Abstract:The transmission and reflection coefficients of ITO materials and glass substrate are similar, so high contrast image is difficult to collect by high speed scanning CCD. ITO circuit of capacitive touch screens is divided into upper and lower double. Illumination light will show disorderly superposition phenomenon, after several transmission and reflection, when the light angle is not parallel with camera angle. Light intensity disorderly superposition phenomenon could be avoided, and contrast value between the glass substrate and ITO images was increased when transmission image way was used, in which the light source was parallel with the camera inclination angle. The illumination intensity optimization experiment shows that CCD insufficient exposure will cause the image too dark; with the light intensity increase, the image gray histogram twopeak phenomenon is obvious; the twopeak phenomenon is most obvious when light intensity reachs 200; then the twopeak phenomenon has no obvious change when light intensity is higher than 200.