Studies On Strobe Lighting For Video Camera And Its Applications In Underwater Imaging

As the same as photographing, video camera always needs artificial lighting. In order to avoid motion blur, the exposure time for dynamic target is generally short and it often needs highlight illumination. In many cases, such as photographing in field and at night or underwater camera, it is very difficult to guarantee an adequate supply of power to maintain such continuous light illumination that utilizing battery-powered. With the help of the camera flash lighting energy-saving methods, a design of LED pulse illumination technology which can be synchronous with the camera frame rate is proposed in this paper. This design can provide light pulses with high peak power for the video camera while maintaining low average power and this strobe lighting method is applied to the underwater video camera.Light transmission in the water possesses absorption and scattering properties. Video capture in the depths of the ocean, not only active illuminating source with high optical power needs to be provided, but also the influence of imaging caused by backward scattered light needs to be overcome. In this thesis, taking into account the absorption and scattering properties of the sea and the variant absorption/scattering ratio under different circumstances, the high-power LED pulse-driven lighting and underwater camera are combined to overcome the influence of absorption and scattering under different Situation to achieve the best imaging effect. This article use a image intensified CCD (ICCD) camera to implement video capture. It has a high sensitivity of the imaging and ultra-short shutter exposure time and allows us to use a very small duty ratio (<0.01) pulse to drive the flash LED and make the ICCD shutter opening time is covered with its pulse width. The synchronization between them is achieved by the external trigger interface of ICCD camera:the single-chip microcomputer, controlled by a PC, output two adjustable pulse signals. They own the same frequency, phase and duty ratio and drive the high-power LED and trigger the ICCD camera respectively. Because there is a certain gap of the response time between the LED and ICCD video capture, in the research, a certain delay pulse signal to drive the LED is implemented by hardware or software. Find the optimal delay time through the comparison of the photo image quality in different delay time and make the time of ICCD acquisition optical be strict synchronous with the LED light-emitting pulses.The choice of LED is one of the key links for whether can achieve good electrical-optical conversion efficiency. We studied the transient photoelectric property of different high-power LED from market under pulse driven, including LED luminous efficiency-injection current characteristics and photoelectric response characteristics. By the research, we found most of LED efficiency in the high peak current pulse drive mode is much lower than the constant dc-driven. These LEDs are not suitable as a camera flash. But the devices produced by some of the advanced enterprises in the industry have better efficiency characteristics under high-current and its efficient of high-current is even higher than the small current. Such LED is more suitable as a pulsed light source. We design and produce interrelated drive circuit and establish synchronous underwater imaging system model whose active lighting is100W blue LED. And the research results were verified exhaustively in laboratory conditions. Finally, according to low signal to noise ratio and weak contrast characteristics of underwater video image, related image processing works are studied.