Green Screen Questions

[Fred Helm]

We are attempting to create some interesting lower thirds using green screen and model cars. The last time I tried green screen fx it looked fine on the computer and horrible on tv. Is there some pointers for smoothe images without the broken up edges I usually get? My set up includes:

Green Screen
quad softbox
JVC GYHD110u or FX1/FX7 or Pany P2
Vegas 8

[Mike Kujbida]

Fred, have you tried the steps in Keith Kolbo's Using Chroma Key and Chroma Blur in Sony Vegas tutorial?
I've followed his steps and can get a pretty good key.

[Ken Steadman]

I second that, I always follow his process and it produces great keys.

[Fred Helm]

very good> we will follow this and post results. thanks

[Ken Campbell]

I find that the chroma keyer in Vegas works well with green screen footage that was lit well and generally easy to key. For more demanding work I pass over to After Effects and use the Keylight filter. In AE the closest thing to chroma blur is Channel Blur, and this trick does help with Keylight (and probably most keyers) as well.

[Buba Kastorski]

I love Vegas and edit on it all the time, but chroma key is something that can be done way better in AE Aftereffects.

[Ian Stark]

I have just edited some greenscreen footage that we shot against a green PowerPoint slide projected onto a screen (I wouldn't have chosen to do it his way, but something was suggested while we were on location 4000 miles from home without the green screen and we had to think laterally about how to achieve it). It worked perfectly, much to my surprise, and Vegas did the keying job admirably. Good lighting of the subject, around 8 feet between screen and subject and nice shallow depth of field all helped to produce a very usable key that didn't even need to have chroma blur applied.

Usually for anything other than perfect green screen footage I would turn to Ultra. Sadly, since Serious magic was taken over by Adobe, Ultra has been neglected and didn't even form part of the CS4 release. Hopefully, the technology will be incorporated into something else in the future (After Effects seems the obvious choice) but I wonder if there is a contractual conflict with the bundling of Keylight that prevents this? I would argue that any other reason for not including it is just shortsighted.

It's a great shame, because Ultra is so powerful and easy to use (oh, and because I spent a lot of money on it the week before the Adobe buyout was announced!).

[Fred Helm]

Nice thinking Ian. Our testing day was a success, we shot miniature robotic toys against green screen with 2 45 degree softboxes and a tota overhead. We used an FX7 at 240 per second and it did very well for a reduced lower third "pop in". We ran the results on a 52" HD monitor and it did loose some edge but we just had to increase blur in the key and it recovered. I am fascinated now with this stuff and wonder if the distance from camera you speak of is a big step froward. Ultimately we are going to bring an off road race car onto a sound stage with massive green screen in place and use that as our show in and out graphics. I wanted to know Vegas could handle this and I think it can.

Cheers

[Seth Bloombaum]

Originally Posted by Ian Stark

I have just edited some greenscreen footage that we shot against a green PowerPoint slide projected onto a screen...

Ian, was the projection system front projection or rear projection? If front, was it a standard matte white surface, beaded glass (as is frequently found on portable tripod screens), or silver lenticular (uncommon)?

The reason I'm asking is that your post reminded me that rear screens have some unique characteristics... and that maybe they would support chromakey very well. Maybe. So I'm interested to know more about your experience.

The help comes from their "directionality", for lack of a better word. Unlike a front-lit screen, which tends to reflect green spill from every area of the screen, an RP surface has some, um, polarization where eg. the light in the upper right corner will not spill down to the subject's left shoulder, but instead will tend to (mostly) keep traveling in a straight line.

Sorta' like the performance of the ReflecMedia system, but probably not nearly so much. Among other tricks, ReflecMedia uses a glass-beaded screen and a lens-mounted ring light to exploit directionality to reduce green spill.

[Ian Stark]

Hi Seth,

I can tell you that it was front projected (we originally were offered a conference room with rear projection but then a paying customer showed up and it was given to them!).

I'm afraid that I have absolutely no idea about the screen material but it was in a very well appointed presentation suite and was a permanent fixture rather than a collapsible screen. It wasn't completely matt as I recall and I'm pretty sure it wasn't beaded. Again, I can't be 100% I'm afraid.

There was an awful lot of green spill onto the talent when they stood close to the screen but I managed to position them about 8 feet in front which eliminated that. We used a real simple lighting setup (2 x 250 Lowell Pros and a 650W something else, set a way back in the room) and we were able to achieve a near complete blackout. We made sure that no light spilled onto the screen to cause hot spots. In fact the screen was perfectly even which I was delighted about.

On close inspection the projection 'dots' showed up but by spending a bit of time getting a shallow DoF we ended up with a pretty much even green that keyed well in Vegas with only a little tweaking.

As an aside (and I know people will raise their eyebrows at how futile this probably was!) I 'eyedroppered' the green colour from a website that had various chromakey background swatches. I know, I know. http://www.sunstudiosaustralia.com/p...lour_chart.pdf if it's of interest!

We shot into DV-Rack as we had no production monitor. This was great because I was able to test a few shots there and then which gave me greater confidence for the rest of that part of the shoot. For safety (in case I needed to key in Ultra) I also shot a few frames of the green screen only, three or four times during the shoot.

We had a few flyaway hair, shiny jewellery and specs reflections that we didn't pick up at the time but all were fine in post.

The sad part about all this is that the original plan for using these shots was scrapped and now the talent is against a pure white background, which is less forgiving and exposes any oversoftened edges. To mask these imperfections I have dropped in a shadow (in track motion) which has the added bonus of lifting the subject out of the frame.

Personally, I think the combination of careful lighting, distance between talent and screen and distance between talent and camera (which helped the DoF) all worked well to deliver a pretty easy key. I was lucky to have such a big room.

I'm sure there will be many people that will scream at the idea but as a makeshift solution it worked well. Not sure I would want to use it as my regular method of shooting against a green screen though . . .

There's a nice Focal Press book by John Jackman called Bluescreen Compositing (it uses the terms blue and green interchangeably in the book, as well as explaining which works best with digital/film). It's a bit light on content (around 230 pages, of which 50 are product-specific tutorials - sadly none for Vegas) but I was struggling (not with the keying part so much as getting a clean shot) so this, for me, was money well spent. I see it's reduced in price at Amazon.com Amazon.com: Bluescreen Compositing (DV Expert Series) (DV Expert Series): John Jackman: Books and at amazon.co.uk Bluescreen Compositing: A Practical Guide for Video and Moviemaking (DV Expert): John Jackman: Amazon.co.uk: Books - only £17.15.

Hope that's of some use.

[Mike Kujbida]

Originally Posted by Ian Stark

... now the talent is against a pure white background, which is less forgiving and exposes any oversoftened edges. To mask these imperfections I have dropped in a shadow (in track motion) which has the added bonus of lifting the subject out of the frame.

Ian, take a look at the Lighting Infinite White clip on Vimeo.
Videopia is actually D. Eric Franks, a moderator on the Digital Juice Vegas forum and he walks you though his technique for doing this.

[Ian Stark]

That was great, Mike, thanks for the link.

I should explain that what happened is that the client chose not to use the green screen footage in the way we had originally planned (composited with rapidly changing stills of office locations). Instead I had to composite the keyed talent against a pure white background, hence the exposure of some imperfections in the key - not that I had to shoot the talent against a white background. Still, a very good tutorial on infinite white.

[Mike Kujbida]

Originally Posted by Ian Stark

I should explain that what happened is that the client chose not to use the green screen footage in the way we had originally planned...

Gotta love clients who change their mind.
Rest assured that the afterlife will have a "special place" for them :-)