Anamorphic Illusion Maker

About the Anamorphic Illusion Maker converter

An anamorphic illusion is a picture drawn wrong on purpose. Flat on the table it is a stretched, unreadable smear. Put your eye in one particular place and it snaps into a perfectly proportioned image standing upright — a word you can read, a shape that appears to rise off the paper.

Type a word or drop in a picture, say how high your eye will be and how far back you will sit, and this works out the distortion and gives you a sheet to print, with the viewing spot marked on it.

Anamorphosis is the oldest trick in perspective drawing and still the most surprising one, because unlike most optical illusions it does not fool the eye at all. The eye is reporting exactly what reaches it. It is an honest picture of an object that is not there.

The idea is nearly five hundred years old

Hans Holbein painted a stretched grey smear across the bottom of The Ambassadors in 1533. Stand to the right of the canvas and look back along it and the smear resolves into a human skull. Leonardo drew an anamorphic eye decades earlier still, and the technique has been used for church ceilings, theatre sets and, more recently, for the enormous pavement drawings that appear to open a hole in the street.

What has changed is that working out the distortion used to be the hard part. Artists used threads stretched from a fixed viewing point, or grids drawn on glass, to transfer each point by hand. The arithmetic is the same; a browser is just faster at it.

How the distortion is worked out

Picture the image you want people to see standing upright on the table, hinged along its bottom edge like a book cover raised to ninety degrees. Now draw a straight line from the viewer's eye through every point of that imaginary upright picture and carry on until it strikes the table. Mark where it lands. Those marks, taken together, are the anamorphic image.

Because light travels in straight lines, an eye at that spot receives exactly the same rays from the flat marks as it would have from the upright picture. It has no way to tell the two apart, so it sees the upright picture. Move your head and the correspondence breaks, which is exactly why the illusion feels like a trick rather than a drawing.

Why the shape comes out as a trapezoid

The distortion is not a simple squash. A point near the top of the imaginary upright picture is seen at a shallower angle than one near the bottom, so its ray strikes the table much further away — and, because it is further away, points either side of it spread further apart too. The printed shape is therefore narrow at the near edge, wide at the far edge, and stretched enormously in depth.

The lower your eye, the shallower every angle becomes and the more extreme the stretch. Sitting at a desk, a picture ten centimetres tall typically needs about twenty centimetres of table to lie on. From a standing view of the floor, the same picture needs far less, because you are looking down at a steeper angle. This is why sidewalk and pavement artists work on enormous stretched shapes: they are drawing in forced perspective for someone standing close by, looking down.

Nothing can be taller than you are

There is a hard limit built into the geometry. A ray from your eye to a point above eye level travels upwards for ever and never meets the table, so there is nowhere to put the ink that would stand in for it. No anamorphic image on a floor can appear to rise above the viewer's own eye.

As a point approaches eye level its mark runs away toward the horizon, so the last stretch below your eye needs an impractical amount of paper. The picture size is chosen to stay well clear of that limit and still fill the sheet.

Printing it so it actually works

The illusion depends on real distances, so the sheet has to come out of the printer at its true size. Print at 100%: any "fit to page" or "shrink to fit" option changes the scale, and the viewing distance printed on the sheet will no longer be the right one.

The near edge is marked with a dashed line and a small cross. Put the paper flat, get your eye the stated height above the surface and the stated distance in front of that line, centred on the cross, and close one eye. Two eyes see the sheet from two slightly different places, and the illusion is built for one.

What to put in it

A word is the most convincing thing to start with, because reading is unambiguous: flat on the table the letters are illegible, and from the viewing spot they simply read. Bold shapes with hard edges work better than photographs, since the far end of the image is stretched over a lot of paper and fine detail is thinned out.

The text mode gives the raw geometry instead of a picture — the four corners of the shape, measured from the centre of the near edge. That is what you need to mark out a driveway or a school hall with chalk and a tape measure, at a size no printer will reach.

Frequently asked questions