Pair your phone and scan

Your phone is prism's measuring tape. The projector shows a series of stripes while the phone watches from beside it, and from what it sees prism works out exactly where every projector pixel lands in your room. Over a cable it takes about half a minute.

1Pair the phone

Open the projector window first (Projectors and outputs), then click Next: pair phone.

1. Point the phone's camera app at the QR code on the laptop and tap the link that appears. It opens prism's camera page.
2. No QR reader? On the phone, open the address shown under the code (it ends in /join) and type the 6-character room code; it joins by itself when the code is complete.
3. On the phone, tap Start camera and allow the camera when the phone asks.
4. The laptop's Status says Phone connected, with the camera's size. Click Next: scan.

2Where to put the phone

• Right next to the projector's lens, as close as you can, pointing at the scene. From there the phone sees what the projector lights, from almost the same angle, so shadows and hidden corners match.
• On its normal 1× camera. Don't zoom in, and don't switch to the wide (0.5×) lens.
• Propped so it can't move. A small tripod with a phone clamp is ideal; a stack of books works. It must not move until the scan is sent.
• Sideways, usually: a projection is wide, and the phone suggests “Turn the phone sideways” when you hold it upright. Whichever way you choose, keep it: if the screen rotates during the scan, the scan stops.
• The whole projection in view, with a gap to every edge of the camera picture.

3Light

• Dim the room. Lights off or low, so the projector is the brightest thing the camera sees. Daylight washes out the stripes: close the curtains.
• Keep the light steady during the scan: no switching lights on or off, no one walking through the beam.
• Shiny or very dark objects scan better with the lights lower still.

4The checks

When you reach the Scan step, the projector starts to blink. The phone uses the blink to find the projection, and the laptop shows what the phone sees: the lime live outline is the projection's edge.

The phone has its own checks: Whole projection in view, Phone steady and Screen stays on.

5Start the scan

1. Click Start scan on the laptop. (The phone has a Start scan too, but touching the phone can move it.)
2. Hands off. The projector shows black, white, and then stripes, each followed by its opposite. The laptop counts Main pass frames; the phone says Hold still.
3. If some areas came out unclear, the phone looks at just those again: Touch-up pass (“Some areas need another look — re-scanning them now.”).
4. The phone sends the scan (“Scan sent — you can put the phone down”) and the laptop finds the surfaces.

6What the stripes do

Each stripe pattern splits the projector's picture into light and dark bands: the first into two halves, the next into quarters, then eighths, and so on down to stripes a few pixels wide. First upright stripes, then lying ones.

Now look at one point on your box through the phone. In each pattern that point is either lit or dark. Written down in order, those lit/dark answers spell out a number: the column of the projector pixel that lights that point (from the upright stripes) and its row (from the lying ones). After about forty patterns prism knows, for every point the phone sees, which projector pixel falls on it.

From this map prism finds the flat faces, curved surfaces and edges, and draws each surface as a clean shape, exactly as the projector sees it. Three more tricks keep it reliable:

• Every pattern comes with its opposite (light where it was dark), so the phone can tell lit from unlit even on dark or shiny surfaces.
• White frames every few patterns check that the phone hasn't moved. If it has, prism repeats what it needs, or stops and tells you.
• Each picture is checked before it's used: a picture the projector hasn't finished showing yet is waited for, never guessed.

7How long it takes

8After the scan

The camera view becomes a heatmap of how well each part was read: Full precision (green), Partial (yellow), Weak (red) and Unlit (grey). Scan quality ▸ Details gives the numbers, and any warnings appear under it in amber.

Review surfaces takes you to What do you want to map?. Scan again starts over.

Advanced Surface detection

Under the Scan step's More…, Surface detection chooses how surfaces are found. AI + geometry (the default) also uses the scan photo, which is best for separate objects that touch; its model downloads once and runs on your computer. Geometry only is fast and fully offline, best for flat walls and simple boxes. While Geometry only is chosen, Simple shows an Advanced · Geometry only chip there.

9If it fails

A scan that can't finish stops with a message on the phone and on the laptop, and a Try again button. The message says what went wrong; this table says what to do.

Hints and tips

• A phone tripod pays for itself. Most failed scans are a phone that moved.
• Start from the laptop, so your hands stay off the phone.
• Scan over HDMI when you can, even if you'll show over Wi-Fi later.
• Charge the phone, and keep its camera page open: if the laptop asks for another scan, the page picks it up.
• Matt, pale objects scan best. Very shiny or black things may come out partial; lower the lights, or add them by hand later.
• Rescan after moving anything: the projector, the objects, or the zoom and focus of the lens.

When something looks wrong

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