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some help with poorly lit blue screen
Hi all,
I’ve receive some blue screen footage which was poorly lit (subject against a fairly dark blue screen). My main issue us with the “crawling” edges around the subjects’ hair as the footage runs. I tried boosting the luminance of the whole footage then keying but there are still dark areas on the edges which cant be resolved. I’m using keylight and i tried shrinking the matte and pe-blurring but it doesn’t seem to help. Does anyone have a remedy?
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6 Replies
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Well, actually to work with poorly blue/green screen is almost impossible…I mean, it’s very hard to achieve good results.
Anyway, you could try to apply several times the Color Key Effect to be sure to hide all the different shades of blue….maybe 6 or 7 times….then use the Simple Choker effect to have a better shape of the footage and then try applying the keylight. -
Oh..I’m working on a 720×576 DV PAL (1.07) footage, exported with the avid codec at 25 fps. My main issue is it seems like ants are crawling over the hair of the subject. I’ll try multiple color keys to get rid of other dark spots on the subject.
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Most of the really good keying apps look at the difference in color values between two adjacent pixels to determine the key. When you select your green background in Keylight, it compares the RGB values of that selected color to every pixel in your frame to determine what should be keyed out and what should stay. Any pixel that falls too far outside of your selected BG color stays while everything else is keyed out. Therefore, applying color correction (of any sort) to the footage before keying will NOT change your situation in the slightest. If you boost the blues, all pixels shift toward blue and their relationship stays the same. This applies to any type of color treatment.
Your best bet might be to do one or all of the following:
– Follow Aharon Rabinowitz’s brilliant Super Tight Junk Mattes tutorial. This will limit the amount of poorly lit blue/greenscreen background that Keylight must deal with, allowing you to use milder settings that degrade your footage less.
– DV is notorious for chroma artifacts, which is probably the main reason for your troubles. Precompose your raw, un-keyed greenscreen footage. Within this new comp, create an adjustment layer above the footage, and apply the “Median” effect (Effects > Channel > Median). There is only one value to play with, change it to 3 or so. Put the adjustment layer in “Color” blending mode. This whole process will remove/smooth some of the artifacting in your footage and make for a better key. You will need to apply Keylight directly to this composition (nest it within another comp), NOT the source footage within the comp.
– To retain fine hair detail, you typically need much more delicate settings than are needed to key sleeves or pants, and one keyer setting applied to both will force you to compromise the quality of both.
For each area that should have its own specific settings you will need to duplicate your footage comp and use masks so that each layer represents one element. This way you have one layer that is just the head, one layer for the clothing etc. Then apply different keyer settings to each layer to suit its needs. You will need to animate these masks (depending on what happens in your shots) but again, this is how the pros do it and if you want the best results, this is a good place to start.Brendan Coots
Splitvision Digital
http://www.splitvisiondigital.com -
I agree with all the comments here about the difficulties of keying with DV. PITA. I have run into these issues as well so i feel your pain.
Here’s my suggestion for what it’s worth. Once you get your best key (Keylight’s the best – I see you are using it too) dup the layer and remove the key effect. On this layer draw a garbage mask around the subject. Not so close to the edges that it becomes a rotoscope job but loosely inside and only in the trouble areas. Most of the time we’re talking about an interview subject and they don’t move around a bunch. Feather the mask a bit too. Now key frame the shape as needed to follow the subtle head bobs. I’ve had to do this lots usually due to bad lighting or because the subject was wearing something with a chroma key color on it.
I find placing the garbage mask beneath the chroma key can yield the best results but most of the time it won’t matter.
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[Brendan Coots] “You will need to animate these masks (depending on what happens in your shots) but again, this is how the pros do it and if you want the best results, this is a good place to start.”
Also check out Pete O’Connell’s Advanced Rotoscoping Techniques for Adobe After Effects DVD. He gets very specific about how best to create multiple masks for difficult keys, and the easiest way to animate them – using motion tracking to do the heavy lifting!
Very entertaining stuff, as well as a crash course in many, many facets of advanced After Effects-ing.
Not just a commercial plug. Seriously, Pete’s disk will help.
Tim Wilson
Associate Director, CreativeCow.net
Associate Publisher, Creative Cow Magazine! -
Thank You everyone for the support provided. I was able to produce a fairly better result. Appreciate the help guys.
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