全息图再现过程中, 由于占据了大部分能量的零级亮斑的存在, 降低了再现像的对比度, 影响了对原始物的观察和记录, 因此需要将其进行消除, 使有用的再现像变得清晰。文章对五种常用的消除零级像的方法进行了介绍和理论分析, 将其应用到计算全息中, 分别做了数字再现的模拟仿真实验, 并利用两种常用的再现像质量评价标准对消零级效果进行了比较。研究结果表明, 所介绍的消零级方法都能够比较有效地消除零级亮斑, 提高再现像的对比度。由再现像质量评价标准综合对比得出, 频谱滤波消除零级像亮斑得到的效果最好, 但这与人眼的直观感受不一致。在对评价方法优缺点及零级像频谱分析的基础上, 提出了一种基于中心亮斑衰减率的再现像质量局部判别法, 并进行了实验验证。实验结果表明, 该方法能够得到与人眼直接观察数字和光学再现像一致的结果, 因此可以认为是有效的。

During the reconstruction of holograms, the presence of the zero-order diffraction image which occupies the majority of energy reduces the contrast of the reproduced image, and affects the observation and recording of the original object. So to make the useful reconstructed image clear, it needs to be eliminated. In this paper, it is given an introduction and theoretical analysis of five measures commonly used for eliminating the zero-order diffraction image. We applied them in computer-generated hologram (CGH), and composed numerical reproduction simulations respectively. Then two common objective evaluation criteria were used to compare and judge the effectiveness of those measures. The results show that all the measures can effectively eliminate the bright spots caused by zero-order image; meanwhile the original images or conjugate images are preserved completely. The contrast of the reproduced images is improved. After general comparison, it is found that the measure of frequency filtering can get the best effect, but it does not jibe with humans intuitive perception. Based on the analysis of the advantages and disadvantages of these two methods and the frequency spectrum of zero-order image, it is proposed a new local method grounded on the attenuation rate of the central bright spot to evaluate the quality of reproduced image, and experiments were conducted to testify the method. The experimental results show that, according to this new method, a result is obtained to be consistent with the intuitive feel through human eyes looking at images directly, and thus it can be considered to be effective.