How to enlarge a mask in Photoshop non-destructively (“bleeding”, “outer glow”)?

I would want to enlarge a mask be it either a pixel based or vector one by adding a “bleeding” effect so to increase the masks’s area. Adding actual “Outer glow” FX doesn’t change the masking area, but only adds FX itself if put on the adjustment layer and if put on a group – cancels the adjustments, that are inside the group. Transforming the mask is not option since I may have several masking zones on a layer and the size increase has just a different result, not identical to an “Outer Glow”. Selecting the mask and then modifying the selection takes too much time and has no live preview.

I’m coming from Affinity Photo, where the “Outer Glow” can actually be used on a layer used as a mask (Affinity’s masks can be their own independent layers). So I wanted to find an identical way of doing so in Photoshop.

Adding feathering(via Gaussian blur) and increasing the area(via Outer Glow) in Affinity Photo of a mask layer.Adding feathering(via Gaussian blur) and increasing the area(via Outer Glow) in Affinity Photo to a mask layer

Answer

An option could be to use a smart object with Maximum or Minimum filter as a shallow Knockout layer in a group. This way the filter expands/contracts the transparent area which drives transparency of the group it’s in. And since it’s on a smart object, it’s non-destructive. Add a gaussian blur on top for blurry mask.

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Update: How this setup works.

In the Blending Options dialog the smart object in the group has Fill Opacity set to 0 and Knockout set to Shallow meaning that the effect will be limited to the group. Opaque pixels of the smart object layer will “stop” the pixels of the layers beneath, transparent pixels will let the layers beneath bleed. Maximum filter is then applied the smart object and it influences transparent pixels of the SO shrinking/expanding the masking effect.

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Attribution
Source : Link , Question Author : Gražvydas Žuklys , Answer Author : Sergey Kritskiy

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