Saturday, February 11, 2006

My Green Screen

With the royal drums beating, the infamous green screen made it's way down the crowded street and finally bestowed it's presence upon my doorstep. The green screen arrived in a very thin box with different colors on each side, just like the green screen itself (top two images). Once I pulled it outside of the box I was pleasantly surprised to find it also came with it's own circular shaped carrying case (bottom left image), with handles! Dare I unzip? No time like the present. I pulled the zipper slowly, eyeing the edges with adoration when somewhere around three fourths of the way down it popped out with such a force that it busted fully open and every cell in my body, screamed in shock! You have no idea how big 5 X 7 really is when it shows itself with out warning. Or, just how big 5 X 7 really is. Anyway, of course I had to test it out right away. I broke out the camcorder and made a short test film. When I introduced it into my editing program I wanted to just be able to pick a keyer and select the color from within my scene to be excluded, there for clearing the way into transparency to show through to my 3 d image below. Using Discreet keyer it did that pretty well, but I noticed that some of the neck (and shirt collar) was also transparent in places. I could mask the neck, but I had some problems controling the layers and even with that figured out I'd have to animate each of those along the scene duration. I tried to use Linear keyer, but it actually left a lot of the original background color in. There are three variables, two of them on my end that could be improved upon, the lighting in my house is soft and warm which I can tell leaves my footage dark and difficult to differentiate colors from. I probably should look into a nice background light, I would need to find one that is portable and requires minimal space since I barely have any left! The second, is that my Sony Handycam has always had a yellow spottiness that I can not eliminate even by going through the manual and tweaking the settings. Yellow is the wrong color to have lingering around when you are trying to key green. The Handycam is a couple years old but I am waiting on a Hello Kitty Camcorder that actually has better specs if you can believe it. I'll see how that works out. The third variable is that my screen is not as bright as I had anticipated, and it is also a velvety texture as opposed to some of the shiney slick surfaces that I have seen in some of the others. I'm sure that this must be to avoid over exposure or shadowing, but it doesn't help with my dull lighting. Perhaps this type of screen is more geared towards photographers? I ended up masking out the whole thing with tiny little points for rotoscoping, but my problem is that there are a whole a lot of them (with less there were obvious and bad looking cut off sections). There are so many that I have to be careful with manually animating each one since the tedious visual work has given me a migraine. I can only do it in small chunks, which will take for ever. There must be a better way. Anyway, the funny part of the story is when I was trying to put the screen away, well it wasn't funny at the time. There were no instructions, so you have to figure out how to put it back into that tiny little circle on your own and it is not intuitive. You can't do it by yourself, hours were spent trying to twist the thing into it's original state. Mind you, as you are trying to figure out how to compact it, it also has a tendency to take you by surprise and pop fully open again, knocking things off tables, pushing you into the wall and spooking the dog etc. I went on the internet and discovered many others in the same predicament. I tried many variations and this is what I eventually came up with: stand in the center of the green screen, with the shortest dimensions between your head and your feet and the longest at your sides. Fold the sides together like a hot dog bun, all the while staying right behind it and at the center. Now, keep it in place while taking your arm and bending down to the floor and grabbing the bottom, pull that bottom flap up and all the way over the top, now the three parts can slide into each other. Hopefully this experience will help some one!


Anonymous Anonymous said...

Keying DV is a nightmare all by itself. has a DVMatte product that is good for keying DV footage. Also there are varying levels of DV. The 3CCD DV camcorders will give you better results than one chip cameras. I have a 3CCD Canon GL2 and a Panasonic 3CCD GS-250. Both have good pictures (for DV), but still require the scene be lit properly. There is a very fine line between over or under lighting a green or blue screen. It is an art and this is why you see most green screen work done in highly controlled and evenly lit studio environments.

You also don't want the subject up close to the screen or else the spill will get all over your subject. Ideally you will have lighting for your subject, then as much distance as possible and the greenscreen lit evenly. If it is lit too bright then it will be totally blown out and difficult to key. Practice makes perfect. Ideally you'd have your camera hooked up with scopes and do test captures and look at the RGB parade (in final cut pro). There are other options like DVRack software.

Greenscreen work is tougher than people realize (good greenscreen work). The other workaround would be to garbage matte out the areas of the greenscreen that the subject never passes in front of... or you can animate the garbage matte. This really helps out big time when a greenscreen is not evenly lit. Because the keyer has too wide of a range of greens to deal with otherwise.

Then there are a whole range of other things one can do to sweeten the matte so that when you composite it over a background it looks good. Like creating a seperate edge matte that just targets the edges so you can then blend "in" the colors of the background over the very edges of the subject that was composited over that background. Called a "LightWrap". It makes it seem like the light of the new background has spilled onto the subject and better integrates the subject into the background.

There is so much to this process that it would take days to type it all out in detail. But your initial woes are not unusual... quite common in fact. It takes practice.

-Mike James :::

6:30 PM  
Anonymous Anonymous said...

Oh... I forgot to mention. The "quality" of the greenscreen makes all the difference. The expensive ones are expensive, because they work that much better. There are no good "cheap" greenscreens anywhere on the market.

-Mike James :::

6:31 PM  
Blogger Gina said...

I don't have the highest quality camera so this is probably a huge factor as well, but I think I will have to find a nice light. I did see some at Dick Blick (online) what do you think? We did have a set up at Mesmer (where I took most of my training) unfortunately we never got to use it. I did have the subject close to the screen so I will be sure to change this next time, and indeed there was a lot of bleeding over on the shoulders. Just to be clear here since you are using Final Cut and I am using Combustion I've put up a picture so you can see what I have done:
images/keyed.jpg (including a little close up in the left box) I am animating the Bezier mask that I drew around him, which is the eye dizzying part I was talking about!

9:04 PM  
Blogger Lady K said...

On a completely non-technical note, I laughed hysterically at your description of trying to fold it up. That would make an excellent workout video all on it's own.

I look forward to seeing your upcoming creations. Sometimes low budget solutions are more interesting than the expensive stuff.

10:29 PM  
Blogger Gina said...

Thanks Lady K! You are so right! I wouldn't have even had to add any special effects! Next time I try and fold it up I'll try to remember to record : ) I really like your take on the situation, that's a good way to look at a problem!

10:48 PM  
Anonymous Anonymous said...

Wow... you are basically Roto'ing the whole thing. The best app on the market for this kind of thing is , but it is $595 for the standalone.

Combustion is pretty decent to do roto type jobs on it's own, but usually you only would attempt to use it to garbage matte out the background and let the keyer deal with the edges. Basically you could do what you are doing a full inch or more with 1/10th the number of tracking points and then just key the edges. That is usually the workflow.

Mike James

8:25 AM  
Blogger Gina said...

Yes, that's exactly what I'm doing, which is visually quite over stimulating. I think I need to know more about modifying my matte or tricking my keyer with it....

6:34 PM  
Blogger Gina said...

Mike, what do you think of this one?

Although I don't see Combustion listed.

1:05 AM  
Anonymous Anonymous said...

I've seen it, but don't know anyone that has used it, so I can't comment. Combustion has decent tools for keying. I'll have to put together a short keying overview and throw it up on or (freebie of course).

It is one of those areas that just does not get discussed in detail that often. I'm in the middle of a project which is why the podcast has been neglected for so many weeks. As soon as I come up for air I'll do one and let you know about it.

Normally I do keying in Shake 4, but I'll try to do an example in Combustion so you can follow along with it.

Mike James :::

8:15 PM  
Blogger Gina said...

Wonderful I look forward to it, good luck with your current project!

1:55 AM  

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