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Design of adaptive artificial facette eyes, micro-optical fabrication using lithography, characterisation and application

Final Activity Report Summary - MICRO FACETTE EYES (Design of adaptive artificial facette eyes, micro-optical fabrication using lithography, characterisation and application)

Natural compound eyes combine a small eye volume with a large field of view (FOV) at the cost of comparatively low spatial resolution. An artificial compound-eye imaging system has been developed consisting of one planar array of microlenses positioned on a spacing structure and coupled to a commercial CMOS optoelectronic detector array of different pitch, providing different viewing directions for the individual optical channels. Each microlens corresponds to one channel, which can be related to one or more pixels due to the different fill factors of the microlens array and the image sensor. Also alignment problems resulting from the matching of the microlens focal spots and the pixels during the assembly and the possible residual rotation between the artificial compound-eye objective and the pixel matrix are considered. We have developed a program to automatically select the illuminated pixels of the sensor which correspond to each channel in order to form the final image.

This calibration method is based on intensity criterions besides the geometric disposition of the microlens array. An image capture program that uses only the channels selected by the calibration is also written. This program additionally implements image post-processing methods adapted to the microoptical compound-eye sensor. They are applied to the captured images in real time and allow increasing the contrast of the captured images. One of the methods used is the Wiener filter that is computed by taking into account an approximation of the multichannel imaging process of microoptical compound-eye sensors. Experimental results are obtained, which show a noticeable increase in the frequency response when the Wiener filter is used, partially compensating the characteristic low spatial resolution of the artificial compound eyes.

In many vision applications there is interest in obtaining three-dimensional information from the captured scene. There are many different techniques to obtain this kind of information, among them one of the most common techniques is stereovision, which obtain the depth information from the differences between several views of the same scene. This process is the basis of the three dimensional perception of the human vision.

The simplest stereovision system uses only two cameras, which have some overlap in their fields of view in order to extract the depth information from the different position or perspective of the same object captured by each camera.

We have studied the possibility to obtain three-dimensional information using micro compound-eye sensors. Firstly testing a stereovision system using two of these cameras, which have been calibrated and used to obtain disparity maps from the captured scenes. Taking into account the low resolution of the images obtained from these sensors and the noise present in them, we have obtained disparity images of the calibration scenes where de differences of depth are detected.

We have also designed a stereo vision system with uses with two micro compound-eye objectives arranged in only one sensor. The study presents the possibility of making this system taking into account the size of the sensor and the optical requirements of the microlenses arrays and considering that they are to be coupled in a parallel stereo configuration. Also an analysis of the behaviour between channels has been done to avoid the ghost images. The study shows the viability of having a micro stereovision system based on two coupled micro compound-eye objectives to obtain three-dimensional information.