adding to existing alpha

[jbills]

What might be a nice feature in the standalone especially would be to have the ability to import an RGBA sequence or a separate rgb and matte render and add s+r shapes to this existing alpha.

This is usually something that exists in paint apps that I think I might use occasionally in s+r.

Say I pull a key on an actor, but the greenscreen only goes up to his neck. Ok, so now the task at hand is to roto his head and neck to match with the rest of this alpha coming from the key.

So, I would export a straight-alpha'd RGBA sequence out of my compositor, and would import this into s+r. Need the ability to add and subtract from the existing alpha using splines. I would simply roto his head and neck, and be sure not to create a visible seam where the key is meeting the roto (so being able to preview the merged alpha is important).

Then, when I go to render, I would like the option of just rendering the splines to import back in to the compositor, or rendering the full alpha, merged. Have run into both situations. (also nice to be able to preview them seperately).

Make sense?

thanks!

[paulm]

You can do most of you want with the "useInputAlpha" roto parameter, if the alpha you want to modify is embedded in your foreground.

Are you saying you would like an external matte input that would let you import an alpha-only sequence which could replace the forerground alpha? IIRC, Elastic Reality could do that.

Maybe I don't understand exactly.

[jbills]

No, you understand. Excellent, if it's in there, then we're good to go.

Yes, it would be a nice feature to be able to load an external matte - as several compositors incorrectly export a straight alpha by not giving the full RGB data! Ideally, the RGB should not be affected by a straight alpha render (just passed through).

But in practice, lots of compositors change the RGB info drastically when rendering a straight RGBA. Unsure what drugs the coders were on? AE crops the image by basically drawing a square crop on the edge-most alpha pixels that equal 0 in x/y (which actually sometimes does result in a full frame). Others (commotion, combustion, etc) give a "stripped" version of the original footage. By stripped I mean giving us the RGB to a certain point - basically an edge several pixels outside of the any alpha data, so you end up with a mostly black RGB frame. It looks "bloomed" for lack of a better term. This makes it very hard to continue doing roto work/etc when a frame's RGB data is completely destroyed!

Luckily for us shake does it right. :)