Free Anamorphic Perspective Grid Generator

The oldest surviving worked example is in Leonardo's Codex Atlanticus, around 1485: a drawing of an eye and a child's head, elongated so violently along one axis that they resolve only when the sheet is viewed from the right-hand edge at a shallow angle. It is a technical demonstration rather than a picture, which tells you the geometry was understood well before anyone thought of using it for a subject.

The famous case is Hans Holbein the Younger's The Ambassadors, 1533. Across the bottom of an otherwise conventional double portrait lies a pale diagonal smear. Move to the right of the canvas and look back along its surface, and the smear resolves into a human skull. The picture contains a memento mori that only appears when you leave the position the rest of the painting was built for.

That structural joke — the portrait works from the front, the skull from the side, and never both at once — is why the painting is the standard reference for anamorphosis. It is not a trick appended to the picture; it is a second picture occupying the same surface with a different viewing rule.

Seventeenth-century Europe produced a great deal of the same thing, much of it in Jesuit contexts, where the mechanics of projection were studied seriously. Emmanuel Maignan's 1642 fresco in Trinità dei Monti in Rome runs the length of a corridor and resolves into Saint Francis of Paola only from one end of it. Jean-François Nicéron's La Perspective curieuse, 1638, is the manual that documented how to construct these things.

The mechanism in all of them is a grid. You draw the image on a regular square grid, then transfer it cell by cell onto a distorted grid whose cells correspond to the same squares as seen from the intended position. The transfer is mechanical; the projection is where the thinking goes.

This overlay is that distorted grid. Two things happen to the lattice, and they are independent.

The rows compress, and this is where the depth control acts. Row spacing follows a curve rather than a straight line, so bands get shorter as they recede. At the default depth of 2.20, the nearest band is 4.09 times the height of the farthest. Turn depth down to 1.10 and that ratio falls to 1.19 — nearly uniform. Turn it up to 4.00 and it rises to 11.4.

Those three numbers are worth having in mind, because depth is the control people misjudge. It corresponds physically to how low and how close the viewer's eye is: a viewer standing right at the edge of a floor piece and looking down needs a high value; a viewer at the far end of a hall needs a low one.

Getting depth wrong produces a specific, recognisable failure. Too low and the piece looks like a picture lying on the ground rather than a hole in it. Too high, and from the intended viewing point the near end reads as absurdly enlarged and the illusion snaps the other way into a distorted drawing.

The viewer point runs across the full width of the frame and answers a different question: where, laterally, the viewer stands. For a piece on a pavement with a marked photo spot, this should sit where the mark is. For a corridor, it is wherever people enter.

Oblique skew handles the case where the viewing position is not on the centre line at all — a piece seen from a walkway running along one side. Skew leans the whole construction up to 45% either way. Combined with the viewer point it covers most real installations, which are rarely as symmetrical as the diagrams in books.

The construction rays are dashed lines running from the viewer point back to the grid, and they are the fastest way to see whether your setup is coherent. If the rays fan evenly, the projection is behaving. If they bunch or cross oddly, the viewer point and the depth are fighting each other and the illusion will not hold.

For pavement and floor work the practical sequence is: mark the viewing spot on the real site first, photograph the surface from exactly there, load the photograph, and fit the grid to what the camera saw. That way the distortion is fitted to the real geometry — the actual slope of the ground, the actual eye height — instead of to an idealised version of it.

Then transfer. Draw your source image on the regular grid the rectangular grid maker gives you, at the same column and row count, and copy cell by cell. The mural scaling calculator works out what one cell measures on the ground. This is the same procedure as the ordinary grid method, and it is deliberately mechanical: the projection has already been solved by the grid, so the transfer needs accuracy rather than judgement.

Column and row counts run from four to thirty each. For a given amount of care, more cells means a more accurate transfer and slower work. For a large floor piece with organic subject matter, twenty or more is usual. For a hard-edged graphic, eight can be enough.

There is a limit worth being honest about. This construction produces a plausible oblique anamorphosis for a flat surface seen from a stated position. It is a practical drawing aid, not a photogrammetric solution. If your surface is curved, stepped or on a slope, the grid gets you most of the way and your eye finishes the job — which is what pavement artists have always done.

The contemporary form of the tradition is street 3D chalk art, and its practitioners work almost exactly as Nicéron described, with the addition that they now check the illusion by photographing it from the spot as they go. The camera is a better judge than the eye, because the eye at the correct position corrects for what it knows about the ground.

The same geometry turns up in stage design, where a set is built to read correctly from the centre of the stalls; in trompe-l'œil ceiling painting, where the viewing position is the middle of the room; and in the road markings that read as upright text from an approaching car and as elongated smears from a footbridge.

That last one is the most common anamorphosis most people see daily, and it makes the principle concrete: the letters painted on a bus lane are wrong from every position except the driver's, and being wrong from everywhere else is what makes them right from there.

For export, remember that the piece is usually much larger than the sheet. SVG scales without loss, which matters at six metres. If you are printing a transfer sheet, export raster at your paper size and 600 DPI, then enlarge on site by counting cells rather than by scaling the print. The anamorphic overlay page works through the painted cases, beside the rest of the perspective overlays.

Everything runs in your browser. The photograph of your site is never uploaded, because there is no server for it to reach — the drawing, the transform and the export all happen on your own machine.