Ok, making a makeshift greenscreen :
Well to achieve such an effect, you need 2 very important elements :
1 - A greenscreen that has 1 cingular color (it can also be a bluescreen) and make sure that the green is a bright green (or blue)... like you see in the movies. Anything too bright or too dark will imply that you will spend alot of time in Post correcting flaws.
2 - A lighting setup that creates a well distributed light. The trick to greenscreening is to EVENLY light the whole screen INDEPENDANTLY from the subject. Basically, you have a lighting setup that lights up the screen by itself and a 4 point lighting setup for your subject (news anchor) that won't cast (or won't cast too much) shadow onto the backdrop. In the end, what you want to tell your editing program is to take THIS COLOR (the green) and take it out of the picture... if you have shadows on your backdrop, well, the computer will see it as a different color and won't take it out.
Lighting the greenscreen :
1 - Get yourself some neons if you can (kinos) and try to avoid spot lights, unless you can get alot of them (i.e CYC lights). Spot lights will create light gradients as for neons cast an even light everywhere. If you must use spots, try to find diffusers (either gels, or use a transparent shower curtain if you're really building this without any budget).
I usually setup my greenscreen lighting overhead, that way you have alot of room to move, make sure the lighting for the backdrop does not hit your subject.
If you have a lightmeter, test different spots on your backdrop to see if the light level is equal everywhere.
2 - Light your subject with different lights than the ones you use to light the backdrop. Try to use a 4 point lighting system (if you don't know what it is, google it or ask me in a reply). The important thing to remember when lighting your subject is to avoid casting shadows (so light from the side) and use you backlight to create a light halo around your subject for easier matting.
Post :
Well now that everything is filmed, bring it into your editing prog for compositing. I prefer to use After Effects for this.
Now what I do for a better greenscreen is I will create 2 mattes, 1 to define the edge of your subject and one to evenly matte him out. I call these mattes the EDGE and CORE mattes.
Use a Difference Matte for your edge matte and use a Color Difference Key for your core matte. This will create a black and white image that you can use as a final matte. You will prolly need to fine tune this stuff by adjusting your levels and Choke.
Now take that black and white matte into another comp, take your original clip, place it over head and set the black and white image as that original clup's matte!
There ya go, add a background and you should be done.
now I know this is alot of info and I had to abreviate the whole process, but this should give you an idea of what to do. Do some research mate, you should be able to figure things out
