Image Displacement Measurement Based On Joint Transform Optical Correlator

Remote sensing system often suffers from carrier’s unwanted motion disturbances, which may bring in mutual motion between imaging devices and observed objects. During a long exposure time, the image quality may be affected by the motion blur. It is necessary to stabilize the imaging system to improve the resolution of imaging. However the key element in image stabilization is image displacement measurement. Obtaining the motion vector in high speed and high precision during the imaging process,has been the vital point in the high resolution earth observation.Those common digital methods’speed is slow,and cannot satisfy the need of real-time and high accuracy. So in this dissertation, an image displacement measurement technology based on joint transform optical correlator is proposed. Due to its calculation is accomplished by optical lens, it can solve a thousand frames per second under nowadays" spatial light modulator.The theory of image displacement measurement based on joint transform correlator (JTC) is explained.JTC based on amplitude spatial light modulators and phase spatial light modulators is compared. Sub-pixel image displacement measurement is provided. Simulation results show that the measurement error could be within0.1pixel.Image displacement based on joint fractional Fourier transform correlator is also provided.Due to fractional Fourier transform, the optical structure could be more flexible and not fixed at4f system.In order to improve the spatial light modulator’s space utilization and detection precision,image displacement based on double phase-encoded joint transform correlator is given.The technology scatters the DC item into system noises,leaves only one peak in the output plane.The space utilization could improve at least by one time. Combined double phase-encode joint transform correlator with fractional Fourier transform.we get double phase-encoded joint fractional Fourier transform correlator.It posses both advantages of them.The optical structure is more flexible as well as high precision.An image rotation and translation measurement method based on joint transform correlator is proposed in order to extend the application. Also a color image displacement measurement method based on JTC is provided. Thus JTC is extended to measure displacement for color images.JTC could deal with three channels of color images in parallel to accomplish image registration.The robustness of motion detection based on joint transform corrlelator for images lack of exposure is studied in the dissertation. When the image’s signal to noise ratio reaches0dB, fringe-adjust joint transform correlator could measure the displacement precisely. When the exposure time is1/32of normal exposure, double phase-encoded JTC could still measure the displacement between images in precise. In order to improve the robustness of JTC, a wavelet-JTC is proposed.A prototype is built.The experimental results based on amplitude spatial light modulator joint transform correlator are given out.The errors which may bring by every component in the system are analysed.The black-matric-effect is analysed.The errors caused by different resolution of spatial light modulator and capture imaging devices is also discussed.Experimental results show that detection error could be within0.2pixels, root mean square errors (RMSE) could be within0.1pixel. It can solve a thousand frames per second under nowadays spatial light modulator.