Using alpha channel as holdout


I have a keyed alpha channel that I would like to use as a hold out at a a given depth.
Currently I’m using DeepHoldout with a projection onto the required depth but could this be done with E_Image as well? Can’t get it to work.


Hi frank,
Its probably best to use your deep holdout for accuracy, i’m not sure. You can make an sdf holdout from image input though yes.

Here’s a small scene with holdout from image.
sdf_holdouts.nk (6.2 KB)

I haven’t tried this out myself, but you could try to plug it into the E_Image node, then subtract a constant value ( 0.5 ) from the alpha so it goes for instance from -0.5 -> 0.5 and then multiply by -1. in theory you should be able to visualise this as an Iso surface and plug it in as a holdout.

As I said I haven’t had a chance to try this myself, so no guarantees.


I ended up using deep, but will try both your suggestions as I’m sure this will be required again before too long.


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