Transcript
LC-Tec Displays AB PolarSpeed®-S-VN dual-band imaging application notes May, 2014
PolarSpeed®-S-VN dual-band imaging APPLICATION NOTES
Introduction Using modern digital cameras utilizing broadband sensors, it is possible to capture and analyze parallel information from several different wavelength bands. In dual-band imaging the normal photographic image captured from the visible (VIS) wavelength region can be combined with a near infrared (NIR) image, enhancing the information and contrast not visible in the pure VIS image. It is also possible to extract 3D and depth information from the NIR image by using Time-of-Flight (ToF) technology. Picture from PublicLab.org, courtesy: Gonzoearth.
Problem One possibility when designing such cameras is to incorporate two internal camera systems with separate sensors and optics, each system being designed for the specific wavelength band. This concept adds cost and complexity, and results in a large foot-print. Furthermore, since the two sensors are set apart, they do not capture the exact same image, giving a parallax problem. If using a single-sensor system there is a need to employ wavelength selective filters only transmitting the desired wavelength band, i.e. the NIR light needs to be blocked during VIS capturing, and vice versa. For this purpose rotating mechanical bandpass filters can be used and the two images are captured time-sequentially. But also this concept results in a large foot-print, and in addition includes moving parts. Another possibility is to use highly customized sensors with a bandpass filter array on top of the image sensor, making individual pixels sensitive to the desired wavelength band. This intrinsic drawback of this design is decreased resolution.
LC-Tec Displays AB │ Tunavägen 281, SE-781 73 Borlänge │ Sweden Tel: +46 243 79 40 70 │ Email:
[email protected] │ Web: www.lc-tec.se
Solution Replacing the mechanical bandpass filter with the PolarSpeed®-S-VN, an innovative, fast-switching liquid crystal (LC) filter alternately transmitting visible and near infrared light, makes it possible to realize compact, full-resolution, single-sensor systems without any moving parts. The transmittance property of the filter is controlled by an applied drive voltage. The filter has a small foot-print and can easily be integrated into already existing broadband camera sensor systems. Furthermore, thanks to the switching speed of the filter, time-multiplexed, high-speed video camera applications can be addressed. The PolarSpeed®-S-VN enables users to explore new innovative human (VIS)/machine (NIR) vision and multispectral imaging applications, improving compact cameras for flaw detection, identification, measurement, positioning, and verification. The patented and proven PolarSpeed® technology is a LC-Tec core invention which is also used in polarization modulators at 3D cinemas world-wide.
Target applications
PolarSpeed®-S-VN advantages
Automotive Biomedical Food and agriculture Manufacturing Surveillance
Unique functionality Fast switching Miniaturized No moving parts Vibration-free Ruggedized
Main characteristics* PolarSpeed®-S-VN 20% 150:1 25% 100:1 0.3ms 60FPS -30°C to +60°C
VIS transmittance VIS contrast NIR (850nm) transmittance NIR (850nm) contrast Switching time** Maximum frame rate** Temperature range
*: Prototype data, model still under development. **: Valid at room temperature, switching time increases and maximum frame rate decreases with decreasing temperature.
Transmittance vs. wavelength; blue curve: VIS open/NIR closed, red curve: NIR open/VIS closed.
Normalized VIS transmittance with filter operating at 60 FPS.
For more information, please contact us at:
[email protected].
© 2014 LC-Tec Displays AB
PolarSpeed®-S-VN dual-band imaging application notes
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