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Chromakey background advice
Old 05-19-2005, 01:56 PM   #1 (permalink)
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Any recommendations based on personal experience?

Thanks,
Clayton

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Re: Chromakey background advice
Old 05-19-2005, 02:35 PM   #2 (permalink)
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Be careful how you light the BG, don't overlight it; try t keep the reflection to a minimum. It will fringe your subject and there's no good way to cleanup the color fringe, it also makes selecting the subject by excluding the key color more difficult. The problem is that the BG paper will reflect colored light, that light fringes (diffuses and refracts) around edges and casts a colored border ON the edges of your subject. It will be most evident at the feet if the subject is standing on the BG paper.

You need your subject at a distance from the BG and the light reflection from the BG needs to be very low and angled away (to either side) from the subject. I think it's most useful for lots of knockouts of images where precision is not a priority.

I gave up on chroma-key and just use white when I need to make the BG transparent. With the exception of hair and hair-like things, I usually select using the path (pen) tool. It was a hassle to learn because it's not a very intuitive tool... but it was a screwed up chroma-key shoot that forced me to learn it. Using the path tool makes selection fast, controllable, versatile and precise. I still use select color or the magic wand to select out a white BG but only when the subject is ideally suited for it.

You will have people tell you to do a 'Select color...' with chroma-key and I agree, it can be done... it's just too tricky to do at a high quality level unless you can go back and reshoot until you have the light perfect. I'll see if I can find some examples later, gotta go right now.

Just my opinion.
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Re: Chromakey background advice
Old 05-19-2005, 02:48 PM   #3 (permalink)
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Chromakey can be a real b**ch, even with a PS plugin like Primatte. It works best for portraiture and types of shots where you can keep the subject far away from the background. If you shoot on blue or green paper, and have the model standing on it, for example, you'll get lots of color spill on the front of the subject. The plugin tries to remove this (by adding in the complementary color), and that sometimes works, but usually the foreground colors look weird that way.

I have had good results when I light the background 1-2 stops below key, and also rimlight the model with a strobe on each side, 45 degrees to the back, gelled with bastard amber, and down 2 stops below key - this tends to kill off some of the spill around the edges, especially the hair.

I have never tried to do chromakey "manually" with photoshop - always used the primatte plugin. When everything is right, it's great, but usually it's easier to shoot on white and knock it out with Maskpro or by hand.

 
 
Re: Chromakey background advice
Old 05-19-2005, 04:37 PM   #4 (permalink)
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Ditto ! Use white over chromakey for all the reasons stated.
Also white can be used as acceptable bg color.
No one wants a funky blue green background
even when it does not spill on fg.
EL
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Re: Chromakey background advice
Old 05-20-2005, 07:42 AM   #5 (permalink)
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In addition to the suggestions already given, the best way to cut down on color fringing is to use a rough surface that diffuses the light across it. Paper, being smooth, tends to reflect light back to the subject. A rough surface, such as found on foam-backed fabric or flannel will work better than paper. When selecting a color, remember that an outdoor scene will normally have blue light from the sky reflecting off the subject, so a bluish tint in the semitransparent areas of a model's hair with a beach scene dropped in, for example, will look more natural that a greenish tint in the model's hair with the same background added.

Also, search the GG forum for a previous thread containing suggestions and examples from Joe Edelman. --Randy
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Re: Chromakey background advice
Old 05-20-2005, 08:23 AM   #6 (permalink)
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I agree with everyone else, Chromakey background is an expensive waste of time and money. You'll get MUCh better results if you do a little pre-planning and match your background color to the ultimate background you desire. For example, I use an orange or yellow seamless paper when I know I'm planning to add a sunset background to the final image. That way, any orange or yellow cast on the model looks natural in the final image.

Good luck.

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Re: Chromakey background advice
Old 05-21-2005, 12:00 AM   #7 (permalink)
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Although I agree chromakey can be a pain in the butt. Sometimes its the lessor pain. It's nice if you can just use a white background but what do you do if there is a lot of white in what your shooting and you want to keep that. Chromakey.... The biggest thing is to light the background evenly, and keep the subject as far from the background as possible. Then in photoshop using color range, select the background and delete it and then immediatly use modify; contract; 2 pixels, and then feather if nessessary 2 pixles. This a basics of what it takes. Sometimes it requires more. I do a lot of large team banners 10 feet long x 48" high, and this is how I start. Some samples for you to see are at this url. http://stenberg.smugmug.com/gallery/542915 (you will have to copy and past) if it forces you to use a password; use gg ) If you want to send your email I can send more detailed instructions. I will agree though, if you dont't have to use chromakey..Don't!

Best of Luck,

Bill
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