Abstract
Demonstrated is the code division multiple access (CDMA)-mode coded access optical sensor (CAOS) smart camera suited for bright target scenarios. Deploying a silicon CMOS sensor and a silicon point detector within a digital micro-mirror device (DMD)-based spatially isolating hybrid camera design, this smart imager first engages the DMD starring mode with a controlled factor of 200 high optical attenuation of the scene irradiance to provide a classic unsaturated CMOS sensor-based image for target intelligence gathering. Next, this CMOS sensor provided image data is used to acquire a focused zone more robust un-attenuated true target image using the time-modulated CDMA-mode of the CAOS camera. Using four different bright light test target scenes, successfully demonstrated is a proof-of-concept visible band CAOS smart camera operating in the CDMA-mode using up-to 4096 bits length Walsh design CAOS pixel codes with a maximum 10 KHz code bit rate giving a 0.4096 seconds CAOS frame acquisition time. A 16-bit analog-to-digital converter (ADC) with time domain correlation digital signal processing (DSP) generates the CDMA-mode images with a 3600 CAOS pixel count and a best spatial resolution of one micro-mirror square pixel size of 13.68 μm side. The CDMA-mode of the CAOS smart camera is suited for applications where robust high dynamic range (DR) imaging is needed for un-attenuated un-spoiled bright light spectrally diverse targets.
Highlights
There are several real world scenarios such as automotive sensing, industrial machine vision and surveillance where one engages bright light targets within scenes having extreme image contrasts
Introduced is a new variant of the point-PD based imager called the coded access optical sensor (CAOS) smart camera [8]. This collaborative camera design engages the digital micro-mirror device (DMD), the point PD, and a prior-art Complementary Metal Oxide Semiconductor (CMOS)/Charge Coupled Device (CCD)/Focal Plane Array (FPA) sensor combined with image processing methods, all working in unison to enable target extraction using Radio Frequency (RF) wireless inspired space-time-frequency coding and processing techniques for the imaged light
Designed and demonstrated is the code division multiple access (CDMA)-mode CAOS smart camera that combines the conventional Photodetector Array (PDA) sensor (e.g., CMOS sensor) with time-frequency agile CAOS pixels operating in the CDMA-mode
Summary
There are several real world scenarios such as automotive sensing, industrial machine vision and surveillance (e.g., night vision) where one engages bright light targets within scenes having extreme image contrasts. Note that the temporal correlation operation implemented to recover the jth CAOS pixel irradiance I j using a decoding real-value signal code cj (t) and the CAOS smart camera point PD real value photo-current iPD(t) is given by:. Using the important condition in Eq (1) that temporal codes deployed for CAOS CDMAmode have ideally zero cross-correlation values, one can write the decoded jth CAOS pixel scaled irradiance I′j as:. By performing P independent time domain correlation operations with the P different decoding signals, all scaled irradiances of the observed CDMA-mode CAOS camera seen image can be recovered to produce the CAOS frame image. Equation (15) using j = 1,2,...,P, indicates that all P simultaneous CDMA-mode CAOS pixel scaled irradiances are recovered using the described design theory when using ideal Walsh function-based orthogonal binary code sequences. To achieve a faster CAOS frame time, NTb product and DSP time should be reduced using faster DMDs and DSP electronics as well as the minimum N (and P) values for sufficient target of interest recovery from an observed scene
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