Running filters on masks and channels in Paint by Zaweba
In Paint by Zaweba, filters run on a layer mask, Quick Mask or channel as a grey picture, so blur, noise and more can shape your masks.
A mask is just a grey picture. White shows, black hides, and the greys in between show partly. Once you see it that way, a whole set of tricks opens up, because anything you can do to a picture you can also do to a mask. Paint by Zaweba makes this direct: while a channel, a Quick Mask, a filter mask or a layer mask is the thing being painted, filters run on it as a grey picture.
The filter respects the current selection and is one undo step, just as it is on a normal layer.
Why filter a mask?
Masks made with selection tools are often too perfect. Hard edges look cut out, perfectly smooth gradients look digital, and straight lines look ruled. A filter can roughen, soften, spread or texture the mask in ways that are tedious or impossible to paint by hand.
Softening and feathering
A Gaussian Blur on a layer mask softens its edge, the same idea as feathering a selection but adjustable by eye with the live preview. Blur a mask on a cut-out portrait a touch and the edge blends naturally into a new background. Blur the mask of an adjustment layer more heavily and the adjustment fades in gradually, which is how you brighten a face without a visible edge.
Motion Blur on a mask makes the effect trail off in one direction, handy for a light beam or a fade across a product shot.
Roughening and texturing
Add Noise, Spread or Diffuse on a mask breaks up its edge, so a reveal looks spray painted or dissolved rather than cleanly cut. Clouds rendered into a mask gives a patchy, organic reveal, ideal for adding haze, dirt or light in uneven patches. A Ripple or Wave on a mask makes a wavy reveal along an edge, a quick way to get a torn-paper or water-line effect.
Growing and shrinking
Minimum and Maximum on a mask shrink or grow the visible area by a few pixels. That is the precise fix for a cut-out with a faint halo of the old background: shrink the mask by a pixel, then soften it slightly with a blur.
Quick Mask and saved channels take filters too. In Quick Mask, your selection is shown as a coloured overlay you can paint. Running a filter there changes the selection itself. Draw a rough selection, enter Quick Mask, run a filter such as Crystallise or Ripple, then return to a normal selection, and you have a selection shape that would be very hard to draw.
Saved channels work the same way. Filter a channel to make a reusable selection or a depth map, for example blurring it for use with Lens Blur, which can take its depth from a channel.
Getting mask filters right
Check what you are working on before running a filter. It is easy to think you are filtering the mask while the layer itself is active, or the other way round. Look at which thumbnail is highlighted.
Keep strengths modest and judge on the picture rather than the mask. A mask that looks wildly noisy may produce a perfectly natural edge in the image.
Mistakes to avoid with mask filters
Running a colour-based filter on a mask does nothing useful, because a mask has no colour; it is treated as grey. Stick to filters that change shapes, softness and texture. And remember that a heavy blur on a mask can let a background leak through where you did not want it, so look closely along the edges.
Filtering masks is one of the quieter strengths of Paint by Zaweba. It turns the filter menu into a set of tools for shaping where effects go, not just what they look like.
