The Project
We had a job in the studio this week to produce a British Sign Language DVD for one of our clients (a council in the South of England). Our company normally provides
translation services so this project was a little unusual for us. We thought it would be great to share our learnings and document the process along the way, via a Google Knol.
We needed to use a Chroma Key background as the
Sign Language Interpreter would need to appear on screen as if they were in front of the DVD interpreting the action, this means that any background behind the interpreter would need to be removed.
First we needed a solid background that would form the Chroma Key. We have experimented with cloth backgrounds in the past – but had very limited success, partly due to the cloth being transparent and difficult to light consistently. Our own brief this time was to make a more solid set-up that we could re-use for future projects.
Painting the Background
We had a few office dividers that we could use to hold the background – we planned to add some ply-board onto these to form the solid base that would be the Chroma Key.
These were first primed (3 coats) and then painted with special Chroma Key paint.
The paint we used was made by
Rosco DigiComp. These paints are specifically formulated to provide
proper luminence and RGB values for optimum operation of all digital compositing systems. In other words you can't get normal blue or green paint from the local hardware store, you need the special stuff.
It took 5 coats each one two hours apart to get a consistent coverage on the boards. We gradually built up the coverage using a roller. BTW - There is a great Knol by The Family Handyman Magazine that explains
interior painting techniques, its well worth a read before beginning any paint jobs.
Mounting the Boards
The plan was to bolt the painted board onto office dividers so they can stand independently in the centre of the studio... but... when we stood them next to the wall it was apparent that it wasn't necessary.
We thought it would be better to bolt the boards together and stand them upright to make an 8ft X 8ft square. This should give us enough room to stand the Sign Language Interpreter well in front of the green screen making it easier to light the board and the subject independently.
The two lines in the picture are because the paint is still wet - after we put the boards together we filled the tiny gap with sealant and then painted over it. This later dried out to a consistent finish.
Lighting the Boards
We had invested so much time in preparing the boards and applying Chroma paint our strategy was to throw as much light onto them as possible. We used two large 800 watt halogen lights set at 45 degrees to the background to light it. These worked brilliantly - it only took a few moments to set-up and was quite easy to get a consistent tone across the background. When we have used fabric in the past this process took a very long time to get right.
Lighting the background independently from the subject meant standing the subject 2 metres in front of the Chroma Key board to avoid any shadows being cast onto it, shadows may effect the Chroma effect from working. In total we used 5 lights, 2 lights on the background and 3 lights on the subject (person) in front of the camera.
Testing
Before filming we tested the camera (Sony DSR500), lighting and Chroma Key setup. As can be seen in the image below the green background is consistent and far enough away from skin tones and clothing to be removed easily. We have removed half of the background and replaced it with a beach scene.
Final Product
This is a picture of our British Sign Language Interpreter in action. The green screen was a nice consistent colour that was removed easily in post production.
In Conclusion
I would give the following advice to anyone about to start on a sign Language/Chroma Key project.
- Use paint if you can. Using the paint made our life easier later on in the process.
- Your subject may have to stand 3 metres away from the green background to avoid things such as shadows and a weird green glow. Allow for plenty of space.
- Allow plenty of time. If this is your first time filming allow at least a day to film a one hour DVD. Get up early and make sure you have everything in place before any filming begins.
- Prepare. If you are making the boards then make sure you know how to paint, have all the rollers, have the proper paint and take your time. You'll get a much better surface to film in front of which will save your hours in post production later on.
- Use plenty of lights. 5 lights in total - 3 on the subject and (at least) 2 on the background are needed.
- Test it first. Sign Language Interpreters are very very busy - and therefore come at a premium - ask someone to move around in front of the camera well before the day of filming and then export the footage into your favourite video editing suite to test (we use Vegas but guess there are lots of there to choose from). Make sure you are 100% happy with everything before the Sign Language Interpreter arrives.
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