Retaining shadows with chromakey...?

NiallT
NiallT Website User Posts: 5 Just Starting Out
edited February 20 in Practical Filmmaking

Hi,

I make language tutorial videos and I'm looking to do some fancy "hands" videos, where I set my camera up looking down on green baize card-playing mat, and then I explain some printed material, with the print changing dynamically under my hands, through the magic of compositing.

Now usually green-screen work means eliminating all shadows to maintain the illusion that the screen isn't there, so the chromakey effect is built under the assumption that that's what we want. However, I'm working with a virtual piece of paper here -- the green screen is a flat surface in exactly the same place the virtual flat surface of the paper is going to be. Because of this, the lack of shadows now breaks the illusion, rather than making it.

I've been looking around for a way to retain luma information from the keyed-out area, and apply that as a shadow in the compositing process.

Is there a straightforward way to do this?

Thanks,

Níall.

Comments

  • DataDesign
    DataDesign Website User Posts: 520 Enthusiast

    Straightforward, maybe. No not really.

    Duplicate your layer with no shadow. Lower the duplicate opacity so it looks like a shadow. Rotate the duplicate into the position where the shadow should be. Make both layers into 3D so you can move the shadow "behind" the main layer. If this is not correct then @Triem23 or one of the other smart people can jump in.

    Hope this helps. Also there is probably several YouTube videos on this.

  • DafterThings
    DafterThings Website User Posts: 937 Enthusiast

    I've managed to keep shadows when green screening. I wanted to do something similar to yourself so made the shadows really strong.

    I had the adjust the key strength a little but they stayed there. Not sure if I used some curves or HSL (it was a long time ago) to make them stand out again but it did work albeit subtly.

  • Triem23
    Triem23 Moderator Moderator, Website User, Ambassador, Imerge Beta Tester, HitFilm Beta Tester Posts: 19,285 Ambassador

    If you can isolate some shadow then Curves (on the alpha channel) or Crush Blacks/Whites Alpha can help solidify them.

  • NiallT
    NiallT Website User Posts: 5 Just Starting Out

    Thanks. There probably are plenty of videos, but unfortunately I can't find them because searching for shadows and chromakey brings back hundreds of videos on eliminating shadows!

  • NiallT
    NiallT Website User Posts: 5 Just Starting Out

    I think I've come up with a workable solution -- three layers:

    Top: main video, greenscreen keyed out completely. (ie. only hands left)

    Middle: duplicate of greenscreen video (no chromakey) converted to greyscale

    Bottom: backdrop images/videos

    Compositing the middle and bottom layer in multiple mode reconstructs the real lighting on the virtual backdrop, although some manipulation of curves will be needed to get the lighting levels just right.

    The full colour hands in the top layer will hide the weird hand-shaped shading from the composited shot below, and I'll get the shot I need.

  • DafterThings
    DafterThings Website User Posts: 937 Enthusiast
  • DataDesign
    DataDesign Website User Posts: 520 Enthusiast
    edited February 21

    @NiallT @DafterThings

    That video is what I was trying to say. :-)

    A picture is worth a thousand word. Right?

  • NiallT
    NiallT Website User Posts: 5 Just Starting Out

    Thanks, but that's a lot of effort for a result that won't look like what I want.

    The point is that I have a matte surface that will be picking up the natural shadows cast by the lights and the environment. Capturing the live shadow data then applying it to the bottom layer means that I will get nearly natural light on my virtual paper.

    Given that my hands will be floating a couple of centimetres above the baize and moving up and down, and that an times I'll be touching the surface with my fingertips, any perspective effect is going to need manually keyframed to adjust for the change in height and angle of my hands.

  • NiallT
    NiallT Website User Posts: 5 Just Starting Out

    I'll show you what I mean when my baize arrives. (I tried it out with my cheap greenscreen backdrop, but it's creased and textured and doesn't look right close up.)

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