About this page
One operation, done properly, with its limits written down.
The one thing it does
ChangeBgPhoto replaces what is behind the subject of a photograph. That is the whole product. It does not crop to a document size, it does not squeeze a file under a kilobyte limit, it does not retouch a face and it does not produce a subject with nothing behind it. Each of those is a real job and each of them is somebody else’s; a page that claimed all five would do the first one worse.
The narrowness is deliberate and it is the reason the page can afford to be opinionated about small things — where the shadow goes, which white a portal wants, how wide the feather should be. Those are the details that decide whether a submitted photograph is accepted, and they are the first things a general-purpose editor abstracts away.
How the selection is worked out
The page samples the colours around the frame’s own border, fits a small model to them, and grows a background region inward from the edges. Each step of that growth costs the colour difference between one pixel and the next plus a share of the local contrast, so a gradient across a wall costs almost nothing to cross and a shoulder costs a great deal. The result is refined against the photograph’s own detail, which is what recovers a soft edge on hair rather than a cut one.
That is arithmetic, not a model, and it runs on your machine with nothing downloaded. It is also exactly what a photograph against a plain wall needs — which is most of what arrives here. Where it struggles, the keep and erase brushes are the answer, and the confidence reading under the controls tells you in advance which case you are in rather than leaving you to find out at the export.
A learned matting network is the other way to do this, and the code path for one is in the repository, unconnected to any weights. Turning it on means publishing a set alongside the site and announcing the download before it starts. Nothing about the interface would change: it would be a second source for the same alpha, feeding the same feather, the same unmixing and the same brushes.
Who this is for, and what it costs
It is free and it needs no account. The intention is that Google advertising in the reading below the working surface pays for it; none is being served yet, because the domain has not been approved and the switch that draws a unit is off, so the space those units are reserved for is simply not there today. Once Google approves it, they appear below the tool and nowhere else: nothing above it, nothing inside it, and no unit between a visitor and the thing they came to do — a page that does that is not worth keeping.
The image you open is read by this page and by nothing else — there is no server behind this domain that could receive it, and the outline is worked out by arithmetic running inside your own browser rather than by something your photo is handed to.