TeknologikL

You've probably heard some fancy terms and numbers thrown around when referring to HDTV, but what's the real difference between 1080i and 1080p? Many people know that 1080p is better quality than 1080i, but they don't know why. Some people might even know that "i" stands for interlaced and "p" stands for progressive, but they may use those terms freely without knowing the meanings.

A Quick History of TV
Even back when Broadcast TV started to take off in the late 1930s, there were a few different technologies and formats fighting to become the standard in home entertainment. To help resolve these disputes, the National Television System Committee (NTSC) was developed in 1941 to issue standards for analog television. This laid down many of the basics of how television picture would be displayed for the next 60+ years. The basic features of an NTSC broadcast included a transmission with a 525-line picture, 30 frames shown per second, a 4:3 aspect ratio, and 6Mhz bandwidth. A similar but different standard called PAL was adopted by European countries due to their alternate power standards. NTSC and PAL both use analog transmissions.

The Original Problem - Bandwidth
NTSC broadcasts were developed before the advent of color TV, which resulted in a few shortcomings including color variation and limited bandwidth for signal transmission. PAL was developed over 10 years later, so it handles color better but still has a bandwidth problem. The bandwidth required to display the video at fast enough rates was not available, so the image would have a noticeable flicker.

The Original Solution - Interlacing
Engineers were working to solve the bandwidth problem on many fronts. The Interlacing method of displaying video was developed for TV Broadcast in the 1930's by RCA engineer Randall C. Ballard. His interlace technique first draws the odd numbered lines and then go back to draw the even numbered lines. Each of these passes is known as a field, with two fields making up a full frame. Even though each field isn't on the screen at the same time, it happens so fast that the eye doesn't notice. CRT (tube) televisions were developed using the interlace method as well, so the picture format would not have to be converted before it was displayed.

The New Problem – Quality
As television and video camera technology improved, a few disadvantages started to arise. Because each field is taken from a different moment in time, some artifacts and aliasing can be noticed. This blurring would be especially noticeable when taking a still frame from an interlaced video.

The New Solution - Progressive Scan
Progressive scan displays all the lines of video in order from top to bottom. Progressive scan was actually developed around the same time as Ballard's interlacing method, but never took off because it consumed twice as much bandwidth. Computer monitors started to take advantage of progressive scan first because video artifacts would be very noticeable when sitting up close, and also more noticeable when displaying text. As HDTV came to market, progressive scan became more necessary for picture quality and by then the bandwidth problems had been resolved.

Deinterlacing
Newer HDTVs, such as LCD and plasma TVs, use progressive display technology; because of this, they run into issues of their own when displaying interlaced video. These televisions have what's known as a deinterlacer built in to try to fill in the missing gaps of the image. Since the interlaced signal was only sending half the lines from each field, the video quality will never be the same as a progressive signal that contained the entire picture.

When it comes down to it, if your TV is under 40 inches most people won't notice much difference between an interlaced and progressive picture unless sitting very close. If you consider decreasing prices and increasing screen sizes, you might as well treat yourself with the 1080p model when in the market for a new television. A few years down the road you won't be sorry.

What type of picture does your TV display and can you notice a difference in video formats? Let us know in the comments below.

Resources
PAL & NTSC & SECAM
SDTV Vs EDTV Vs HDTV Differences
Progressive-scan video
What is Deinterlacing? Facts, solutions, examples.

TeknologikL