Removing a background by hand with a mask

One-click background removal is genuinely good now. Preview on macOS will do it, your phone will do it, and for a product shot against a plain wall the result is often perfect.

Then you give it a photograph with fine hair, a wire-frame chair, motion blur, or a subject the same colour as what is behind them, and you get a cut-out with chunks missing and a halo around the edge. At that point you either accept it or do it by hand.

Why a mask instead of the eraser

The instinct is to select the background and delete it. That works and it is permanent: those pixels are gone, and if the selection was slightly wrong you find out later when the image is composited against a different colour.

A mask achieves the same visual result without destroying anything. It is a greyscale layer attached to your image that controls visibility:

• Black conceals. Painted black on the mask, that part of the image is hidden.
• White reveals. Painted white, it comes back.
• Grey is partial. Mid-grey gives you 50% opacity, which is how soft edges work.

Nothing is deleted. If you hide too much, you paint white and it returns. If the client wants the background back next month, you switch the mask off.

The method

1. Duplicate the layer first. Always. The original stays untouched underneath.

2. Make a rough selection. Use whatever selection tool gets you 90% of the way — a rectangular or freehand selection around the subject is fine. Precision is not the goal yet.

3. Turn the selection into a mask. The background is now hidden. It will look wrong at the edges. That is expected.

4. Zoom in and paint. This is the actual work. A soft brush at moderate opacity, painting black to hide and white to reveal, working around the outline. Zoom to 200–400% so you can see what you are doing.

5. Match the brush to the edge. A hard edge — a table, a phone, a book — wants a hard brush. A soft edge — hair, fur, a blurred shoulder — wants a soft brush at partial opacity, built up in passes rather than one stroke.

6. Check against a contrasting colour. Put a bright red or green layer behind the subject temporarily. Every mistake in the mask becomes immediately visible. This step catches more errors than any amount of squinting at a white background.

The edges that cause trouble

Hair and fur. Do not try to trace individual strands. Mask the solid mass, then use a soft, low-opacity brush along the fringe so the transition is gradual. A slightly soft hairline reads as natural; a crisp one reads as cut out.

Colour fringing. A subject photographed against a green wall picks up green light along its edge. After masking, that green rim is still there and it looks wrong on any other background. Fix it by painting slightly further in, or by desaturating a thin band along the edge.

Semi-transparent things. Glass, smoke, a veil. These cannot be cut out cleanly because the background is genuinely visible through them. Use partial grey in the mask and accept that a perfect result is not available.

Motion blur. Same problem — the edge is genuinely ambiguous. Feather it rather than choosing a hard line.

The hybrid approach

The fastest route is usually not either extreme. Run the automatic removal, then add a mask and fix what it got wrong. Ninety per cent of the work is done in one click, and you spend your ten minutes on the hair rather than the torso.

This only works if your editor lets you edit the result as a mask rather than delivering a flattened cut-out.

Saving it properly

A masked layer only survives in a project file. Export to PNG and you get a flat image with transparency — correct as a deliverable, useless as something to adjust later.

Keep the project file. Export the PNG. If you only keep the PNG, the next revision starts from scratch.

Doing this in Miyu Paint

Miyu Paint's full access includes mask layers alongside pixel, text, shape, group and adjustment layers, plus the brushes, pencils, erasers, fills and selections this method needs. It saves editable .mpaint project files, which is the part that makes masking worth doing — a mask you cannot save is a mask you redo.

The free tools cover opening, cropping, resizing and drawing, with PNG and JPEG export up to 2048 pixels on the longest edge and no watermark. Masking is a full-access feature; full access also removes the export ceiling and adds adjustments, effects, advanced formats and printing.

The trial is fourteen days, you start it yourself, and it does not renew into a charge. Document processing happens on your Mac — no account, no advertising, no analytics.