How Green was my Green Screen

[kerwin kanago]

For our Easter "Breaking News" video I need to shoot a newcaster at a desk and key pictures/video in behind him. I've read the other green screen threads here and I've actually done this before (would have worked ok, if we had noticed one green thing that got in the shot).

I'm going to paint a board or two, but I started wondering "Which Green would work the best". So I did a little testing. First off I went to the hardware store, video camera slung over my shoulder. Went to the paint section and shot the "wall of paint colors". I got a full screen shot, a close up of the area I thought would be best and then closer so I could read the letters/numbers.

Then I headed back home, pulled the video from the camera and into my editing software. Stick a full screen red image behind the video. Turn on green screen and start playing. By adjusting the sliders I could wipe out anywhere from the whole wall, down to just a couple shades of green. I set it so the minimum number of colors were selected. In the real video I'll be dealing with shadows, slightly different colored light, reflected colors, etc. But those colors *should* be the best choice for the background.

Below are shots of the paint store with and without keying (in case anyone wants to try it in their software). The color cards are lettered top to bottom and numbered left to right, with another number after the dash for which one on the card. Note there were two, choices. I went with the lower left one since other advice on the forum says go with darker colors. So the winner for me was Ace color A33-7, "Par Three".

Not too surprising. The top row of cards are the most saturated with more gray in the colors as you work down, so mine was in the top row. Left to right wise things just looked yellower left of this and bluish to the right. Higher on the card has more white, therefore more colors of white, so I ended up with a "bottom of the card" color.

Seems like even if you want to do green screen with cloth, carpet, paper, etc. this trick would get you a sample of a really good color.

I'll post results when I finish.

[brenthomer]

After you shoot your green screen you will realize the truth....the exact color of the screen ends up less important then the almost perfectly evenness of the lighting you will need to make a decent key.

Especially if you are shooting with DV.....man that is terrible stuff to key with...

[rbcyouthdude]

I go to wal mart and buy lime green posterboard for 88 cents a sheet and staple them to the wall. I have a whole wall in our youth room covered with this.
Brenthomer is right, it's about how you light the wall and subject.try this link it helps a lot.
http://www.kenstone.net/fcp_homepage...ey_part_1.html

the spill light (backlight) is important
michael

[st1x10]

Yes lighting is the most important part and in all reality you could use any color and then key it in the software. That color green should work just fine. I think the paint I got was parakeet green. I painted a small foam core to start with and next I will probably do a wall in our studio at the church. Make sure to light the subject and the green screen separately when possible. Also get an even light on the background.

http://www.digitaljuice.com/djtv/seg...searchid=46264

[tedanderson]

Although an evenly lit background is the most important thing, good software can help compensate for some of the bad things that DV or a bad backgrouind leaves behind.

I have used the trial version of Serious Magic and have gotten much better results than I have with Adobe Premiere. The keyer in Serious Magic allows you use a color picker to sample over 100 different points on the background so that it knows how to ignore wrinkles, shadows, and any other imperfection of the background. And then it has other parameters in it to eliminate things like the stair-step effect and the green highlights.

[brenthomer]

I am at the point when I know my keys are going to work perfectly...when you use a field monitor and you light the key perfect it actually starts to glow..when that happens you are golden...unless you have your subject too close to the screen...then all that glowiness ends up tainting your subject.

My point is, once you have seen that glow, on a monitor you will know when your key is going to be perfect. It's all in the lighting.

[kerwin kanago]

No argument that the lighting is critical. Lots of experiments and lots of peoples experience shows this and there are some GREAT articles on this site about how to light things, etc.


The sad truth is many of us *are* trying to do this with a $600ish 3ccd dv and a three light set... or less. While I *know* it won't be usable with bad shadows, its got to be better to use the "right" green than the wrong one, and if its a matter of an extra trip to the paint store it seems worth the cost.

How much difference does it make? I pulled that image into my video software and adjusted it to take out my "best" color and (at least) one color above, left, and right. (to simulate differences in light color, intensity, reflected light from a non-green object, wrinkles, etc)

Count how many different colors/shades this covered. Now pick a different shade of green, take the one left and just above. Again adjust the keying to get the one above, left, right. Again count how many colors are covered.

With my setup it ends up selecting 3-4 times as many colors.

slightly wrong color => a lot more colors selected => More chance of selecting stuff you don't want to select, etc.

The most important factor? Nope.
Worth an extra trip to to the HW store and 20 minutes of time? ...seems likely.

[kerwin kanago]

After weeks of filming and editing....

I would definately use this trick again... but next time I'd take a few paint sample strips to my shooting site, tape them to the wall, turn on all the lights and video THAT, rather than in the paint store. The paint store has lovely color corrected lights, but they are no where as bright as video lights.

Brents comment about "glow" makes sense now. I'd seen that discription before but couldn't quite "get" it. Ideally it should look like this: (ignoring the 3 boxes of different colors).


Thats slightly faked, though I got close. Like that, the video software can use the tightest/least tolerant setting, therefore, getting the least "wrong" stuff.

Right Color, vs Very Light, vs Very Even...
Well they all "matter". They all matter a LOT.

The right paint is a "dark" green with a lot of green (or blue and yellow) pigment, but little or no BLACK and little or no WHITE. You don't want to match paint to what this image looks like.You'd get paint with too much white, therefore too much "non green" light reflected.

Even is important, but we had some Halogen Garage Work Lights on the background that cast faint shadow lines (from the grill on the front) that, in the end, didn't matter, because the "shadows" were still brighter than NOT having the lights, or moving the lights back until the lines disappeared.

I put the image above into my video software and started adjusting the tolerance on the keying to see which of the little boxes were better/worse.

Clearly the nice bright (glowing) background green is the best. Its "0,255,0" so it works with the tolerance set to "zero".
Second best is the box with the "blah blah blah". Its the right color, and in spite of the pattern the darkest part of it is still pretty bright.
Third best is the upper right corner. Its 0,192,0, so its really green but only 75% of full green.
The worst is the upper left. Its "lighter" but gets there by adding red and blue so more "white" and its slightly off color. In spite of looking brighter, it takes the widest tolerance to key it out.

Having way too much fun with this!
kk

[Steve G.]

What kind of camera did you use? I remember shooting and editing a newscast we did for our church that we used an xl2 for... it was really hard to get a good key but it ended up working... with 4 lowels and about 6 par cans

I read up on it before shooting and made sure I had the anchor 15-20 ft away from the screen and had the camera 40ft away from the screen.

[kerwin kanago]

A little panasonic gl something or other. Its mini-dv. It has 3ccd's and the ability to go manual on white balance, focus, etc, but beyond that its just a "nice" consumer camera. I definately seperated the anchor and the screen enough to get lights in between and get his shadow to fall off to the side, but didn't have nearly as big of a room as you had.

[Steve G.]

I cleared half the sanctuary of chairs just so we could get the shoot done. And another time I had the anchor on the stage and the camera 100ft away at the back of the sanctuary.

[petereit]

I just went to Lowes and bought two pieces of plain white bathroom panelling. Then I went to the paint aisle, pulled out the Nickelodeon brochure and picked the brightest, loudest green I could find.

Back at church, we masking-taped the two boards together and painted them green. Then we spent an hour setting up lighting to get the board lit as absolutely even as we could.

Next, we set up our hair lights with red gels (amber gels if your shooting against a blue screen). This REALLY helps to separate the talent from the green screen in post!! Even though the final product was SD, we shot in HD so we could retain as much detail as possible. When we sampled down to SD, the key was awesome!

I just recently watched an online video that showed how to use a differential matte to create an absolutely flawless key (down to individual hairs). I am now kicking myself for not bookmarking it, and I don't think it was a Digital Juice DJTV clip (though they do have a bunch of excellent key tutorials!)