Background Remover

A Colour Key, Not a Subject Detector

This page answers one question, pixel by pixel: how far is this colour from the colour you chose? Pixels close to it become transparent and pixels far from it stay. Nowhere in the code is there a model of what a person or a product looks like. Earlier copy here described automatic subject detection, edge-detection algorithms and brush tools. None of those ever existed, so the descriptions are gone.

Choosing the colour to remove

Click the background on the canvas and the tool reads the colour under your cursor from the full-resolution file. There are shortcuts for white (products on a sweep), black (dark studio work) and the standard green screen, and if you already know the value you can type it into the hex field.

Sample a typical spot, not the brightest one. A white backdrop is never a single white, because the lighting puts a gradient across it. If you pick a mid-tone from the middle of that gradient, the tolerance control has far less work to do than if you'd picked the hottest corner.

Tolerance and edge softness

Tolerance is the radius, in colour distance, around your chosen value. Raise it and more of the backdrop vanishes. Raise it too far and it starts eating the subject, usually beginning with whatever part of the subject shares a hue with the background.

Edge softness adds a band around that threshold where pixels fade out gradually instead of flipping from opaque to invisible in one step. At zero you get a hard, aliased cut. Around 30 percent gives you an edge that sits convincingly on a new background. Both controls work in colour distance, not screen pixels, which is why the preview and the exported file make identical decisions.

Check the mask before you commit

Turn on the magenta mask and the tool paints everything it's about to remove instead of removing it. It's the quickest way to catch the usual failures: a shirt cuff the same shade as the wall, a shadow the key has decided to keep, or a fringe of backdrop colour still clinging to hair.

Where this approach breaks down

It can't separate a subject from a cluttered room, a street or a lawn. Heavy shadows on the backdrop are a problem too. A shadowed white wall is grey, and grey sits a long way from white in the distance being measured. Semi-transparent things like glass, smoke and flyaway hair come out partly keyed, since each of those pixels really is a blend of subject and background.

If you control the shoot

Light the backdrop separately from the subject so it stays even across the frame. Move the subject a metre or two forward, so their shadow doesn't land on the backdrop and backdrop colour doesn't spill onto their edges. And don't dress the subject in the key colour. That's the reason blue screens exist alongside green ones.

The output has to keep an alpha channel

Transparency needs PNG or WebP. JPEG and BMP have no alpha at all, so if you pick either, the tool upgrades the output to PNG for you instead of quietly filling the cut-out with a solid colour.

If a desktop viewer shows your transparent area as black or as a checkerboard, that's how the viewer draws it and the file is fine. Open it in a browser to confirm the alpha survived. If you'd like the subject on a flat colour instead of on nothing, Convert Image will composite it onto a background of your choosing during the format change.