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Image reading apparatus

  • US 5,124,810 A
  • Filed: 05/14/1990
  • Issued: 06/23/1992
  • Est. Priority Date: 05/26/1989
  • Status: Expired due to Term
First Claim
Patent Images

1. An image reading apparatus for reading an image on a sheet, comprising:

  • image reading means for scanning a predetermined area including the sheet scanning line by scanning line, said image reading means reading an image pattern on the predetermined area including the image on the sheet and producing an output image signal indicative of the image;

    a white reference image part provided within said predetermined area so as to be scanned by the image reading means;

    a black reference image part provided within said predetermined area so as to be scanned by the image reading means;

    white reference memory means supplied with the output image signal from the image reading means in response to the image reading means scanning the white reference image part, for storing the output image signal supplied thereto;

    black reference memory means supplied with the output image signal from the image reading means in response to the image reading means scanning the black reference image part, for storing the output image signal supplied thereto;

    image correction means supplied with the output image signal from the image reading means line sequentially in response to the image reading means scanning the sheet, said image correction means being supplied further with a first reference signal indicative of the image signal stored in the white reference memory means and with a second reference signal indicative of the image signal stored in the black reference memory, for producing a corrected image signal so that the corrected image signal has a maximum level corrected with reference to the first reference signal and a minimum level corrected with reference to the second reference signal; and

    control means for controlling the white reference memory means and the black reference memory means so that the white reference memory means stores the output image signal of the image reading means only when the image reading means scans the white reference image part and so that the black reference memory means stores the output image signal of the image reading means only when the image reading means scans the black reference image part;

    wherein said image correction means comprises an analog-to-digital converter supplied with the output image signal from the image reading means for producing a digital image data, said analog-to-digital converter being supplied with the first reference signal and the second reference signal from respectively the white and black reference memory means for setting the range of the incoming image signal from the image reading means, and said digital image data being supplied selectively to the white reference memory means and to the black reference memory means under the control of the control means; and

    wherein said white reference memory means and said black reference memory means comprise first and second line buffers for storing the digital image data corresponding to one line and first and second analog-to-digital converters respectively connected to the first and second line buffers for producing said first and second reference signals.

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