Evaluation of imaging quality of CCD camera by measuring MTFs at different contrasts

Aiming at the environmental lightness influence on MTF, MTFs at different contrasts are proposed and used to assess the imaging quality of CCD camera in this paper. Based on the MTF measurement principle with the slit target, the measurement system is designed and developed. In order to get different contrasts, two integrating spheres are used to illuminate the face and back of the test target uniformly. The target luminance and background luminance of the test target are regulated by self-developing luminance measure and control parts. The contrast can be adjusted conveniently. The experimental results of many groups indicate that the luminance differences between the values by the system and those by L88 first level luminance meter, which is checked by National Institute of Metrology P. R. China, are within ±0.3 cd/m². Thereby the measure precision can be ensured in MTF test of CCD cameras. The imaging qualities of Sony camera and Cannon camera are measured by this system. The experimental results show that the assessments are corresponds with the fact; MTFs at different contrasts can demonstrate the imaging quality fully and objectively. This study provides an effective method to evaluate the imaging quality of visible imaging systems.