See it on your wall

Photograph the wall. Use Take a photo (or Live camera), choose one you already have, or drop or paste one. An angled view is fine. If you want things at their real size, tape a sheet of A4 or Letter paper flat on the wall first, or make sure a door is in the shot.
Add what you want to see there. Add image loads a picture from your files; Snap an object photographs it. A PNG with a transparent background goes on as it is. A photo with a background can be cut out (below).
Place it. Each overlay has three ways to sit on the photo:
- Free — drag to move; drag a round corner handle, pinch, or scroll to scale and rotate. Level squares it up.
- 4 corners — drag each square handle onto the spot where that corner should be, so a picture lies flat on a wall seen at an angle. The picture is warped with the perspective (homography) the four corners define.
- True size — needs a reference (next step). Type the object’s real width and height and it is drawn at that size, in the wall’s perspective. Drag it and it slides along the wall, getting smaller as the wall recedes; twist with two fingers or type an angle to turn it.
Mark a reference for true size. Pick what it is — A4 or Letter, portrait or landscape, a 30, 32, or 36 × 80 in door, an 80 × 200 cm door leaf, or something else whose size you type — then drag the numbered corners onto its corners: 1 at the top-left, then clockwise. A magnifier shows what is under your finger. While a reference is set, the size label above the selected overlay shows how big it would really be, even in Free or 4-corner mode, so you can also size something by eye and read off its real dimensions.
Adjust the look. Opacity, brightness and warmth help a picture taken in different light match the room; Shadow adds a soft drop shadow; Mirror flips it. The overlay list sets which is in front (↑ ↓), and hides or shows each one.
Compare and keep. Before/After (or the B key) switches the overlays off and on. Save PNG downloads the picture at the photo’s full resolution; Share hands it to your phone’s share sheet where the browser supports it.

⛶ Full screen (or F) gives the photo the whole screen — the browser’s full screen where it is allowed, otherwise a full-window layer (iPhone); the toolbar stays at the top and ◫ Panels hides the layer and reference panels. Escape leaves.

Cutting out a background

Cut out… opens the selected image in an editor:

Remove background floods inward from the edges and corners — the quickest way to lift an object photographed against a plain wall, floor, or sheet.
Magic wand — tap the background; the touching area of similar colour goes. Tolerance sets how similar: raise it if too little goes, lower it if the object starts to disappear.
Colour key — tap a colour and it goes everywhere in the picture, with a soft edge (good for a green screen or a coloured sheet behind the object).
Crop — drag a rectangle around the part to keep. On the wall, what is left stays exactly where it was.
Erase and Restore — paint pixels out, or back in; the faint ghost shows what can come back. Pinch with two fingers (or scroll) to zoom in for detail.
Shrink edge pulls the cut in by a pixel or two to lose a halo of background colour; Soften edge feathers it. Undo steps back; Start over puts everything back.

How it works

The reference’s four corners and its real size give the homography — a 3 × 3 projective matrix — that maps millimetres on the wall to pixels in the photo, solved as an 8 × 8 linear system on normalised coordinates. An object of a given size is a rectangle on the wall, mapped through that matrix to four points in the photo; dragging maps your finger back through the inverse. Each overlay is drawn by splitting it into a grid of triangles and drawing each with its own affine transform, which approximates the projective warp closely (a plain rectangle is drawn in one piece). Everything happens in the page: the photos are never uploaded, and nothing is kept after you leave.

Limits

True size is only true on the plane of the reference. A sofa standing in front of the wall, or a rug on the floor, is not on that plane; use 4 corners and judge it by eye, or mark a reference on the floor for a rug.
The bigger the reference, the better: a sheet of paper a few pixels wide gives a rough answer for a whole wall. A door, or a sheet photographed close-up, is far more accurate. Lens distortion from a wide-angle phone camera bends straight lines near the edges of the frame.
The cut-out tools work on colour, not on what the object is: they do well against a plain background and need help with brushes against a busy one. There is no AI background removal.
Overlays keep their own lighting; brightness and warmth help, but reflections and the room’s shadows are not simulated.
Photos are scaled to at most 3200 pixels on the long side (2048 for overlays) to keep phones responsive. Nothing is saved: reloading the page starts again.