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MoviePlus Questions about using MoviePlus for video editing

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Old 1st November 2007, 09:37 PM   #1
chris Ryan
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Lightbulb Shadows on green screen overlays

I have just started using the green screen (Chroma) function in movie plus 4 and I am having difficulty with shadows, the chroma key removes most of the background excpet for small shadows created by the object being filmed. I have experimented with different lighting and levels, multiple light sources, any help would be gratefully appreciated.


Old 2nd November 2007, 01:31 AM   #2
Jim B.
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Lightbulb Re:*Shadows on green screen overlays

For chromakey to work well...

1. The background must be iluminated separately from the foreground. That is, the background gets its own lighting, separate from the lights used to illuminate the foreground.

2, The background must be evenly illuminated across the entire area as seen by the camera. Within 1 F-stop is good within 1/2 stop is better. Use an incident meter held at the front of the background to measure the entire area as seen by the camera.

3. Shadows from the foreground must not fall on the background. That is, the foreground items must be far enough from the background, or the foreground lights positioned in such a way, that shadows from the foreground items do not fall on the background as seen by the camera. A greater foreground to background distance also helps reduce "spill"; where some of the green (or blue or whatever color) light reflected from the background illuminates and "wraps around" the edges of the foreground item(s). This "spill" can result in a weird type of halo around the foreground items.

Here http://en.wikipedia.org/wiki/Chromakey#Even_lighting is some information about chromakey that might be helpful.

Jim B. :> )

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Old 8th November 2007, 05:49 AM   #3
Phil Steller
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Lightbulb Re: Shadows on green screen overlays

I'm no video expert, but I've learned a few things by reading and/or experimenting:: Don't forget that with MoviePlus you can apply any number of filters "on top" of each other on each and every video track (any number of those too). In other words, say you key out the primary portion of green with a chroma key effect, but you have some pesky shadows left over. Well, you can apply another chroma key filter, selecting the color(s) found in the shadow areas. This is not always an ideal solution because if the shadows are dark enough, they will too closely resemble colors in your subject, and you will lose pixels in your subject (not good)... but it's worth a shot and may narrow your focus to a smaller stubborn area. If you are having trouble selecting the color to key out, don't forget to hide (by way of the "eye"con on each effect) all the chroma key effects while selecting your color. Hiding the effects allows you to see and sample from the video file's original colors before the filters are applied.

Another idea: you can also use masks in combination with your chroma key. If there is a consistent area, like a shadow, that you can't get rid of with any combination of chroma key filters, create a mask layer using any number of mask sources (you can use a bitmap mask you import, a quickshape object/text, another movie layer, etc) to completely eliminate that area. If you get tricky like me (at least in my imagination), you might even use an animated mask layer in the case that the pesky areas move, or your subject moves around a lot.

Of course, ideally, you'll keep shooting the video until you get good source to work with - proper lighting as described by Jim above. The better you shoot your video, the more likely you will succeed with chroma keying and/or masking.

Don't forget that you can keyframe your chroma key effects. If you move the camera around at all, it's guaranteed that the lighting and exposure will change, resulting in a change of color on your green screen. Luckily MoviePlus allows you to change all your filters over time, so one second you could be masking out all the blue, and the next, switch to green or red (or more likely ever so slight variations of the same color).

Part of your "enemy" is also going to be the quality of your equipment. Anything less than a standard MiniDV, such as a Hi8 or VHS-C, etc. camcorder will produce horribly compressed and blurry source video, especially after translating it into bits and bytes. It will be nearly impossible to get smooth edges where you clearly erase your green area. Even with a MiniDV camcorder, the compression used to store the video is against you, breaking down your imagery into rectangular groupings of pixels. If you are serious about making quality effects and have the money to invest, a HD camcorder (Hi-Definition, not hard drive - there's a huge difference!) will give you far more clarity in your source video, giving you greater chance of success with effects. I shouldn't be talking though... I don't even have the budget for a Hi-Def camera. I have a friend with one though, and the results are amazing.

Phil Steller

Old 8th November 2007, 05:57 AM   #4
Phil Steller
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Lightbulb Re: Shadows on green screen overlays

Your problem might also be found in your "green screen". How bright is your green? If it is not very vibrant, or some of its saturation is lost in the recording/translation process, it will not be easy to key out. Or, if you are using fabric, you will naturally have wrinkles and shadows all over your screen. There's nothing magical about green either. The idea is to choose a color that is as far away from any of your subject's colors as possible. Red and warm colors are generally a bad choice because skin tones are naturally warm and will be severely desaturated when trying to key out a warm color background. This is why green and blue are typically the best choices.

Phil Steller



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