Research On The Quality Of Reconstructed Image And Applications Of Digital Holography

In digital holography, the holographic information is directly recorded on a charge-coupled device(CCD,CMOS)camera and the optical reconstruction is replaced by a computer numerical reconstruction, so the holographic full process including recording, memory and reconstruction is entirely digital. With the rapid developments of the megapixel CCD sensors and the computers, digital holography have recently became feasible and have been used in many fields, such as 3-D profilometry, grain size analysis, holographic microscopy, information security etc. The purpose of this research is to discuss the principle of hologram recording and numerical reconstruction in detail, research the methods of improving the quality of reconstruction image, analyzing the application of digital holography in digital watermark and 3-D profilometry.Based on theoretic analysis, computer simulation and optical experiment, this paper focus on the following aspects mostly:(1) The digital image processing methods such as spatial differential operator processing, spectrum filtering, mean value of hologram subtraction and reference and object beams value subtraction are introduced. Then prove and comparision about their effects on filtering the zero-order diffraction and conjugate images is carried out. The research shows the quality of reconstruction image is also infiuenced by speckle noise.The method is proposed using multiple images superposition to suppress speckle noise. When the number of pixel is not equal in the direction of horizontal and vertical,the reconstruction images will distort.We correct the distortion.(2) Three auto-focus algorithms of digital imaging process are compared and analyzed. And these three algorithms are gray variance method, gray entropy method and the Fourier spectrum method. The Fourier spectrum method has the good sharpness.(3) By means of the research on the recording condition of digital holography, the main factors that influence the resolution of reconstructed images are definite. Begin with these factors, synthetic aperture digital holography based on image matching technology and in-line phase shifting digital holography has been proposed. The experimental results prove that synthetic aperture technology is all effective means to overcome the problem of CCD, it is not only able to record large.sized objects,but also can significantly improve the resolution of the reconstructed digital holographic images.(4)The application of digital holography in digital watermark and 3-D profilometry has been investigated. The digital watermark technique is proposed based on Fresnel hologram and discrete cosine transform (DCT). The algorithm has high security and practical .The method based tomography to rebuild the 3-D objects has been researched, and it only need the information of intensify.(5)The program of digital holography has been developed with matlab .It can be used to preprocess the digital hologram, reconstruct the image, filter phase image, unwrap the phase and measure the surface shape etc.