alpha bbox

[bwanaghana]

I'm trying to create a script that creates a bounding box around a node's alpha channel. Does anyone know if there is a way to isolate the nonzero area of a node's alpha channel (preferably without using sample()) in order to get its bbox coordinates?

[Void]

Curvetool. There's also a python command to run it.

[lucjulien]

this feature is already integrated in nuke.

press X select TCL type autocrop

[bwanaghana]

Now I just need to figure out a way to make it auto-update whenever the alpha map is changed upstream. Would nuke.addKnobChanged work for something like that? I'll have to experiment.

[Void]

Not sure if that possible. You might have to just get the user to update it. Not sure what exactly that you're doing but making everything automatic often leads to stupid users.

[bwanaghana]

I was hoping to incorporate it into a rather complicated gizmo in order to improve processing performance by limiting the area of the image being calculated to everything within the alpha bounding box. I guess the manual recalculation will have to do for now. Sometimes it's relieving to hear that it might not be possible. Thanks for your help. :D