JP2000278498A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image reader that suppresses deterioration of an outputted image caused by a defective photodetector. SOLUTION: When white reference data Dw, proper to pixel data stored in a white reference storing part 21, is compared with a prescribed reference value and it surpasses the reference value, pixel data Dn from an A/D converting part is entered to a subtraction circuit 23, where a difference Dn-Dk between the data Dn and black reference data Dk of a black reference storing part 22 is calculated. Next, a division circuit 24 divides an output Dn-Dk from the circuit 23 by the data Dw proper to the pixel data to calculate compensated data Dn'. The data Dn' is stored in a register 25 and also outputted to a gamma-compensating part, whereas when the data Dw proper to the data Dn stored in the part 21 falls below a prescribed reference value, the data Dn' stored immediately prior to the register 25 is outputted to the gamma compensating part again.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus for reading an image by scanning the image using an optical sensor.

[0002]

2. Description of the Related Art Digital copying machines, scanners, facsimile machines and the like are known as image reading apparatuses for reading an image on a document. For example, in a scanner, an original is illuminated,
An image is scanned by subjecting the reflected light or transmitted light to photoelectric conversion by a CCD linear image sensor through an optical system. The output signal of the optical sensor is converted into a digital signal by an A / D converter via an amplifier, subjected to shading correction, gamma correction, and the like, and output as image data.

The output voltage of each light receiving element constituting an optical sensor such as a CCD linear image sensor or the like increases the product of the illuminance of incident light and the charge accumulation time, that is, increases uniformly with an increase in the amount of light. Ideal for improvement.

[0004]

However, in general, when light of uniform illuminance is irradiated to a photosensor for a predetermined period, the following variations in output voltage between light receiving elements are observed. There is a light receiving element having substantially no output, that is, having no linearity. Although there is linearity, there is a light receiving element whose output voltage is higher than other light receiving elements due to a large influence of dark current. When an image is read using an optical sensor including a light receiving element having such a defect, a false color line in the sub-scanning direction is output at the main scanning position of the light receiving element. Further, when dirt or dust exists on the optical path from the document to the optical sensor, the same problem occurs.

The present invention has been made to solve such a problem, and an object of the present invention is to provide an image reading apparatus which suppresses a decrease in output image quality due to the influence of a defective light receiving element. Another object of the present invention is to provide an image reading apparatus that suppresses a reduction in output image quality due to the influence of dirt and dust. Still another object of the present invention is to provide an image reading apparatus that improves the output image quality with a simple configuration.

[0006]

According to a first aspect of the present invention, there is provided an image reading apparatus comprising: a plurality of light receiving elements for converting reflected light or transmitted light from an original image into electric signals; and pixel data output from the light receiving elements. And an output value at the time of measuring the white reference data is less than the first predetermined value based on the pixel data stored in the storage means of the light receiving element whose output value at the time of measuring the white reference data is equal to or more than the first predetermined value. Pixel data correcting means for correcting the pixel data of the light receiving element.

Generally, pixel data obtained by converting an electric signal output from a light receiving element into a digital signal is output from an image reading device after performing shading correction, gamma correction and the like. According to the image reading device of the first aspect of the present invention, before output from the image reading device, the pixel data of the light receiving element whose output value at the time of measuring the white reference data is equal to or less than the first predetermined value is output to the other light receiving devices. The correction is performed based on the pixel data of the element. For this reason, a decrease in output image quality due to the presence of a light receiving element having no linearity due to the influence of an initial defect or dust is suppressed, and the output image quality is improved.

According to a second aspect of the present invention, there is provided an image reading apparatus comprising:
A plurality of light receiving elements for converting reflected light or transmitted light from an original image into an electric signal; and a specific black reference storage means for storing black reference data of the light receiving element having an output value higher than a second predetermined value when measuring black reference data A storage means for storing pixel data output by the light receiving element; and a memory for storing white reference data based on the pixel data stored in the storage means for the light receiving element whose output value at the time of measuring the white reference data is greater than or equal to the first predetermined value. The pixel data of the light receiving element whose output value is smaller than the first predetermined value is corrected, and the output value at the time of measuring the black reference data is higher than the second predetermined value based on the black reference data stored in the specific black reference storage means. Pixel data correcting means for correcting the pixel data of the element. Therefore, a decrease in output image quality due to the presence of a light receiving element having a higher output than other light receiving elements due to the influence of dark current is suppressed, and the output image quality is improved.

According to the image reading apparatus of the present invention, the pixel data correcting means converts the pixel data of the light receiving element whose output value at the time of measuring the white reference data is smaller than the first predetermined value at the time of measuring the white reference data. Since the output value is replaced with the pixel data stored in the storage means of the light receiving element adjacent to the light receiving element having a value smaller than the first predetermined value, the pseudo color line is not output in the sub-scanning direction in the output image, and the output image quality is reduced. Can be improved.

According to the image reading apparatus of the present invention, the pixel data correcting means converts the pixel data of the light receiving element whose output value at the time of measuring the white reference data is smaller than the first predetermined value at the time of measuring the white reference data. Since the output value is replaced with the average of the pixel data stored in the storage means of the light receiving elements adjacent to both sides of the light receiving element whose value is less than the first predetermined value, the change of the color tone in the main scanning direction in the output image becomes continuous, Output image quality can be improved.

According to the image reading apparatus of the present invention, the pixel data correcting means converts the pixel data of the light receiving element whose output value at the time of measuring the white reference data is equal to or more than the first predetermined value based on the white reference data. The output image quality can be improved with a simple configuration for correcting and transferring to the storage means.

[0012]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a first embodiment of the present invention; (First Embodiment) FIG. 2 shows a flat bed type image reading apparatus according to a first embodiment of the present invention. As shown in FIG.
The image reading apparatus 1 has a document table 3 provided on an upper part of a box-shaped casing 2. The document table 3 is a rectangular plate made of a transparent material such as glass. A document guide 7 for positioning the position of the document 4 when reading the document and restricting the movement of the document 4 is provided on the side of the periphery of the document table 3 opposite to the carriage 10. The surface of the document guide 7 on the side of the document table 3 is a white reference 8 which is a uniform reflection surface having a high reflectance.

As shown in FIGS. 2 and 3, a carriage 10 is provided inside the housing 2 so as to be reciprocally movable in parallel to the document table 3 by a driving device (not shown). The carriage 10 includes a light source 11 for irradiating the original 4, a lens 12 for collecting light emitted from the light source 11 and reflected on the surface of the original 4, and an optical sensor 13 for converting the collected light to an electric signal. Is installed. As the optical sensor 13, a charge accumulation type optical sensor such as a CCD linear image sensor in which a plurality of light receiving elements are arranged perpendicular to the moving direction of the carriage 10 is used.

The electric charges stored in the light receiving elements constituting the optical sensor 13 are processed by a signal processing device as shown in FIG. The A / D converter 15 converts the output from the optical sensor 13 input via the amplifier 14 into a digital signal and passes the digital signal to the shading corrector 16.

A shading correction section 16 as a pixel data correction means is digitized by using previously stored black reference data and white reference data for each light receiving element constituting the optical sensor 13. The pixel data is corrected by the following equation. Dn '= A. (Dn-Dk) / Dw Here, Dn is pixel data before correction, Dk is black reference data, Dw is white reference data, A is a constant, and Dn' is pixel data after shading correction. . The constant A is A = 256 when the read gradation is 8 bits, and A = 4096 when the read gradation is 12 bits.

The gamma correction unit 17 performs gamma correction using a predetermined gamma function, and the other correction units 18 perform various conversions such as color correction, edge enhancement, and area enlargement / reduction. The control unit 19 includes a microcomputer including a CPU, a RAM, a ROM, and the like, controls the entire image reading apparatus, and is connected to an external host such as a personal computer via the interface 6.

Next, the operation of the image reading apparatus 1 will be described. When an external host or the direct image reading apparatus 1 instructs to start reading a document, the reading is performed as follows.

(1) Setting of White Reference Data and Black Reference Data Before reading, white reference data Dw and black reference data Dk are set. The carriage 10 is moved to the end of the document table 1, the light source 11 is turned on, and the light reflected from the white reference 8 is photoelectrically converted by each light receiving element of the optical sensor 13. The output of the optical sensor 13 is digitized by the A / D converter 15 and stored in the white reference storage unit 21 shown in FIG. 1 as white reference data Dw. The white reference data Dw is stored as a unique value for each light receiving element of the optical sensor 13, and a memory such as a RAM can be used as the white reference storage unit 21.

As the black reference data Dk, a representative value obtained by digitizing the pixel data when the light source is turned off when the power is turned on by the A / D converter 15 is stored in the black reference storage unit 22 shown in FIG. , That value can be used.

(2) Reading of Document When reading is instructed, the control unit 19 turns on the light source 11 and sequentially moves the carriage 10 to each reading line position. As a result, at each reading line position, a charge in an amount proportional to the reflectance of the
Is accumulated in The charge accumulated in the optical sensor 13 is output to the amplifier 14 after a predetermined time has elapsed, and the optical sensor 13 moves to the next reading line position.

(3) Shading correction The output signal from each light receiving element of the optical sensor 13 is
4, is converted into digital pixel data Dn by the A / D converter 15,
6 are sequentially output.

The circuit of the shading correction unit 16 is represented as shown in FIG. 1, and correction is performed as described below. The white reference data Dw unique to the pixel data stored in the white reference storage unit 21 is compared with a predetermined reference value, and if it exceeds the reference value, the following processes (a) to (c) are performed. Here, the control unit 19 compares the white reference data Dw with a predetermined reference value.

(A) The pixel data Dn from the A / D converter 15 enters a subtraction circuit 23, where the difference Dn-Dk between the pixel data Dn and the black reference data Dk in the black reference storage unit 22 is calculated. You. (B) Next, in the division circuit 24, the output D from the subtraction circuit 23
The corrected data Dn 'is obtained by dividing n-Dk by the white reference data Dw unique to the pixel data. (C) The corrected data Dn 'is stored in the register 25 as storage means and output to the gamma correction unit 17. (D) When the white reference data Dw unique to the pixel data Dn stored in the white reference storage unit 21 is lower than a predetermined reference value (hereinafter, the pixel data whose white reference data Dw is lower than the predetermined value is referred to as The pixel data Dn-1 ′ stored in the register 25 after the processes (a) to (c) have been performed immediately before is output to the gamma correction unit 17 again. (E) Thereafter, the processing of (a) to (c) or (d) is repeated for the pixel data Dn output from each light receiving element of the optical sensor.

(4) Output to the Outside The pixel data output from the shading correction unit 16 is subjected to gamma correction, color correction, edge enhancement, and area enlargement / reduction in a gamma correction unit 17 and other correction units 18. Various conversions are performed as needed, and output to a personal computer or the like via the interface 6. Regarding the next read line, the above (2) to (4)
Is repeated, and the image in the designated range is output to a personal computer or the like.

An image recording apparatus 1 according to a first embodiment of the present invention.
According to the method (d), the defective pixel data is replaced with the pixel data of the adjacent light receiving element by the above-described processing (d). When an image of a document whose reflectance is shown by a broken line graph in FIG. 4, for example, a reflection document having a gradation of white to black in the main scanning direction is read, the output of each light receiving element before shading correction is as shown in FIG. It is represented by a solid line graph. The difference between the change in the reflectivity of the document and the change in the output of the light receiving element at the left and right end positions of the light receiving element generally indicates that the illuminance of the light source is low at the left and right end positions of the reading line. The singular point shown in the center position indicates the influence of dust existing on the optical path from the original to the optical sensor and the light receiving element without linearity. Assuming that the pixel data is processed in order from the left to the right light receiving elements, when the above-described shading correction is performed on such pixel data, the output of the corrected pixel data is represented by a solid line graph in FIG. The singular point shown in FIG. 4 substantially disappears. The effect on the output image quality due to the replacement of defective pixel data with the pixel data processed immediately before is further reduced by performing other corrections. Further, since the shading correction unit 16 performs such correction processing of the defective pixel data, the output image quality can be improved with a simple configuration.

(Second Embodiment) FIG. 6 shows a circuit of a shading correction section of an image reading apparatus according to a second embodiment of the present invention. Parts substantially the same as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

The pixel data Dn 'having passed through the subtraction circuit 23 and the division circuit 24 are stored in registers 26, 27 and 28 as storage means for storing pixel data of three consecutive light receiving elements.
Is forwarded to Pixel data D of registers 26 and 28
n ′ and Dn−2 are stored in the register 27 as defective pixel data Dn−
When 1 'is transferred, (Dn' + Dn-
2 ') / 2 and averaged and replaced with Dn-1'.
The determination that the defective pixel data Dn-1 ′ has been transferred to the register 27 is made by a counter (not shown). Here, the number of pixel data stored in the register as the storage means is not limited to three.

According to the image reading apparatus of the second embodiment of the present invention, the defective pixel data is replaced by the average of the pixel data of the light receiving elements adjacent on both sides, so that the color change in the sub-scanning direction becomes continuous. Output image quality can be improved.

(Third Embodiment) FIG. 7 shows a circuit of a shading correction section of an image reading apparatus according to a third embodiment of the present invention. Parts substantially the same as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

At the time of setting the black reference data before reading, the representative value obtained by digitizing the pixel data when the light source is turned off by the A / D converter 15 is stored in the black reference storage unit 22, and the digitized individual black data is stored. The reference data that exceeds a predetermined reference value is stored in the specific black reference storage unit 30. When pixel data (hereinafter referred to as "leakage pixel data") in which unique black reference data is stored enters the subtraction circuit 23, the specific black reference storage unit 30 uses the black reference data unique to the leaky pixel data to obtain Dn-Dk. Is executed. The determination that the leakage pixel data has been transferred to the subtraction circuit 23 is performed by a counter (not shown).

According to the image reading apparatus of the third embodiment of the present invention, the black reference data unique to the light receiving element having an excessively large dark current is stored and reflected in the shading correction.
A decrease in output image quality due to dark current can be suppressed.

As described above, in the embodiments of the present invention, only the flat bed type image reading apparatus has been described.
The present invention can also be applied to a mirror moving image reading device, a sheet feed type image reading device, a digital copying machine, an OCR device, a facsimile, and the like.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a shading correction unit of an image reading device according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating an image reading apparatus according to a first embodiment of the present invention.

FIG. 3 is a block diagram illustrating an image reading apparatus according to a first embodiment of the present invention.

FIG. 4 is a graph showing an output of each light receiving element before shading correction in the first embodiment of the present invention.

FIG. 5 is a graph showing pixel data after shading correction in the first embodiment of the present invention.

FIG. 6 is a schematic diagram illustrating a shading correction unit of an image reading device according to a second embodiment of the present invention.

FIG. 7 is a schematic diagram illustrating a shading correction unit of an image reading device according to a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image reading device 13 Optical sensor 16 Shading correction part (pixel data correction means) 25, 26, 27, 28 Register (storage means) 30 Specific black reference storage part

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5C072 AA01 BA08 DA02 DA12 EA05 FB12 FB15 FB17 LA15 RA16 UA02 UA03 UA06 UA11 UA13 5C077 LL02 MM03 MP07 PP06 PP07 PP15 PP20 PP44 PP45 PP51 PQ12 PQ22 RR01 RR12 SS01

Claims (5)

[Claims] A plurality of light receiving elements for converting reflected light or transmitted light from an original image into an electric signal; storage means for storing pixel data output from the light receiving element; Pixel data correction means for correcting pixel data of a light receiving element whose white reference data measurement value is less than the first predetermined value based on pixel data stored in the storage means of the light receiving element having a first predetermined value or more; An image reading device, comprising: 2. A light-receiving element for converting reflected light or transmitted light from an original image into an electric signal, and black reference data of a light-receiving element having an output value higher than a second predetermined value when measuring black reference data is stored. Specific black reference storage means, storage means for storing pixel data output by the light receiving element, and pixel data stored in the storage means of the light receiving element whose output value at the time of white reference data measurement is equal to or greater than a first predetermined value. The output value at the time of measuring the white reference data is corrected based on the pixel data of the light receiving element having a value smaller than the first predetermined value based on the black reference data stored in the specific black reference storage means. An image reading device comprising: pixel data correction means for correcting pixel data of a light receiving element having an output value higher than a second predetermined value. 3. The pixel data correction means according to claim 1, wherein the pixel data of the light receiving element whose output value at the time of measuring said white reference data is less than a first predetermined value is less than a first predetermined value. The image reading device according to claim 1, wherein the image data is replaced with pixel data stored in the storage unit of a light receiving element adjacent to the light receiving element. 4. The pixel data correction means according to claim 1, wherein the pixel data of the light receiving element whose output value at the time of measuring said white reference data is less than a first predetermined value is less than a first predetermined value. The image reading apparatus according to claim 1, wherein the image data is replaced with an average of pixel data stored in the storage unit of the light receiving element adjacent to both sides of the light receiving element. 5. The pixel data correction unit corrects pixel data of a light receiving element having an output value at the time of measuring the white reference data equal to or greater than a first predetermined value based on the white reference data, and transfers the pixel data to the storage unit. The image reading device according to any one of claims 1 to 4, wherein