The Design And Implementation Of Video Text Overlay Using FPGA

Video text overlay refers to mixing text and time signal into video signal,and thus displaying them simultaneously at some specific position of screen.Video image processing is one of the most important components of military graphic display and control system.To ensure that system can work stably in complex and bad war field environments,special designs should be made,aimed at improving the system stability,security and robustness under possible extremely complex occasions in war field.Therefore,though specific video overlay chips can provide various video processing functions including video overlaying,windows zooming out&in,video dragging and multi-windows displaying,most of these chipsets are only commercial level,which can not meet the environmental demands.At present,there are field programming logic array(FPGA)chipset of commercial,industrial and military level,which can met the requirements of environmental adaptation.Moreover,the design of FPGA is of flexible structure and strong universality.FPGA is suitable for modular design,which can improve the algorithm efficiency.FPGA is also of short development period,easy to be maintained and extended.Therefore,this thesis research on the design and implementation of video text overlay using FPGA.The aim is to adopt a simplified circuit structure by fully exploiting the FPGA resources and realize video text overlay without significantly improve the cost.The main works are contributions are summarized as follows.First,by using FPGA,a circuit for video text overlay is designed in a modular way.The image capturing chip ADV7401 converts both PAL analog signal and 18-bit LVDS signal into digital video signal and send it into FPGA for video overlay.Finally,it is displayed via LCD after device driving.Second,waveform simulation and verification is conducted for FPGA circuit,and the correctness of the designed circuit is verified.FPGA is made up of four modules.That is,YCbCr video stream processing module,SDRAM controlling module,video overlay and output module and controlling and peripheral device interface module.The YCbCr video stream processing module converts the YCbCr signal into RGB signal,and Gamma adjusting and image sharpening is also conducted.SDRAM controlling module controls the mechanisms of frame buffering,interface and judging.Video graphics overlay&output module is a key module,which overlays the graphics,generates HS and VS signal,and outputs digital RGB signal to D/A device.Peripheral device interface module communicates with main computer and controls overlay and adjusts various video parameters.Software and hardware experiments are conducted for the above-mentioned circuit.Experimental results show that the proposed video overlay circuit using FPGA is stable and have the characteristics of display format and contents to be easily changed.It has also been preliminarily used in an airplane cabinet.