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You should also try and separate the subject from the background as much as possible. This isn’t the distance point that was made a moment ago, but rather using a backlight to help separate the head and shoulders of the subject from the background. A good backlight can also help to reduce color spill. Instead of using a white light for the backlight, a very common technique is to use a gel to bring a little color to the subject. Many DPs will use a magenta gel when shooting against a green screen, and an amber or orange gel when shooting against blue screen. It really depends on the situation and the subject. When doing DMNTV, we typically shoot against a green cyc wall and use an amber gel with the backlight. This ads just the right amount of color to the hosts hair and achieves the results desired -- separating the subject from the background.
This brings up another very important point about lighting. Make sure when lighting your subject that it matches your background elements that you are eventually going to key in. Nothing looks worse than a subject who is lit with the key light on the left side and a background element where the main light source is coming from the right.
One final tip about shooting for chromakey. The reason video looks like video is because of the sharpness of the image. The softer it looks, the more film-like it appears. When shooting against a green screen this sharpness is very apparent and with digital video, the effect can be accentuated because of the DV compression. A tip Paulo de Andrade showed me a while ago was to turn down the sharpness on the camera (or turn it off) to soften the image. This will reduce the hardness of the edges and produce a key that is similar to shooting with an analog camera.
Because the subject is far enough away from the background, you can also use a shallow depth of field to throw the background out of focus to help blend any unevenness or imperfections in the screen.
For this tutorial the subject was shot against a chromakey blue flat wall. Because of the size of the studio, lighting was a bit difficult and the blue screen was not as evenly lit as I would have liked. The good thing is, with the many keying plug-ins available on the market, we can correct this problem in post. The subject was lit with the key light nearly above the subject to cause the hard shadows hiding the eyes and giving an ominous feel to the subject. Some backlighting was used to help separate the subject from the background, but because the end result will be a bluish tint, it is okay if there is a little spill on the subject.
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Posting it
Okay, let’s bring the footage into After Effects 5.x and make a hologram.
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| Click for larger image to use with this tutorial. |
The capture process doesn’t really matter as long Adobe After Effects can read the file. Try to keep the footage as uncompressed as possible - meaning, don’t convert it from the native captured format (DV) to another media file (compressed QuickTime), as it will further deteriorate the image.
If you want to follow along with my sample footage, you can download the larger image. It will be enough for you to finish the entire tutorial.
Import the footage into After Effects making a new composition the same size and duration as your green/blue screen footage. An easy way to do this is to drag the imported file to the Create New Composition icon in the Project Bin.
Turn the background color of the comp to any color but black, so we can easily see what is being keyed out and what isn’t. If you remember your color theory, it is often better to differentiate colors if you use opposites. If you shot against blue, use orange, if you shot against green, use red.
It will also help to turn the composition quality to high and view it at 100% or more to fine-tune the key.
Create a garbage matte around your subject to help in the process. The garbage matte will help tremendously because then we do not have to deal with areas of the blue screen that don’t matter. If the subject moves around a lot, you will need to create an animated garbage matte.
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| Creating a garbage matte around your subject can help get rid of unwanted or poorly lit areas of your backdrop. |
Source
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