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DPChallenge Forums >> Hardware and Software >> Chroma-Key blue backdrop....
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 01/24/2008 05:29:46 PM · #1
.....how do I use it? I have access to one for about a week and I'm not sure how to use it. I know the theory behind it. Could I get some suggestions on how to use it and how to PP with it. Thanks Monique
 01/24/2008 05:50:31 PM · #2
Originally posted by Monique64:
.....how do I use it? I have access to one for about a week and I'm not sure how to use it. I know the theory behind it. Could I get some suggestions on how to use it and how to PP with it. Thanks Monique


Chroma key is to make it easier to put your subject into a new environment with an editing platform such as Photoshop, or Gimp.

The trick is to try to make the blue screen ( also they come in green, and red ) to have an even amount of light.

In my industry, fluorescents work great for an even fill. But, any light will work as long as it is even.

Then follow this tut to help you get rid of the blue. Or another way is to go into Selct/Color Select to 'grab' the blue.

However you choose to do it, you get the blue out, and put your subject anywhere else you want.

One more thing, don't have your subject wear blue, that blue will also be 'grabbed' and sure, you can fix before grabbing, but it's easier if you just don't have any extra blue.

Did I just throw up, any questions, just ask.

Hope I helped.

Message edited by author 2008-01-24 17:51:01.
 01/24/2008 06:16:04 PM · #3
I had a quick look at the tutorial but at first glance it weems like a long winded way to select something. How is this better than masking?
 01/24/2008 06:31:31 PM · #4
Originally posted by Monique64:
I had a quick look at the tutorial but at first glance it weems like a long winded way to select something. How is this better than masking?


Think fractal. Hair, tree limbs, brush.

Masking involves a lot more "hand tools", where as an Alpha Channel gets more detail with a lot less use of hand tools.

Sure, you may have to make small fixes here and there, but nothing like a pure mask.

If I re-up my membership, I plan on doing a part 2 on this tut to go further into detail on even more detail and even less fixes.
 01/24/2008 06:32:33 PM · #5
Chroma-key is used much more in video work than still photography. It's pretty easy to select an object from any single picture in still photography. You can use any color for chroma-key, but the special blue and green seem to work a little better due to saturation or something. I've made a couple of chroma-key screens from regular fabric with decent results on video. A yellow one I made seemed to give yellow fringes on objects using cheap Roxio Videowave (edit)Power Edition (/edit) software, so blue would be much less objectionable. Even lighting across the screen is primary importance to being able to select out the color. Watch out for shadows. Video software has % tolerance for slightly uneven lighting.

Message edited by author 2008-01-24 21:10:45.
 01/24/2008 06:35:39 PM · #6
Originally posted by Monique64:
I had a quick look at the tutorial but at first glance it weems like a long winded way to select something. How is this better than masking?


It is and it isn't

To do keying right is actually a lot of work
As mentioned eariler the background needs to be lit very evenly and the subject needs to be placed well away from the background to prevent spill. Another concideration is "up spill" from the floor if you are doing a full length shot

Hair is a problem also ... you must make sure that the hair is separated well and that there is no hint of the background color or you will have a crappy knockout.

You need to make sure that your image is blended into the background so that it doesn't look fake and lighting matches

On the plus side ... it is faster and cleaner than pen masking

I have software dedicated to doing chromakey but I can do a clean knockout in 45 seconds.

Here are a couple of mine

01/24/2008 06:39:12 PM · #7
Originally posted by nomad469:

I have software dedicated to doing chromakey but I can do a clean knockout in 45 seconds.

Here are a couple of mine



Nice stuff David.

What software do you use?
 01/24/2008 06:48:05 PM · #8
I got Ultimatte Advantedge a couple of years back.

It still is the best for dealing with spill IMHO.
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