This paper presents a film scanner that utilizes linear CCD array technology and adjacent pixel summing of m pixels to scan large format films. Pixel summing is employed to optimally increase the dynamic range of the system, providing the ability to scan films with wider exposure latitude without compromising radiometric resolution. The digitized CCD data is presented to a hardware processing unit that acts as both an interface to the data storage device and controller of clocks on the CCD array. If the first-of-m data level is below a predetermined threshold, the CCD array clocks are modified to allow the next m-1 charges to accumulate in the output stage of the CCD array (analog summing). If the first-of-m data level is above the predetermined threshold, the processing unit switches to digital summing and the next m-1 pixel values are digitally added to the first-of-m value. This pixel summing scheme not only increases SNR and dynamic range of the scanner, it also allows the user to change m, the number of pixels summed, giving him the ability to vary scanner spatial resolution without changing the optics.
Michael H. Davis,
"CCD-Based Film Scanner With Extended Dynamic Range", Proc. SPIE 1075, Digital Image Processing Applications, (5 April 1989); doi: 10.1117/12.952624; https://doi.org/10.1117/12.952624