Keying and Mattes - A trip down the yellow brick road.
If you are editing video, you use mattes and keying almost daily. Whether you are hitting the 'Color Matte' button on your Video Switcher or you select 'chroma key' in Premiere or Avid, as a video editor, you use keying and mattes almost every day. Few people know that these terms originated long before there was such a thing as video.
Examining keying and mattes through the early beginnings will help you understand better how it works and how to use some of the techniques that go as far back as silent movies.
THE MATTE
Every video switcher or NLE program has a 'color matte' button. What it does is create a color or gradient background for overlaying titles. The term comes from the early days of silent movies when a 'matte painter' was painting backgrounds to superimpose images unto. The term 'matte' was used because these images have to be created using 'matte' (non-glossy) paint, otherwise you would see the reflections of the studio lights in the painting and it wouldn't look real. The most famous matte painting of all time? Probably the shot of the 'yellow brick road' in the Wizard of Oz. Even though that image obviously looked painted, matte paintings are still used in today's movies and most movie viewers can't tell that it is a painting.
TIP #1 - You need less detail than you think
The reason why even today, movie producers still use matte paintings rather than computer generated pictures is that somehow these paintings blend in better and look more 'real' than most computer generated images. If you look closely at any oil or watercolor painting, you see that there really isn't much detail in the picture. The soft strokes of a painting blend much better with film or video. Computer generated backgrounds often have too much detail and that can create flicker and hard lines that to the human eye just don't look too realistic.
These days, animators and computer graphics artists realize this and use many tricks to make their images softer and blend in. For example most of my virtual studio sets and video backgrounds that I designed for 3DVideoBackgrounds.com are processed through special filters to make them softer. We avoid hard edges like the plague. When you see these graphics on your video screen, the magic happens and you get pleasing backgrounds that blend well and look 'real' .
If you want to create your own background pictures for keying, avoid hard lines and geometrical patterns.
TIP #2 - Out of Focus is a good thing
When it comes to creating realistic backgrounds for keying, a very soft focus or even an 'out of focus' effect will work wonders for realism. For the Virtual Sets I created for 3DVideoBackgrounds.com, I use many completely 'out of focus' shots because in reality, in 90% of all close up shots the actual background is out of focus. You can see some of this for yourself at http://www.3dvideobackgrounds.com
TIP#3 - To Gradient or not to Gradient
One of the most common mattes used to superimpose titles over is the color gradient. It gives a lot of depth to your graphics and most editing systems generate these for you on the spot but here's a tip:
Most video productions these days end up on DVD rather than tape and due to the nature of the compression used, Color Gradients often don't look very good on DVDs. So, when looking for a background for titling on DVD projects, more patterned backgrounds will generally look better than gradients.
Mattes have been around the the dawn of silent film and looking at how they were used in movie production will help you use them better in today's digital age.
KEYING
We examined mattes, let's move on to its counter part: Keying. Again, the word is as old moving pictures. In the early days, the only way to do a 'trick shot' was through double exposure of the same film.
A 'matte box' was placed in front of the camera with a cut out 'a keyhole' - hence the name keying. Only the part of the film inside the cut out was exposed the first time around and during the second exposure, the dark areas of the matte box were replaced with, you guessed it....a matte!
The famous shot of Dorothy going down the yellow brick road was shot through a tiny 'key hole' on a sound stage and then the large matte painting of the 'yellow brick road' etc. was placed around it.
Look back at that shot and tell me...can you tell where the key ends and the matte begins? You progbably can't and that has to do with the placement of that cutout in from of the camera. Since the key hole is placed only a few inches away from the camera lens, the edges are naturally out of focus and soft.
Tip #1 - Soft Edges are key
What worked then, still works today. Try to soften your key areas. Use blur, soft key or any other trick possible to avoid hard edges when keying. Especially important here is the background. Obviously, you can't soften up the subject itself too much, so work on the background. Use soft, flowing or even out of focus backgrounds for more pleasing results. A lot of the stuff discussed in the Matte section applies here too.
Tip #2 - Back to the Yellow Brick Road
I know it's tempting to use all those fancy options on your NLE System, but very often, the old fashioned way of keying (with a matte cutout in front of your camera) will work just as well or better. You can't do a modern type key like the weatherman in front of the chart that way but when you need to place a subject into a background, the old fashioned matte box soft key will work.
Here's a modern day example of the 'Matte Box technique. You have filmed an announcer against a black background but the whole shot looks kind of dull so you want to spice it up. You can replace a part of the shot with a still shot of TV monitors and your shot looks like it was filmed inside a editing suite. Replace part of the picture with a still of a window, a roman column.... the possibilities are endless. To 'apply a key' afterwards, you simple select an appropriate transition in your editing system and stop it at the appropriate point to create the matte cutout. This is called a stop-wipe. Simple transitions like circle or vertical wipes work best here.
I hope you found this little expose of keying and mattes interesting. We still use most of the same techniques that were used at the turn of the century. We have more modern tools today but the same techniques still work today.
Article by Alan Steward, Animator and Sound Designer - www.musicleads.net
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