High-quality and high-efficiency hologram generation method based on complex amplitude constraint algorithm

Abstract

The invention provides a high-quality and high-efficiency hologram generation method based on a complex amplitude constraint algorithm. The method comprises the following three steps of: 1, performing hierarchical processing on a three-dimensional scene based on an intensity image and a depth image of the three-dimensional scene to obtain a group of hierarchical images; 2, performing reverse wavefront propagation calculation on the layered image to generate an initial complex amplitude field on a hologram plane; and then wavefront propagation calculation is carried out on the initial complex amplitude field on the hologram plane to generate a target complex amplitude field on the target plane. 3, initializing the hologram by using the initial complex amplitude field on the hologram plane, and carrying out wavefront propagation calculation on the hologram to generate a reconstructed complex amplitude field of the hologram on the target plane; and performing complex amplitude constraint on the reconstructed complex amplitude field by using the target complex amplitude field on the target plane, and finally generating a high-quality hologram by iteratively optimizing the reconstructed complex amplitude field.

Description

1. Technical Field

[0001] The present invention relates to holographic display technology, and more specifically, to a high-quality and efficient hologram generation method based on a complex amplitude constraint algorithm. 2. Background Technology

[0002] Computer-generated holographic display technology can realistically reconstruct three-dimensional scenes and provide viewers with a comfortable visual experience, so it has attracted widespread attention. However, it is still challenging to achieve an ideal holographic display, which mainly lies in the wavefront propagation process from the three-dimensional scene to the hologram plane, and the phase encoding process from the complex amplitude distribution on the hologram plane to the pure phase hologram. These two processes jointly determine the calculation time of the hologram and the image quality of the holographic reconstruction. In recent years, iterative algorithms have been widely used in the calculation of pure phase holograms. However, most of the existing iterative algorithms neither consider the connection between the two processes of wavefront propagation and phase encoding, nor fully consider the important role and influence of phase information in hologram generation, resulting in poor image quality of holographic reconstruction. In addition, although iterative algorithms can also be used to calculate holograms of three-dimensional scenes, the calculation time of existing algorithms is affected by the complexity of the three-dimensional scene, and the calculation time is too long when processing complex three-dimensional scenes. Therefore, how to reduce the calculation time of holograms and improve the quality of holographic reconstruction, that is, to efficiently generate high-quality pure phase holograms, is an urgent problem to be solved in the field of holographic display. III. Summary of the invention

[0003] The present invention proposes a high-quality and efficient hologram generation method based on a complex amplitude constraint algorithm. Figure 1 As shown, the method of the present invention includes three steps: the first step is to perform layered processing on the three-dimensional scene based on the intensity map and depth map of the three-dimensional scene to obtain a set of layered images. The second step is to perform inverse wavefront propagation calculation on the layered images to generate the initial complex amplitude field on the hologram plane; then the initial complex amplitude field on the hologram plane is subjected to wavefront propagation calculation to generate the target complex amplitude field on the target plane. The third step is to initialize the hologram using the initial complex amplitude field on the hologram plane, and perform wavefront propagation calculation on the hologram to generate the reconstructed complex amplitude field of the hologram on the target plane; then the target complex amplitude field on the target plane is used to perform complex amplitude constraints on the reconstructed complex amplitude field, and the reconstructed complex amplitude field is iteratively optimized to finally generate a high-quality hologram. The present invention reconstructs the complex amplitude field on the target plane based on the complex amplitude constraint, which helps to restore all the wavefront information of the three-dimensional scene, thereby improving the quality of holographic reconstruction. In each iteration, only two wavefront propagation calculations are completed, and the number of calculations is independent of the number of layers of the three-dimensional scene, thereby greatly improving the computational efficiency of complex three-dimensional scene holograms.

[0004] In step 1, the intensity map of the 3D scene is a color image with three channels of red, green and blue, and the depth map of the 3D scene is a single-channel grayscale image. According to the different depth distributions of different parts of the 3D scene, the intensity map of the 3D scene is divided into a group of layered images at different depths, where scenes with the same depth range are located in the same layered image.

[0005] In step 2, the distance between each layered image and the hologram plane is different, and the wavefront propagation method considering occlusion is used to generate the target complex amplitude field on the target plane. Specifically, a binary mask is first generated for each layered image, in which the pixel value corresponding to the non-zero area of ​​the layered image is 0, and the pixel value of the remaining area is 1. Then, the inverse wavefront propagation is performed on the layered image of the first layer to obtain its complex amplitude distribution at the position of the layered image of the second layer, and the complex amplitude distribution is multiplied by the mask of the second layer to obtain the complex amplitude distribution after being occluded by the second layer. Next, the complex amplitude distribution after occlusion is added to the layered image of the second layer, and the inverse wavefront propagation is continued to obtain its complex amplitude distribution at the position of the layered image of the third layer. Repeat the above process of occlusion using a binary mask and wavefront propagation layer by layer until the inverse wavefront propagation calculation of all layers is completed to obtain the initial complex amplitude field on the hologram plane. Finally, the wavefront propagation calculation is performed on the initial complex amplitude field on the hologram plane to obtain the target complex amplitude field on the target plane. Preferably, the wavefront propagation method in the present invention is an angular spectrum method.

[0006] In step 3, the phase of the initial complex amplitude field on the hologram plane is first taken to initialize the hologram, and the phase distribution range of the initialized hologram is [0,2π]. Secondly, the complex amplitude field reconstructed on the target plane of the initialized hologram is obtained through wavefront propagation. In particular, the target plane can be divided into a signal area and a noise area, where the size of the signal area is controlled by the shear factor c:

[0007] p signal =(p hologram -p image ) / c+p image (1)

[0008] Among them, p signal , p image and p hologram Represent the number of pixels in the signal area, image area and the entire hologram area respectively. Then, the target complex amplitude field generated in step 2 is used to constrain the reconstructed complex amplitude field. The complex amplitude constraint algorithm is expressed as:

[0009]

[0010] Among them, U (n+1) and U (n)denote the complex amplitude field reconstructed on the target plane in the (n+1)th and nth iterations, n>1, A t and They represent the amplitude and phase of the target complex amplitude field respectively, signal region is the signal region, and free region is the noise region. w is the weight of the complex amplitude constraint, which is expressed as:

[0011] w=exp(A t -A (n) ] (3)

[0012] Among them, A (n) Represents the amplitude on the target plane at the nth iteration.

[0013] After completing a single complex amplitude constraint, the complex amplitude field reconstructed on the target plane is subjected to reverse wavefront propagation to obtain the complex amplitude field on the hologram plane, and then only the phase of the complex amplitude field is retained as the newly generated hologram. Finally, the above wavefront propagation and complex amplitude constraint process is repeated between the hologram plane and the target plane until the iteration is completed and the final hologram is generated. IV. Description of the drawings

[0014] Attached Figure 1 This is a flow chart of a high-quality and efficient hologram generation method based on a complex amplitude constraint algorithm of the present invention.

[0015] Attached Figure 2 A comparison chart of the amplitude results of holographic reconstruction using the method of the present invention and the traditional amplitude constraint method.

[0016] Attached Figure 3 A comparison diagram of the phase results of holographic reconstruction using the method of the present invention and the traditional amplitude constraint method.

[0017] Attached Figure 4 This is a comparison chart of the holographic reconstruction quality of the method of the present invention and the traditional amplitude constraint method as a function of calculation time.

[0018] Attached Figure 5 It is a comparison diagram of the calculation time of the method of the present invention and the traditional amplitude constraint method as the number of three-dimensional scene layers changes. V. Specific implementation methods

[0019] The following is a detailed description of an embodiment of a high-quality and efficient hologram generation method based on a complex amplitude constraint algorithm proposed by the present invention, and further describes the present invention. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Personnel skilled in the art in this field may make some non-essential improvements and adjustments to the present invention based on the above invention content, which still fall within the scope of protection of the present invention.

[0020] The embodiment of the present invention is as follows: a spatial light modulator with a resolution of 1920×1080 and a pixel pitch of 4.5μm is used to load a hologram. Color lasers with wavelengths of 638nm, 520nm and 450nm are used as coherent light sources. The emitted lasers are collimated and irradiated onto the spatial light modulator, and color holographic display is achieved through time division multiplexing. A three-dimensional scene with a resolution of 1300×730 is used as the target scene. The three-dimensional scene is divided into 256 layers based on its intensity map and depth map, and the depth interval between each layer is 0.02mm. Wavefront propagation is performed by the angular spectrum method, and the distance between the hologram plane and the target plane is 8cm. The shear factor c that controls the size of the signal area on the target plane is set to 8.

[0021] The amplitude of the holographic reconstruction based on the above embodiment is shown in the attached figure. Figure 2 As shown, Figure 2 (a) and (b) are the reconstruction results of the traditional amplitude constraint method focusing on the foreground and background of the 3D scene, respectively. Figure 2 (c) and 2(d) are the reconstruction results of the method of the present invention focusing on the foreground and background of the three-dimensional scene. Figure 2 The peak signal-to-noise ratio of each reconstruction result is indicated in the figure. The peak signal-to-noise ratio of the amplitude of the holographic reconstruction of the method of the present invention reaches 21.96dB, which is about 62% higher than the 13.55dB of the traditional method. The phase of the holographic reconstruction based on the above embodiment is shown in the attached figure. Figure 3 As shown, Figure 3 (a) and (b) are the phases reconstructed in the target plane by the conventional method and the method of the present invention, respectively. Compared with the conventional method, the peak signal-to-noise ratio of the phase reconstructed by the method of the present invention is improved by about 60%. The comparison of the peak signal-to-noise ratio of the reconstructed amplitude of the method of the present invention and the conventional method based on the above embodiment with the number of iterations is shown in the attached figure. Figure 4 The results show that the proposed method has a faster convergence speed and achieves higher image quality with fewer iterations.

[0022] Based on the above embodiments, the comparison of the calculation time of the method of the present invention and the traditional method with the change of the number of layers is shown in the attached figure. Figure 5 As shown in the figure. The computation time required by the traditional method increases exponentially with the number of layers, while the phase encoding time required by the present method is independent of the number of layers, and the time increase mainly comes from the wavefront propagation process. When the number of layers is 256, the time required by the traditional method is 11626s, and the time required by the present method is 317s, and the computation time is reduced by about 97%. This result shows the high efficiency of the present method in terms of computation time.

Claims

1. A high-quality and efficient hologram generation method based on a complex amplitude constraint algorithm, characterized in that: The method comprises the following three steps: first, layering the three-dimensional scene based on the intensity map and the depth map of the three-dimensional scene to obtain a set of layered images; In the second step, the layered image is subjected to inverse wavefront propagation calculation to generate an initial complex amplitude field on the hologram plane; then the initial complex amplitude field on the hologram plane is subjected to wavefront propagation calculation to generate a target complex amplitude field on the target plane; The third step is to initialize the hologram using the initial complex amplitude field on the hologram plane, and perform wavefront propagation calculation on the hologram to generate a reconstructed complex amplitude field of the hologram on the target plane; then, the target complex amplitude field on the target plane is used to perform complex amplitude constraints on the reconstructed complex amplitude field, and the reconstructed complex amplitude field is iteratively optimized to finally generate a high-quality hologram.

2. According to claim 1, a high-quality and efficient hologram generation method based on a complex amplitude constraint algorithm is characterized in that: In step one, the intensity map of the three-dimensional scene is a color image with three channels of red, green and blue, and the depth map of the three-dimensional scene is a single-channel grayscale image. According to the different depth distributions of different parts of the three-dimensional scene, the intensity map of the three-dimensional scene is divided into a group of layered images at different depths, where scenes with the same depth range are located in the same layered image.

3. The high-quality and efficient hologram generation method based on the complex amplitude constraint algorithm according to claim 1 is characterized in that: In step 2, a wavefront propagation method considering occlusion is used to generate a target complex amplitude distribution on the target plane. First, a binary mask is generated for each layered image, wherein the pixel value corresponding to the non-zero area of ​​the layered image is 0, and the pixel value of the remaining area is 1. Then, reverse wavefront propagation is performed on the layered image of the first layer to obtain its complex amplitude distribution at the position of the second layer, and the complex amplitude distribution is multiplied by the mask of the second layer to obtain the complex amplitude distribution after being occluded by the second layer. Next, the complex amplitude distribution after occlusion is added to the layered image of the second layer, and reverse wavefront propagation is continued to obtain its complex amplitude distribution at the position of the third layer. The above process of occlusion using a binary mask and layer-by-layer wavefront propagation is repeated until the reverse wavefront propagation calculation of all layers is completed to obtain the initial complex amplitude field on the hologram plane. Finally, wavefront propagation calculation is performed on the initial complex amplitude field on the hologram plane to obtain the target complex amplitude field on the target plane.

4. The high-quality and efficient hologram generation method based on the complex amplitude constraint algorithm according to claim 1 is characterized in that: In step 3, the phase of the initial complex amplitude field on the hologram plane is first taken to initialize the hologram. The phase distribution range of the initialized hologram is [0, 2π]. Secondly, the complex amplitude field reconstructed by the initialized hologram on the target plane is obtained through wavefront propagation. In particular, the target plane is divided into a signal area and a noise area, where the size of the signal area is controlled by the shear factor c: p signal =(p hologram -p image ) / c+p image Among them, p signal , p image and p hologram Represent the number of pixels in the signal area, image area and the entire hologram area respectively. Then, the target complex amplitude field generated in step 2 is used to perform complex amplitude constraints on the reconstructed complex amplitude field. The complex amplitude constraint algorithm is expressed as: Among them, U (n+1) and U (n) denote the complex amplitude field reconstructed on the target plane in the (n+1)th and nth iterations, respectively, A t and They represent the amplitude and phase of the target complex amplitude field respectively, signal region is the signal area, free region is the noise area, and w is the weight of the complex amplitude constraint, which is expressed as: w=exp[A t -A (n) ] Where A(n) represents the amplitude on the target plane at the nth iteration; After completing a single complex amplitude constraint, the complex amplitude field reconstructed on the target plane is subjected to reverse wavefront propagation to obtain the complex amplitude field on the hologram plane, and then only the phase of the complex amplitude field is retained as the newly generated hologram. Finally, the above wavefront propagation and complex amplitude constraint process is repeated between the hologram plane and the target plane until the iteration is completed and the final hologram is generated.

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