Optimized and Quality Improved Incoherent Optical Fiber Bundle Calibration Method for Image Transmission

Artificial vision, in spite of all theoretical and practical progress accomplished during last thirty years, still cannot be employed technically in some hazardous and strong industrial areas, where conditions are such that cameras would not operate properly. Alternatives on such problem are the quite recent IP65 and IP67 industrial cameras, and associated connectors, protected by an anticorrosive, waterproof, and high temperatures resistive carcass employing a dedicated electronic, in addition robust to almost 3G accelerations. Nevertheless, such cameras are still very expensive compared to conventional industrial cameras and would still not be enough in hardest conditions (explosive gas or dust environment) or in electromagnetic interferences environments. A good alternative in extreme conditions is the use of optical fiber bundle. Since such cable only transmits light, they intrinsically have electromagnetic interferences immunity and depending on the fiber material could be exposed to very high temperature (over 1000oC for sapphire fibers for example), could be employed in almost all corrosive environment, and are totally submersible. Nevertheless, the coherent optical fiber bundles are very expensive, and for large distances could be non-competitive facing the other hardware solutions. Thus, the best suitable option to develop a competitive system in those particular cases is the use of incoherent optical fiber bundle (IOFB), nowadays just employed for illumination tasks. Image transmission in this case is not direct but require a calibration step that we discuss in this paper. We propose in this work on a new calibration method of incoherent optical fiber bundle (IOFB) for image transmission purpose. First, we present the calibration method (an enhancement of previously published calibration methods), some resulting reconstructed images and a discussion on its quality improvement employing simple denoising methods. We finally depict the two new post calibration methods that efficiently refine the reconstruction Look Up Table (LUT) used for the output image reconstruction. Those two post calibration method are: correction of the input plan chromatics aberrations, and extraction of a unique pixel (almost centered) for each fibers. Key-Words: image transmission, incoherent optical fiber bundle, hazardous environment, calibration