为了提高再现像质量，对数字全息常见算法进行了比较研究。根据全息理论和线性系统理论，研究了利用菲涅耳近似法和基于瑞利－索末菲衍射积分的卷积法数值重建离轴无透镜傅里叶变换全息的方法，并做了计算机模拟。结果表明，在记录距离很短的情况下，尽管记录距离不满足通常的菲涅耳近似条件，菲涅耳近似公式仍然成立；自由空间脉冲响应的快速傅里叶变换在不同的记录距离性质不同，由瑞利－索末菲衍射积分利用卷积方法得到的再现像质不理想；对于离轴无透镜傅里叶变换全息显微来说，菲涅耳近似重建方法优于卷积方法。

In order to improve quality of reconstructed images,the common algorithms used to reconstruct digital holograms was studied by means of comparison. According to the theorems of holography and linear system,the reconstructing methods of the off-axis lens-less Fourier transform hologram by Fresnel diffraction formula and by the convolution method based on RayleighSommerfeld diffraction integral were studied through simulation. The results show that Fresnel diffraction formula is still correct within very short recording distance,although the traditional Fresnel approximate condition isn't fulfilled. The characters of the fast Fourier transform of the free space impulse response are different at different distance,so the quality of the reconstructed image by the convolution isn't perfect. For the microscopy by off-axis lensless Fourier transform holography,Fresnel reconstructing method is better than the convolution method.