Scanner integrated circuits and reference designs


Scanners vary greatly in several basic ways: scan speed, bit resolution, and signal-to-noise ratio (SNR). There are tradeoffs to each of these parameters.

Resolution: There is a direct correlation between the bit resolution and the AFE (analog front end). Higher bit resolutions (more digitized bits per pixel) give smoother grays, more natural colors and more "photorealistic" images. The higher bit resolutions also give more dynamic range, the difference between the black level and the white level. Dynamic range is particularly important for seeing details in dark or shadowed regions or when an image includes both shadow and sunlit areas.

Scan Speed: There is a direct tradeoff between scan speed and resolution and signal to noise ratio. Slower scanners will tend to be higher resolution and have a higher signal to noise ratio, but these specifications can be improved at higher scan speeds with a faster AFE and processor. This may also require the implementation of a more precise scanner motor.

Signal-to-Noise Ratio: The signal-to-noise ratio or SNR is dependant upon the entire signal chain, from the image sensors to the AFE. This is important for document scanners if OCR (Optical Character Recognition) or other image processing will be performed. It is important in photo quality scanners to eliminate graininess in images. A higher resolution necessitates a better SNR to maintain quality.

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