Study On The Image Edge Enhancement Technology Using A Spiral Phase Filter In Spatial Frequency Domain

The image edge enhancement is an important application of optical information processing. In the methods of image edge enhancement, the usual one is processing of image spatial frequency, for example the dark ground method. The spiral phase plate is an optical element that produces sequential phase delay azimuthally. It is usually used in generation and detection of vortex beams. The spiral phase plate can be applied to the image in spatial frequency domain, realizing image energy redistribution with less loss, and enhancing image edge with higher spatial frequency. This technology is so-called image edge enhancement technology using a spiral phase filter in spatial frequency domain. One application of this technology is image edge enhancement for amplitude or phase objects in the microscope, which overcomes the limit on observing pure phase object of the ordinary microscope. The microscopic imaging method with a spiral phase filter has potential applications in biomedicine, judicial examination, micro-electronics industry and other fields. This method has certain advantages relative to other methods, but the details needs further study. This work mainly studies the theoretical analysis, numerical simulation and experimental verification of image edge enhancement using spiral phase filter in spatial frequency domain.The main works are list below.1. Several methods of making spiral phase filter are introduced, and their advantages and disadvantages are given in this work. The computer generated hologram method is applied to make the fork-like amplitude gratings here, which can embed a spiral phase on the spatial frequency domain of the image. In addition, the principle and simulation of producing spiral beam with the amplitude fork-like grating are explained in details.2. The principle of radial Hilbert transform in 4f optical system with spiral phase filter is analyzed here, and the isotropic edge enhancement is explained theoretically. The size of spiral phase filter and the focal length of lens in 4f system are found to be influent to imaging theoretically. Further more, image isotropic edge enhancement with the fork-like amplitude grating is also explained theoretically. It shows that only the plus or minus first diffraction orders is effective in realization of image enhancement. In addition, isotropic edge enhancement of amplitude and phase object in microscopy with the fork-like amplitude grating is verified experimentally, and image contrast and resolution are greatly improved.3. Two methods for realizing relief-like shadow effect with spiral phase filter, i.e. setting the center phase value of the spiral phase filter and minute shift of the spiral phase filter, are analyzed theoretically and verified numerically. Moreover, the relief-like shadow effect by minute shift of the spiral phase filter is also demonstrated experimentally.