Introduction to interactive projection principles

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Interactive projection has been very popular recently, but it is very expensive. Recently I have studied it. The principle is actually very simple.

We know that light is an electromagnetic wave, and its wavelength ranges from several nanometers (1nm = 10-9 m) to about 1mm (mm. What is visible to the human eye is only one part. We call it visible light. The wavelength range of visible light is micron nm ~ Nm, visible light wavelength from long to short divided into red, orange, yellow, green, blue, purple light, wavelength shorter than purple light called UV, wavelength longer than infrared light called infrared light. Ordinary camera photosensitive chips are divided into CCD or CMOS. CCD features better color and lower CMOS cost. They all have a special skill, that is, to perceive areas invisible to human eyes. They are also very sensitive to near-infrared rays. Then, when the filter technology is used to filter out visible light, what the camera sees should be an image composed of infrared radiation.

The light projected by the projector is the visible part, and its infrared part is filtered out by its internal filter film. In this way, the camera cannot see the content projected by the projector. If the infrared light is strong, the camera can see the human body. How can we enhance the image of the object seen by the camera? Fortunately, the active infrared emission technology on the market is very mature, for example, the night vision camera sold in the monitoring market can launch near infrared (850 nm), and the larger the power has a dedicated long-distance infrared light, but the current night vision camera can reach 5 m distance, so no. The night vision camera actively emits infrared light and then the CCD sensor receives infrared light. Therefore, the most difficult part of the interactive projection is the separation of the human body and the background virtual object, what the camera gets is a black-and-white monochrome background that includes a human image.

An image of an infrared camera

Next, how can we detect the human body. In terms of computer vision, this is a very simple technology, that is, difference. Difference Is to subtract two consecutive frames of images from the camera. What is the result, what we get is the moving part, so as long as the person is moving, the difference will cut down the moving part. The next step is to analyze the data, and then project the virtual part. It's not complicated.

Differential Image example:
Of course, complex interactive projection is not just these technologies. These are just the most basic principles. They also involve camera calibration, optical flow method for moving direction, performance optimization, and special effects.

What are the most basic devices for interactive projection,

A infrared camera (only look at the infrared part, you can use the type of night vision camera sold on the monitoring market between-yuan, if the pursuit of higher real-time interaction, you can use high-speed infrared cameras .),
B-infrared filter (filtering visible light, and the figure shows the spectral range)

C. High lumen projector (if you don't have a projector, you can use your LCD display instead to interact with your hands .)
D Computer (strong CPU is the key, if you need to display 3D graphics, efficient graphics card is also indispensable .)
E. One Video Acquisition Card (responsible for transferring analog signals from cameras to digital signals of computers)

F video connection lines

 

Software has

A video gets the DirectShow or VFW or Acquisition Card Development Kit

B video analysis (BMP can be used directly, better opencv)

C interface display (DirectX 3D, OpenGL, or flash)

D. Other auxiliary libraries, such as the physical engine ode, loading the 3D model library (lib3ds), etc.