| Real scenes produce a wide range of brightness variations, while the dynamic range of the typical solid-state image sensor is much lower—about 60 to 70 dB for CCDs and 70 to 80 dB for CMOS Active Pixel Sensors (APS). This results in low quality images where details in the scene are concealed in shadows or washed out by bright lights. In this research, a new visible image sensor with 108 dB intrascene dynamic range is proposed, designed and tested. We introduce a new sensor architecture that can capture four linear response images with different sensitivities simultaneously. This technique eliminates the need for devices with logarithmic response, which reduce the image contrast, and avoids taking several sequential images at different exposures, which introduces motion blur to the final image. This research also proposes a real time fusion and dynamic range compression algorithm which generates a high dynamic range image from the four images of different sensitivity, compresses the composite image's dynamic range to match that of a normal display unit, and displays it at video rate.; The high dynamic range image sensor is fabricated using a 0.5 μm standard CMOS process, with a photogate pixel. This pixel has two collection areas with different light sensitivities. The two signal outputs from each pixel are multiplied by two different gains, producing four images of different sensitivity simultaneously. Four flash ADCs are implemented on chip to digitize the four images. The pixel array is 352 x 288 CIF size. The sensor runs at a maximum frame rate of 60 Hz.; The high dynamic range image is reconstructed by aggregating the four images of different sensitivity. The histogram of the combined image is then calculated and dynamically modified to achieve dynamic range compression. The algorithm is implemented on an FPGA, which interfaces with the image sensor chip to demonstrate a high dynamic range imaging system at 60 frames/second.; This work simplifies the design of the high dynamic range imaging system, and can be used in many automotive, security and military applications. |
