Research on 3D holographic display system based on Da Vinci technology

Abstract: As people's visual demand for stereoscopic images is getting stronger and stronger, a research scheme of a three-dimensional holographic display system based on DieFinch technology is proposed. An embedded system is constructed using the DieFinch processor TMS32 0DM6446 and other peripheral circuits and optoelectronic devices. The system uses the embedded operating system, namely Linux, as the software platform, fully utilizes the rich peripherals and storage interfaces of TMS320DM6446 and gives full play to the powerful control function of ARM926EJ-S and the powerful numerical calculation ability of C64x+DSP. The final three-dimensional stereoscopic display graphics are displayed on the LCD to realize digital holographic three-dimensional display. The results show that after the original image data is processed by the system, it perfectly displays the original object from all angles. This research provides a good embedded experimental platform for the three-dimensional holographic display of images, which has good application prospects and innovative value.
Keywords: Da Vinci technology; 3D holography; DSP; TMS320DM6446

0 Introduction
Today, when video innovation has become a hot topic in the digital information industry, people's visual demand for stereoscopic images is becoming stronger and stronger. The display effect of two-dimensional images lacks realism, depth, and stereoscopic sense, and has long been unable to satisfy people's sensory stimulation and psychological feelings. Therefore, various three-dimensional display implementation schemes continue to emerge, and holographic display technology is one of the most common three-dimensional display technologies. Computational holography uses computers to synthesize holograms, and replaces physical interference with computer numerical calculations. It does not require the actual existence of objects, but only needs to know the mathematical description of the object light wave. After the mathematical description of the object light wave is input into the computer for processing, the hologram is drawn by the imaging device, and then reproduced by optical methods. Computational holograms can not only comprehensively record the amplitude and phase of light waves, but also comprehensively reproduce holograms of objects that do not exist in the world. Therefore, they have unique advantages and great flexibility, and observers can observe from all directions without the help of auxiliary devices such as glasses.
This paper combines the advantages of computer-generated holographic three-dimensional display technology and Da Vinci technology to give a new three-dimensional stereoscopic display solution: using the Da Vinci processor TMS320DM6446 and other peripheral circuits to build an embedded system and realize computer-generated holographic three-dimensional display. The system uses the embedded operating system - Linux as the software platform, uses the rich device drivers and system calls provided by Monta Vista Linux, makes full use of the rich peripherals and storage interfaces of TMS320DM6446, and gives full play to the powerful control functions of ARM926EJ-S and the powerful numerical calculation capabilities of C64x+DSP. The final three-dimensional stereoscopic display graphics are displayed on an LCOS liquid crystal display with a resolution of 1 024×768, providing a good embedded platform for the study of three-dimensional holographic display of images.

1 Three-dimensional holographic display system based on Da Vinci technology
The system uses the Da Vinci processor TMS320DM6446 instead of a general-purpose computer to realize the computational coding of two-dimensional holograms, in which the ARM subsystem controls the entire system, and the DSP subsystem completes the two-dimensional computational holographic coding and the calculation of three-dimensional object holograms. The whole system is an embedded system composed of the Da Vinci processor TMS320DM6446 and its peripheral circuits, LCOS and other optoelectronic devices.
1.1 Computer holographic three-dimensional display system based on TMS320DM6446
The system software and hardware are modularly designed. In terms of software, the ARM and DSP subsystems support Linux and DSP/BIOS operating systems respectively, and can work relatively independently. Such division meets the design requirements of modularization of system software, facilitates the parallel development and debugging of various parts, and is conducive to the division of labor and cooperation among members of the project team. The later software testing complies with the testing principle from unit testing to integration testing to system testing, shortening the system development cycle and reducing design costs. The overall structure diagram is shown in Figure 1.

The original image data is transmitted to the Da Vinci processor TMS320DM6446 through the USB interface, and then the data is transformed by FFT, and the computational holography algorithm is implemented on the transformed data. The image data after inverse transformation is sent to the LCOS display, and finally the three-dimensional display of the image is realized. Among them, FFT transformation, computational holography and inverse transformation of FFT are performed in the DSP subsystem, and the ARM subsystem controls the DSP data processing subsystem through the control bus. The host computer can realize the control and secondary development of the system through the JTAG interface. The keyboard here is set as a 4×4 independent keyboard, the purpose is to set the system, realize data input and command transmission.
1.2 Characteristics of Liquid Crystal Display LCOS
LCOS (Liquid Crystal on Silicon) is a new type of reflective liquid crystal display device. Compared with traditional display technology, it has the advantages of high light utilization, small volume, high aperture ratio and small size. The principle of LCOS displaying text or image information is roughly the same as that of ordinary liquid crystal display. It uses the characteristics of liquid crystal molecules with strong induced dipole moment to make the arrangement of liquid crystal molecules related to the external electric field through the action of external electric field.
The display system uses the HX7308BTJFA LCD with 1024×768 pixels. The HX7308BTJFA is embedded with a timing controller to generate internal control signals, and the chip displays images with high image quality and contrast. The HX7308BTJFA receives 8 b×4 dots of digital display data from the outside at the rising and falling edges of each clock and generates the corresponding grayscale output voltage value. Its internal system block diagram is shown in Figure 2.

2 Development of ARM and DSP
The processor of this system is TMS320DM6446, which is a DSP+ARM dual-core architecture chip. Different development tools should be selected for ARM and DSP. This system runs the Linux operating system in ARM, and the CCS emulator is needed for DSP to develop and debug.
2.1 Embedded Linux system development
Embedded software development requires a cross-compilation environment because it is necessary to generate executable code on the target platform on the host platform. First, install and build a cross-compilation environment on the host Linux, then use the shared file system method to download the embedded bootloder and Linux kernel image to the target board through the switch, and start the embedded Linux kernel. Then you can develop applications in the cross-compilation environment of the host Linux and download the generated executable code to the target board.
In this way, through the rich application interface function APIs provided by Linux, users can regard DSP as a black box. They only need to call these APIs to use the encoding and decoding functions on the DSP side, and the DV-SDK development kit can provide support for direct programming on the DSP side.
2.2 Implementation of FFT operation on CCS
FFT is a fast algorithm for Fourier transform, which can transform a signal into the frequency domain. Some signals are difficult to see their characteristics in the time domain, but if they are transformed into the frequency domain, it is easy to see what characteristics they have. Therefore, many signal analyses choose to use FFT transformation. In addition, FFT can extract the spectrum of a signal, which is also often used in frequency domain analysis.
2.3 DSPLIB library function
The function library (DSPLIB) of the TMS320C64X+ series is a DSP library function that can be optimized for C language programming. It is written entirely in assembly language and can be called by C language, which facilitates mixed programming of C language and assembly language. These programs are used in real-time operations with high computational intensity and important execution speed. By using these programs, you can achieve a much faster running speed than related programs written in C language. In addition, by using ready-made programs, the development speed can be greatly accelerated. The operations that DSPLIB can perform include: FFT operation, filtering and convolution operation, adaptive filtering operation, correlation operation, trigonometric function operation, etc.
2.4 FFT operation
The FFT operation provided by DSPLIB is a time extraction algorithm based on 2. The operation can directly call void cfft (DATA x, nx, shortscale). Among them: x[2*nx] is the input/output data storage array; nx is the operation length of FFT; scale is the normalization setting variable; scale=1 is the normalization setting variable, and scale=0 is not normalized. The normalization function makes the output result divided by the operation length n, in order to prevent the FFT operation result from overflowing. A simple program is used to illustrate the use of DSPLIB. In this program, the input data is placed in the x[512] array, and the result after operation is still in the x[512] array. In

this way, an FFT transformation with an operation length of 256 points in DSP is completed.

3 Result Analysis
The spectrum analysis of the square wave signal with a frequency of 50 Hz is performed, the number of sampling points is 128, and the sampling frequency is adjusted so that the sampling time of 128 points is 40 ms, that is, the period of the input 2 signals. The results are viewed through the DSP integrated development environment (CCS), as shown in Figures 3 and 4.

4 Conclusion
This paper combines the advantages of digital holographic 3D display technology and Da Vinci technology to provide a new 3D display solution. The results show that after an original image data passes through the system, it perfectly displays the original object from all angles. Therefore, the embedded system platform has great use value.