White-level correction circuit used with an analog-to-digital converter for an image reading apparatus

A method of correcting white-level reference data used for an analog-to-digital converter, which converts an analog image signal, input thereto and corresponding to a pixel, to output digital image data based on a white-level reference voltage input thereto, said method comprising the steps of:

• (a) storing white-level reference data for the pixel in a first storage means;
• (b) reading the white-level reference data from the first storage means when the analog image signal is input to the analog-to-digital converter;
• (c) converting the white-level reference data, read from the first storage means, to an analog signal and which analog signal is supplied to the analog-to-digital converter as the white-level reference voltage which is input thereto;
• (d) decoding the digital image data output by the analog-to-digital converter;
• (e) generating white-level correction data by correcting the read white-level reference data, based on said decoding in step (d);
• and
• (f) storing the generated white-level correction data in the first storage means.

In an analog-to-digital converter which converts an analog image signal, input thereto and corresponding to a pixel, to output digital image data based on a white-level reference voltage input thereto, a white-level correction circuit comprising:

• a first memory storing therein white-level reference data for the pixel and from which the stored white-level reference data is read and the stored and read white-level reference data is produced as an output thereof;
• an acess controller unit, in synchronism with input of the analog image signal to the analog-to-digital converter, accessing the first memory and reading therefrom and producing as the output thereof the stored and read, white level reference data;
• a digital-to-analog converter converting the white-level reference data, output by the first memory, to an analog signal which is supplied thereby to the analog-to-digital converter as the white-level reference voltage input thereto;
• a decoder decoding the digital image data output by the analog-to-digital converter;
• and
• a white level correction circuit, operatively connected to said decoder, generating white-level correction data by correcting the read white-level reference data, based on the decoding by the decoder, and storing the white-level correction data into the first memory.

A method of correcting white-level reference data used for an analog-to-digital converter, which converts an analog image signal, input thereto and corresponding to a pixel, to output digital image data based on a white-level reference voltage input thereto, the method comprising the steps of:

• (a) storing white-level reference data for the pixel in a first memory;
• (b) reading the white-level reference data from the first memory in synchronism with the input of the analog image signal to the analog-to-digital converter;
• (c) converting the white-level reference data, read from the first memory, to an analog signal supplied to an analog-to-digital converter unit as the white-level reference voltage which is input thereto;
• (d) decoding the digital image data output by the analog-to-digital converter;
• (e) generating white-level correction data by correcting the read white-level reference data, based on the decoding in step (d);
• and
• (f) storing the generated white-level correction data in the first memory.