Green Screen Advice

[HoosierGuy]

I want to buy a green screen to do chroma key green screen shooting. I've never done this before but now that I have Sony Vegas Suite and a DVD tutorial and a DV cam, I want to get into this area.

I've never bought a green screen before. I saw a video online that said the best place to get them is eBay. Are green screens just simple fabric? Can you go to a crafts store and buy green fabric instead and use that? I'm looking for some advice, what to look for, what to pay for a simple one for a beginner, nothing fancy.

Thanks.

[redwudz]

The preferred green color is a bit obnoxious for clothing or drapes, but give a fabric store a try. Fabric stores may only carry something like that in 36" or 48" width, though. I would get a fabric sample and see if your software can key to it before purchase.

This video may give you some ideas: http://www.youtube.com/watch?v=PHHvO-YkaZM

Another alternative is rigid background of plywood or just a wall, painted with green screen paint. You may even be able to get a paint store to mix up a color for you. Even lighting is the big key with green screen, plus a smooth background with the fabric or paint.

How big are you planning to go? That may somewhat determine what type of screen would suit you.

[zoobie]

www.eefx.com has what you need...blows the others away

[Cornucopia]

You actually can use ANY color and ANY material, but the quality is determined by:

1. How DIFFERENT is this color to most naturally occuring colors (so that you can separate it cleanly without influencing other colors in the shot)
2. How UNIFORM is the color so that the subtracting technique recognizes it as ALL being the color to be removed

That's why the specific choice of that color (doesn't normally occur in standard shots), but depending upon the subject matter, you could use black, white, magenta, orange...
It's just got a premium $$ tag because businesses know they can charge for it.

Uniformity is achieved by a consistent color of the material, along with little to no seams/folds, along with VERY EVEN lighting.
Those requirements also usually add up to $$$.

Note: there was a recent thread here where a user posted a link to an AVISynth plugin that did an AMAZING job at green screen with even mediocre materials and lighting. Check it out...

Scott

[Cornucopia]

Just looked at redwudz's link: notice how badly there is black "fringing" around the guy that jitters throughout the shot, including even a little bit ON his shorts.

Works great for quick and dirty, but is NOT pro enough for a believable movie. Has to do with the lighting (particularly no opposing colored rim light and no specific bkgd lights).

Scott

(Hope that wasn't you, redwudz - No offense)

[redwudz]

No it wasn't me. I just found that on a quick internet search. The author there does mention that he just used the regular lighting in his room. Even with that, not bad for a simple green screen. I sort of like the idea of having some paint mixed up by a paint store if you have a blank wall. Might be fun to play with. You could always hang a tapestry over it if the wife objects too much.

[bendixG15]

....................... I sort of like the idea of having some paint mixed up by a paint store if you have a blank wall. Might be fun to play with. You could always hang a tapestry over it if the wife objects too much.

In my house, if my wife objected, I would just put her in the movie, and all would be fine..

[HoosierGuy]

I have Bill Myers 101 Tips and Tricks for Sony Vegas Studio. He's got a some sections on chroma key. I watched them last night and was impressed. He also said the background can be other solid colors other than green or blue. I didn't have a solid background to try though so I tried some bed room curtains that were very wavy and different shades of dark brown/black. That turned out horrible looking. From that I assumed I must use something very flat and something very uniform in color - complete colors with no shading or tints of other colors at all.

I'm new to all this so I don't want to spend a lot. My first goal is to use a clip from the old Lost in Space TV series when they are in their spaceship and chroma key my brother into that ship. He's going crazy wanting in that ship. lol.

I think I'll try buying some green fabric, two pieces at the fabric store. But will the seam running down it cause a big problem?

[edDV]

I'd recommend you buy a chromakey optimized green screen from a video products seller or buy the Rosco chroma Key green paint.
http://www.bhphotovideo.com/c/product/90460-REG/Rosco_150057110128_Chroma_Key_Paint_Green.html

The idea is to get a single tight green dot on the vector scope, not a range of color blob. The tighter the Cb,Cr dot, the better the key, even if luminance varies.

A fabric store Green may in fact be multi-colored when viewed on the vectorscope.

Green is used because Rec 601 video has more detail in green. Blue is the worst and red is bad for keying humans. Single sensor cameras have many more green samples than red or blue in the Bayer pattern.

DV cams suffer from 4:1:1 sampling. The color pixels can be blocky (too sharp) on key edges. This can often be improved by capturing analog S-Video for the foreground camera to soften the edge.

Pros get great keys using RGB cameras or film. In those cases, blue screen can be used.

[HoosierGuy]

I went to the store and bought a light greenish bed sheet for $12.00 To my surprise it worked very nicely! But my lightly made it look horrible. I had a spotlight shinning from one side and it caused a shadow to form on the other side of me back to the green screen. That caused the green screen to show up in the video. I can see I'm going to have to work on lightly the whole area evenly. Still I'm happy with the results. I showed up clearly in the video. Not perfect but for a newbie, nice.

[budwzr]

The green background is only half of the process. The other half is pulling a good matte, and this requires constructing a multipass lumakey/difference mask.

[HoosierGuy]

The other half is pulling a good matte, and this requires constructing a multipass lumakey/difference mask.

When you say 'matte' you mean the background that I put behind the chromakey subject? I was going to order a DVD with some background Virtual Studio sets to play with from www.zkad.com or something like swipes from http://www.digitaljuice.com/. Anybody familiar with these stores? Any other stores that offer products like they do that can be used on Sony Vegas Studio Platinum 10?

[Cornucopia]

budwzr, I don't think HoosierGuy was doing it film-style with a separate mask/matte. More likely it was TV-style with a live chromakey effect channel that just has 2 controls: Hue and Threshold. This is used on the upper layer of a 2-layer timeline.

HoosierGuy, the idea behind mattes/masks is to have a 3rd/4th image.

1st image is the foreground
2nd image is the matte (or "keyhole") - a high-contrast grayscale image (akin to "alpha channel")
3rd image is the inverse matte
4th image is the background

Add 1+2, then add 3+4, you get the foreground with all else around it cut out (usually black), and a background with a hole in it the shape of the foreground.

Then add these2 images and you get a CLEAN composite.
Note: works best when both FG & BG are lit so it looks like the light source is coming from the same direction(s).

Scott

[HoosierGuy]

budwzr, I don't think HoosierGuy was doing it film-style with a separate mask/matte. More likely it was TV-style with a live chromakey effect channel that just has 2 controls: Hue and Threshold. This is used on the upper layer of a 2-layer timeline.

HoosierGuy, the idea behind mattes/masks is to have a 3rd/4th image.

1st image is the foreground
2nd image is the matte (or "keyhole") - a high-contrast grayscale image (akin to "alpha channel")
3rd image is the inverse matte
4th image is the background

Add 1+2, then add 3+4, you get the foreground with all else around it cut out (usually black), and a background with a hole in it the shape of the foreground.

Then add these2 images and you get a CLEAN composite.
Note: works best when both FG & BG are lit so it looks like the light source is coming from the same direction(s).

Scott

Here's how I do it (how I learned from the Bill Myers DVD on Sony Vegas Studio)

1. I shoot video of myself in front of the green bed sheet.
2. transfer video to PC.
3. Load video in Vegas Studio 10
4. Load my background footage in Vegas Studio 10.
5. Add Chroma Blur and Chroma Key to the video of me.
6. Turn on Chroma blur to Light Blur.
7. Turn off Chroma Key and take the color picker and pick the green sheet in the preview window to set the color.
8. Turn on Chroma Key and turn on "Show Mask Only. "
9. I turn down the High Threshold until I turn solid white.
10. I turn up Low Threshold to turn the rest of the image black.
11. I add a little blur amount.
12. I turn off "Show Mask Only."


And I'm done! Except for fine tunning it. The Bill Myers DVD has four or five sections on using Chroma Key.

[edDV]

This has all been discussed before. Ideal chroma key lighting puts some distance between green background and the talent to prevent green reflections on the talent. You want flat lighting on the background. Use your vector scope to control the green blob.



Note the green blob on the vectorscope. The tighter the dot, (e.g. Rosco paint) the easier it will be to key.



See

https://forum.videohelp.com/threads/291243-TV-show-Survivor-intro-video-effect?highligh...roma+key+point
https://forum.videohelp.com/threads/256469-Canon-Elura-Big-problem?highlight=chroma+key+lighting

[HoosierGuy]

Now I'm looking for lights! lol. I went to Menard's and looked at their lights.

EdDV - is that three lights in your diagram or five?

[HoosierGuy]

If I were going to an appliance store and get lights, what would I want to look for with regards to doing green screen. Nothign fancy I remind you, I'm new to all this.
I have March issue of Videomaker magazine and they have small article on green screen and says it's best to use daylight attuned incandescent lighting. Daylight attuned? Is this something that can be found in a store?

[budwzr]

budwzr, I don't think HoosierGuy was doing it film-style with a separate mask/matte. More likely it was TV-style with a live chromakey effect channel that just has 2 controls: Hue and Threshold. This is used on the upper layer of a 2-layer timeline.

I was going to recommend the channel blend with secondary color correcter as a more accurate matte maker for poorly lit greenscreens.

[edDV]

Now I'm looking for lights! lol. I went to Menard's and looked at their lights.

EdDV - is that three lights in your diagram or five?

Ideally five.

[budwzr]

For greenscreen, I use a green blanket from Ikea. It's very bright. The fabric doesn't shine, it's like felt. It's very easy to light evenly. Also I use white posterboard from WalMart as bounce cards.

Don't get the subject too close or you'll get spill.