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superjab
02-18-2005, 12:09 AM
Hi everyone.
When people are filmed in real actions and we want to use a different location, a green/blue screen is located behind them, after filming the sequence you can substitute the background with some digital landscape or matte painting.

Do you know how to do this? i guess it is possible during the post production with after effects but i would like to have further information.
thanks

superjab

MadSkillzMan
02-18-2005, 01:26 AM
hey super jab,

This is an EASY EASY EASY task as far as the computer goes. Almost EVERY NLE can do it, not just AE (although it is effective)

There are some VERY importand things to do though. ONe must have perfectly even lighting, no shadows, etc..

What format are you shooting? I can help you decide which color.

Most people expect you to buy a fancy pro greenscreen. I just used neon felt my gf found me at a local fabric store.

If you have even lighting its cake. If not, you better learn masks and hand touching in green frame by frame.

Ask away. this is the first thing i learned

michaeljr
02-18-2005, 03:10 AM
exactly what do you want to do with the greenscreen?

do you want to do the news report with just someone sitting in front of a weather map?

or are you looking at things like Sky Captain with digital sets and camera movement?

I wouldn't worry that much about shadows and perfect ligthing. even under the best conditions you will never get rid of shadows or have the most even lighting. especially if you are on a budget. take a look at any of the behind the scenes from Star Wars or Sky Capatain. You can see they have shadows all over and different colored sections of the blue / green screen. Especially if you are going after dramatic lighting, you will always have a shadow on the ground. Unless you have a lot of room you will most likely be standing close your greenscreen anyway, casting your shadow. Or in my case I have a green floor and I cast shadows onto that. Layering your chroma keys will allow you to pull out the shadows and mixed colors you don't want. Also most keyers have something built in to deal with shadows and spill. (I use Combustion myself)

we just talked about this a bit ago, so why don't you check out this thread

http://www.cgtalk.com/showthread.php?t=206801

I wrote a quick "how to" for building a green screen and lights for under 100$, maybe that will help answer some of your questions.

and not to disagree with MadSkillzMan, but it isn't as EASY EASY EASY as he puts it, not unless you have a pefictly lit green screen and a uncompressed 4:4:4 camera will you ever be able to pull a key with the first click. if you are using a DV camera, that only adds to the frustration as DV compressed footage fights you all the way. be sure to write down all your settings to make sure once you get working camera settings, set lighting, and key settings, you will be able to concentate on the movie rather the tech behind it.

michael JR.
www.mjrworld.com (http://www.mjrworld.com/)

MadSkillzMan
02-18-2005, 05:12 AM
michaeljr,

I will admit, its not easy, at least for me it used to not be. I figured out my own way that literally lets you do one click with a miniDV.

I just do this in my basement. Ceiling is 8 feet all. Green screen is positioned about 6 in from the ceiling, we tack it to a bookshelf. Keep in mind this is felt, not real chroma key screen.

Built into the ceiling is a flourescent light, a 4 foot common household flourescant light fixture. We have ours directly above the screen. Actually there was one, and i love how it did half the screen, so i just put 2 hooks in the ceiling, so i can take down my fixture when i want but anyways.

The light is about a foot away from the screen, shinning directly down. This way all shadows are projected to the floor, and the light hits the screen. Being that its flourescent, it really complements the neon green.

Now, have you ever been in a fish store? Im an aquarium guy. I loved how flourescent lights made the fish look. I also noticed, some tanks the plants would be a rich glowing green. ( i have not tried this yet but i will) There are the growth bulbs for fishtanks, they have a semi black light effect. They dont affect skin or other colors (as a pure blacklight would) but they affect green and neons harshly. So, my girlfriend is gonna let me borrow one from her 75 gallon to try it.

Thats only why its easy for me. AEFX has a better chroma keyer IMO, premiers is weak. BUt it only requires me to turn it up to about 4 or 5 to completely remove the backround.

i was also just gonna throw my blacklight in one side of the fixture, and white in the other to see how thatd come out.

This is why i suggest green. Blue, which ive worked with, can be alright, but i found its pickier with lighting and if your using DV (i was using VHSC) can SUCK

what do you gusy think of my method?

EDIT: I will be using this setup in the upcomming days, if anyones interested i can post pics, measurements, a tutorial, etc, but honestly, its only 1 chroma key applied, not mulitple with masking.

superjab
02-18-2005, 10:40 PM
Thanks guys i appreciated the help.
Anyway i'm not quite sure if i understood it. Do you know any tutorials about matches real footage and digital landscape? Something step by step in After effects.
What i want to do is easy, i would like to know how i can achieve the effect. For instance, i film someone on a blu/green screen after that i do a CG animation and then i blend the video with the animation together in after effects.(put on the screen the CG animation and keep the real actor in foreground). That's all.
Thanks

MadSkillzMan
02-18-2005, 11:27 PM
so you just need a simple green screen tutorial in AEFX? i could write one up for you in the next few days.

michaeljr
02-19-2005, 01:50 AM
superjab, do you have a movie or scene you could give as an example of what you want to do?

the reason I ask is that it might help everyone understand the complexities that may be involved.

for example, if you had just a flat green screen that is just big enough for a actor to stand in front, your camera will be locked off. with a locked off camera, your character in the digital environment will only be able to do so much. you won't be able to move around that much in the digital world because of the perspective shift, you actor will become THIN if you go to far one way or another. he's just a flat still over a 3d background.

if you had a corner green screen with tracking markers, then you would be able to move 180 degrees or more around that character, then using that tracking data you could move around more in the digital environment. this is a much more complex setup.

michael JR.
www.mjrworld.com (http://www.mjrworld.com/)

thecmpguru
03-03-2005, 10:18 PM
I read that someone (I forget who) preferred After Effect's chroma key over Premiere's. I have seemed to have better luck with Premiere Pro's than AE becuase it's easier to adjust and seems to do a better job. But maybe I'm missing something. Could someone walk me through applying a chroma key in AE (and help with removing shadows!)?

Also, I read about the possibilities of a 180* tracking corner screen set up. I have seen what they look like on bonus features of movies like Star Wars. But how do you perform the tracking in software like AE or Premiere?

michaeljr
03-04-2005, 11:56 PM
you can't track with premiere or AE. you need a 3d pixel tracker. like PFHoe from

http://www.thepixelfarm.co.uk/contentfull.aspx?content=pfhoe.htm

and then you will need a 3d background to put in there also.

AE only offers a 2d tracker and will not calculate the camera settings and movement, just X and Y movements.

you could FAKE something if you did basic camera pans that you could match by hand. I guess you can match anything by hand, if you took the time to do it, but it would be extremely time consuming.

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