Cutting out an object with Foreground Extraction

Some objects refuse to be selected with a lasso. A cat on a patterned rug, a bunch of flowers against a hedge, a person standing in front of a busy shop window: drawing round them point by point takes an age, and the edge still looks cut with scissors. Foreground Extraction is the tool in Paint by Zaweba built for exactly those pictures, and it asks you for very little drawing.

It lives in the selection tools under the L key. The idea is that you show the app roughly where the object is and what it looks like, and it works out the rest from colour.

How the tool decides what to keep

There are three steps. First you drag a rough border around the object, loosely, leaving a margin of background all the way round. Then you paint over the object itself with a few strokes, covering its main colours. Finally you press Enter.

When you press Enter, the app builds Lab colour signatures from your strokes and from the background close to the border. Lab is a way of describing colour that sits closer to how the eye sees differences than plain red, green and blue, so two shades that look different to you are also treated as different by the tool. Every pixel inside the border is compared with both signatures, and the ones that match the object are kept. Along the edge, alpha matting works out partial transparency, so soft or fuzzy edges are kept as soft edges rather than chopped into a hard line.

Getting a clean result

The strokes matter more than the border. If the object has a red jumper, blue jeans and pale skin, make sure your strokes pass over all three. Any colour you never touch is a colour the tool has to guess about, and if that colour also appears in the background it may be thrown away.

Keep the border loose but not huge. A border that hugs the object too tightly can cut through parts of it, while one that wanders far out takes in background colours that have nothing to do with the edge. A margin of a little background all round is the sweet spot.

Two options let you tune the result. Sensitivity controls how strictly pixels are compared with the signatures, so raise or lower it if too much background is creeping in or bits of the object are being lost. Edge detail affects how much of the fine edge structure the matting tries to keep, which helps with hair, fur and leaves.

Where it fits among the selection tools

Foreground Extraction gives you a selection, and from there everything else in the Select menu and the Layers panel works as normal. A sensible habit is to extract first, then look closely at the edges at full size. If a stretch of hair still looks wrong, Select and Refine and its Refine Brush are the next stop, because they recalculate the edge under the brush. If the problem is a solid chunk that was missed or included, it's quicker to add or subtract with the lasso or Quick Mask.

Once the selection is right, turn it into a layer mask rather than deleting the background. A mask hides pixels without destroying them, so if you later spot a missing ear or a stray shadow you can paint it back. Masks also let you place the object on a new background and keep adjusting the fit.

Where cut-outs go wrong

The most common one is painting the strokes too thinly and in one place. One line down the middle of a person gives the tool only a few colours to learn from. Several short strokes across the different parts of the object work much better.

Another is expecting the tool to read meaning. It works from colour, not from knowing what a dog or a bottle is. When the object and the background share colours, such as a grey car on a grey road, expect to tidy up afterwards. That is normal, and it is also why the result is predictable: Paint by Zaweba has no AI services, so every decision the tool makes comes from the pixels you can see and the strokes you made.

Last, don't judge the result zoomed out. A cut-out that looks perfect at a quarter size can show a faint halo of old background at 100 percent. Check the edge at full size before you move on.

A quick routine

For most product photos and portraits the routine is short. Press L, drag the border, paint across each main colour of the object, press Enter, check the edge, then add a layer mask. For hard cases, nudge Sensitivity and Edge detail and try again. It is an older and very dependable way of cutting things out, and once you've used it a few times you will reach for it before the lasso.