A Study Of Digital Image Encrypting Fulfiled By Optical Computer-generated Hologram

Computer-generated hologram is to imitate optical hologram by a computer. One characteristic of the computer-generated hologram is that only one diagram is needed to synchronously record both the amplitude and the phase of the encrypting image,and it does not use coherent light and preventing vibration platform. In this thesis we chiefly study the computer-generated hologram of an optical system to carry out digital image encrypting. Its main contents and innovations summarized as follows:This thesis analyzes the image encryption technology research background and research state at home and abroad, Raised by increasing the number of key images to enhance image of the concept of system security. Designed a new optical system image encryption method: First a digital image mixed with a random phase mask undergoes a fractional Fourier transformation under the plane-wave irradiation. Then we add another random phase mask to the latter plane of the fractional Fourier transformation and the latter plane passes a Fresnel diffraction process. The Fresnel diffraction field and the reference light field interfere to form a hologram;Using a fractional Fourier Transformation and a Fresnel diffraction, the fractional Fourier transform of the parameters as a digital image of the key generation holographic, Generated hologram image can not be directly identified, achieved the encryption effect, the whole process from Matlab program to simulate the implementation. Because the key number of the encrypting method is increased compared within the single encrypting process such as a Fresnel diffraction or a fractional Fourier transformation encrypting process, the safety of the encrypting is greatly improved. Throughout the analysis , we use a fast Fourier transformation of a weighted function to calculate a Fresnel diffraction and a fractional Fourier transformation, therefore, the calculating speed is high.Finally,I summarized the thesis and prospected.the calculation of the optical system applied to digital holographic image encryption technology reaearch.