Compositing stereo image with different cameras for an effect

[Nchanta]

Hello all. I am researching for a project I am doing next year.


To keep it brief and to the point I want to use a stereo rig in order to composite the image from a modified camera over the top of my normal shooting image. Camera A is a Blackmagic Cinema camera, but due to the nature of the camera I can't modify it In the way that I need to. So we are looking into modifying a hacked GH2.


—There would be no interaxial separation. I would simply be overlaying the two images, masking out the areas I want shown by the modified camera in post.


—Neither cameras have Genlock so I would have to LANC the two together, but I realise there will be shutter drift very quickly.


—Whilst both cameras are m4/3 mount the GH2 has a slightly larger sensor. This will affect my field of view obviously, but not my depth of field. Technically all I am doing is using more of the image circle by a crop factor of 0.3. Same lenses will be used on both cameras.


—The modified camera image will look very different to the standard camera


—I am at no point utilising the whole frame with the modified camera. Only the areas I am masking out in post.


So I am desperately looking for opinions on what potential issues I might have and whether this experiment will work with the option I detailed above. I don't really want to shoot with two GH2 fir these shots but if this is the only way to do it I may have to.


Thanks for your time.


Tim

edit: I think I put it in the wrong section but can't delete it and move it

 

[Duke M.]

Both DOF and FOV will be affected since the larger sensor is being pulled down into a standard image size. In addition, color, saturation, noise, brightness, contrast and just about everything will be different.

So really it depends on the effect you're trying to create. You might be better off shooting flat or raw, then processing the file two different ways then masking.

Or you might want to put one image on top of the other with the top one semi transparent in certain areas and masked in others.

 

[Nchanta]

Thanks for your input. Why would DOF be different if you were using the same lens and basically the same settings (excluding minor variables between sensor performance). There might be a perceived change in DOF because of the change in FOV, but the distance from image plane to subject is the same.

If DOF were different in any way, I don't think it will matter, there won't be any depth as it's just mainly just skin tones that I am masking out. So there will be no real apparent depth, as it will all fall between the area of focus.

The noise characteristics are the one thing that I am slightly concerned about, but as for the colour, contrast, saturation etc...I'm not worried about, it won't matter with the modified camera. I will be shooting raw on the BMC, to give me the extra range in post so marrying the image together shouldn't be a problem.

Combining the two images is an interesting idea, especially when it comes to noise, but I will likely be heavily denoising the modified camera. Worth experimenting with, also might be worth trying to desaturated the areas under the masked area to give it an additional something.

food for thought

thanks for yours...