Shading correcting method and shading correcting apparatus

Claim 2

An improved shading correction apparatus for correcting read image data read in by an image reading means to provide shading-corrected image data, said apparatus comprising: operating means; first means for applying to said operating means, read image data read in by a certain image reading means; second means for applying to said operating means, black reference data indicative of reading in of a black reference image by said certain image reading means, and white reference data indicative of reading in of a white reference image by said certain image reading means; and third means for applying offset value data to said operating means, said operating means being responsive to receipt of read image data from said first means, black reference data and white reference data from said second means, and offset value data from said third means for calculating shading-corrected image data, and including an adding means, a subtracting means and output means to determine shading-corrected image data, SOUT, and to output such shading-corrected image data according to the relation ##EQU7##

Claim 3

An improved shading correction apparatus as claimed in claim 1, further comprising means for determining said predetermined offset value, OFFSET, based upon a parameter of white reference data from said second means and a parameter of read image data, and providing an offset value signal representative of said offset value to said means for applying an offset value signal.

Claim 4

An improved shading correction apparatus as claimed in claim 2, wherein said offset value determining means determines a difference between maximum output data from an analog-to-digital converter of said certain image reading means and white reference data from said second means.

Claim 5

An improved shading correction apparatus as claimed in claim 3, wherein said offset value determining means determines said difference at a time when said certain image reading means reads a white reference image.

Claim 6

An improved shading correction apparatus as claimed in claim 1, wherein said operating means includes a divider circuit, said at least one adder circuit connecting said divider circuit to said at least one subtractor circuit.

Claim 7

An improved shading correction apparatus as claimed in claim 5, wherein said operating means includes two subtracters, and two adders which connect said subtracters to said divider circuit, and wherein said divider circuit includes a data selector, a shift register, and a subtracter which connects said data selector to said shift register.

Claim 8

An image processing apparatus comprising: image reading means for optically reading an image and generating read image data indicative of the image; a memory for storing read image data generated by said image reading means; an image processing circuit for processing read image data from said memory; means for supplying data indicative of a predetermined value, OFFSET; and control means for controlling said image reading means to generate black reference data indicative of reading of a black reference image, and to generate white reference data indicative of reading of a white reference image, and for controlling said memory to apply read image data to said image processing circuit, said image processing circuit including a shading correcting section which receives read data from said memory, and black reference data, and white reference data generated by said image reading means, and data indicative of said predetermined value, OFFSET, from said supplying means, for correcting read image data from said memory to provide shading-corrected image data, SOUT, according to the relation: ##EQU8## wherein: ID is read image data, BST is black reference data, WST is white reference data, OFFSET is said predetermined value, and K is a constant value.

Claim 9

An image processing apparatus comprising: image reading means for optically reading an image and generating read image data indicative of the image; a memory for storing read image data generated by said image reading means; an image processing circuit for processing read image data from said memory; means for supplying data indicative of a predetermined value, OFFSET; and control means for controlling said image reading means to generate black reference data indicative of reading of a black reference image, and to generate white reference data indicative of reading of a white reference image, and for controlling said memory to apply read image data to said image processing circuit, said image processing circuit including a shading correcting section which receives read data from said memory, and black reference data, and white reference data generated by said image reading means, and data indicative of said predetermined value, OFFSET, from said supplying means, for correcting read image data from said memory to provide shading-corrected image data, SOUT, according to the relation: ##EQU8## wherein: ID is read image data, BST is black reference data, WST is white reference data, OFFSET is said predetermined value, and K is a constant value.

Claim 10

An image processing apparatus according to claim 7, wherein said image reading means has a sensor for optically reading an image to output an analog signal, and analog-to-digital converting means for converting an analog output signal from said sensor to digital data, and wherein said apparatus further comprises offset operating means for determining a difference between maximum digital data from said analog-to-digital converting means and white reference data, WST, to obtain said predetermined value, OFFSET.

Claim 11

An image processing apparatus according to claim 8, further comprising means for causing said offset operating means to determine said difference at a time when said image reading means generates white reference data, WST.

Claim 12

An image processing apparatus as claimed in claim 7, wherein said shading correction section includes at least one subtracter circuit and at least one adder circuit.

Claim 13

An image processing apparatus as claimed in claim 10, wherein said shading correction section includes a divider circuit, said at least one adder circuit connecting said divider circuit to said at least one subtracter circuit.

Claim 14

An image processing apparatus as claimed in claim 11, wherein said shading correction section includes two subtracters, and two adders which connect said subtracters to said divider circuit, and wherein said divider circuit includes a data selector, a shift register, and a subtracter which connects said data selector to said shift register.

Claim 15

An image processing method comprising the steps of: reading an image and generating read image data indicative of said image; storing said read image data; recording said image on a medium to provide a recorded image; and prior to said step of recording an image, correcting said read image data to provide corrected image data, said step of correcting said read image data comprising the steps of: obtaining black reference data indicative of reading of a black reference image, obtaining white reference data indicative of reading of a white reference image, obtaining data indicative of a predetermined value, OFFSET, correcting said read image data based upon said black reference data, said white reference data, and said data indicative of said predetermined value, OFFSET, to provide shading-corrected image data, SOUT, according to the relation: ##EQU9## wherein: ID is read image data, BST is black reference data, WST is white reference data, OFFSET is said predetermined value, and K is a constant value.

Claim 16

An image processing method comprising the steps of: reading an image and generating read image data indicative of said image; storing said read image data; recording said image on a medium to provide a recorded image; and prior to said step of recording an image, correcting said read image data to provide corrected image data, said step of correcting said read image data comprising the steps of: obtaining black reference data indicative of reading of a black reference image, obtaining white reference data indicative of reading of a white reference image, obtaining data indicative of a predetermined value, OFFSET, correcting said read image data based upon said black reference data, said white reference data, and said data indicative of said predetermined value, OFFSET, to provide shading-corrected image data, SOUT, according to the relation: ##EQU9## wherein: ID is read image data, BST is black reference data, WST is white reference data, OFFSET is said predetermined value, and K is a constant value.

Claim 17

An image processing method as claimed in claim 13, wherein said step of correcting read image data includes the step of calculating said predetermined value, OFFSET, as a difference between maximum output data from an analog-to-digital converter used in an image reading means to convert analog data provided by a sensor of such image reading means, and said white reference data WST.

Claim 18

An image processing method as claimed in claim 14, wherein said step of calculating said predetermined value is performed when said white reference data is obtained.