Green Room — check your light, framing and wall before you join.

Three steps and you are looking at yourself. No account, no sign-in, nothing to install — your browser asks for the camera once, and that is the only question anybody puts to you.

Two of the three checks wake up faster than the third. Light is judged from the picture alone, so it is running inside a second. Framing and Backdrop first need to know which pixels are you and which are the room, and that model loads once. Until it lands, those two show a dash rather than a guess — the app will not tell you something it does not yet know.

Ask a photographer what good light is and you lose an hour. Ask your webcam and the answer is duller and far more useful: enough of it, coming from in front of you, and roughly the same amount on both cheeks. That is the whole test, and it is nearly everything that ever goes wrong.

Green Room works from brightness, four times every two seconds. It averages the whole frame, compares the middle — where your face is — against the edges, then the left half against the right. Three numbers, and five verdicts about the room.

Then, once the room is behaving, it stops looking at the room and looks at you: the top third of your outline, your face pixels and nothing else, split left against right and upper against lower. A bright window on the wall cannot fool that second pass, which is why it is the one allowed to say where your light actually is — and therefore which way to move the lamp.

This check needs to know where you end and the room begins, so a small model traces your outline, thirty times a second, entirely inside your browser. From that outline come four measurements: how much of the frame you fill, how far down your head starts, how far off centre you sit, and whether your head is above your shoulders.

Think of a passport photo booth. It is not judging your face. It is judging whether your face is where a face is meant to be. Six things can be wrong — find yours below, and the fix is one you can do sitting down.

Here is the part that surprises people. Your background is measured on the background only — you are cut out of the sum before anything is counted. Leave yourself in and it never works: your eyes, your hair, your collar are full of edges, and every room on earth would come back BUSY.

What it counts is busyness — how much the picture changes from one pixel to the next, across everything that is not you. A plain wall barely changes and scores low. A bookshelf, a drying rack and a half-open door change constantly and score high. Three verdicts fall out of it: CLEAN, MIXED, BUSY.

And then the backdrop view, which is the button worth the whole app. Tap it and you are filled in flat, so you disappear and only your room is left. Suddenly you can actually see it.

Next to it sits the button that does the opposite: it keeps you and changes the room. One press softens the wall behind you the way a portrait lens would; a second press takes it away completely and stands you on plain paper; a third gives you your room back. It runs on the same outline, live, with a softened edge rather than a hard one — the hard edge is exactly what makes cheap background removal look cheap. And your photo and your ten seconds keep whichever look you left switched on. Use it when the wall is not yours to tidy: a hotel room, a kitchen, somebody else’s desk.

Two ways to capture yourself. The shutter takes a still. The record button runs for ten seconds and stops itself, with a ring draining around it so you can watch the time go — which matters, because ten seconds of your own face is longer than you think.

Both play back un-mirrored. This is the honest bit and the uncomfortable bit: that is not the you in the mirror, that is the you in the meeting. Your smile sits on the other side and you are lower in the frame than you imagined. Watch it once, sit up, and go in.

So where do they go? Nowhere. There is no server behind this page.