How to Build a Large Blue/Greenscreen for SFX
A bluescreen / greenscreen is a solid blue or green background used in special effects work. Actors are filmed in front of this colored background, and the color of the background is then replaced with a different image to create various illusions.
Whether for filmmaking or Photoshop work, photographing your models and subjects on a bluescreen or greenscreen makes placing them on a different background a breeze!
Don't have a lot of cash to spend? No problem - let's look at how you can build your own bluescreen indoors to enhance your special fx abilities, relatively inexpensively. (On a bluescreen your actors cannot wear blue clothing because all blue will become invisible, and on a green screen green can't be worn so it may be beneficial to build both blue and green screens. For this article we will pick a blue screen.)
Blue or green cloth as the backdrop is very popular among DIY video people for compositing work, but the problem is cloth is very difficult to stretch so tight that there aren't any folds, bends or wrinkles. You want as close as a solid blue color as you can, and folds and wrinkles will create shadows which create different shades of the color.
Any smooth surface will do, but if you cannot paint with blue paint directly onto a smooth wall, a better and relatively inexpensive material we have tried and tested is polystyrene sheets, an inch or more thick. Buy the biggest sheets possible that will fit into the space you'll be using - the possible sheet size is usually determined by the size of your vehicle to transport them with (even better if the foam store will deliver the sheets with a big truck) and the doors you'll be carrying them through (hopefully you have double garage doors to the area you want to use), but smaller sheets are also no problem.
With the purest blue paint you can find at the paint store (make sure in no way that it leans towards a slight turquois or slight purple - you want a pure, rich, slightly lighter blue), paint your polystyrene sheets. You may need to wait until it dries and apply more layers to make sure you have a single shade of rich lighter blue all over.
Once dry, depending on the size of your sheets you may work on the floor or stick your sheets with something temporary in place on a wall - you will be applying slight pressure in the next step so they need to be counter supported either by the floor or the wall. You may start needing a ladder at this point.
Apply clear silicon (using either a tube or a silicon gun) all along the lines where the sheets join together, and then using a scraper at a reverse angle you completely flatten and smoothen the silicon all along the lines so that it's just a very thin spread of clear silicion joining the sheets together almost seamlessly. Do not press too hard for this will damage the polystyrene.
Once the silicon is dry (and make sure it is completely dry!), you might want to apply more of your blue paint over the seams to make sure they're as invisible as possible.
Now you should have one huge blue background. You can affix it to a wall or since it's very light polystyrene, it can be held up with rope or string tied to beams or small brass hooks you can affix to the ceiling. Just be very careful when putting strings or cables through the edges of your bluescreen that you keep pressure evenly and not tear it.
Once your blue backdrop is in place, you can paint the floor in front of it if you need to have your actors in the shot full body, feet and all.
Now you just need to correctly light it. Pay attention to shadows and light on the backdrop when lighting the scene you're filming. Keep the light very even on the backdrop itself - you might install fluorescent tube lighting on the ceiling in front of it as these create a soft, virtually shadowless light.
When editing your blue screen footage, though most editing software programs have a bluescreen key feature, the results are usually quite poor - we recommend using more powerful software that specialize in doing compositing. The serious video hobbyist or independent filmmaker might look into CompositeLab Pro from fxhome.com for far superior results.
Your bluescreen will open doors to doing sequences you never knew you could!