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Geek Culture / Green Screening in Movies.

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Xenocythe
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Posted: 17th Dec 2006 19:09
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I don't get it. How does it work? I'm trying to accomplish something like this. I have a webcam that takes pretty good quality videos.

What do I do? Is there a program I can download that can do this?

The only cheap, time taking method I can think of is taking a video in front of a sollid colored wall, cut up the frames, open them in photoshop and use the magic wand?

Or is there some program (free or pay) that can do this with ease?

-Mansoor Siddiquie

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Agent Dink
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Posted: 17th Dec 2006 19:11
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Thats basically what you'll have to do as far as I know.

I hear Adobe Premiere has a decent tool for greenscreening, but I have never used it personally. I'd google it if I were you, you might find some cool results.

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David R
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Posted: 17th Dec 2006 19:21
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The technology you're looking for here is Chromakeying. Adobe Premiere has a piece of technology in particular called "keylight" - it is actually pretty simple how it works; it simple removes specific colours (be it green, blue, what ever) within a specific range, and creates a 'matte plate' (I might have my terminology wrong here actually, there's a load of different matte types, but I'm pretty sure it is that one).

Its akin to a PNG with an alpha channel - although it'll appear void with nothing behind it, once something is put behind it, it clips nicely, and just behaves like an image with transparency.

Most apps do the matte layering automatically I believe, but Premiere is designed for maximum control, so it lets you do all sorts of weird stuff (composite layers, matte layers etc.)

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PowerSoft
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Posted: 17th Dec 2006 19:25
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So if you dressed in complete green/blue/red and had a background I presume you could implant images upon that figure?

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David R
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Posted: 17th Dec 2006 19:28
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In most cases, if you were dressed in the same colour as the screen, you would disappear

By the way, Red is usually avoided due to its similarity to human skin tone, blue is OK, but difficult to light, and green is usually preferred due to its high luminosity, and with older cameras, green is double-sampled I believe (making detail of a higher quality than blue)

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Xenocythe
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Posted: 17th Dec 2006 19:50
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Thanks alot guys

I'll pick up Adobe Premiere and try it.

-Mansoor Siddiquie

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David R
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Posted: 17th Dec 2006 20:34
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Quote: "I'll pick up Adobe Premiere and try it"


Premiere costs a bomb (~£600) by the way, and if I remember, KeyLight is a separate component which costs a hell of a lot on its own too (~£200)

Premiere elements is cheaper (~£60) but I'm doubtful of its keying abilities.

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Matt Rock
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Posted: 17th Dec 2006 21:37
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Poor lighting can cause blue screens to go bad, and so can any shades of blue in an actor's outfit. Green screens are brighter, and thus lighting is far easier using green screens because the green reflects light better than the blue, which is darker and thus absorbs some of it. Also, with green screens, you need to match a very specific color value to the green on the screen in order to make something in the scene transparent... with blue screens, they pick up multiple shades of blue, and that's why you're more likely to see that dark, fuzzy outline surrounding a blue screen actor than a green screen actor.

Sony, Adobe, and Apple all make pc-compatible software that can utilize green screen technology, but there's more to it than software alone. I might be wrong about this, but I'm pretty sure you have to match the right RGB value for it to work... if I remember correctly, if the screen is off by only a few shades or hues or whatever, it won't work properly. The problem with using a webcam is that it more than likely adjusts itself for lighting. It's virtually impossible to shoot on a green screen using a resolution that's less than modern "hardcore" cameras, or at least that's how I understand it. By "hardcore" cameras, I mean cameras like the Sony HVR-V1U (regardless of what you think of their game consoles, Sony makes some bad-a** cameras!). Home camcorders and actual movie cameras are (obviously) completely different, in price and design, and you won't see many green screens set up in front of cameras cheaper than a grand, because most cameras cheaper than that can't properly handle green screen stuff. But again, I might be wrong... this is entirely based on stuff I've heard from other people.


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indi
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Posted: 17th Dec 2006 22:07
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virtual dub is free and has a keying feature.
most of what's said above is correct.

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Grandma
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Posted: 17th Dec 2006 23:06
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Or you can try out Adobe After effects, it's the l33t version of premiere. I tried it once and it was a difficult program, but you have greater keying possibilities with that then with premiere i believe......if you wanna go all the way that is.

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David R
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Posted: 17th Dec 2006 23:22 Edited at: 17th Dec 2006 23:25
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Quote: "I might be wrong about this, but I'm pretty sure you have to match the right RGB value for it to work..."


Most of the better software auto-detects a range for each frame, so its dynamic - it doesn't have to be exact, but at least in close proximity.

'Lesser' or older software is RGB specific though, so in that respect you are right

EDIT: I'm pretty sure that VirtualDub doesn't offer a chroma keying feature - it has loads of keying features, but nothing with chroma (and it can't generate a matte from what I can remember of using it)

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indi
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Posted: 17th Dec 2006 23:39
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im pretty sure there is a plugin for keying in Virtual Dub.
doom9.org and videohelp.com is the best place to look

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H4ck1d
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Posted: 17th Dec 2006 23:51
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The Gimp has a plugin that you can use for video editing, personally I find it difficult to use, with little/no documentation, but if you can figure it out I believe it has the ability to do what you need.

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Matt Rock
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Posted: 18th Dec 2006 03:11
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Quote: "'Lesser' or older software is RGB specific though, so in that respect you are right
"

That makes sense. The height of my cinematic experience took place in 2000, and that's probably when I heard that, back when I talked to film people a bunch.

Here's an interesting (but probably impossible) concept: Could you use a green screen in DarkBASIC? There's the whole colorkey thing... I'm wondering, if you set up a green screen and shot a video of someone dressed up like a spaceman or something, could you then import the video as an AVI to DBP, set the background as transparent, and then impose a background of, say, mars or something, behind the actor? How cool would that be!

Eh, but colorkey doesn't extend to avi's, does it . I smell a need for a new command or DLL! hehe


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Benjamin
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Posted: 18th Dec 2006 05:59
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Quote: "Eh, but colorkey doesn't extend to avi's, does it"

Not to mention the fact that it's one solid colour, not a range.

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Matt Rock
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Posted: 18th Dec 2006 06:00
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Yet another good point


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Agent Dink
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Posted: 18th Dec 2006 06:00 Edited at: 18th Dec 2006 06:00
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Color key is also only 1 color. Most likely there will be disimilarities in lighting even if it's not visible to the human eye. There will be compression and all that stuff. Colorkey wouldn't take care of anti-aliasing and feathering around edges either. Though you could have it do a range of colors in one pass perhaps. It would not look very good, but it's possible. Maybe...

Edit: Benjamin beat me to it

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The crazy
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Posted: 18th Dec 2006 06:29
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Ha! Good luck with a webcam! You're much better off even with a dv camcorder.

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Dextro
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Posted: 18th Dec 2006 07:20 Edited at: 18th Dec 2006 07:23
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I made a program in DBPro that changes every green pixel to white; the program is quite good actually, it can detect all sorts of green , it takes the name of the batch pictures (i.e i have 40 files named frame1.bmp, frame2.bmp... frame40.bmp), the program asks for the "base filename" (in this case "frame", then it processes each file automatically.
But, for it to be succesfull, you'll need proper illumintation to be able to get a pure green color.
Basically you need strong white light so there are no "shadows" in the green "screen".
I know this because I'm making a Mortal Kombat clone, using the same technique.
I just film 3 seconds of an action (for example, walking), then I decompile the mpg/avi into separate bmps, then I just take 8 bmps that will be the animation frames for my character.
Pretty neat if you ask me
But then again, strong white light is expensive (talking about high power white light bulbs, each $300US.)
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BatVink
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Posted: 18th Dec 2006 10:00
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I have tried using a green screen. It's actually a very difficult thing to do.

I have a bright green sheet, just over 3 metres square. I have 2 holes drilled in the top of my dining room wall (with little white covers to keep the missus happy ) that I can stretch the sheet across, using a rope which is sewn into the cloth edge. Nex, it is stretched downwards to the floor and held in place to make it silky smooth with no creases, ruffles or anything else to cast shadows. I have a 300 watt light to illuminate it, and a semi-decent JVC video camera.

All of the above is not enough to get the perfect setup. The best results I get are from using the sheet in the garden on a bright summer's day, stretching it across our summerhouse (posh shed ). Even then, it takes a lot of post processing.

I use Serif Movie Plus to edit the video. The chroma tool allows me to "draw a line" across the green background, and it generates the range of greens I wish to eliminate. In addition, I can set a tolerance to extend the range a little further. Using the timeline, I create keys every 3 seconds or so, and repeat the process of selecting the greens. The software interpolates between the key frames, and ensures that any minor changes in lighting are accounted for.

It's still not perfect in some places, but it's adequate for my needs. But the point of this post is to let you know it's not a cheap, quick trick. It takes time, some cheap but necessary equipment, and a lot of messing!

Quote: "Or you can try out Adobe After effects, it's the l33t version of premiere"

After Effects isn't an alternative to Premiere, it's the "special effects" component of your studio. It's not designed for composing the final cut.



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Scraggle
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Posted: 18th Dec 2006 10:51 Edited at: 18th Dec 2006 11:03
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I would recommend taking a look at Ultra2 from Serious Magic. You can download a free trial if you wish. It cost $499 so a free trial is certainly the first option.

Adobe has just bought out Serious Magic and they are incorperating Ultra2 into the next version of Premiere. The reason I know? ... I am part of the help file writing team

Quoting Agent Dink:
Quote: "Color key is also only 1 color. Most likely there will be disimilarities in lighting even if it's not visible to the human eye. There will be compression and all that stuff. Colorkey wouldn't take care of anti-aliasing and feathering around edges either."


That's a load of tosh!
Download the trial of Ultra2 and you will see that it can do all of the things that you say are impossible.

It is also incredibly easy to use. If you have got $499 burning a hole in your pocket then Ultra2 is certainly worth getting. It is a lot easier to use than BatVinks method but I am guessing that BatVinks method is a lot cheaper


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Zappo
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Posted: 18th Dec 2006 11:12
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Quote: "That's a load of tosh!"

I think Agent Dink was refering to the Color Key in DarkBasic being only one solid colour and not a range.

Its certainly possible to do it with a webcam but it does require some decent lighting. I wrote an application many years ago in Delphi which did it. You picked a colour and set the tolerance level and it exchanged all pixels of that colour range with those from a bitmap image. Worked a treat although there was no blending (i.e. it left jagged edges around people) and it could only manage about 5 frames a second so no good for live action but okay for taking still images. It would no doubt be much quicker on modern PCs but I doubt I have the source code anymore. I will have a look though as it would make an interesting 'toy' application.
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Manic
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Posted: 18th Dec 2006 11:37 Edited at: 18th Dec 2006 13:46
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interesting thread. My work doesn't involve green screens, simply because of the set up costs etc, and by the time i've finished, it should be so far removed from the original anyway, it shouldn't matter.

I wish i'd got in there to say "use DB" first though. I might suggest a different way about it though.

use memblocks to gather your keying info, which would let you cover a range of colours, then use that information to create an alpha map per frame. (something like if pixel.greeen>225 then alphapixel=rgb(0,0,0) ). then take those frames (which you saved out of DB) and recompile them into a video. You can then use that as a Track Matte.

however, you might run into the problem of finding a program that can handle track mattes, Premiere does, but then you might as well have used its colour keying. lol


for those interested in what my work looks like, have a look at this. It took about a week, using Premiere, After Effects and 3D Studio Max, Filmed against a white wall, altho, the actual video isn't used in the final piece. WARNING: Contains one use of coarse language. PG-12 rating? (again, sorry batvink)

Martin

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Grandma
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Posted: 18th Dec 2006 11:55
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Quote: "After Effects isn't an alternative to Premiere, it's the "special effects" component of your studio. It's not designed for composing the final cut."


Okay thanks for clearing that up, i was a bit unsure. I only tried it for at a friends house some weeks ago, he's really into filming and FX.

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BatVink
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Posted: 18th Dec 2006 13:00
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Gee, thanks Manic, I rally appreciated the warning, what with my 9 year old son standing next to me.



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indi
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Posted: 18th Dec 2006 13:34 Edited at: 18th Dec 2006 13:36
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Industry standard keying in Shake 4.1 - $700 AUD
Image /footage stabilization etc.etc.

DV cameras and below will need a lot of tweaking to get a decent range.
any colour can be a screen, any combinations of colours can be a screen.

Primatte and CFC keylight are the big daddies you want to use for the best keying effect.
Using them in conjunction also improves your key.

in the preview screen attached to this post is a snapshot of the keying in action in Shake.

the video footage is HD 720p and you can see even with high quality keying, my first grab which is what is shown is not up to par. the black area is being keyed which was a sky blue light.

with a little more tweaking it can be near perfect, however his shirt will eventually fade out as well because they share a similar blue spectrum.

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Manic
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Posted: 18th Dec 2006 13:44
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@ Batvink: really sorry about that, i forgot about the T word in there. I'll put a warning on it.

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BatVink
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Posted: 18th Dec 2006 14:28
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Cheers Manic



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Zappo
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Posted: 18th Dec 2006 16:02 Edited at: 18th Dec 2006 16:03
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I couldn't find my original source code for doing a WebCam Chromakey type application in Delphi, so I thought I would knock up a quick one to prove it can be done. It was also quite a good programming excersize. Attached is a screenshot of it chromokeying(?) on black and replacing it with a mountain road picture.

This version has no optimization so only does about 2 frames a second but the results aren't too bad as a demo. The lighting (as you can see) is very poor too. With lots more work it could be useful, although I don't know if its worth the effort.

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David R
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Posted: 18th Dec 2006 17:46
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@Zappo: Just out of interest, when apps like yours mention 'Tolerance' is that a +/- range (in RGB) from the original colour that the pixels could be? Since I've never quite understood the exact meaning of tolerance

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Dextro
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Posted: 18th Dec 2006 20:09 Edited at: 18th Dec 2006 20:21
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I think, tolerance in this case, means how wide the range of colors it will "convert". For example. in the program I made, I can set the color I want to turn transparent, in this case green.
But what if my green foamie sheet has darker spots?
I set a tolerance of how light or dark shades of green my program will convert.
This is a shot i took with my camera, and the resulting image using my program. Note that I wasn't using good white ilumination, so you can see a bit of shadow.

Edit:
Ups, thats not the original green background image. But you can see the picture below which was the result of the original, you can see how accurate it is.
It was done in under 4 minutes, using my program (about 30 secs per frame, there were 8 frames).

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Xenocythe
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Posted: 19th Dec 2006 02:54
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Good god, I left here at 5 posts thinking this would drop to the dead

Well, I have like 5 new programs to try out, thanks so much for all the suggestions guys

And thanks for the explanation on how green is better- that answered a lot of questions of mine

-Mansoor Siddiquie

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indi
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Posted: 19th Dec 2006 03:55
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when my friend worked painting the star wars sets at Fox Studios in Sydney, they used blue for foreground and green for back grounds. this allowed for the blue to offset skin tones and the green for sky and atmosphere not to bump into the blue.

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Manic
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Posted: 19th Dec 2006 11:49
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now that's a good idea!

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Zappo
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Posted: 19th Dec 2006 12:07
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Sorry for the delay...
Yes, tolerance in my case is simply a range used for the R,G and B values. As WebCams do continually adjust brightness and colours are always changing on a frame by frame basis, it simply looks for a range of shades. If a pixel falls between a minimum and a maximum value in all three colours (Red, Green and Blue) then it is exchanged for the corrisponding pixel from the alternative bitmap.
It was a very quick and dirty solution which works okay for a demo. For a proper production app though the R,G and B ranges would probably need to be slightly different as they have different intensities. I think blue is the least intense (so might require a wider range), red is next and green is the most intense. I could be wrong though, its been a while since I looked into it.
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indi
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Posted: 19th Dec 2006 12:28
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did you know.
webcams are mostly infrared cameras with a filter over the front.
take a piece of exposed film and apply it twice fold to the front and you can get a infrared camera from your crappy webcam sitting on your monitor etc...
its a well known hack for those silly enough not to try.

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Manic
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Posted: 19th Dec 2006 16:20
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thats interesting too...

with two camera's close enough together, you could film a colour version and an alpha version (using your subjects body heat as the map) It'd look well trippy because of the slight difference between the camera's location. I'll have to give it a try.

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Xenocythe
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Posted: 20th Dec 2006 04:11
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My webcam was $120 USD, good qualtiy, you can set light modes too, so its not on auto

But I would be using my much more expensive digital camera if I could find the wire

-Mansoor Siddiquie

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