Proceedings PaperImage analysis of discrete and continuous systems: film and CCD sensors
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A model has been developed to compare the system sharpness of continuous and discrete imaging systems. The continuous system consists of the traditional photographic process including the camera lens the film the printer lens and the photographic paper. The discrete system is an electronic still camera (ESC) and is built around a CCD imaging sensor and a laser printer the camera lens and the photographic paper are the same for both systems. The model uses CMT acutance to measure sharpness and introduces the concept of using the ratio of the aliased signal to the non-aliased signal as a measure of the probability of system aliasing. The model allows the user to study the trade offs between system sharpness and aliasing as a function of sensor resolution pixel size and the nature of the optical anti-aliasing pre-filter used in the ESC. The results of the model indicate that when a well-defined optical anti-aliasing pre-filter is made from a birefringent filter then when the pre-filter introduces a shift of about one-half the pixel pitch of the sensor then the potential for aliasing is minimized. For a given sensor resolution as the pixel size is reduced the potential for aliasing increases as does the system sharpness and when the potential for aliasing is minimized by use of the pre-filter the smaller pixel size still results in a greater potential for aliasing than for the pixels. For a given resolution it is possible to move from the Frame Transfer format to an Interline Transfer format and have the same system sharpness and potential for aliasing thus allowing flexibility in system design but the potential for aliasing is greater than the minimum value associated with the Frame Transfer format. As the system resolution increases the minimum in the potential for aliasing is more sharply defined as a function of the image shift introduced by the pre-filter. Also the potential for aliasing drops off sharply as the sensor resolution increases. In the case of the ESC system the number of lines used to form the final print can have a very large impact on the system sharpness and the amount of aliasing seen by the observer. 1.