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An image reading apparatus comprises a light source for illuminating an original, an imaging optical system for forming an image of the illuminated original on the focal plane of the system, and a sensor unit arranged in front of the focal plane. At least two infrared cut filters are arranged on the

An image reading apparatus comprises a light source for illuminating an original, an imaging optical system for forming an image of the illuminated original on the focal plane of the system, and a sensor unit arranged in front of the focal plane. At least two infrared cut filters are arranged on the optical path between the light source and the sensor unit. Those infrared cut filters show respective spectral characteristics that are different from each other. The imaging optical system typically comprises a plurality of lenses and the infrared cut filters are arranged on at least two of the respective surfaces of the lenses.

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1. An image reading apparatus comprising:a light source for illuminating an original image; an imaging optical system for forming an image of the illuminated original image on the focal plane of the system; a sensor unit arranged in front of said focal plane; an A/D converter for converting the outp

1. An image reading apparatus comprising:a light source for illuminating an original image; an imaging optical system for forming an image of the illuminated original image on the focal plane of the system; a sensor unit arranged in front of said focal plane; an A/D converter for converting the output signal of said sensor unit into an n-bit digital signal; and an infrared cut filter unit arranged on the optical path between the light source and the sensor unit, said infrared cut filter having a wavelength zone satisfying the relationship as expressed by the formula below: T.ltoreq.100(2**n), where T is the transmittivity of said infrared cut filter, ** indicates exponentiation, and n is the number of bits of the digital signal, said infrared cut filter unit including at least two infrared cut filters arranged on the optical path between the light source and the sensor unit, said infrared cut filters showing respective spectral characteristics that are different from each other.