The Refine Edge Brush for soft selection edges
Paint along a selection's edge and Paint by Zaweba works it out again by alpha matting. Alt+paint makes it crisp. Here is when to use each.
A selection edge can be wrong in two opposite ways. Sometimes it is too hard, a sharp line where the real object fades into the background through hair, fur or blur. Sometimes it is too soft, a smudgy fringe where the object actually has a clean outline. The Refine Edge Brush in Paint by Zaweba handles both, without opening a dialog, and it sits in the same tool slot as the Magic Wand.
How it works
With a selection active, pick the Refine Edge Brush from the wand slot and paint along the selection's edge. The part of the edge under the brush is recalculated by alpha matting, which estimates how much of each pixel belongs to the selected object and how much to its background. The result is a graded edge that follows fine detail.
Hold Alt while you paint and the brush does the reverse. The edge under it becomes crisp again. That second mode is just as useful as the first, because matting is not always what an edge needs.
When to paint soft, and when crisp
Think of the edge of a portrait. The hair needs soft treatment: strands pass over the background and the pixels there are a real mix of hair and wall. Paint the brush over that band and it keeps the mix. The shoulder of a jacket next to it is a different story. Its edge is a firm line, and matting might wrongly decide that some background belongs to it. There, Alt+paint puts the hard edge back.
The same goes for product shots. A furry toy wants soft edges; the plastic base it stands on wants crisp ones. Being able to switch with one key, along the same edge, is what makes the brush quicker than refining the whole selection at once.
Using it with the other selection tools
The brush refines a selection you already have. Make the shape first with whatever is fastest: Quick Selection, the lasso, Colour Range or Foreground Extraction. Then switch to the Refine Edge Brush and pass over the edges that need it.
If the job is large, the Select and Refine workspace (Select > Refine Edge) offers its own Refine Brush with seven views and a choice of outputs. Use the workspace when you want to see the selection against different backgrounds or send it to a new document. Use the tool in the wand slot for quick fixes directly on the canvas.
Once the edge is right, convert the selection into a layer mask. That way nothing is deleted, and any area the brush got wrong can be painted back on the mask later.
Habits that help
Paint a band that straddles the edge, partly over the object and partly over the background. The matting needs to see both sides to decide. A stroke that sits wholly inside the object has nothing to compare against.
Keep strokes short and look after each one. A long sweep round a whole head may treat a crisp ear the same way as loose hair. Two or three short passes, with an Alt stroke here and there, give you better control.
Zoom in. Edge work done at fit-to-screen size hides problems that show up at 100 percent, especially faint halos of the old background colour.
Slips that spoil an edge
Don't use the brush to add or remove solid chunks of the selection. It's for edges. If a whole hand is missing, add it with the lasso or Quick Selection first, then refine its edge.
Don't forget Alt. Many people only ever use the soft mode and then wonder why a sharp outline looks fuzzy. The crisp mode exists for that.
And don't flatten too soon. Keep the result as a mask while you place the object on its new background. A change of background colour often reveals edge problems you couldn't see before, and with a mask they are easy to fix.
Edges decide whether a cut-out looks real. This brush puts the decision about each stretch of edge in your hand, soft where the object is soft and crisp where it is firm, and it does so with classical matting on your own computer.
