Common Chroma Key Mistakes

Well, I promised you all a movie review. I shot the footage. I started the editing... and.. well... the chroma keying sucked. It suffered from what is called COLOR SPILL. That happens when the light on the green screen is too bright and it reflects off the subject. This results in a green halo appearing around the talent. The steps to fixing this are as follows:

1. Decrease the amount of light on the green screen. Dimmers are not the best solution as they tend to alter the color tempeture of the light. The best solution is switching out the bulb for a weaker one OR you can use some metal screen material to act as a scrim. You can layer this material to get the desired effect.
2. Make sure the subject is five to eight feet from the green screen. This also helps to eliminate shadows.
3. Increase the amount of light on the subject. Using the three point lighting system you would have your strongest light on the subject at about a forty-five degree angle from center; this is called the KEY LIGHT. You then place a second light on the opposite side of the subject to fill in the remaining shadows. This light can be about 75% of the strength of the key light. This is called the FILL LIGHT. Then you can place a third light, just behind and above the subject. This light can be 50% of the strength of the key light and is called the BACK LIGHT or HAIR LIGHT. 

I also attempted to film video of my own hand, splattering blood and scratching at a green board to use in the logo video. This did not turn out well either. The shadows were unavoidable as I made contact with the board. Also the transparent areas of the blood made keying it impossible. 

So, next weekend I will try recording the hand and the blood splatter separately. I will record the hand on a black surface the chroma key of the black. Any color spill or shadows will better blend in with the logo image. Then I will paint my hand white and do the blood splatter on a white board. With that I should be able to use a blend method(multiply, max, min) and the opacity setting to add it to the video.