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Blue/Green Chroma key background


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Rosco make chromakey (CSO) paint. Probably green is the best colour to go for, as blue is pretty comon in clothing nowadays.


The essential idea is that you need a paint that has just the single pure pigment. Don't do what I did - I went into the local Dulux trade centre and we looked for the most blue colour we could find. The helpful bloke then looked up the mix info, and as they had the old big syringe machine, not the new clever ones, and we saw it had loads of blue, a tiny squidge of yellow and a bit of red and some grey stuff. We worked out that we could remove all the colour except blue, and make up the volume with more blue. They said they couldn't guarantee the result, but I said I'd take the chance.


Result - Amazing blue. painted the wall (plastered) and while wet tried it out, fine.


Next day, it had slid off the wall, leavinglight blue at the top and a mess on the floor!


I assume some of those extra colours aren't colours, but binders of some sort to make it stick and set?


Next time it will be real chromakey paint



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Basically, Chroma key will turn every 'pixel' of a certain colour clear. The purest color possible is what you need (ie a paint that when looked at closely contains a number of shades is no good as you will have to turn up the 'tollerance'). The color also needs to be non existant in whatever you are recording against. There are 3 fairly common ways to go about it - Chroma paint, Chroma-Cloth backdrops (bolts of cloth) or Chroma-screens. Chroma-screens are more for stationary shots - used a lot in photography, they are usually highly portable. The one I own is a wire framed thing which 'twists' into a small bag, and has both a blue and green side - if you have ever seen those wide brim hats that are about 60cm in diameter an you twist one side forward, the other side backwards, and it folds up to about 30cm, that is how it works. The screen is really meant to be put behind someone when taking photographs, or for news report style substitution - ie minimal movement. Chroma paint is great if you want permanancy, and Chroma-cloth is a handy thing for tacking to a wall if you need a quick chroma wall which is temporary and is handy thing to have in the scene store for a theatre - great if you want to film things on the stage.
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