Patent ID: 7477431

Claim:
An image reading apparatus for effecting line reading in a main scanning direction by scanning in a sub-scanning direction to thereby read the image of an original, the apparatus including: a photoelectric conversion device for resolving an optical signal representative of an inputted line image into a number of basic colors exceeding a predetermined number and outputting them as analog electrical signals; an analog/digital conversion circuit for inputting said predetermined number of the analog electrical signals differing from one another at a time, and converting respective ones of the analog electrical signals into digital signals; and a selection circuit for selecting the analog electrical signals equal to or less than said predetermined number from the output of said photoelectric conversion device at each image reading of one main scanning line and also selecting the analog electrical signals of a different combination at the reading of the images of both adjacent main scanning lines, and outputting them to said analog/digital conversion circuit, wherein said photoelectric conversion circuit is configured to resolve the inputted optical signal into four basic colors and outputting them as analog electrical signals, and said analog/digital conversion circuit is configured to input up to three analog electrical signals at a time, and converting them into digital signals, and wherein said selection circuit selects first and second analog electrical signals from the output of said photoelectric conversion device at the reading of the image of a first main scanning line, and selects third and fourth analog electrical signals from the output of said photoelectric conversion device at the image reading of a second main scanning line adjacent to said first scanning line.