In order to acquire images of specified bands with high-speed, high time resolution and high spatial resolution, a prototype of the observation system utilizing sequentially controlled LED illumination is developed. As a performance validation of this prototype, the human skin extraction based on Normalized Difference Human Index (NDHI) is attempted. An illumination unit consists of LEDs with 1070nm and 1550nm wavelengths of light. An infrared vidicon camera with high-sensitivity over the range of 400nm to 1700nm wavelengths is installed as an imaging equipment. Light intensities of the LEDs are sequentially controlled by a pulse width modulation (PWM) driver. An improvement method for response delay in the infrared vidicon camera is evaluated by the experiment based on the prototype. Finally, two image-lag elimination methods utilizing series of intensity modulated pulses for LED illuminations are proposed. The effectiveness of the proposed methods is confirmed by simulation results of the estimation of the attenuation coefficient and the true intensities after eliminating the after-image effect.
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