Introduction

In this guide, we're going to learn about deinterlacing and, more important, what solutions are there and which one are better or more suitable to our needs.

I'm sure you have all seen a movie on the computer or at the TV. You have surely noticed it's two main parts: the video and the audio.

The video part is built out of pictures that appear on the screen, with a precise frequency. This frequency of the pictures, which I will call from now on frames, must be over a determined standard value, 24 frames per second. People watching video files with less than 24 frames per second are likely to notice fliker.

This small amount of frames may be enough for cinema but it's not enough for the rest of the applications such as the TV. If you would watch a football game, recorded at just 25 frames per second, the movement of the ball in the air would seem at least weird, it would seem the ball stands still in the air or jumps from one location to another.

Something had to be done to increase the number of frames shown on the screen but, unfortunately, in the 30's, when TV was invented, there simply was no technology powerful enough to accomplish this. Therefore, the inventors resorted to a nice trick: they've reduced the vertical height of the image to half of the original and interlaced (mixed together vertically) two frames together. This way, there are now 50 frames per second, which brings fluidity but the video resolution is a bit lower. After all, the height is only half the original.

In conclusion, a regular PAL video broadcast, 768 pixels wide, 576 pixels tall and 25 frames per second interlaced is actually a video broadcast 768 pixels wide, 288 pixels tall, with 50 frames each second. The TV or the video player on the computer, before showing the image on the screen, deinterlaces the video, splitting and processing each video frame in order to obtain the two original two frames.

So, what is deinterlacing ?

It's the art of converting this interlaced sequence of video frames into a non-interlaced form, while preserving as much quality as possible.

Let's move on and see what kind of problems we may be faced with during the deinterlacing process.

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