Cameras

Camera Specifications

The camera's in the Motion Capture Lab are Vicon MX40's; which have the following specification:

  • Sensor Type: CMOS
  • Sensor Resolution: 2352 (W) x 1728 (H) = 4,064,256 pixels; ~4x106 pixels
  • Sensor Depth: 10bits / pixel grayscale; 1024 gray levels
  • Sensor Dimensions: 16.46mm (W) x 12.10 (H); 20.43mm diagonal
  • Pixel Size: 7 microns x 7 microns (Square Pixels)

Strobe

The camera's strobe (the red LED lights that circle the front of the camera) are used to illuminate the markers in order that they are more visible. The strobe attached is a "Visible" wavelength strobe, which on the MX40 cameras is 623nm wavelength of light. There are two other types of strobe that can be used (but not available for this system) which is the Near Infra-Red (780nm) and Infrared (875nm). Red has a wavelength between 622 and 780 and is therefore the strobe is well into the visible spectrum.

The "Visible" strobe type is the most effective for motion capture, as long as the light in the room can be controlled; if there are bright studio lights "Visible" red can become washed out, and thus infrared or near-infrared need to be used

Warning: due to the intensity of the strobe, it is best not to look directly at them

Onboard Processor

Each camera has its own processor onboard; which collects information from the sensor and processes it (according to commands from the computer) before sending it to the camera network switch (MXNet) and then onto a program called Tarsus. The information presented to tarsus is generally in the form of compressed 2D data containing only the grayscale reflections of the markers

Note:The onboard processor is necessary in order to keep the data transmission rate down. If all the data from a 4M Pixel camera @ 120fps were transmitted, it would require a bandwidth of 4.9Gbits/s (or 4.9x109 bits/second) → 4,064,256 Pixels/Frame x 10bits / Pixel x 120 Frames / Second

Vision

The vicon cameras are slightly different from normal cameras in that they have a small filter attached between the lens and the image sensor; this filters out light of wavelengths outside the range of strobe (623nm) and therefore the image is essentially light in the red spectrum (and grayscale because only luminosity is required). If we wanted to change the strobe, we would need to change this filter in order for it to match properly.