Diff. Masking Tutorial Question: Background

kentwolf wrote on 3/25/2006, 8:23 AM

In the VAAST Difference Masking tutorial, one of the steps is to ensure you have a clip/image of the background with the subject not in the picture.

If you don't have that background-only clip, presumably, you could use different sections of the video in conjunction with Bezier masks to essentially create a background image.

Question: Is there any reason you could not use a high resolution frame grab of the background with the subjects in it (the whole videoed area), then take the frame grab into Photoshop, use the clone tool to replicate the background into the subject area, thereby removing the subject? I would also think that since you are just looking for luma differences, you would not even need a precision clone tool job. I would think you could just put patches of the existing background right over the subjects.

Is there any reason this would not work.

I am not at my computer right now, so I cannot actually check this for some time.

Thanks!!

Comments

FrigidNDEditing wrote on 3/25/2006, 9:06 AM

if the entire images is all the same then it's no problem - but if there are discrepincies in the lighting color etc... then everytime they sway left to right or anything like that, the BG they revieal may be different than the BG you created. Now - if you really REALLY watch it it may work - but I am inclined to say that it would be a pretty substantial task, and though it may be possible, it may not be anywhere near easy.

Dave

johnmeyer wrote on 3/25/2006, 9:07 AM

Question: Is there any reason you could not use a high resolution frame grab of the background with the subjects in it (the whole videoed area), then take the frame grab into Photoshop, use the clone tool to replicate the background into the subject area, thereby removing the subject? I would also think that since you are just looking for luma differences, you would not even need a precision clone tool job

I guess a lot depends on how your foreground subject is lit, and how much work you want to do with keyframes and garbage masks. Even with the perfect shot of the real background, the technique will not ensure that nothing shows through. Just like in a green or blue screen technique, if the talent wears blue, you've got a horror film or comedy instead of a nicely keyed shot.

The ultimate way to do a mask like this is to look for differences between frames and create or modify the mask using that information. Anything that moves is considered part of the foreground talent. Something like that is only found in very advanced applications, however.

So, you can go ahead and create a background that has been cloned, and it will probably work, but if it differs too much from the real background, you're going to see a lot of the background popping through.

kentwolf wrote on 3/25/2006, 9:54 AM

Got it.

Thanks guys!