2. Pictures You Can Pick Up

As well as having two projectors rather than one, SecondLight also has two ImagingSource infra-red cameras and 264 infra-red LEDs around the edge of the display. One camera detects fingers touching the surface, and this supports the same multi-touch capabilities as Surface for stretching and rotating images. The other is triggered when the PSCT-LC surface is transparent and that can see quite a way above the surface, which means SecondLight can understand 3D gestures in mid-air as well as multi-touch gestures on the screen – or even objects like a paintbrush.

Fingers touching the surface are clear and bright in infra-red ; as soon as you move your hand away even a few millimeters, the image SecondLight sees when the PSCT-LC surface is opaque becomes blurred. SecondLight could see faces leaning over the display and know which way up to put the image, or even do facial recognition to know who’s using it.

IR images of hands on SecondLight using FTIR (left) and through the PSCT-LD surface when opaque (middle) and clear (right).

Being able to see more than fingertips also gives SecondLight a better chance of working out which hand individual fingers are attached to so that it can understand multi-touch gestures better. The sheet of tracing paper or plastic you use to see the second image with SecondLight doesn’t have to stay on the surface either. Instead of leaning over to look at something on the display, you can pick it up and hold it in your hand to look at – or to show to someone sitting next to you - and SecondLight can still project onto it.

To give the image the correct perspective when you hold it at an angle, SecondLight needs to know where the sheet it’s projecting onto is so it can pre-distort the image. It can detect anything that reflects or emits light so you can use two reflective strips down the sides of the sheet. But if you want to be able to control SecondLight by touching the sheet you pick up, it needs to get more precise information from the sheet.

To do that, Hodges fitted a row of the same infra-red LEDs onto the sheet of plastic (which only takes two AAA batteries to drive it), which he refers to as a ‘magic lens’. The infra-red is reflected inside the sheet and a laser-etched line on each end of the sheet produces the same kind of frustrated total internal reflection (FTIR) that Perceptive Pixel uses for its multi-touch system. That shows SecondLight the edges of the sheet and so it can see how big to make the image it projects and how to distort it so you see the whole image in the right perspective – and use multi-touch to control it.

Using a sheet of plastic and a magic lens to pick images off the SecondLight surface.

At the moment you have to keep the secondary display over the SecondLight surface although you can hold it almost vertically, but that’s just because of the angle the projector is mounted at, says Steve Hodges. It would be possible to change the angle so you could pick up a window from the surface and sit back to work with it.

Pick up images on a secondary SecondLight screen using infrared