15 video clips are widely spreading over the Internet, of 10 to 20 minutes long each, capturing divers from the Beijing Olympic Games practicing in “Water Cube”. The odd about the clips is that it sees-through the divers’ swimsuits with infra-red, resulting a picture of the decades of both male and female athletes hang around naked.
Very few is known about who was capturing the video, and how. Communities from the Internet reproves the act, stating that it is an infringement on privacy, and urging the police to investigate, and to stop these things from happen again. But before the police does their jobs, how can the others protect themselves? We gonna be familiar with how the see-through thing works.
It is infra-red
You likely have heard about infra-red. In fact, it is a mature technology that is widely used in our daily life. Your TV remote control probably has an infra-red light bulb in front of it. It sends signals to the TV receiver, to tell the TV to turn on/off, or to change channels. “But I can’t see the light?” you said. Well, it is because infra-red is invisible. To be precise, let’s rephrase it to: our eyes cannot see infra-red.
The trick here is that, while human eyes cannot see infra-red, our digital cameras can!
In order to make see-through works, one must separate the visible light entering the camera lens from infra-red light. One common way to do it is to use IR-through filters. A better way is to use computer software to filter out the visible light from the raw data collected by the camera's CCD; the advantage of using software is that it can do an optimal cut, resulting in much clearer pictures. The down-side of the software approach is that you cannot reprogram a digital camera; it only works on customized (programable) devices.
Does it work with web cams/my phone’s camera?
Yes. And in fact, they do better. It is easily a common mistake that expensive cameras give better IR images. They do not. Because of the smaller form factors, web cams and phone cameras have thinner IR-cut filters and let go more infra-red. Web cams may be limited by their resolutions, but phone cameras do a great job!
Update: Eventually, someone has implemented the idea in a iPhone app; anyone interested can try it yourself: