Holo Flash Projector App Apk Download
Ji Weinheimer
Using a projector, our DVDs bring spine-tingling scenes to life both indoors and outdoors on any surface. With our projection screen material, it seems like these creepy apparitions are materializing from thin air. It's the realism and creepiness that make our scenes unforgettable.
In this paper, we propose a holographic capture and projection system of real objects based on tunable zoom lenses. Different from the traditional holographic system, a liquid lens-based zoom camera and a digital conical lens are used as key parts to reach the functions of holographic capture and projection, respectively. The zoom camera is produced by combing liquid lenses and solid lenses, which has the advantages of fast response and light weight. By electrically controlling the curvature of the liquid-liquid surface, the focal length of the zoom camera can be changed easily. As another tunable zoom lens, the digital conical lens has a large focal depth and the optical property is perfectly used in the holographic system for adaptive projection, especially for multilayer imaging. By loading the phase of the conical lens on the spatial light modulator, the reconstructed image can be projected with large depths. With the proposed system, holographic zoom capture and color reproduction of real objects can be achieved based on a simple structure. Experimental results verify the feasibility of the proposed system. The proposed system is expected to be applied to micro-projection and three-dimensional display technology.
It is difficult to acquire the image source in real time. For the imaging capture process, in order to realize high quality holographic projection effect, we hope to reproduce real or virtual objects with full color and ideal size. In the process of image acquisition, virtual objects can be obtained by modeling, and real objects are usually captured by a CCD camera [8]. The traditional zoom camera is achieved by changing the distances between the solid lenses [9], so that detailed information of the image can be captured. But the bulky size is inconvenient to be designed for micro projectors. To acquire a 3D object, multiple cameras are required for shooting [10, 11]. Therefore, the current cameras are difficult to meet the needs of real-time acquisition for different scenes [12].
The size of reproduced image is relatively small. For the holographic reconstruction process, a solid lens is usually used to implement the Fourier transform [13]. When the position of the receiving screen changes, the image becomes unclear. Therefore, it is necessary to change the position and size of the reproduced image by adjusting the position or focal length of the solid lens [14, 15]. Some researchers used scaled Fresnel diffraction to realize zoomable holographic projection [16]. Liquid crystal lens has also been used in the holographic system to adjust the size of the reproduction [17]. However, the size of the liquid crystal lens is small and the aberration exists, so it is difficult to achieve color reproduction.
On the other hand, the chromatic aberration in the system also affects the effect of holographic projection. Color reproduction method based on time-division multiplexing is to load red, green and blue holograms in turns onto the same SLM [18, 19]. This method requires the switching time of the light source and the hologram to be strictly consistent. Color reproduction method based on spatial multiplexing is to divide an SLM into three parts or using three SLMs. When three color light beams are used to illuminate the corresponding regions, color reconstructed image can be seen due to the accurate coincidence in space [20, 21]. Some researchers put forward the methods of frequency shift and image shift to realize the perfect coincidence of color image [22]. However, the system uses a 4f lens and the size of the reproduction cannot be changed. At present, in order to achieve color zoom projection without chromatic aberration, the system is usually more complex. In addition, these holographic zoom systems currently reproduce virtual objects. If the real scene is acquired, the system will be even larger.
Adaptive liquid lenses have been studied recent years due to the unique advantages of large focal length tuning, fast response, and light weight [23,24,25,26]. In 2014, two liquid lenses were produced and used together with a digital lens, then the holographic projection system with an optical zoom function can be realized [27]. In 2018, an optical see-through head mounted display was proposed by using a liquid lens [28]. Although the liquid lens can change the size and position of the reproduced image adaptively, the depth of the reproduced image is constant. When the receiving screen is moved away from the focal plane, the reconstructed image becomes blurred.
In order to solve the above problems, in this paper, we propose a holographic capture and projection system of real objects based on adaptive lenses. Different from the traditional holographic system, a tunable zoom camera is produced based on liquid lenses in order to capture the real objects. The liquid lens is electrically driven, so the zoom camera has a fast response speed. Real objects can be captured and the detail part can be optically magnified by adjusting the focal length of the zoom camera. Moreover, in the holographic reproduction, we use a digital conical lens instead of the other lenses. By loading the phase of the conical lens on the SLM and adjusting the focal length of the corresponding colors, color holographic projection of the real object can be realized without chromatic aberration. Compared with the previous systems that use liquid lens or digital lens for reconstruction [29], the size and position of the reconstructed image can be changed easily without any optical components. The structure of the proposed system is simplified to a great extent and the reconstructed image can be projected with a large depth.
Figure 1 is the schematic diagram of the proposed system. It consists of a zoom camera, three lasers, three filters, three solid lenses, a mirror, three beam splitters (BSs), an SLM, a computer and a receiving screen. In the process of acquiring images, the zoom camera is used to capture the image of the real object. The zoom camera is connected to the computer, then the information of the real object can be transferred to the computer. The hologram of the object can be generated through the computer. The lasers, filters and solid lenses are used to generate the collimated light. The mirror and the BSs are used to adjust the angle of light so that the collimated light can illuminate the SLM. When the hologram is loaded on the SLM, the diffracted light is reflected by the BS. Finally, the reconstructed image can be seen on the receiving screen.
In the holographic reconstruction part, three colors of the collimated light illuminate one third of the SLM area, respectively. When the collimated light is used to illuminate the SLM loaded with hologram, the reconstructed image can be displayed on the receiving screen after the modulation of the SLM. In the traditional Fourier holographic system, a solid lens (assuming that the focal length is f0) is used for Fourier transform and the receiving screen is placed at the focal plane of the solid lens. Then the light field on the receiving screen Uf0 (u, v) can be expressed as follows:
In the second experiment, when the object is captured, the scene information of red, green and blue colors is separated. The holograms of the recorded object for three colors can be generated by the iterative Fourier transform algorithm. The phase information of the digital conical lens can be generated according to Eq. (5). The final hologram can be generated by adding the phase of the digital conical lens to the that of the recorded object, as shown in Fig. 9.
In order to eliminate the lateral chromatic aberration, the sizes of the three color components are scaled at the process of color separation. We verified the three colors separately. Since the conical lens has the large depth, when the position of the receiving screen is fixed, the reproduced images of the three colors can be clearly displayed, as shown in Figs. 12a-c. Therefore, axial chromatic aberration can be eliminated. In order to achieve color coincidence based on an SLM, the SLM is divided into three parts in space and each part is illuminated with the corresponding color light respectively, as shown in Fig. 12d. Figure 12e is the color reconstructed image, and the result shows that three color reconstructed images can coincide in the same position without chromatic aberration. When the focal length of the zoom camera changes, the size of the captured object is different accordingly. In this way, the magnified scene of the object can be captured. The results of the holographic reconstructed image on the receiving screen for different captured object are shown in Fig. 13. Fig. 13 shows the partial reconstruction of the object. With the proposed system, we can take the detail of the object by optical zoom and project it simultaneously.
In the proposed system, as the digital conical lens has a large focal depth, the reconstructed image of the object can be clearly seen in the focal depth, as shown in Fig. 10c and f. On the other hand, by changing the focal length of the digital conical lens, the size and the position of the reconstructed image can also be adjusted easily, as shown in Fig. 11. In the holographic reconstruction, the reproduced image is disturbed by zero-order light and high-order diffraction images. Figures 10, 11, 12, 13 show the first-order diffraction images. We can load the offset on the hologram to separate the reproduced image and zero-order light, then the undesirable light can be eliminated using an aperture or a filter in the system. Compared with the existing holographic projection system, the proposed system is designed with a zoom camera, which is very small in size and fast in response time. Therefore, the proposed system can easily capture the details of the object without moving the position of the zoom camera. In addition, compared with the previous systems, we use digital conical lens instead of solid lens or other lens for projection. For the same focal length, the digital conical lens has a large depth of focus and the projected image is clear in the focal depth range. Color holographic projection can be realized without chromatic aberration. The size and position of the projected image can be changed according to the requirement easily. In the process of generating the hologram, the iterative Fourier transform algorithm is used to calculate the phase information of the object. Of course, if we use GPU or other acceleration algorithms, the calculation speed can be faster. For the zoom camera, we are developing a circuit board and a control software for tuning the focal lengths of the liquid lenses, synchronously. Through the above methods, the whole response time of the system can be improved effectively. With the decrease of switching time of zoom camera and the improvement of hologram calculation, the real time capture and projection of 3D object can be realized eventually. In the next work, we will continue our research to improve the performance of the system. We believe that our work can promote the development of micro-projection technology and 3D technology.
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