The Analysis and Correction of Factors Influencing Imaging Quality of Digital Radiographic Testing System

-The factors influencing imaging quality of industrial digital radiographic imaging system are analyzed detailedly. This imaging system is a new type industrial digital radiographic imaging system developed by author, The structure of ray conversion screen and its non-uniformity, the discordance analysis of scientific grade CCD and vignetting effect of the optical system are introduced. The correction method of non-uniformity for testing system is studied, the correction arithmetic is given and the methods of reducing circuit random noise and the noise produced by scatter ray are illuminated. The correction image and the one that don’t be corrected are given, the merits of this system and problem need to be more studied are illuminated. Key-Words: digital radiographic imaging, non-uniformity correction, x ray conversion, scientific grade CCD, dark current 1. Based on scientific grade CCD camera imaging of the new industrial Radiographic Testing System Introduction In the field of Radiographic NDT, despite the large number of film imaging is still in use but with the development of non-film imaging ,it becomes a trends in radiographic testing therewith real-time detection of the highly efficient, no supplies caused by low-cost, in particular the exchangeable and the characteristics of convenience storage. At present, applications and more research is based on the image intensifier and CCD camera or flat panel detector compose digital imaging system. This two main systems is more used in low energy X-ray source (450 kV) to compose testing systems, the first imaging systems has a poor imaging quality and ask for high requirements of X-ray source , the last one has high price. In order to resolve the problem of under large and medium sized component’s high-energy X-ray (greater than 1 MeV) digital imaging as well as to provide a more universal, lower prices , high-performance digital imaging systems for industry, whit support of national defense project, a new type of opening digital radiographic imaging system developed by the author, which is based on single-crystal scintillation conversion screen, scientific grade CCD camera-found refrigeration, the system WSEAS TRANSACTIONS on MATHEMATICS Cheng Yao-yu, Li Yong-hong , Hu Yan, Liu Yan-hua ISSN: 1109-2769 283 Issue 5, Volume 7, May 2008 components as shown in Figure 1. Outside countries use the way of direct coupling ray-cone to industrial CCD camera [2]. The function of conversion screen is hold the ray distribution that permeated workpiece transform to visible light images which carry the work piece’s internal information, the purpose of 45 °reflector is reflecting the visible light images to the CCD camera, and the residual ray through the conversion screen can straight drill through the reflector so that they can not shoot into the camera, to avoid the damage to camera and the image noise by ray (This point has been proven by experiments). Because of the image after transforms is shimmer image, adopt the scientific grade CCD camera-found refrigeration,which has big dynamice range, small noise, many element and good uniform ,to gain image for long exposal time, namely slow scan imaging, this method similar to film imaging (time short), compares with the fast imaging system, may greatly reduce the image noise by radial fluctuation and electronic enhancement. Moreover this system can be used in X-ray of low energy or high energy andγ-ray, extend the apply scope, at present it is a single system that suits the strongpoint of low price and high testing level, its shortcoming is imaging time is long compared to above two kinds, could not carry through real-time imaging to the movement work piece. high energy to area array imaging it also has 2. The analysis of System ops successfully, throu