Do I need to deinterlace my video? What does interlaced and deinterlaced mean? Why do I get these jagged lines on my video?

I recently uploaded two versions of the same video to my facebook page to demonstrate the visible difference between a video that is interlaced and one that is deinterlaced or scanned progressively. I have attached a couple stills from each clip to demonstrate the point. You can see artifacts in the first video. This is the combing or “mouse teeth” effect that can occur with interlaced video. It is always more apparent when you watch an interlaced video on computer monitors because they natively use progressive scanning. Notice that you don’t see artifacts in the second still, that is because I deinterlaced this version.

Interlaced VideoProgressive Scan Video

For those of you who do not know what interlacing is, I will give you a brief description. There are basically two methods of scanning when a video is played, interlace and progressive scan. Interlacing involves the displaying of even horizontal lines of resolution followed by odd lines of resolution in a single frame of video. Whereas, progressive scanning, involves displaying a single frame of video by scanning horizontal lines of resolution from the top to the bottom of the screen. This translates into a smoother and crisper video especially when there is a lot of motion being displayed, particularly in sports broadcasts, which is why some HD stations choose to broadcast major sporting events in 720p as opposed to 1080i. They are willing to sacrifice the higher resolution for a more clean look. It is still open to debate, however, whether the tradeoff is worth it.

As demonstrated by the pictures, interlacing can lead to some bizarre results. You might be inclined to ask why this method is even used. The answer is because it is the standard used by television sets (CRTs) and has been for many years. Nonetheless, when we display our videos online or just keep them on our computer, it is usually wise to deinterlace them when possible because there aren’t the same standards and restrictions in the computer world as there is on a standard NTSC broadcast. Therefore, we should take advantage of the freedom we have in displaying our videos on sites such as youtube and facebook, so that our videos look as good and as sharp as possible.

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