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Abstract

An image reading apparatus having a high-contrast mode of operation for reading character images and a halftone mode of operation for reading halftone images, including an image sensor converting optical image information into electric signals, an optical system for projecting an image on a document onto the image sensor, a threshold signal generator capable of generating a plurality of first threshold signals and operative to output one of the first threshold signals, a threshold signal generator capable of generating a plurality of second threshold signals and operative to output one of the second threshold signals, a mode selector circuit for selecting the high-contrast or halftone mode of operation, a density selector circuit for selecting the first threshold signal during the high-contrast mode of operation and the second threshold signal during the halftone mode of operation, and a combination of circuit networks for outputting halftone image signals during the high-contrast mode of operation on the basis of the electric signals from the image sensor and the first threshold signal from the first threshold signal generator and outputting high-contrast image signals during the halftone mode of operation on the basis of the electric signals from the image sensor and the second threshold signal from the second threshold signal generator.

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