I know nothing about backscreen help teach me!

[nigel101]

Ive made or in the making a spacecraft I was going to use black sheets but some people on her say use a greenscreen.

www.ngmfilms.com

Then i've read there are white, green and blue screens.

Im using a miniDV camcorda. And the spacecraft will be grey.

What you recommand?.... Also I dont know much about CGI if I film it with a backscreen will I have to put it into my software and frame by frame add the space (which would take years).

What software you recommand? ....professional software which is effordable.

[Radiate]

If your using grey, u dont want the backround to be black or white..... so i would recommend either a green or even a red screen. And for software, u could just get adobe premiere or even adobe premiere elements. You can key out certain colors, add mattes and all sorts of stuff and it does the whole clip at once, not frame by frame.

[BrownCowStudios]

Man, you really like to plug your site...

Anyway, After Effects will do the job much better than Premiere. You'll have more control, and you'll end up with better results. Not to mention the many other uses of After Effects. It's a worthy investment.

[Almondo99]

Another alternative is Final Cut Express, but After Effects is much better.

[Radiate]

yeah but after effects is way more expensive, yeah it'd do a better job so get that if its not too much....

[Almondo99]

It depends on how good you want it to look and what will fit your budget.

[jcdenton]

BTW: I have several green- bue- whatever screening options in my Editor (MAGIX video deluxe), but I think the MATTE LINE is pretty low quality. No matter if I use a green towel that is made of one single green tone and is lighten perfectly, or if I use one that has diffrent shades of green, no matter what I do, due to Antialiasing of the contours of the actor who stands in front of the green towel his contours always include unmasked shades of green, unless I set the masking tolerance to a value that will cut off too much of him.

How does AE deal with this Antialiased Contour problem to get a decent Matte line?

Are there any tricks?

[Epsilon]

Any color screen will work as long as it is (reflectively) flat, evenly lit, and an easily isolated color. So if you were filming a rich green flower with blue petals, red may be the best keying choice. The only reason it doesn't work very well in our world is because there is a lot of red in human skin. Blues and greens are less common.

For a spacecraft, pick any strong color that isn't in the object. I use Premiere Pro for keying, myself.

[Raptor]

Blue or green if you have skin tones, but as Epsilon said, any color that is not in the foreground. The problem with the edges is not caused by true antialiasing, but by the DV 4:1:1 sampling rate. The chroma channel is sample only once every four pixels, resulting in the blocky edges when you key out the color. Premiere and most editors have a basic keyer, but as jcdenton said it is tough to get a clean line without losing some of the edge of the foreground. After effects realy has the same problem if you try to use a single key effect to get it, however creative cow has a great tutorial on building a multilayer matte using two different types of keys, I believe it is something along the lines of how to build an edge matte. Takes a little more work, not much, but it definitely gives much cleaner results. If you only have a small amount of keying to do, or for a single project, AE is definitely the most cost effective way to do it since you get all the other tools in AE for other uses.
Since we do a lot of chroma key for the television show we got SeriousMagc Ultra, which is dedicated keying software. The controls are relatively imple, and allow color corection and good spill suppression. That being said, if the scene is poorly lit, it can still be a daunting experience to get it looking like the talent still was really in front of the BG. The edge control however is great, it allows any color, and allows you to sample multiple points in the background to build our matte, which is helpful if you have any wrinkles or some uneven lighting. Now while that sounds contradictory, the lighting with Ultra can be further off than with anyting else I've used to establish a key, and still get good results. the trick is to get the lighting so that your talent is speparated from the background, aoiding any spill of reflective color onto your talent.
Some basic rules.
1) Light the screen and talent separately
2)Separation, have the talent as far away from teh screen as possible. WHile this is toughter to do in a full body shot where you see the feet, do the best you can. We usually only use upper body shots, and work witht he actors about 6 to 7 feet in front of the screen.
3) Even lighting on the screen. I use the cameras Zebras to make sure the light is as evenly distributed as possible.
4) Use of a hair light behind the talent helps to cut down on spill and increase the separation. We use a couple of 40 watt tungsten balanced mini floods for hair lights at floor level, about 300 watts of tungsten balanced forground light on the talent off of white foamcore reflectors, and light the screen with 2 - 200 watt daylight balanced bulbs reflected off teh white ceiling.

[jcdenton]

Wow, that's a lot of useful information, thanks a lot.

I asked myself why it isn't possible to code greenscreening this way:

- recognize any green tone pixel (where green is bigger than red and bigger than blue)
- mask green pixels that are within a certain tolerance range - as usual
- if it's above a certain tolerance value, but still a significant green tone, then get the color tone of the background pixel and use the foreground pixels brightness and mix them. This way the smoothed edge is saved, but the greenish Matte Line will dynamicly use the background color tone, like a chameleon.

(well probably you'd need to use the offset to the key green as a transparency value, instead of brightness, a lot of trial and error to do)

Probably I'll find the time to code this myself.

A friend told me he's using Chromanator (from the same company as AlamDV). Personally I try to stay close to the NoBudget Philosophy, so I have downloaded the free "Zwei-Stein" because some people wrote its greenscreening capabilities are very good. I still got to test it.

And as a final thought: If you get a color Matte Line, use a key color that is seen often in the background. Of course, this can't be done in all situations. But sometimes it's pretty easy. EG: if you make a Prediator like Movie that plays in a forest, a green Matte Line won't be obvious at all. When your background is more blue-ish, you should use bluescreening instead. I would prefere Bluescreening for a grey background (city etc.) since green over grey still looks very disturbing.

This Multilayer Matte thing sounds very interesting tho. Do you have a link to the mentioned tutorial?

[Raptor]

Here ya go - Procedural Matte Creation Tutorial
http://www.creativecow.net/show.php?pag ... index.html

[jcdenton]

Thanks a lot. Just bookmarked. Probably I'll try to use that method. Not sure since I am working on a one-pass optimized greenscreening thing.

I just managed to implement the Matte Line Blending I was talking about before. It looks much better than what I get by Magix or by Zweistein.
It takes 2 parameters: green separation 1 and green separation 2. If a pixels Green minus separation value 1 (EG. 100) is still bigger than its red and blue, it will be masked as usual.
If it's not, but Green minus separation value 2 (EG. 15) is still bigger than its red and blue, it is recognized as a Matte line pixel. The diffrence from seperation value 1 and the current green value will then be used as a transparency value to let the pixel of the background shine trough: the less green the matte line pixel is, the less transparent it is.
The rgb components of the foreground pixel will be converted to greyscale before mixing it with the background pixel.

Now I have also added an optional Contour blur function (variable radius etc.) that may also be used for X bluring only, this way the contour will be very soft while the interlaceing will not be messed up.

I still need to add a user interface and optimize a few thing.