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CantonVideoMan
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Casting a shadow on the floor with green screen footage

May 12, 2009 6:10 AM

Hi,

 

I have green screen footage of an actor walking with a green screen background. After keying out the green screen I want to cast a shadow of the subject on the floor. Seems simple enough :-) I have tried everything I can think of such as making my green screen footage a 3D layer and then adding lights, which seem to cast shadows/lighting on the actor, but no casted shadows. Drop shadow places a shadow directly behind the actor but no way to "move" it to the floor.

 

If anyone could provide any guidance I would greatly appreciate it.

 

Thanks

 

Bob Barnes

 
Replies
  • Currently Being Moderated
    May 12, 2009 6:36 AM   in reply to CantonVideoMan

    The light must be set to cast shadows, the layer must be set to cast shadows, and the floor layer must be set to accept shadows.

     

    From the "Light settings" section of After Effects Help:

     

    "The Casts Shadows material option must be On for a layer to cast shadows; this setting is not the default."

     
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  • Currently Being Moderated
    May 12, 2009 8:00 AM   in reply to CantonVideoMan

    rotate it 90 degrees on the y axis so it's flat, move it down in the scene.

    Forget the black floor till you understand how this works, then go back and try to find a color for the solid that works for your illusion.

    However, this will NOT get you realistic shadows. the feet hitting floor are not 3D objects, they're flat projections of 3D objects.

    you might be better off reshooting to include a green floor or using the RADIAL SHADOW drop shadow effect.

     

    bogiesan

     
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  • Currently Being Moderated
    May 12, 2009 10:35 AM   in reply to CantonVideoMan

    CantonVideoMan wrote:

     

    If so, How can I create the layer so it lays flat like the floor? Also, if I create the floor layer as black, will it be seen as transparent if I render my composition with transparency?

     

    You can play with your 3D layer's material options for the shadows to get the desired result. Furthermore, you could unmultiply your shadows - cast them on a white floor, apply Shift Channels based on Luminance, apply the Invert effect. As David said, though, there are limits as to how realistic it will look. As another alternative, consider Red Giant Warp's Shadow effect. At least it allows you some more intuitive control in 2D...

     

    Mylenium

     
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    May 15, 2009 12:54 AM   in reply to CantonVideoMan

    For your purposes it may be easier to fake the shadow:

     

    Duplicate your keyed layer, ensure it is set to 3D.

    Apply the Generate/Fill effect and set the colour of the effect to black.

    Use the Pan Behind tool to move the anchor point of your duplicate layer to the bottom of the subject's feet.

    Rotate the X value of the layer until the "shadow" looks right - should be about 90 degrees.

    Apply a Blur effect to soften the shadow to taste.  (If you're feeling adventurous, you could apply a compound blur and ramp the amount of blur across the shadow with a gradient layer.)

     

    Once you're happy, you may want to parent the shadow layer to the main layer, so that any position changes to the main layer will drag the shadow layer with it.

     
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  • Currently Being Moderated
    May 15, 2009 8:51 AM   in reply to CantonVideoMan

    CantonVideoMan wrote:

     

    Hi bogiesan,

    Thanks for the help.

    My footage is actually shot with a green floor. The problem I'm having is the final product needs to be an actor walking out with a transparent background, but casting a shadow on the floor. So that the shaow will show up no matter what background the customer decides to use the video with.

    If I try applying a drop shadow or a Radial Shadow the shadow shows up BEHIND the actor not below. I must be making this 10 times harder than it needs to be.

    Any Advise would be appreciated.

    Thanks again,

     

    Bob

     

     

    I'm not grasping the issue, then, sorry. Just use the shadow you have captured. Setting a chromakeyer to pass the shadow is not difficult.

     

    The problem with faking a shadow is, yes, it's ten times more difficult than getting it in the original shoot because of all the problems we've discussed. with a shadow layer there is not interaction with the feet and the 3D projection is not realistic enough to be accepted by an audience; it will always look fake. You CAN create a projected 3D shadow by carefully placing a light in a 3D scene and placing a copy of your matted character perpendicular to the light source and setting the layer to project the shadow only. But it still is not real.

     

    bogiesan

     
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  • Currently Being Moderated
    May 15, 2009 10:27 AM   in reply to Mylenium

    Pulling a realistic shadow out of a hat is a tough trick. I had a job a few years ago where we needed to do exactly what you are trying. After some experimentation we found that the easiest solution was to make a really good shadow on the greenscreen when we shot, then run a separate pass just to knock out the shadow. The shadow was then blurred and used as a track matte for a layer with a ramp. The whole thing was placed between the Actor and the virtual set (just solids).

     

    This was the only we could get a perfectly convincing shadow. I hope the technique was clear. Key out the actor on one layer, key out just the shadow and garbage matte out the actor layer on another layer, blur the shadow layer and use it as a track matte for a ramp set to overlay for the shadow.

     

    If you haven't got a good shadow in the shot this trick won't work. If you do, it's by far the easiest solution. If you have a still or a few frames of your shot I'll be glad to throw together an example project.

     
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