Automatic masks

[Joe Moya]

Well… yes rotoscoping can be avoided… but that requires a blue/green screen background…

If your video doesn’t have a distinquishable background to seperate (as in a blue/green screen) then the answer is no… or at least that I know of using AE. On the other hand, Mocha by Imagineer can do this easily if you can afford the software.

Joe

[Reuben Lemer]

I dont mean separating footage from a green screen. that can easily be done with keylight. What I want is for it to automatically create a mask around anything that isn’t transparent for every frame of the clip. Is this possible?

r4z2

[Joe Moya]

Hmmm… OK… it sounds like what your asking for is called the alpha channel of the video that has been rotoscoped or keylighted with a green/screen. But… some how I don’t think I am answering your question.

What I want is for it to automatically create a mask around anything that isn’t transparent for every frame of the clip. Is this possible?

An alpha channel does this… and you can invert the channel to make either the background transparent or the foreground.

An alpha channel can be created (or automatically created) with any rotoscoped video. The alpha channel is the matte.

Are you asking… Can you create multiple mattes of a video with more than one object within a video at one time?

… Not that I know of… but, you can make many layers for each object within the video to create multiple mattes for each object within the same video.

[Reuben Lemer]

Sorry, still not quite what I want, once I’ve created the alpha channel so that its just me moving on a transparent background, is there a way of automatically creating a mask around it, not key out the background, but a mask, as in the pen tool, without having to rotoscope each frame.

r4z2

[Joe Moya]

Yes… this is what I referred to as inverting the alpha channel…

Normal alpha channels make the background transparent… inverting the alpha channel does the opposite… it makes the background visible and makes the foreground invisible.

I typically do this with editiing software since it much easier… in AE, you can do this a couple of ways… you can switch the layers between what is forground vs. background relative to the matte…and/or… use inverted version of luma matte or alpha matte with or without invert effect (Effect>Channel>Invert).. each method produces different matte inversion matte effects.

Basically, if you have a rotoscoped or keylighted seperated elements of you videio… then you can make either elements transparent. But first, you need to rotoscope each frame (or use Mocha) if you want to create tight mattes.

There are ways to make rotoscoping process a tad bit more easier, but I have never used AE for this purpose because even with this process the rotoscoping is still very time consuming. If memory is correct… this rotoscoping “help” is done by using Paint and changing the duration for the paint stroke (or erase) that will interpolate between frames by changing custom setting (in the paint pallette) to 2 f (frames). If you do a search you will probably find better instructions for this process.

Good looking manually producing rotoscoped frames is difficult to get… most instances, you will get a “lava lamp” effect for the edges because you can not get the edges to match from frame to frame… this is why having AE interpolate between frames helps (specially, if you use more than 2 frames… the trade off is this… more frame interpoliation produces smoother edges for the matte but less accurate… less frame interpolaltions produces greater edge accuracy but less smooth edges (i.e., lave lamp edges).

If you are doing trees/people moving, you will find that rotoscoping is EXTREMELY difficult… specially, if you have motion or moving legs involved or Hair. You might notice that most tutorials use objects as samples and not people… why?… because they are much easier to rotoscope than organic shapes that are moving (i.e., such as people/persons).

Hope this helps.

Joe

[Reuben Lemer]

I’m sorry but this still isn’t what I’m looking for, let me try and think of a different scenario… Ok, so, imagine you have a picture of a square imported into ae, you use luma key to get rid of the white background, so now you have transparency behind the cube. So, say then you wanted to draw a mask around the cube, but didn’t want to do it manually, is there a tool which automatically draws a mask where transparency meets opaque, in this case, around the cube?

r4z2

[Joe Moya]

I am not sure why you would want to draw a mask/matte in this fashion…the cube is already a mask/matte. You simply need to invert the alpha channel and the “square/cube” becomes transparent… to replace the cube back into the video… you simply need to add a layer behind the now transparent “square/cube”.

A convalute way to change the background and still keep the “square/cube” in the video would be to take the original alpha matte with a transparent background… add what ever background you want… save as an AVI file… then, import this new matte (i.e., new background with transparent area where the “square/cube” use to be)… then, add back the “square/matte” by placing a new layer with the “square/cube” under the saved AVI file(w/alpha) to put the missing object back into the video.

If you got rid of the background in the video… then you have your matte… there is no rotoscoping needed. Rotoscoping (or keylighting using Luma or what ever) is process used to remove backgrounds from a chosen forground element. In your example, you already got rid of the background with the luma key.

Invert the matte…. that is the solution.

Joe

[Reuben Lemer]

Ok, this is my situation, I have, on a piece of paper, a watch design which needs to be filled in, I am going to do this digitally perhaps with advanced lightning or something like that. Now, I have scanned this into the computer and put it in ae, I have keyed out the white background and added the lightning, but oh no! the lightning actually goes off the edge of the outlined watch! I need a mask to restrain it just to the watch, now the watch is just one color and there are lots of little holes and awkward edges, I need something that masks them automatically, is this possible?

r4z2

[Joe Moya]

This may not be a matting issue at all…

… can’t you just narrow the lighting? That may create the effect you want… if not…

…then it is still a alpha matting issue…

…Add an alpha matte layer (perhaps inverted?) to the layer between the light layer and the scanned photo. That’s it… the lighted area will only come through where the matte is transparent with the watch in the layer below the matte (i.e., background).

You can feather the alpha matte layer for the image if you want to make the lighting appear as a smooth transition… this is called an edge matte. You can duplicate the (inverted?) matte footage, apply a Channel>Shift Channels to this track footage and apply a Alpha>Full On Red>Alpha Green>Alpha Blue>Alpha… Then, apply a Stylize>Find Edges effect and (invert it – maybe?). Then, blur the edges a bit and use Color Corrections>Curves, Color Correction>Levels or Channels>Mini-max to +/- the range of the matte.

Joe

[Reuben Lemer]

Sorry, still didn’t work 🙁 but thanks for all the suggestions 🙂 I’ll manually do it, I was just wandering if there was an automatic way.

Thanks,

r4z2