Image reading apparatus

An image reading apparatus for reading documents by optical scanning, said image reading apparatus comprising:

• an imaging system which includes a line sensor and an imaging lens for forming an optical image of the document on said line sensor;
• a color correction filter which has characteristics for shielding light of a predetermined wavelength;
• a mode selecting means for selecting one from a plurality of imaging modes, each of said modes being provided based on the type of the document;
• and
• a driver which selectively inserts said color correction filter into said imaging system based on the result of the mode selection.

An image reading apparatus comprising:

• an imaging element for reading a document;
• an imaging lens for forming an optical image of the document on said imaging element;
• color correction means for changing the spectral characteristics of the optical image, said color correction means including a first filter having characteristics for shielding light of a predetermined wavelength and a second filter having characteristics for shielding light of wavelength different from that of said first filter;
• and
• a control means for controlling said color correction means based on the type of the document.

An image reading method for reading documents disposed face upward on a document platen by optical scanning, said method comprising;

• a first step of scanning a document with a first filter for produce document height data which are used to align the focal point and correct image distortion;
• a second step of changing the first filter into a second filter, said second filter having a characteristics different from that of the first filter;
• and
• a third step of scanning a document with the second filter for produce document image.

An image reading apparatus for reading documents comprising;

• an imaging system which reads images from a document via scanning by a sensor during a main scanning operation;
• a first color correction filter which has characteristics for shielding light of visible light range including red color, green color, and blue color;
• a start key for starting a reading operation;
• and
• a controller for executing a prescanning operation with said first color correction filter prior to the main scanning operation in a response to signal from the start key to measure the height of a document.

An image reading apparatus for prescanning documents to determine height data of a document to determine imaging conditions and subsequently for reading images from the document during a main scanning operation comprising:

• support means for supporting a document to be read;
• a sensor member;
• an imaging system for realizing an image of the document in the sensor member;
• a color correction filter assembly including a first filter for shielding light in the red, green, and blue color range of a visible light spectrum to enhance measurement of height data, a second filter for transmitting light in the visible light spectrum to enhance a photographic image and a third filter for transmitting light in visible light spectrum to enhance a printed text image, the filter assembly is positioned between the support means and the sensor member for selectively inserting a filter into the imaging system;
• and
• control means for selectively inserting the first filter into the imaging system during a prescan mode of operation for a measurement of height data and subsequently removing the first filter and inserting one of the second filter and the third filter during a main scanning mode of operation.

An image reading apparatus for prescanning documents to determine height data and for reading images from documents during a main scanning operation comprising:

• support means for supporting a document to be read;
• a sensor member;
• an imaging system for realizing an image of the document in the sensor member;
• a color correction filter assembly including a first filter for shielding light in the red, green, and blue color range of a visible light spectrum to enhance measurement of height data and at least a second filter for transmitting light in the visible light spectrum, the filter assembly positioned is between the support means and the sensor member for selectively inserting a filter into the imaging system;
• and
• control means for selectively inserting the first filter into the imaging system during a prescan mode of operation for a measurement of height data and subsequently removing the first filter and inserting the second filter during a main scanning mode of operation.