You might have seen mobiles, TVs, tabs and any device with a screen advertised as HD 720p or Full HD 1080p, and on TV settings you may have seen options like 1080i. What do the ‘p’ and the ‘i’ mean? Let’s find out.
The ‘p’ stands for progressive and the ‘i’ stands for interlaced. Progressive scan is one of the two main methods of scanning used in broadcast transmission. With progressive scanning, all the lines of a particular frame are transmitted at once and are displayed at once on the viewer’s screen. Whereas interlaced scanning is an alternative method where the lines forming a frame are alternated as odd or even. Only one of these is broadcast at a time, meaning half the frame. So, on the viewer’s screen at first, even lines are displayed and then odd lines. But it happens so fast that it is not visible to the naked eye.
The difference between interlaced and progressive was very clear during the CRT era of television. There was only so much information that could be transmitted through the coaxial cables and airwaves. So, to compromise clarity for speed, the broadcasters decided to go for interlaced scanning. With the emergence of digital technology, interlacing is being slowly phased out.
Advantages of interlacing-
Broadcasting interlaced video was cheaper since you were sending only half a frame at a time, although this resulted in a lower quality image with many visual imperfections. But the technical savings were so high that this allowed stations to transmit 1080i interlaced footage where otherwise they could send only 720p progressive footage. Interlacing compromised visual fidelity for accessibility and cost.
Advantages of progressive scanning-
Interlacing doesn’t send two halves of the same frame, instead, it sends adjacent frames. This used to cause issues in the final render, where the images wouldn’t match up. TVs or Set Top Boxes usually have de-interlacing software that solves this. But in the end, the image quality is still compromised. Whereas progressive scanning used more bandwidth and was costlier but it had a superior image quality to interlaced footage. Even though interlaced was used during the CRT era, in the digital era where bandwidth is plenty, we see progressive scanning becoming more and more popular.
In the end, it depends on what is being transmitted and to whom. If your audience has digital transmission TV sets, they would prefer progressive scanning. But if your audience has analogue transmission TV sets and they are watching content where image quality is secondary like in soap operas and sporting events where speed is more important than visual quality, interlacing will be preferred.