How to track a mask when the mask is not always in the shot

[gordo299]

Hi,

I have 3d tracked my scene and want to put a hole in a wall using a mask.  But the mask is not always in the shot.  I'm fine with creating a null on  a track point and attaching text or an image to this but I'm unable to track the mask.

How do I achieve this?

Any help would be greatly appreciated.

Thanks,

Gordon

[Roei Tzoref]

I'm unable to track the mask.

if you 3d tracked the scene you get a virtual camera and any 3d layer you place in the scene will react to the camera. if you have placed a null near a feature, just copy the nulls position to that element and it will stick in there. maybe you should be more specific and show some screenshots/video capture of exactly what it is you are trying to accomplish so we my offer the proper workflow.

guessing here on what you want to accomplish but you could create a solid with a mask, place it where you want in the 3d scene, and set it as a track matte the masked solid by choosing "invert Alpha matte" on the wall. now there will be a whole on the wall that will travel as the camera moves.

[gordo299]

Here is a link to a video I recorded.  I would like to put a hole in the wall next to the coloured fish.  I have tried putting a mask on a solid and inverted the alpha matte on the wall.  This does create a hole but the mask follows the camera. 

How do I get the hole to stick to the wall?

[Roei Tzoref]

what exactly are you set out to do with this shot? you either want to add something or remove something (which is the same thing, only you are adding a clean patch). specify exactly

[gordo299]

I want to mask a section of wall and behind the mask place an out door scene like a sky to give the impression there is a hole in the wall.  I can achieve the hole in the wall look but the hole does not stick to the wall,  it stays in frame and moves with the camera.

I want to get the mask to stay in one position.

thanks,

gordon

[Roei Tzoref · Accepted solution]

he hole does not stick to the wall,  it stays in frame and moves with the camera.

1.find a target that sticks, create a solid from that target. cut out a mask. this will be your matte.

2. put your sky layer below the matte. set it to 3d. hold shift as you parent the sky layer to the matte layer - it will shift the sky layer to the matte's position. unparent.

3. set the sky layer to Alpha matte the matte layer. not it will show in the masked area

4. take it further down in Z space, and scale up accordingly until you get the desired result.

[gordo299]

This is exactly what I was trying to do.

Thanks for all your help.

Gordon

[Roei Tzoref]

you are welcome Gordon! looks like you marked your response as correct, making it confusing to others as to what exactly is the right solution to the original post.