"Erode" effect to replace "Simple Choker"

[oskarmatzerath]

I'm copying this from Spencer Tweed's suggestion from December 2, 2019--of course, since the ideas forum is not searchable I couldn't find this in this forum, just the old features suggestion, so I'm cutting-and-pasting someone else's idea, as follows:

It would be very nice to re-write the "Simple Choker" effect to perform more closely to the Nuke "Erode" node. Specifically the precision is much higher and the results more reliable. When using "Simple Choker" any feathering is lost and the matte becomes hard, it seems to exponentially get less effective the wider you go, and it does not keep the original shape of your mask very well (there seems to be a blurring effect which rounds out edges). On the other hand the Nuke "Erode" node works in pixels and no precision is lost in terms of your mask shape, so it is reliable and predictable. It is behaves much like "Mask Expansion" does for a mask (no precision is lost, it is measured in pixels, etc).

[Mylenium]

That would be quite a lot of work to re-create this effect. AE doesn't have a generalized vector fields API like Nuke. Some enhancements to the matte effects would generally not hurt, though. Even just a more graceful roll-off behavior would already improve matters so succeeding effects have actually more headroom to process data.

Mylenium 

[oskarmatzerath]

The main problem is that there is a point where choking a matte with negative values, theoretically expanding the alpha, actually begins eroding the matte, so there is less visible when it's choked at -100 than at -50. There is a definite limit to how much you can expand a matte.

[Christopher Power]

I have been able to control this with a curves adjustment on the alpha channel. I don't know how different it is from nuke, but I'd be interested to hear opinions.

[Christopher Power]

On second thought,curves only works to choke the matte. It cannot expand it. Very interested in how others are doing this... Perhaps a simple choker we with negative values (expanding the matte), and then curves? It would still have a hard edge mid curve I imagine.. hrm