How do I make anamorphic art?

[Fish]

In my new apartment I have a nice well-lit bathroom with a big mirror. The mirror/sink area is in a little alcove, with walls on both sides.

I want to draw a piece of art for the wall that only looks right if you're looking at the picture in the mirror. What's the best way to figure out the proper anamorphic perspective thing?

[Mangetout]

The easiest way (IMO) is to make a sketch of the desired end result, then project it onto the wall (overhead acetate projector or scan and project from a digital projector), trace the sketch, then fill in the details - If you site the projector lens in the position of the intended viewer, the projected rays should follow the same path (but in reverse) that the light will that enables the viewer to see the image properly.

I've never actually tried it for distorted or forced perspective images, but it works really well for ordinary murals and stage scenery.

One potential issue is the depth of field of the projector - if you're projecting onto a surface that isn't perpendicular to the axis of the lens, then it probably won't all be in focus at the same time, so you might need to trace it piecemeal, adjusting the focus as you go, as well as being aware that adjusting the focus does also sometimes entail a slight zooming effect.

[garygnu]

Mangetout's idea would also work with an opaque projector like this one. That depth-of-field issue could be a problem.

You could go really complicated and stretch it in Photoshop or even use a 3D program to project it on a virtual wall first as a texture.

[Chronos]

If your mirror is flat, it won't work. Any piece of art that looks right in the mirror will also look right directly, and vice-versa. About the only things you could do would be to do something with lettering, and put it on backwards, or to get something which only looks right from a distance, since you'll be able to see it from further away in the mirror.

[rowrrbazzle]

The most basic thing that would work with a flat mirror is a trapezoid. Put the shorter of the parallel sides closer to the mirror, and when the perspective is correct, in the mirror you see a square or rectangle.

Slightly more elaborate would making the distance between the parallel sides very large. A trick I remember from a book is to add extremely height-stretched letters. They'd be normally illegible but would look normal height when observed from a low angle. The horizontal portions of the letters must be thickened to look normal at that angle. Assuming the art would be on the side walls, the letters would have to be rotated 90 degrees for this to work, and so you'd have to look at it with your head leaning in the right direction.

Here's a professional variation of this: http://users.skynet.be/J.Beever/swim.htm