GreenScreen

[jasonsco]

Let's see, where to begin? If you really wanted to do it right, you would probably want to consider using Rosco's green screen paint, which is a good shade, but more importantly, very flat, with no specularity or shininess. Hot spots could really mess up your mattes. However, that paint can easily be $50-60 per gallon (at least, last I checked. Anyone purchase any recently?).

But, in today's wonderful world of digital compositing, you have a lot of leeway with the shades of color that you can use. More important than the exact shade would be that the color be generally different from anything else in front of it (your actor's costume, for example), and that it is generally painted and lit evenly.

So, yes, you can get away with a basic green paint from your neighborhood hardware store, but be careful how you apply it and how you light it.

But then we haven't even started to consider the dangers of doing green screen with DV (which is what I'm assuming you're shooting on). That opens up a whole new set of questions . . .

[GallenWolf]

Hi I came across this article, perhaps it could help?

http://www.detonationfilms.com/low_budget_chroma_green_paint.htm

(Also check out the explosions!)

Alvin

[hiphopcr]

I second Jason, it doesn't really matter what the exact color is, as long as it's well lit and is different from your actors. You'll end up tweaking the colors to pull the key anyway.

[nendo_3d]

oh right. cheers people. i'll check out that article in one second after av finish reading this post.

Whats this DV you mentioned.

oh i just though. it also depends on the program u use doesn't it? like if its a good program then it will be better at getting rid of the green?

[jasonsco]

Well, these days for what you're probably doing, most of the compositing programs would be fine, and will work about the same: Shake, Combustion, After Effects, Digital Fusion, etc. I wouldn't suggest trying to pull a matte (terminology for removing the green screen) in an editing program like Premiere or Avid.

As for DV or DVCam, I'm assuming that's the format you're going to be shooting on. I could be wrong in that assumption, and you could be shooting in HDCam or on film, but I'm guessing not. If you are, however, go ahead and say so, and we'll give some advice on those formats as well.

Anyway, with DV and DVCam, you won't have as much color information per pixel due to compression, so good mattes are harder to pull. It ends up looking pretty aliased. Both NTSC and Pal DV formats have pretty low sampling (4:1:1 for NTSC and 4:2:0 for Pal).

Now, I understand that for a lot of people, the above paragraph might just read as a bunch of techno-babble, but it's good to try to understand what's going on in those formats. That's why usually I suggest people don't shoot green screen on DV in general.

[parallax]

Not true. When shooting DV, you should prefer using green instead of any other color, as it is sampled 4 times as much as all other colors (because green is carried in the Luma) AFAIK

[jasonsco]

Not exactly. Yes, it is true that the "Y" component (or what is sometimes referred to as luma) in YUV is calculated by Y = .299 R + .587 G + .114 B. However, that doesn't mean that there is 4 times the amount of green information. That just means that luminance (luma, luminosity, etc., although Charles Poynton would have a fit with me because technically each of those is different--but I digress) is mostly composed up of the brightness from green areas (because green is naturally brighter than red or blue).

In order to completely reconstruct the color information, however, you would also need the "U" and "V" components. However, since those are only being sampled 1/4 the number of times as the "Y" component, you will never have good information to key.

Now, I see your point that you might be able to get more out of a green screen as opposed to a blue screen, but that's not really the point. Any chroma keying (trying to pull the matte based on color) in a 4:1:1 compression environment won't be pretty. You would probably get better results trying a luminance key, since that's the area that would have the most information.

[parallax]

Yeah your totally on point, i guess 'effectively' is the keyword here. Keying DV is horrible, so maybe using luma and/or contrasting colors will work best.

I here red is sometimes used?!

[NickJushchyshyn]

>> Not true. When shooting DV, you should prefer using green instead of any other color, as it is sampled 4 times as much as all other colors (because green is carried in the Luma) AFAIK

This is a very VERY common misconception that comes from several generalizations and misunderstandings about both compositing and the DV compression scheme.
Green is often the best choice, but DV or not, there are other situations where blue will be easier to key from and allow you to extract more fine detail.

Jason's reply helps explain some of this, but really, your best bet is to pick up Steve Wright's book on digital compositing:
Digital Compositing for Film and Video (http://www.amazon.com/gp/product/0240804554/104-1411381-8629562?v=glance&n=283155&n=507846&s=books&v=glance)

Steve does a great job of using plain (often humerous) language explaining the core mathamatics behind compositing, and by understanding this, almost all the ambiguities and quirks of green/bluescreen compositing suddenly become clear. (he also covers the fundamentals of video and film formats. This really is a must-read.)

If you take in the material in this book, you will gain a genuine fundamental understanding compositing to where you could calculate the proper alpha and color values of a pixel on paper if needed!

Without an understanding of this book (and/or Brinkmann's), you're pretty much left guessing with "rules" and fiddling with the comping plugin of your choice.

Get the book.

[nendo_3d]

Thanks for all your posts.

I did some more research. Don't know why because its a friends project not mine

But I found out u could use any colour u wanted realy. Aslong as it contrasts or depends on the situasion, but they general use 4 different colours. Like ,for example, taking a picture of a model. as in like a 12 inc replica or something they generaly use orange screen if there is alot of blue and green in the model. green and blue are for films. and grey is for like special effects. easier to create alpha maps and stuff.

well that my understand of them so far.

again thanks for your posts and help.

I am guessing DV stands for Digital Video, and yes he will be use a digital Video to record his shots.

I will mention the book to him to see if he is willing to pay for the book :D

thanks again

[jasonsco]

I would second Nick's opinion on Steve Wright's book, as well as Ron Brinkmann's. I think those are probably the two best books out there to get a good overall idea of what compositing is all about.

As for Parallax's question about red screen, yes, it is also used on occasion, but I've really only seen it used with miniatures and the like, obviously when those things have no red in them. The reason it's never used with humans is due to skin tone. Almost all skin tones have some amount of red in them (as opposed to blue, which is most opposite skin tone), so you wouldn't be able to pull a matte.

The reasons for using red, green, or blue originate with the chemical process for film (emulsion, layers, etc.). The red layer is first, then green, and blue on top. This made it somewhat easier to remove the blue layer for compositing optically, but it also has the most grain. The red layer actually has the finest grain, so a tighter matte can be pulled, but at the expense of not having anything red in your shot.

But yes, nendo_3d, you can use almost any color these days in a digital environment. As for "DV", yes, I am referring to Digital Video (with capital letters), but also specifically the DV format/codec, which has the YUV compression of 4:1:1. The term "digital video" in general can refer to any type of video signal that is encoded digtally, but "DV" and "Digital Video" is a specific format (http://en.wikipedia.org/wiki/DV/). It's the format that most consumer cameras these days use. It is also referred to as "MiniDV", but that actually refers to the tape size.

So, totally confused now?

[nendo_3d]

The last part. isn't conufssing more. needs some time to process it correctly. lol i understand it basicly. but i'll need to re-read a couple of to actualy get it correctly into my head.

thanks for all your help.

[TiskO]

I would second Nick's opinion on Steve Wright's book, as well as Ron Brinkmann's. I think those are probably the two best books out there to get a good overall idea of what compositing is all about.

As for Parallax's question about red screen, yes, it is also used on occasion, but I've really only seen it used with miniatures and the like, obviously when those things have no red in them. The reason it's never used with humans is due to skin tone. Almost all skin tones have some amount of red in them (as opposed to blue, which is most opposite skin tone), so you wouldn't be able to pull a matte.

The reasons for using red, green, or blue originate with the chemical process for film (emulsion, layers, etc.). The red layer is first, then green, and blue on top. This made it somewhat easier to remove the blue layer for compositing optically, but it also has the most grain. The red layer actually has the finest grain, so a tighter matte can be pulled, but at the expense of not having anything red in your shot.

But yes, nendo_3d, you can use almost any color these days in a digital environment. As for "DV", yes, I am referring to Digital Video (with capital letters), but also specifically the DV format/codec, which has the YUV compression of 4:1:1. The term "digital video" in general can refer to any type of video signal that is encoded digtally, but "DV" and "Digital Video" is a specific format (http://en.wikipedia.org/wiki/DV/). It's the format that most consumer cameras these days use. It is also referred to as "MiniDV", but that actually refers to the tape size.

So, totally confused now?


Jasonsco is right. shooting green or blue screen with dv, or any format which captures at 4:1:1 creates problem after problem. The other year, for a uni assignment, we shot on greenscreen with a DV camera at 4:1:1, and good-luck keying it. We tried AE, Combustion, and DF and neither could key the green. We resorted to rotoing 750 frames! I dont know too much about camera, but if you an, try get your hands on a camera which outputs in a 4:2:2 format, or 4:2:0 as a bare minimum.

[nendo_3d]

so what exactly happened when u shot 4.1.1?

because my friend has recently did a test shot. and to be honest it didn't work well. well the actualy removing of the green. it was all pixelated and jagged edges.

how do u get around this.

[TiskO]

so what exactly happened when u shot 4.1.1?

because my friend has recently did a test shot. and to be honest it didn't work well. well the actualy removing of the green. it was all pixelated and jagged edges.

how do u get around this.


Exactly that. It looks like rubbish. That's why we roto'd 750 frames cause we couldn't key it! 4:1:1 doesnt store as much colour information as 4:2:0 or 4:2:2; that's why it basically impossible to shoot green-screen on miniDV cam-corders.

[digikris]

I did a green screen project with Dvx100A edited in final cut pro with filter color smoothing 4:2:2 and exported to shake for smothing the jaked edges remember if you do a advanced 24p or 24p for action its not going to work out. Its easy.
I got better results. Its that we are not patient enough to read through the shake manual.
You should deinterlace, add color space change it from out rgb out yuv add a blur and add another colorspace change in rgb to in yuv. That's it just in the blur properites change the x pixels so that the jaked edges smoothens out. After that you can use the xor node to use it as a wraper to have the background wrap around the edges of the foreground.

[boboroshi]

We did some DV stuff (with some nicer DV cameras) back in 2000 and it was painful to say the least. We actually ended up using a static digital camera for shooting some background plates as opposed to filming them. Resulted in a lot of locked off shots, but the backgrounds had less issues. for the foregrounds, once you pull the key and garbage matte it, your biggest issues are going to be spill supprsession and the jaggies.

If you're locked into the technology, you might consider one of the following approaches:


Make it all black and white as a stylistic element. This is more something to think about when shooting, but it can help cover up some of the spill issues.
give the whole thing a bit of blur/glow as a stylistic element. Make it almost dreamlike, again covers the crap. We did this for some scenes in my partner's senior thesis back in 2000 that were just not keying well. Made it a dark smoky room basically. Worked great for a quick fix (since we couldn't reshoot)
A lot of places will rent cameras at discounts to students, get a nicer DV cam (or HD even) and then work with that footage, even if your output is only NTSC or PAL

[Daniel-B]

Getting nice keys from DV is very difficult, but not impossible. Here is a shot I composited a little over a year ago. I shot it on a Canon GL2.

http://img.photobucket.com/albums/v58/PixelMagic/DVsuperbrawlComp.jpg

[NickJushchyshyn]

We meet again, Daniel-san. :)

If you can plan your DV shot to have mostly dark subjects (dark hair & clothing) in front of a green screen (or bright/blond subjects in front of blue), you can use the color difference key to pull a quick core matte, then turn to a luma-based solution to bring out the edge details.

Basically, a color-only solution with a DV plate will be challenging at best, but that doesn't mean you can't get a good key from a greenscreen shot with DV.

[Daniel-B]

I actually captured that shot through a JVC Mini DV Professional Deck. When I inspected the color channels, they did not appear to exhibit the DV compression artifacts. Maybe the JVC deck does some sort of upsampling to the footage during capture. I don't know.

But anyway, it allowed me to keep the fine hair detail in the composite above.

[NickJushchyshyn]

The color compression would still be there, but it wouldn't have much impact on a shot like this where you have dark hair in front of a green screen. This is the fundamental recipe for an easy DV key: Dark subject in front of green. The overall luma contrast is carried through to the RGB channels, so the color difference keying calculation picks it up quite cleanly.

If your subject had blond hair, this same setup would have been much more challenging to key.

[schwastika]

I recently had a project, keying on miniDV. The result is quite bad, and my company ends up buying 3rd party keying program which manage to get quite a decent matte.

Bottom line, miniDV is a no no. You surely end up doing rotoscoping which is tedious.

[bartrobinson]

This is the fundamental recipe for an easy DV key: Dark subject in front of green. The overall luma contrast is carried through to the RGB channels, so the color difference keying calculation picks it up quite cleanly.

If your subject had blond hair, this same setup would have been much more challenging to key.

So here's kind of a what if to spark a little more discussion. It sounds like you're suggesting green for the dark fg subject, perhaps because of the contract of dark on the brighter green. Yes, no? So for your blond haired subject, would it perhaps be best to have a darker blue backing?

[bartrobinson]

so what exactly happened when u shot 4.1.1?

because my friend has recently did a test shot. and to be honest it didn't work well. well the actualy removing of the green. it was all pixelated and jagged edges.

how do u get around this.

The technique that I've heard used most often is that you blur the UV channels (the chromanance part of the YUV) then mix that back in with the Y (luminance) and your ready to pull a matte. Do just enough blur so the pixelated jagged edges soften. Use that only for pulling the matte. Once you've got your matte, go back and use the original footage for applying the matte.

[Ooze3d]

Although a week ago i'd have told you the same as everyone above, but just a couple of days ago i found MiniDV chroma "Holy Grail"

It's called DVMatte Pro:

http://www.dvgarage.com/prod/prod.php?prod=dvmatteae&sub=features

I couldn't believe my eyes when i saw what it could do. I shot myself against a green cloth that wasn't very well lit (it had also plenty of creases), i played around a bit with the plugin and that was it. Perfect.

Try it. It's great for those like me who don't have more than a miniDV cam and still want to make digital fx.

There're also two other answers to DV keying. They're called Chromanator and Serious Magic Ultra Key. The last one has something called "vector keying", specifically created for DV.

[bartrobinson]

Although a week ago i'd have told you the same as everyone above, but just a couple of days ago i found MiniDV chroma "Holy Grail"

It's called DVMatte Pro:

http://www.dvgarage.com/prod/prod.php?prod=dvmatteae&sub=features



As far as I know DV Matte Pro uses that exact technique. Not that it's expensive, but if you have a decent comping application, you can do it yourself easily.

[thatoneguy]

Drop by your neighborhood photography and lighting store. They'll often sell large green screen sheets which you can use to fashion into a green screen, they're also really good for backlighting.

If your friend is planning on using a greenscreen but not spending the time and $$ to setup a nice evenly lit screen and is using a DV camera, he should be aware he's going to be spending weeks doing tedius roto work. Like other here, I've spent endless hours rotoscoping thousands of frames because of poor screen lighting and craptastic compression.

If anybody has any doubt about the validity of using Green for DV though, load up some DV footage into a compositing package and extract each RGB challen individually. The blue is useless, the Red is pretty good and the Green is by far the least artifacted of the bunch.

[Stong]

Me and a few friends purchased a color called "Reptar Green" from LOWES. It keys really well.

[NickJushchyshyn]

If anybody has any doubt about the validity of using Green for DV though, load up some DV footage into a compositing package and extract each RGB challen individually. The blue is useless, the Red is pretty good and the Green is by far the least artifacted of the bunch.
Which is exactly why green will be a major pain to key for a blond subject, since the green channel value of the hair and screen are the same high value, and you'll be left with keying off the blue and red. :p

So here's kind of a what if to spark a little more discussion. It sounds like you're suggesting green for the dark fg subject, perhaps because of the (contrast) of dark on the brighter green. Yes, no? So for your blond haired subject, would it perhaps be best to have a darker blue backing?
Yes to both. :)

[JackW]

DV pro matte looks good :o must try it

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