CMOS Image Sensors with Multi-bucket Pixels for Computational Photography
Author: Chung Chun Wan
Publisher:
Published: 2011
Total Pages:
ISBN-13:
DOWNLOAD EBOOKWhen applied to multi-image computational photography such as flash/no-flash imaging, multiple exposure high dynamic range imaging, multi-flash imaging for depth edge detection, color imaging using active illumination, and flash matting, an image sensor that can capture multiple time-interleaved images would provide a dramatic advantage over capturing and combining a burst of images having different camera settings. In particular, this interleaving eliminates the need to align the frames after capture. Moreover, all frames have the same handshake or object motion blur, and moving objects are in the same position in all frames. A sensor with multi-bucket analog memories in each pixel can accomplish this task. Whereas frames are acquired sequentially in a conventional sensor, in a multi-bucket sensor photo-generated charges in a photodiode can be transferred and accumulated in the in-pixel memories in any chosen time sequence during an exposure so multiple frames can be acquired virtually simultaneously. Designing a multi-bucket pixel which is compact and scalable is challenging because space is required to accommodate the additional in-pixel memories and their associated control signal lines. This research explored and developed a new multi-bucket pixel technology by adapting the concept of virtual phase charge-coupled device into a standard 4-transistor CMOS pixel such that area overhead is small and true correlated double sampling is preserved to cancel kTC noise. Based on the developed pixel technology, two prototype CMOS image sensors with dual and quad-bucket pixels were designed and fabricated. Pixel sizes are the smallest among similar pixels reported in the literature. Some computational photography applications were implemented using the two multi-bucket sensors to demonstrate their values in avoiding artifacts that would otherwise occur when a conventional sensor is used.