Design Of Color Imaging System For Bayer CMOS Sensor

As a research hotspot of image technologies in recent decades,the good quality of digital image processing has achieved higher requirements for image processing.As the source of images,image acquisition is also the focus of attention.Imaging systems play an important role in medical,national defense,and traffic monitoring.With the continuous advancement of science and technology and the gradual rise of the semiconductor industry,people have put forward higher requirements for imaging systems and processing technologies.The traditional processing based on computer serial structure can no longer meet the requirements for real-time performance.Digital cameras are one type of current imaging devices.Due to their production cost and people’s need for miniaturization and portability,most color digital cameras use a CCD(Charge-coupled Device)or a CMOS(Complementary Metal Oxide Semiconductor)that covers a color filter array.For the sensor,only one color component can be obtained at each pixel of the image through the filter array,and a complete color image can only be acqiried by implementing color restoration processing in the later stage.The process of capturing and processing the original image from the sensor to obtain a full-color image is called the demosaicking process.The processing result of the demosaicing algorithm has a decisive influence on the quality of color images,and also affects other subsequent image processing links.In view of the current miniaturization of image acquisition equipment and the real-time requirements of image processing,this thesis mainly does the following work.(1)This thesis designed a set of miniaturized hardware platform system from image acquisition to image preprocessing and output.The image acquisition part uses SONY’s IMX185 sensor as the core to design the peripheral circuit,and the image algorithm processing part uses Xilinx’s 7 series FPGA(Field Programmable Gate Array)chip as the core.The DDR3(Double Data Rate3)cache,HDMI(High-Definition Multimedia Interface)output and other peripheral circuits are designed,and FFC(Flexible Flat Cable)connector is used to connect these two parts.Thus,a complete hardware system from image sensor input to output display is built.(2)Aiming at color imaging,this thesis inverstagates the development process of image sensors,and the algorithm – is designed to remove Msaic effect for sensors whis are most widely used Bayer format images.At present,some high-order demosaicking algorithms are difficult to meet the real-time requirements of embedded hardware due to their complex calculation process and large amount of calculation,which is not good for miniaturization.However,the demosaicking algorithm for embedded hardware platform is still improved based on bilinear interpolation algorithm.In this thesis,based on the simulation and research of several de-mosaic algorithms,the gradient interpolation algorithm is improved,the image edge is divided more carefully,and the interpolation formula of 45° tilt direction is added.After the green component is interpolated by gradient detection in 5×5neighborhood,the red and blue components are not restored simply based on the color difference law,but are restored by gradient detection combined with the color difference law,and the restoration of the three components is placed in the same pipeline to reduce the delay of image output.(3)It is found that there is color bias in the images taken by the self-designed image acquisition system through the simulation comparison of Mosaic removal algorithm.Therefore,on the basis of color recovery,this thesis also added color correction algorithm for processing,the grayscale world algorithm adopted in this paper,through simulation comparison,the effect is improved significantly,it will be hardware logic implementation.(4)Based on the self-designed complete image acquisition and processing system,the IMX185 sensor initialization mode configuration logic design,the FPGA as the core of the image processing part of the module logic design,the Mosaic removal algorithm and color correction algorithm are implementated by hardware logic,the processed image could be displayed and saved.The results are summarized and analyzed.Through practical tests,the color image acquisition and preprocessing system designed in this thesis has the function of real-time color image display and output,and is easy to carry,can realize different resolutions,which can be applied to different fields such as security monitoring,has high use value and reference significance.