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Canon XL H Series HDV Camcorders
Canon XL H1S (with SDI), Canon XL H1A (without SDI). Also XL H1.

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Old April 15th, 2009, 08:36 PM   #1
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Canon XL-H1 Green Screen Help


I'm Henry Hoyos, I'm a film student at Full Sail University and I'm going to be making an independent short film. It's a Big Epic Western but in order to save money we're shooting it "Sin City/300 Style" on the green screen stage. The environments will be inserted in post-production using 3DS Max, Vray and Boujou for 3D Tracking and matchmoving.

The thing I need you're help with is the keying itself. I'm using Keylight, filming with The Canon XL-H1.

The funny thing is I get a nearly perfect key, aside from some edge pixelation, when the shot is keyed into a grey 50% brightness background. However when it's keyed into a brighter or darker background the edges become unusable. When it's a brighter background the edges become too transparent and it looses alot of hair detail. It looks like the edge is being washed out into the background and reduces it's opacity, where as with the grey background it looks perfect except for the pixelation.

In the case of darker backgrounds the edges do something I can't explain very well. It's like theres a black hole in between the edge and the inner matte of the subject. It's weird.

The problem is I plan on having night scenes, dark chiaroscuro interiors, bright washed daylight scenes in the desert, and even silhouetted shots. Probably every environment is going to have differences in contrast which makes me a bit uneasy seeing the current results. If anyone could please help me fix these edge things as well as the pixelated edges and the slight halo in the greys, It wouldn't only be great it would make this film possible.

I've posted some reference pictures here,

Thanks very much.

Henry Hoyos
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Old April 16th, 2009, 05:26 AM   #2
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I have a few different guesses, and I'm not sure that any well help but you should give them a shot if you can.

1) make sure you don't have a "feathering" option dialed in on your keyer, this is a post thing but it looks like that's the issue to me, you don't notice it on the 50% gray because it's neutral, but the issues you're seeing are still there (look at the shoes in the gray/white example.

2) a back light/edge light will help you a lot and I think if you drop some magenta/ -green in you'll lose a little bit of the wash that your keyer is trying to key out.

3) this last one is purely conjecture, I've heard that when lighting a green screen for chroma keying the green needs to be hotter in the background then the foreground object, however when lighting for a luminance key you can have the item lit at your current level's.

If none of these work I'll take your source footage and drop it into a keyer after my gig today and see if I can be of more help.
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Old April 16th, 2009, 05:39 AM   #3
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If you are a film student at Full Sail I would pose this question to my professor instead of the internet. But in my opinion you are too close to the green screen, and lit with a typical lifeless criss-cross front light pattern, without proper backlighting. How do your flesh tones read on the waveform monitor before going to tape? They look a little flat.
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Old April 16th, 2009, 10:36 AM   #4
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Thanks for the reply guys. I did post the question to my professors and they say it's the HDV compression. I think even though it's compressed it can be done. I'm posting on the internet because I've tried several different things and asked several different professors and they suggested I post here.

If you put the source picture into your keyer I'd be very interested in seeing your results and your suggestions.

Thanks very much.

Henry Hoyos
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Old April 21st, 2009, 07:30 PM   #5
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Each various scene you plan will need a distinct lighting setup to make the talent merge with the background. Night scene will need a light source and darker shadows. Day scene will need lot's of light on the talent dependent on full sun or cloud cover of the scene.
Plan your scenes carefully first

If possible use a little camera switcher with chromakey capabilities on set during the shoot to preview the key matching for the director. It doesn't have to be a high quality key, but it will give you great insite as to the lighting of the screen and talent for the distinct scenes. All you need is a still from the proposed background.

HDV is quite capable of the task. Recording the camera feed to a computer with the Intensity Pro card or similar card capable of less compression, will help, if available.

You can also shoot the talent as close-up as you can to fill the frame and later in post reduce the size of the talent to fit the scene. This will simulate a higher resolution recording medium....and produce better edges on the key.
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