore it works great with the progressive 60fps playback of 720p. Progressive scanning also tends to work better with the fast motion, which is quite common in sports. On the other hand, interlacing is usually thought better for shows where fast motion isn’t as present such as drama or comedy shows. One of the common stated advantages of 1080i is that is has 1080 lines compared to 720 lines. This is essentially the same thing as when you have a 6-megapixel camera instead of a 3-megapixel camera. More pixels means better resolution. However 1080i is better for CRT HDTV’s and it has to be deinterlaced before it can be shown on the 1080p or 720p sets. While this may lower the images quality some it usually still creates a slightly crisper image than 720p due to there being more lines of resolution.
Many networks seem to agree with the fact the more lines is better. Approximately 3 out of 4 networks that broadcast HD have chosen to use the 1080i format. This includes CBS, NBC, TNT, and Discovery’s HD Theater. Networks that have chosen the 720p include ESPN (for sports reasons), Disney, FOX, and ABC.
Lastly let’s talk about 1080p. 1080p TV sets are being sold more and more often. So why is it better than 720p and 1080i? Well essentially it is the best of both worlds. It has the progressive technology of 720p with the 1080 resolution of 1080i. However, because of its high bandwidth size, no networks are currently using it, nor are any expected to in the near future. Therefore the only 1080p content that would currently make the upgrade worth it would be if you had a blue-ray player or if you used your pay-per-view satellite service. If you use blue-ray a lot this may be worth it as most blue-ray discs are encoded in 1080p. I’m sure someday broadcasters will move to 1080p once they can figure out how to either send more bandwidth or to develop better compression techniques. However it could be a while, if I had to predict a date I would say at least 5-10 years.
