Best use of green screen for Cinemagraph effect?

[swedefilm]

Hi,

I´ve been searching the forum (and the rest of the web for information on this topic but I still can´t figure out the best way to solve this issue.

We are going to shoot a school class photography cinemagraph style (a short clip, at first appearing like a still image, where a small part of it is moving). The scene starts with a still image of a class with one chair empty. Then the missing student enters the frame from the right, walks diagonally towards the empty chair, sits down and finally blends into the still image. I guess this would be quite easy to achieve if we were only going to use a film camera. We´d just tell the other students to stand real still for the shot and freeze one frame in post production. Then we´d make a quick matte around the moving person and we´d be done. However, the production also calls for print images to be made. Unfortunately no film camera resolution will be enough for this use. And this is where things are getting complicated for me.

The still image of the class will be shot with a Hasselblad camera to achieve the highest possible print resolution. Our plan is to place the film camera on the same spot as the still camera, using the same focal length and light, to capture the sequence of the student walking towards the chair and sitting down. Then we will match the grading of the film sequence with the still shot.

Now, what is the best way of keying out the person in the film sequence in order to place it above the still shot?

1) all green screen wall/floor with the problem of green spill onto the chair and actor
2) green screen wall behind actor and rotoscope the floor shadow/reflection manually, trying to match position and color of the film sequence with the still shot.
3) another solution that hasn´t occured to me

I´ve attached a shot from the location where you can see the reflectiveness of the floor.

Kind regards

 

[Michael Carter]

Since your keyed plate will align with the background, it may be easy to roto out the floor - the floor will be "the same" in both plates so a soft mask might work, unless there's stuff that gets in the way - I'd leave everything possible in the shot such as chairs, etc.

I don't get the "there will also be print" thing - unless the uses have to be exact, shoot for your print with the hassy, and shoot for video with the camera you'll use for all plates, etc.

But your print or scan from the hasselblad is likely to be radically different when you get to keying - the floor just won't be close enough to "the same" to hold areas of the still floor. I'd try absolutely to use the same camera for both plates and shoot stills for stills use.

If you must use the hasselblad, have the shooter bring a polaroid back and peel a proof print. (Fuji still makes 3000 B&W and 100 color pack films). Take some static cling film and a fine point sharpie, and trace the polaroid details and put it on the video LCD or production monitor - this will help you align the video frame to match the still - it's going to be tough to eyeball it. (You could also pull the finder off the hassy and do a tracing right on the ground glass).

If there was a reason the floor had to be keyed tightly, I'd use savage chroma seamless paper on the floor. It's not as saturated as a fabric screen, but lays down well. And this job will likely take several layers and masks.

Here's an example of "not keying the floor":

 

[swedefilm]

Thank you for your very informative reply. It seems like they went for the all green screen solution on the day of the shoot and I think it will work out fine for our purpose.

It was important for the client to have the exact same facial expression and position of the children on the still image backplate as in the print campaign. Therefore we had to use the print still as the backplate for the movie.