Shoot photos that cut out perfectly

A segmentation model finds your subject by looking for the boundary between subject and background. The clearer that boundary, the cleaner the cut. So the single most effective thing you can do costs nothing: put the subject in front of something that doesn't look like it.

• Dark subject → light background. Light subject → darker background.
• Watch colour too: a green plant against a hedge, a denim jacket against a blue wall, blonde hair against a beige curtain, all technically "different", all needlessly hard.
• Busy backgrounds aren't automatically bad, but a background containing things that look like the subject is: a person in a crowd, a mug on a shelf of mugs. The model may honestly keep the wrong twin.

You don't need a studio backdrop: a plain wall, a large sheet of card, or simply three steps away from the clutter is enough. Distance alone helps: the further the background, the more it blurs, and blur is contrast's best friend.

Hard light from one direction throws a dense shadow that touches the subject's edge, and to a segmentation model, a shadow glued to a shoe looks like part of the shoe. The result is a cutout with a dark blob bleeding out of the outline.

• Best free light: an overcast sky, or a window without direct sun. Soft, even, no hard shadows.
• Indoors at night: don't aim a lamp at the subject; bounce it off a white wall or ceiling.
• Avoid backlight. A subject shot against a bright window becomes a dark silhouette whose edges dissolve into glow: hair detail is unrecoverable.
• Skip on-camera flash. It flattens the subject and paints a hard shadow directly behind it, exactly where the edge needs to be clean.

Of everything on this list, motion blur is the one mistake that cannot be fixed afterwards. A blurred edge isn't an edge anymore: it's a gradient where subject and background are physically mixed in the pixels. No tool, and no person, can decide where one ends and the other begins, because the photo itself no longer contains that information.

• Brace your elbows, lean on something, or set the phone on a surface and use the timer.
• Photographing kids or pets? Take a burst and pick the sharpest frame: one frozen moment is all you need.
• In dim light, phones silently choose slow shutter speeds. If edges look soft, add light rather than trying again in the same gloom.
• Zoom to 100% and check the edge before leaving the scene. Sharp overall but soft on the moving hand? That hand will cut out soft, too.

Give the subject room to be the subject:

• Fill most of the frame. A subject that occupies 10% of the photo gets only 10% of the pixels: edge detail like hair is described by a handful of pixels and comes out coarse. The same rule applies when you're photographing an old print with your phone instead of a person — PicReviver's guide to scanning old photos covers the framing, light and DPI that make that shot usable.
• Don't crop mid-limb. Keep the whole subject inside the frame with a little margin, so nothing important is amputated.
• Whole subject in focus. Strong portrait-mode blur on parts of the actual subject (an outstretched hand, the back of a jacket) makes those parts as hard to cut as motion blur. Step back slightly instead of shooting extremely close.
• One clear subject. The model keeps what looks most "foreground". If two people overlap, expect them to be cut as one: you can separate them afterwards with the erase brush, but a small gap at shooting time is easier.