Produxion

Oops.

After I finished writing my last post on interlacing, I realised that I missed out one important aspect of the whole de-interlacing discussion, and more specifically, another very good reason why you would want to use de-interlacing: creating a film-look for your video.

When you watch most soap opera or current affairs programmes on TV, you’ll notice that they have a much sharper and crisper look than the picture of a drama or film you watch on the same TV. It has a distinctly “video” look to it, which creates a very immediate and “real” image.

Part of that is down to the way images are captured on most video cameras, and the way in which the signal is processed. There are video formats which create a softer, richer image, such as digi-beta. But for those of us who work with cheaper, less-cumbersome formats (such as DV, HDV, XDCAM etc) there remains the issue of how to change that “video” look to one which looks more like film.

Well, there are three basic things I do which create that magical film-look.

The first is to desaturate the image a little – using a more less vivid colour palette instantly gives your image more subtlety. The hyper-reality of video is dampened.

The second thing to do, is to recoup some of the richness you lost when desaturating, but increasing the contrast of the image. This will tend to “bleach” the image, and you’ll lose some detail, but the detail which remains will be sharper and add more depth.

And then the third, and final thing: de-interlacing. There’s a very good reason for this, and even if you don’t want to apply desaturation and increased contrast, if you don’t apply a de-interlace, you just aren’t going to get anywhere near a film-look. Here’s the reason why:

Film consists of 24 unique frames per second. Even if those frames are being displayed several times in a row (for instance, due to a faster shutter speed when projecting at say 50fps) the fact remains that there are only ever 24 unique images being shown every second.

TV has a similar “shutter speed”, showing 50 frames per second. But those frames are split into two sets of fields (see my previous post for a fuller explanation of this), and a video signal records one field every 1/50th of a second. So, rather than there being 25 full frames being displayed every 1/25th of a second, there are 50 half-resolution frames being displayed every 1/50th of a second. When your eye sees this and feed the signal to your brain, everything gets merged to fill in the gaps between the missing fields, and that’s what creates that super-crisp, video look.

So to get rid of that video look, and to simulate more closely the mechanism of film, you de-interlace the video image, combining each set of fields, which creates 25 full frames, instead of the 50 “half” frames. Even if the video ends up being interlaced again (for DVD for example), then it will still retain the filmic look, because the interlacing will still only be showing one full frame every 1/25th of a second.