Research On Image Processing Methods And FPGA Implementation Of Special LCD

With the development of digital warfare mode, Liquid Crystal Display (LCD) will be widely used in the military equipments, such as the aircraft-borne, ship-borne and armored-vehicles because it is light, thin and low power. But there are some special performance requirements in the military application of LCD, for example, the operating ambient temperature range, the contrast controlling, the night-vision compatible and sunlight readable. The controlling board of commercial LCD, however, is not suitable for operating in the military fields (-4O'C~6O'C and the special illumination condition), because it can only operate in 0"C~40'C, and the adjustable range of brightness and contrast ratio is very narrow. Therefore, now nearly all of military special LCD comes from the rugged commercial LCD. By using "rugged" technology, not only the power dissipation is increased, the reliability is reduced and the volume is enlarged, but also functions of rugged LCD are single, and system compatibility is limited.Therefore, this paper mainly studies the image processing methods for the special LCD and implementation with FPGA, and successfully designs several actual application systems based on FPGA to solve current problems effectively. The main research work of this paper is as follows:(1) A color adjustment method based on color space conversion is presented, then color-distorted phenomenon could be avoided, because brightness and chroma are separated into different components in YCrCb, but they both change at the same time in RGB. And the logic architecture of 3*3 Matrix operation is improved by using pipeline, so that 2/3 logical resources are reserved in FPGA and the maximum running frequency of this module is enhanced. A contrast adjustment method based on median histogram stretching is presented, which stretches histogram at the middle of image gray-scale, so it is gray-scale adaptive and is better than conventional methods. A programmable LCD gamma correction module is designed in FPGA with double-port RAM, which applies a method based on six calibration points, and corrects gray-scale in each segments of gamma curve, then image color restores accurately.(2) The image scaling method using FPGA is studied. Bilinear interpolation algorithm is satisfied with special LCD, and then is implemented in FPGA. Interpolation coefficient "dx" and "dy" are computed real-time, interpolation computation is archived by using pipeline, and only three line buffers are used to store image data in stead of expanding large capacity frame memory, so the cost is reduced and system compatibility is improved.(3)A simple, direct and effective de-interlacing method is discussed, which applies image scaling algorithm to scale one field (odd or even) image to the resolution of LCD. So the image of PAL/NTSC video could display full-screen in LCD, and the functions of existing special LCD areimproved in information-losing and display effect not-well.(4) A digital OSD controller based on character and bitmap is designed. Two kinds of logical resources, "Distributed RAM" and "Block RAM", store reasonably character and bitmap information. OSD image is composed automatically by digital logic in FPGA, and programming method is simple and flexible, so that parameter adjustment of special LCD is more convenient.(5) A special LCD controlling board based on FPGA is developed successfully, it can display three kinds of resolution, 640*480, 800*600, 1024*768, and can adjust brightness, contrast, position and other parameters, meanwhile provides the full functions transparent OSD menu. This board passes -40*C~65*C temperature and performance experiment, the results show that it is better than existing system in performance, functions, system compatibility, and achieves Military LCD standard.(6) An image adjustment board of special LCD based on FPGA is developed successfully, which is used to update certain model aircraft-borne special LCD, and already passes by the performance test and the temperature experiment, and has been installed in equipment. In order to i...