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Abstract: Based on the working principle of ternary optical computer encoder and decoder, a new concept of stereoscopic display on double-layer liquid crystal display is proposed. On this basis, the S3C44B0X-based binocular stereo digital camera solution is designed. The hardware interface and software structure of this scheme are introduced in detail. The prototype of the project is awarded the Excellence Award of Shanghai Embedded System Innovation Design Application Competition.
Keywords: stereo digital camera; S3C44B0X microprocessor; double-layer liquid crystal display
1 Introduction
With the development of optics, microelectronics and computer technology, according to the principle of "binocular parallax stereo imaging" of human eyes, a variety of three-dimensional stereo imaging and stereoscopic display technologies have been formed. At present, people are beginning to use these technologies to develop stereoscopic television sets and stereoscopic cameras. And devices such as stereo cameras. [2]
Recently, we have tried a new concept of stereo camera and stereo display system. The basic principle is: simultaneous imaging with dual lens to simulate the binocular parallax stereo imaging process, and then store the obtained two image data separately. When displaying, the two image data are time-divisionally sent to a display composed of a double-layer liquid crystal, and the display respectively displays the captured left-eye image and right-eye image by vertically polarized light and horizontally polarized light, and the human eye passes through a special one. The polarized glasses view the pair of left and right eye images with certain parallax, and the stereoscopic visual effects of the objects are felt through the processing and fusion of the optic nerves of the brain.
The two-layer liquid crystal display in the system is our main innovation, which utilizes the optical rotation of the liquid crystal and the selective absorption of the polarized light by the polarizer. This article summarizes this work as follows.
2 hardware design
The binocular stereo digital camera consists of two cameras (composed of image sensor OV7620 and lens), an ARM microprocessor (model S3C44B0X), SDRAM, liquid crystal display (model G35II), liquid crystal rotator and polarized glasses. The structure is shown in Figure 1. In the figure, bold lines with arrows indicate electrical signals (control and data signals), and thin lines with arrows indicate optical signals.
The S3C44B0X microprocessor has a built-in memory controller and LCD controller with 71 general purpose I/O ports, 8 external interrupt sources and a serial I2C bus interface, which are used as control cores in the system. Two cameras are used for stereo image pairs (left eye and right eye). A two-layer liquid crystal display composed of a liquid crystal display and a liquid crystal rotator is used for stereoscopic display of image pairs. The SDRAM is used as a storage body of image data, and image data output by the two image sensors is stored during image acquisition, and the image data is taken out from the time division and displayed to the double-layer liquid crystal display. The left lens of the polarized glasses is a vertical polarizer, and the right lens is a horizontal polarizer.
2.1 double-layer LCD display production and stereo display principle
The double-layer liquid crystal display is composed of a G35II type liquid crystal display and a liquid crystal rotator covered thereon, and the outgoing light of the G35II is horizontally linearly polarized light. The rotator is made by peeling off two polarizing plates and a backlight plate from the M12864COG type graphic dot matrix liquid crystal module of Shenzhen Yaoyu Co., Ltd., which is used for polarization modulation of image light emitted from the liquid crystal display. When the G35II displays the left eye image, no voltage is applied to each pixel of the rotator, which rotates the polarization direction of the incident linearly polarized light by 90 degrees to become vertically polarized light; when the G35II displays the right eye image, the rotator is Each pixel is applied with a voltage, which does not change the polarization direction of the incident light, so that the left-eye image and the right-eye image are respectively separated from the two-layer liquid crystal display by two polarized lights perpendicular to each other, and the left and right eyes of the person respectively pass through the polarized glasses. The left eye image and the right eye image were observed.
2.2 microprocessor and double-layer LCD display interface
The double-layer liquid crystal display consists of a G35II liquid crystal display and a liquid crystal rotator, so the microprocessor has two parts to it, as shown in Figure 2.
2.2.1 Microprocessor and LCD interface
The G35II liquid crystal display is an STN type liquid crystal graphic display module with 16 levels of gray scale and EL backlight. The external interface signals are defined as follows:
VFRAME: frame sync signal; VLINE: horizontal sync signal; VCLK: pixel clock signal; VM: driver AC signal; VD[0..7]: data signal; DISP: display control signal.
The interface between the microprocessor and the liquid crystal display, as shown in Figure 2: use the PC, PD and PG port of S3C44B0X as the drive interface of G35II. When initializing, set GPC4~GPC7 of PC port to VD[4..7] function, The GPD0 to GPD7 of the PD port are the VD[0..3] function and the GPG4 is the output function.
2.2.2 Microprocessor and optical rotator interface
The optical rotator is essentially a M12864COG liquid crystal module with built-in LCD controller NT7502 chip and display data memory (DDRAM). The external interface signals are defined as follows:
D[0..7]: data bus; RES1B: reset signal, active low; E: read/write enable signal, valid when the level is high; A0: data/command control signal, high level is data, Low level is instruction; R/W: read/write control signal, low level is write operation, high level is read operation; VCC/GND: power supply, 3V.
The interface between the microprocessor and the optical rotator is as shown in Figure 2. The PE and PG ports of the S3C44B0X are used as the drive interface of the rotator. During initialization, GPE0 to GPE7 of the PE port and GPG0 to GPG3 of the PG port are set as output functions.
2.3 microprocessor and camera interface
The camera consists of image sensor OV7620 and lens. OV7620 integrates image sensing array, frame (row) control circuit, video timing generation circuit, analog signal processing circuit, A/D conversion circuit, digital signal processing circuit, digital video output circuit and SCCB. Programming interface. [4]
Its external interface signals are defined as follows:
VSYNC: frame synchronization; HREF: horizontal synchronization; PCLK: pixel clock; Y[7..0]: 8-bit image data; RESET: reset; SIO_1: SCCB bus clock; SIO_0: SCCB bus data; SBB: SCCB bus interface Can; SLAEN: mode enable; CS0~CS2: SCCB bus Slave ID configuration. MID: Multiple SCCB slave IDs are enabled.
The interface between the microprocessor diagram and the image sensor is shown in Figure 2:
Use the PF and PC port of S3C44B0X as the drive interface of the left image sensor. When initializing, set GPF2~GPF4 of PF port as input function, GPF0 and GPF5~GPF8 as output function and GPC8~GPC15 of PC port as input function, GPF1 is It is an output function when writing, and an input function when reading.
Use the PE, PF, PG and PC port of S3C44B0X as the drive interface of the right image sensor. Since Y[7..0] and D[0..7] of the optical rotator multiplex GPE0~GPE7, the image sensor works. GPE0~GPE7 and GPG4~GPG6 are set as input functions, and GPC0~GPC3 are output functions. CS0~CS2 and Y[7], Y[6], Y[4] are multiplexed, and the corresponding S3C44B0X GPIO port is set as the output function. .
3 system working process
3.1 Collection of stereo image pairs
During initialization, the microprocessor configures the function register through the SCCB bus to set the working mode and initial working state of the two image sensors to: single channel 8-bit Y output, progressive scan, output window 320x240 standard VGA format and Auto exposure, auto gain, and auto white balance.
After the image sensor is in a stable state, the video digital data and the three sync signals are continuously output: the frame sync signal VSYNC, the horizontal sync signal HREF, and the pixel clock signal PCLK. The microprocessor receives the digital video signal and the synchronization signal sent by the two image sensors in time, generates corresponding data, address and control bus signals, and writes the image data into the corresponding image buffer.
When the image sensor adopts single-channel 8-bit Y output and progressive scan mode, 30 frames per second can be acquired, that is, it takes about one-third of a second to acquire one image, and the two image sensors collect images for the total time. More than one-fifth of a second, so the camera is required to remain substantially still for about a tenth of a second when photographing. In order to improve the overall processing speed of the system, two image buffers (called left eye image buffer and right eye image buffer) are opened for each image sensor in SDRAM, one for storing the collected image data, and another for storing the collected image data. It is used to provide image data to the LCD screen, and two pieces are used alternately.
3.2 Display of stereo image pairs
When the G35II liquid crystal display is initialized, first set the resolution of the LCD, the display mode and the number of colors by configuring the registers of the LCD controller, and then allocate a continuous area in the memory as a frame buffer and write its address to the LCD controller. The buffer address register is configured with both the color lookup table register and the jitter mode register.
When the liquid crystal rotator is initialized, first set RES1B to low level. When the voltage is stable, set RES1B to high level, and then use the control command to set the output direction, bias ratio, internal resistivity and full-screen display of the row and column.
In this design, the memory DDRAM of the liquid crystal rotator is all set to 0. When the display is turned on, the full-screen pixel of the LCD turns on the optical rotation function, and when the display is closed, the full-screen pixel of the LCD turns off the optical rotation function, so the display command is used as the optical rotation switch of the optical rotator. .
When the stereo image pair is displayed, the image data saved in the left eye image buffer and the right eye image buffer in the SDRAM are alternately fed into the frame buffer, and the built-in LCD controller of the microprocessor uses the DMA method to buffer the frame buffer. Image data is sent to the G35II LCD display.
When the left eye image is displayed, the optical rotation function of the liquid crystal rotator is turned on; when the right eye image is displayed, the optical rotation function of the liquid crystal rotator is turned off.
4 software design
 The system uses a bare metal-based software development method, and the program is written in a mixture of C language and assembly language. So the software consists of two parts: the bootloader and the application.
The boot program completes the initialization of the system hardware, such as the embedded microprocessor, SDRAM, interrupt, stack, PLL clock, and the memory space configuration required by the C language.
The application has three modules: an external device initialization module, which completes the setting of the camera and the double-layer liquid crystal display; the image acquisition module completes the camera function, that is, simultaneously collects the left eye image and the right eye image and stores them in different areas of the memory SDRAM; stereoscopic display The module finishes sending the image in the memory to the LCD screen and synchronizing the optical rotator. The flow chart of the image acquisition module is shown in Figure 3.
5 conclusions
Based on the working principle of the integrated ternary optical computer encoder and decoder, the binocular stereo digital camera constructed with the embedded microprocessor S3C44B0X, double-layer liquid crystal display and CMOS image sensor OV720 is reliable, technically feasible and practical, and the prototype is participated. In 2006, Shanghai Embedded System Innovation Design Application Competition won the Excellence Award.
The author of this paper innovates: According to the optical rotation of liquid crystal and the selective absorption of polarized light by polarizers, a two-layer liquid crystal display is constructed to realize stereoscopic display.
references:
[1]YAN Junyong, JIN Wei et al. Feasibility Experimental Study of Three-value Optical Computer Multi-bit Encoder and Decoder[J]. Computer Engineering, 2004(14): 175~177
[2]隋婧, Jin Weiqi. Implementation and development of binocular stereo vision technology[J]. Electronic Technology Application, 2004(10): 4～6
[3]S3C44B0X Data Sheet. SAMSUNG Electronics Corp,
[4]OV7620 Data Sheet. OmniVision Technologies Inc,
[5]胥é™. Detailed explanation of embedded system design and development examples [M]. Beijing University of Aeronautics and Astronautics Press, 2005.1
[6]He Ankun, Chen Ming et al. Design of Tax Control Cash Register System Based on S3C44B0X Microprocessor[J].Microcomputer Information,2006,22-1:128-130
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