Research On The Vignetting Correction Method Of Mosaic Images Based On Relfector

With the need of high ground resolution and large ground cover in remotecarema system, monolithic image sensors are not large enough to achieve therequirement. Also because the manufacture technics of large area Charge CoupledDevice(CCD) are more complex and more cost, CCD mosaic technics have beenproposed to meet the requirement in the large field of view(FOV). In this paperseveral mosaic methods are analyzed and compared. To avoid their drawbacks themethod based on reflectors is proposed because of its advantages in higher energyefficiency, longer splice length, no-abberation, et al.In the paper, the reflector to be used is commonly and suits to extend, so it has abroad application prospect. However there is vignetting phenomenon in the mosaicsystem based on reflectors which will be discussed and disposed. The primarycoverage of this paper is as follows:First, from geometrical optics and physical optics, we analysed the generationmechanism of the vignetting phenomenon, and proposed the vignetting distributionmodel in the middle of the optical field separately. An equivalent optical model basedon muti-configuration technique is set up in ZEMAX for the analysis in the system'soptical characteristics. The system's Point Spread Function(PSF) and ModulationTransfer Function(MTF) are calculated through dynamic data exchange and opticaltrail methods to analyze the causation of the vignetting phenomenon. Second, in order to prove the feasibility of the vignetting correction methods andunderstand the technology difficulties in the design, a prototype camera using thereflector mosaic structure was built which has two area CCD. We analyzed theinterline transfer area CCD KAI-2093's working principle in detail to put forward anappropriate driving and high speed image collection scheme. we use cache in FPGAand RAM working in ping-pang mode in order to realize signal's integrality and realtime working mode,. An auto-exposure algorithm was designed to compensate thecamera's exposure parameters which takes advantage of the large brightness contrastamong different elements in the image, dynamically distinguishes the main object andthe background. All of the above are prepared for the vignetting corrections.Third,the methods based on the theory, the radiate calibration and the degeneratemodel are proposed in this paper, separately. The theory correction method is based onthe optical model gained in Chapter Three, which compensates the pixel's grey valueaccording to the compensation factors achieved by dividing the image plane. But thismethod does not consider the impact of electronics, so it only has sense in thetheoretical analysis. The second method uses the data from the radiate calibration, sothe compensation factors are more accurate but not flexible. So in order to make upthe limitation, after the analysis of the actual image's grey distribution, the degeneratemodel method is proposed to compensate the vignetting image, which uses thesteepest descent method to get the parameters.Fourth, in the end we use the image registration and mosaic algorithm to correctthe vignetting image. The output mode is turned to single, and the scheme uses theHarris operator to pick up the feature points, the NCC function to rough match, thetwo-way matching method for further purification, and finally the RANSACalgorithm to remove all the wrong matching points to obtain the transformation model.The segment weighted average method and the method based on gradient arecombined to process the overlap area to ultimately get the uniform brightness image.