CCD Requirements for Digital Photography

Digital photography has the potential to supersede conventional film photography. In order to realize this potential, digital photography needs to provide the best image quality and highest utility. We have used our modeling of photographic systems and our experimental measurements of CCDs in order to estimate the photographic potential of specific CCDs. We have also extrapolated the future requirements for CCDs that can compete with film. In order to make meaningful sensitivity comparisons, we have developed a model that can be used to predict the ISO speed potential of a digital camera, based on the characteristics of the CCD. The model is briefly described in the second section of the paper. The model can also be used to qualitatively analyze the effect of CCD parameters on camera performance, and examples of the effects that limited charge capacity have on image quality and read noise have on ISO speed are presented. A simple relationship for the ISO speed in the monochrome case is also presented in order to illustrate the scaling laws. We have tested a large number of CCDs of varying architecture in order to collect input data for our speed model. We have designed a universal CCD evaluation camera in order to test these CCDs under similar conditions, with minimum hardware modifications. We have used the camera and an optical monochrometer system to measure parameters including the full-well capacity, linearity, quantum efficiency, dark current, read noise, smear and angular response of many of the CCDs that represent the current state of the art. The camera and the methods that we have used to perform these tests are described in the second section of this paper. The effect that different CCD characteristics have on image quality and camera utility are described in the third section of this paper. For comparison, we present the measured characteristics that represent the current state-ofthe-art for commercially available CCDs. We also postulate the performance required for CCDs to compete with film The paper concludes with our comments on the most appropriate CCD architectures for digital photography, and suggestions for future CCD development.