3 Replies Latest reply on Aug 11, 2011 1:59 PM by Paul R Stark

    Question on lighting to avoid bleeds with green screen-CS4

    Paul R Stark Level 1

      I'm having occasional trouble with some background bleeds. Here's an example where you can see the flare thru the shoulder area:

      BleedThru.JPG

      I applied the matte choker, took Choke 1 down to 0, and this is what I got:

      MatteChoker.JPG

      Not a bad result and simple enough, although other color adjustments could be made. But I think the problem derives from how I'm lighting the subject. The subject is five feet from the green screen and the camera is five feet from the subject. The background is evenly lit, although not very bright, using 8-100 watt fluorescents, and there are no significant hot spots.

       

      I think the bleeds are coming from some lighting changes I made:

      1. I moved the key and fill lights back a tad to attempt a softer look (500 and 100 watts fluorescent respectively-no scrims). They came out too dark, requiring Colorista adjustments, so I'll move them back in again.

      2. I changed the background lights from bowl-shaped work lamps to cone-shaped work lamps because the bowl-shaped lamps were too bright, causing significant hot spots (also no scrims). However, the cone-shaped lamps do not fully cover the bulbs like the bowl-shaped ones did, so the subject is getting some of that light since the bulbs extend a fraction beyond the edge of the cones.

       

      So, if it's the cone-shaped lamps, then perhaps I can try to go back to the bowl-shaped ones and just use less lamps and play with the positioning to avoid the hot spots. The only effect I'm using is Keylight 1.2 in CS4. But I'm really not sure I'm thinking this through correctly, so I would appreciate some advice and suggestions.

       

      With thanks,

       

      Paul

        • 1. Re: Question on lighting to avoid bleeds with green screen-CS4
          Rick Gerard Adobe Community Professional & MVP

          You're seeing bleed because the matte is not strong enough. You need to do more tweaking than a simple choke matte. You should always look at the combined matte and the status when using Keylight. Adjust the white and black clipping to clean up the matte. A Google search for keylight tutorials will give you a handful of great keying tutorials.

           

          Your lighting may have a little to do with the quality of the key, but I couldn't tell that unless I saw a raw frame. Keylight is capable of pulling satisfactory keys from some pretty terrible footage.

          1 person found this helpful
          • 2. Re: Question on lighting to avoid bleeds with green screen-CS4
            Navarro Parker Level 3

            Generally speaking, there's almost always spill on your subject. (Especially with very luminous green like Rosco DigiComp). You can minimize this by draping black curtains around areas that are not visible by the camera.  It's less of an issue with flat wall screens versus soundstages you walk on.

             

            But as usual, Rick is absolutely correct. Your core matte simply isn't strong enough. To get a really great basic key, there's only a couple things you need to mess with on Keylight: Screen Matte> clip back and clip white.

             

            Switch the view mode to Screen Matte. Adjust both so that your talent is completely white inside and the green background is completely black.  You can also use View>Status for an exaggerated view of this (Black is 100% transparent, white is 100% opaque, and gray areas are translucent. Green areas are also receiving despill correction.)

             

            And that's pretty much it to get a really good basic key.

             

            You might want to check out Primatte 5 for After Effects. It's a more intuitive keyer that has a surprisingly good one-click "auto compute" mode. You can also draw on the screen to tell it what parts to keep and what parts to key out.

            • 3. Re: Question on lighting to avoid bleeds with green screen-CS4
              Paul R Stark Level 1

              Thank you Rick and Navarro for some very helpful tips.

               

              Please accept my apology for not posting my Keylight settings. Here they are (were):

              KeylightSettings.JPG

              Looking at the key in Screen Matte view, it was clear the settings were woefully inadequate. I had to adjust both according to your simple guidelines, Navarro, and presto, no more bleed. My settings were based upon one tutorial I watched 1-1/2 years ago, so I guess I just got lucky with the background images I used until this one.

               

              Rick, I will indeed watch a bunch of tutorials now on Keylight.

               

              For what it's worth, here is the raw frame if you want to comment on the lighting. Now that I look at it again, maybe it isn't so evenly lit.

              RawFrame.JPG

              Thank you, gentlemen. You have made me a much better "keyer". It certainly cannot be a much better matte[r].

               

              Paul