Navy

High-speed, high-dynamic range video system

Senses accurate tonal distinction for real-time video conditions

Photonics Electronics Sensors

One of the challenges high-speed digital camera manufacturers face is a limited dynamic range. The dynamic range of a digital camera is the ratio of light captured by the pixel to the noise floor (composed of camera read noise, shot noise, and dark current noise) of the camera. High-speed cameras must have high sensor gains, large fill factors, and large pixels to account for the very short exposure times required in high-speed videography otherwise they succumb to noise limitations. The high-speed operational requirements limit the total dynamic range that most high-speed digital cameras can operate within, typically close to 60 dB, or about 10 stops.

A photographic series of imaged frames of this new system that has been demonstrated utilizing COTS cameras. 2610 is a plasma cutter filmed at 1,000 fps, dynamic range 1×106; 2620 is an arc welder filmed at 5,000 fps, dynamic range 1×107; 2630 is a flash Bang Grenade filmed at 8,000 fps; 2640 is a flashbulb peak output filmed at 10,000 fps, dynamic range 1×108, 27-stops. With this system, several HDR videos have been taken ranging from 1,000 fps to 100,000 fps spanning over 28-stops in dynamic range. This capability has never before been observed in high-speed videography. Additional comparison images for a tone-mapped frame from a plasma cutter include 2650 for 22-stops, 2660 for 24-stops and  2670 for 26-stops.

Breaking through the above restrictions, Navy researchers have developed a cascade imaging system with commercially available parts to capture full scene radiance information and video. The system has been demonstrated to capture a scene in excess of 160 dB or 27-stops dynamic range, limited only by the parts that were readily available. Specifically for a high dynamic range (HDR) image, the light beam from a scene is divided by beam-splitters and attenuated by neutral density filters. After acquisition by separate cameras, the radiant exitance from each beam division is combined from which to estimate original scene exitance. Weighting functions are employed to minimize symmetrical errors. The final HDR image is constructed from the weighting averages of the original scene exitance.

This method has been used to capture explosive detonations without the typical oversaturation that occur in close proximity to flash as well as the optical enhancement of events occurring in low-light surroundings. This process can view several different phenomena from a rail gun launch, welding, flashbang grenade detonation, 6-inch gun muzzle blast at 25,000 frames per second (fps), and the burning of a flashbulb at over 10,000 fps spanning over 150 dB dynamic range.

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