JPH1198355A - Device and method for correcting shading - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain satisfactory shading correction for original picture data. SOLUTION: A reading operation is operated in a state that a white reference board 6 and a correction chart 16 are moved to a readable position 8, and first white reference data Xi are obtained. An image forming position CXj of a scale line C of a correction chart 16 on a line sensor 12 is detected based on the first white reference data Xi. Then, the reading operation is operated in a state that an opening 7 and the correction chart 16 are moved to the readable position 8, and second reference data Yi are obtained. Image forming position CYj of a scale line C of the correction chart 16 on the line sensor 12 is detected based on the second white reference data Yi. Then, the variable power rate of a lens 11 is adjusted so that the scale line position CYj can be made coincident with the scale line position CXj. Then, the correction chart 16 is removed from the readable position 8, and the reading operation is operated with the adjusted variable power rate so that third white reference data Wi can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a shading correction device and a shading correction method applied to an image reading device such as a scanner.

[0002]

2. Description of the Related Art Conventionally, there has been known an image reading apparatus such as a scanner for reading a document image by a line sensor having a plurality of CCD elements arranged in a main scanning direction. In such an image reading apparatus, so-called shading correction is performed on document image data read by a line sensor in order to compensate for uneven illumination of a reading light source and variations in sensitivity among CCD elements.

In the shading correction, two correction data, that is, white reference data and black reference data are obtained before reading a document image. The white reference data is acquired by, for example, turning on the reading light source and performing a reading operation in a state where nothing exists on the reading line. The black reference data is obtained by performing a reading operation with the reading light source turned off, for example. Thereafter, the original image is read, and the image data output from each CCD element included in the line sensor is corrected based on the white reference data and the black reference data according to the following equation.

[0004]

(Equation 1)

[0005] Here, k is a predetermined shading correction coefficient. Some image reading apparatuses read an original image while holding the original with an original holder made of, for example, a transparent glass material or a resin material. In such an image reading apparatus, even if correction based on the black reference data and the white reference data acquired as described above is performed on the document image data,
The output of each CCD element included in the line sensor is not correctly corrected. The reason will be described with reference to FIG.

FIG. 6 is a conceptual diagram for explaining how an optical path to a line sensor changes depending on the presence or absence of a document holder. For simplicity, an imaging optical system is omitted. In FIG. 6, the optical path from the reading light source 51 to the line sensor 52 at the time of document reading is shown by a solid line, and the optical path from the reading light source 51 to the line sensor 52 at the time of obtaining white reference data is shown by a two-dot chain line. ing. At the time of obtaining the white reference data, there is nothing on the reading line, so the light emitted from the reading light source 51 and passing through the point A
Irradiated at position a on On the other hand, the light passing through the point A when reading the document is refracted when passing through the document holder 53 and irradiates the position a ′ on the line sensor 52. That is, the image formation state on the line sensor 52 is different between when the white reference data is obtained and when the document is read, because the optical path length from the reading light source 51 to the line sensor 52 is different. Therefore, in the shading correction based on the white reference data acquired as described above, the reading light source 51
Lighting unevenness cannot be compensated correctly.

Therefore, conventionally, a white reference member having the same transparency as the original holder is arranged at the original reading position, and the light transmitted through the white reference member is read by a line sensor, so that the white reference data is obtained. How to get it has been proposed. According to this method, the image formation state on the line sensor when the white reference data is obtained matches the image formation state on the line sensor when the document is read. Therefore, by applying shading correction to the document image data based on the white reference data acquired by this method, it is possible to compensate for uneven illumination of the reading light source.

[0008]

However, in the above-described method of arranging the white reference member and acquiring the white reference data, for example, if dust or the like adheres to the white reference member,
Light from the reading light source is blocked by the dust, and white reference data in which the output of the CCD element corresponding to the portion is reduced is obtained. As a result, if shading correction is performed based on the acquired white reference data, the output of the CCD element corresponding to the portion where dust has adhered will be excessively corrected.

An object of the present invention is to solve the above-mentioned technical problems and to provide a shading correction device and a shading correction method capable of satisfactorily correcting original image data.

[0010]

Means for Solving the Problems and Effects of the Invention According to the first aspect of the present invention, there is provided a line sensor having a plurality of photoelectric conversion elements for converting a document held by a transparent document holding member. A shading correction device for performing correction based on correction data on document image data obtained by reading, a light source for illuminating a predetermined position readable by a line sensor, the light source and the line An image forming optical system interposed between the sensor, a white reference member having the same transparency as the document holding member, and a reading operation performed with the white reference member advanced to the predetermined position. A first data acquisition unit for acquiring first white reference data; and a second white reference data obtained by performing a reading operation with the white reference member retracted from the predetermined position. The second data acquisition unit to be acquired and the image formation state on the line sensor when the second white reference data is acquired coincides with the image formation state on the line sensor when the first white reference data is acquired. Optical system adjusting means for adjusting the imaging optical system, and after adjusting the imaging optical system by the optical system adjusting means, by performing a reading operation in a state where the white reference member is retracted from the predetermined position, A shading correction device comprising: a correction data obtaining unit that obtains the correction data.

According to the first aspect of the present invention, the image forming optical system is adjusted by the optical system adjusting means so that the white reference member is retracted from a predetermined position readable by the line sensor to perform a reading operation. The image forming state on the line sensor is matched with the image forming state on the line sensor when the reading operation is performed with the white reference member arranged at the readable position. And
In a state where the image formation state on the line sensor coincides with the time when the first white reference data is obtained, the reading operation is performed by retracting the white reference member from the readable position, so that data for shading correction is obtained.

Thus, unlike the conventional method in which the data obtained by reading the light transmitted through the white reference member disposed on the readable position is used as the correction data as it is, the acquired correction data is the white reference member. It is not affected by dust or the like adhering to the surface. Therefore, a problem that occurs when shading correction is performed based on correction data affected by dust or the like attached to the white reference member can be avoided, and excellent shading correction can be performed on document image data. .

Further, the image formation state on the line sensor at the time of acquiring the correction data coincides with the image formation state on the line sensor at the time of reading the original. Therefore, in the shading correction based on the correction data acquired by the above-described configuration, what is the case where the shading correction is performed based on the correction data acquired in a state where the image formation state on the line sensor is different from that at the time of reading the document? In contrast, uneven illumination of the light source and variations in sensitivity among the CCD elements can be correctly compensated.

According to a second aspect of the present invention, a document image data obtained by reading a document held by a transparent document holding member with a line sensor having a plurality of photoelectric conversion elements is corrected based on correction data. A light source for illuminating a predetermined position readable by a line sensor, an imaging optical system interposed between the light source and the line sensor, and a document holding member. A reading operation is performed in a state in which a white reference member having the same translucency, a correction chart in which a predetermined image is formed on a transparent film-like member, and the white reference member and the correction chart are advanced to the predetermined position. First data acquisition means for acquiring first white reference data by performing
Means for identifying, from the plurality of photoelectric elements included in the line sensor, a photoelectric conversion element that has read an image formed on the correction chart, based on the acquired first white reference data, Evacuate from the predetermined position,
A second data acquiring means for acquiring a second white reference data by performing a reading operation with the correction chart advanced to the predetermined position; and a line sensor based on the acquired second white reference data. Means for identifying a photoelectric conversion element which has read an image formed on the correction chart from among a plurality of photoelectric elements included in the first white reference data, and the position of the photoelectric conversion element identified based on the first white reference data and the second white Based on the amount of deviation from the position of the photoelectric conversion element specified based on the reference data, the imaging state on the line sensor at the time of acquiring the second white reference data changes on the line sensor at the time of acquiring the first white reference data. After adjusting the imaging optical system by the optical system adjusting means and the optical system adjusting means for adjusting the imaging optical system so as to match the imaging state at By fine correction chart performs a reading operation in a state of being retracted from the predetermined position, a shading correction apparatus characterized by comprising a correction data acquisition means for acquiring the correction data.

According to the second aspect of the present invention, with the white reference member and the correction chart arranged at predetermined positions readable by the line sensor, the position of the photoelectric conversion element reading the image formed on the correction chart is determined. In a state where only the correction chart is arranged at the predetermined position, the amount of deviation from the position of the photoelectric conversion element that reads the image formed on the correction chart is obtained. Then, based on the obtained shift amount, the image forming state on the line sensor when the reading operation is performed by retracting the white reference member from the predetermined position readable by the line sensor is changed to the white position at the readable position. The image forming optical system is adjusted so as to match the image forming state on the line sensor when the reading operation is performed with the reference member arranged. Then, in a state where the image formation state on the line sensor coincides with the time when the first white reference data is obtained, the white reference member and the correction chart are retracted from the readable position and the reading operation is performed to perform shading correction data. Is obtained.

Thus, the same function and effect as those of the above-described configuration can be obtained. The invention according to claim 3 further includes storage means for storing the adjustment amount of the imaging optical system by the optical system adjustment means in association with the state of the imaging optical system before adjustment. 1 or 2
It is a shading correction device of the description.

According to the third aspect of the present invention, when the image forming optical system is adjusted by the optical system adjusting means, the adjustment amount of the image forming optical system is changed to the state of the image forming optical system before adjustment, That is, it is stored in the storage unit in association with the reading magnification of the document image. Accordingly, when a new shading correction is performed, if the reading magnification of the original image is the same as that at the time of the previously performed shading correction, the adjustment amount of the imaging optical system corresponding to the reading magnification is stored from the storage unit. The data for correction can be obtained by adjusting the imaging optical system based on the readout and the readout adjustment amount. Therefore, the adjustment of the imaging optical system can be performed once at an appropriate position based on the adjustment amount read from the storage unit without performing trial and error adjustment of the imaging optical system. Can be shortened. As a result, the time required for shading correction can be reduced.

Further, the amount of adjustment of the imaging optical system corresponding to each value of the original reading magnification in the adjustable range is obtained in advance and stored in the storage means, so that each time the reading magnification is changed, correction is made. There is no need to perform a troublesome operation such as acquiring correction data using a chart. According to a fourth aspect of the present invention, the imaging optical system is a zoom lens, and the optical system adjusting means adjusts a magnification of the zoom lens.
The shading correction device according to any one of the above.

According to the fourth aspect, the adjustment of the image forming state on the line sensor can be achieved by adjusting the magnification of the zoom lens. Since the image forming optical system is a zoom lens, the image forming state is favorably maintained before and after the adjustment. The invention according to claim 5 is characterized in that the imaging optical system is a fixed focus lens system, and the optical system adjustment means adjusts the position of the fixed focus lens system with respect to the line sensor. A shading correction device according to any one of claims 1 to 3.

According to the fifth aspect of the invention, the adjustment of the image forming state on the line sensor can be achieved by adjusting the position of the fixed focus lens system with respect to the line sensor.
The fixed focus lens system forms a document image on a line sensor at a predetermined reading magnification. That is, the fixed-focus lens system does not have a zoom mechanism for greatly changing the reading magnification of the document unlike the zoom lens, and cannot change the reading magnification of the document positively. Therefore, when the imaging optical system is constituted by a fixed-focus lens system, the lens position adjustment mechanism provided for focusing is manually operated to change the lens position by a very small amount. What is necessary is just to adjust the imaging state on the sensor.

Since the change in the image forming state on the line sensor due to the presence or absence of the document holder is delicate, the adjustment amount of the image forming optical system is also small. In many cases, even if the image forming optical system is adjusted within the adjustable range, the image forming state on the line sensor can be kept good. Therefore, when the specification of the image reading apparatus is, for example, the reading magnification is a fixed magnification and the image forming state on the line sensor can be favorably maintained within the adjustable range of the image forming optical system as described above. A fixed focus lens system is sufficient as the imaging optical system. In this case, by using a fixed focus lens instead of the zoom lens, the apparatus can be reduced in cost.

According to a sixth aspect of the present invention, an original image data obtained by reading an original held by a transparent original holding member with a line sensor having a plurality of photoelectric conversion elements is corrected based on correction data. A shading correction method for performing a first reading operation by performing a reading operation in a state where a white reference member having the same light transmission property as that of the document holding member has advanced to a predetermined position readable by the line sensor. Obtaining white reference data; obtaining second white reference data by performing a reading operation with the white reference member retracted from the predetermined position; and a line sensor for obtaining the second white reference data. The image formation state on the line sensor coincides with the image formation state on the line sensor when the first white reference data is obtained,
Adjusting the imaging optical system provided between the light source and the line sensor, and performing the reading operation with the white reference member retracted from the predetermined position after adjusting the imaging optical system. And obtaining the correction data.

According to the method of the sixth aspect, the same operation and effect as the configuration of the first aspect can be obtained. According to a seventh aspect of the present invention, original image data obtained by reading an original held by a transparent original holding member with a line sensor having a plurality of photoelectric conversion elements is corrected based on correction data. A shading correction method, wherein a correction chart in which a predetermined image is formed on a white reference member and a transparent film-like member having the same translucency as the document holding member is provided at a predetermined position where the line sensor can read the correction chart. Acquiring the first white reference data by performing a reading operation in a state in which the line sensor has advanced, and, based on the acquired first white reference data, converting the plurality of photoelectric elements included in the line sensor into the correction chart. Identifying the photoelectric conversion element that has read the formed image, and retracting the white reference member from the predetermined position; and Acquiring a second white reference data by performing a reading operation in a state where the normal chart is advanced to the predetermined position; and a plurality of photoelectric elements included in the line sensor based on the acquired second white reference data. Identifying the photoelectric conversion element that has read the image formed on the correction chart from among the above, and identifying the photoelectric conversion element based on the position of the photoelectric conversion element identified based on the first white reference data and the second white reference data. The imaging state on the line sensor at the time of acquiring the second white reference data matches the imaging state on the line sensor at the time of acquiring the first white reference data, based on the amount of deviation from the position of the photoelectric conversion element. As
Adjusting the imaging optical system provided between the light source and the line sensor, and retracting the white reference member and the correction chart from the predetermined position after adjusting the imaging optical system by the optical system adjusting means. Acquiring the correction data by performing a reading operation in a state where the shading correction is performed.

According to the method of the seventh aspect, the same operation and effect as the configuration of the second aspect can be obtained. The invention according to claim 8 further includes a step of storing the adjustment amount of the imaging optical system by the optical system adjustment unit in the storage unit in association with the state of the imaging optical system before adjustment. A shading correction method according to claim 6 or 7.

According to the method of the eighth aspect, the same operation and effect as the configuration of the third aspect can be obtained. According to a ninth aspect of the present invention, the image forming optical system is a zoom lens, and the step of adjusting the image forming optical system is a step of adjusting a magnification of the zoom lens. 9. The shading correction method according to any one of claims 1 to 8.

According to the method of the ninth aspect, the same operation and effect as the configuration of the fourth aspect can be obtained. According to a tenth aspect of the present invention, the imaging optical system is a fixed-focus lens system, and the step of adjusting the imaging optical system is a step of adjusting a position of the fixed-focus lens system with respect to the line sensor. The shading correction method according to any one of claims 6 to 8, wherein

According to the method of claim 10, claim 5 is provided.
The same operation and effect as the described configuration can be obtained.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below.
This will be described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing an electrical configuration of an image reading apparatus to which an embodiment of the present invention is applied. The image reading apparatus is an apparatus for reading an image of a transmission type original 1 such as a film original, for example, and includes a transparent original table 2 which is horizontally movable along the sub-scanning direction Y. The document 1 to be read is set at a predetermined set position on the document table 2 while being held by, for example, a transparent document holder 3.

An original table 2 includes a white reference portion 4 used for obtaining white reference data and a black reference plate 5 used for obtaining black reference data in a shading correction process described later. For example, it is provided along one edge in the sub-scanning direction Y so as not to conflict with the set position No. 3. The white reference portion 4 includes a white reference plate 6 fixed on the upper surface of the document table 2 and extending in the main scanning direction (a direction perpendicular to the plane of FIG. 1), and a long reference plate formed on the document table 2 in the main scanning direction. Opening 7 is included. The white reference plate 6 is made of a material having the same translucency as the original holder 3 and has the same thickness as the original holder 3. The black reference plate 5 is a plate-like body made of a material having a light-shielding property and elongated in the main scanning direction, and is fixed to the upper surface of the document table 2 adjacent to the white reference portion 4.

A predetermined position 8 on the moving path of the original table 2
Above the light source 9, a light source 9 constituted by, for example, a fluorescent lamp is provided. When reading an image, the original table 2 is moved in the sub-scanning direction Y while the light source 9 is turned on, and the original held by the original holder 3 is illuminated with the light from the light source 9 at the predetermined position 8. . That is, in this image reading apparatus, the predetermined position 8 on the moving path of the original table 2 is
Are read positions by the line sensor 12 described later (predetermined positions readable by the line sensor 12).

The light applied to the original 1 is transmitted through the original 1, the original holder 3, and the original table 2, guided to the lower side of the original table 2, reflected by the reflection mirror 10 in the horizontal direction, and incident on the lens 11. I do. The lens 11 as the imaging optical system has a built-in zoom mechanism (not shown), and the light incident on the lens 11 is enlarged or reduced by the zoom mechanism to form an image on the line sensor 12.

The line sensor 12 has n (for example, 5000) CCD elements arranged in the main scanning direction, and each CCD element photoelectrically converts incident light and outputs an electric signal. An analog electric signal output from the line sensor 12 is amplified to an appropriate level by an amplifier 13 and then input to an A / D converter 14 to be converted into digital image data. The converted digital image data is subjected to signal processing such as shading correction by a DSP (Digital Signal Processor) 15,
Output as post-processing data.

This image reading apparatus is also provided with a correction chart 16 used for obtaining white reference data in shading correction processing described later. The correction chart 16 is a member that is made of a thin transparent material such as a transparent film and is long in the main scanning direction, and is provided so as to be horizontally movable in the sub-scanning direction Y. The correction chart 16 has m (m = 5 in this embodiment) graduation lines (see FIG. 4) that extend linearly in the sub-scanning direction. Note that the thickness of the correction chart 16 is so small as to be negligible, and the light transmitted through the correction chart 16 is not affected by refraction or the like.

The image reading apparatus further includes a CPU 17 and a memory 18 including a RAM and a ROM connected to the CPU 17 for controlling the operation of each unit of the apparatus. The CPU 17 realizes the function of the DSP 15 by executing software processing according to a program stored in the memory 18. Also, the CPU 17
Controls writing and reading of image data to and from the memory 18.

Further, the CPU 17 includes a table motor M1 for moving the original table 2 and a chart motor for moving the correction chart 16 via a table motor drive circuit 19, a chart motor drive circuit 20, and a zoom drive circuit 21. The driving of the zoom motor M3 for the zoom operation is controlled. Table motor M
1. The chart motor M2 and the zoom motor M3 can be constituted by, for example, a stepping motor.

FIGS. 2 and 3 are flowcharts showing the flow of the shading correction processing. Also, FIG.
FIG. 4 is a diagram for explaining the positions of the document table 2 and the correction chart and the output state of the line sensor 12 during the shading correction process. This shading correction processing is performed based on white reference data and black reference data.
Is a process for obtaining two correction data and performing shading correction on image data obtained by reading the document 1 based on the obtained correction data. This is executed when the image reading conditions are changed.

When the document holder 3 holding the document 1 is set on the document table 2 and a start signal is input to the CPU 17, the table motor M1 and the chart motor M2 are driven and controlled, and the white reference plate 6 and the correction The chart 16 is moved to a position 8 where the line sensor 12 can read the chart 16 (step S1). Next, the light source 9 is turned on, the white reference plate 6 and the correction chart 16 on the readable position 8 are illuminated, and the light transmitted through the white reference plate 6 and the correction chart 16 is read by the line sensor 12 (FIG. a)). Then, the data Xi (i = 1 to n) obtained by this reading is stored in the memory 18 as the first white reference data Xi (step S2). In this embodiment, steps S1 and S2 correspond to the function of the first data acquisition unit.

The CPU 17 stores the first
Based on the white reference data Xi, the position CXj (j = 1 to m) of m scale lines C formed on the correction chart 16 is detected (step S3). That is, the CPU 17 executes a later-described scale line detection process (see FIG. 5),
From the n CCD elements included in the line sensor 12, the CCD element that has read the graduation line C of the correction chart 16 when the first white reference data Xi is obtained is detected. The detected scale line position CXj is stored in the memory 18.

Next, the drive of the table motor M1 is controlled, and the opening 7 formed in the original table 2 is moved to the position 8 where the line sensor 12 can read (step S4). Thus, as shown in FIG. 4B, the opening 7 and the correction chart 16 are located on the readable position 8. In this state, the reading operation is performed by the line sensor 12, and the obtained data is stored in the memory 18 as the second white reference data Yi (i = 1 to n) (step S5). Thereafter, similarly to step S3 described above, the correction chart 16 is obtained when the second white reference data Yi is obtained based on the second white reference data Yi stored in the memory 18.
The CCD element that has read the scale line C of
(J = 1 to m) is detected (step S6).

In this embodiment, steps S4 and S5 correspond to the function of the second data acquisition means. Next, it is determined whether or not the scale line position CXj stored in the memory 18 matches the scale line position CYj detected in step S6 (step S7). As described above, the first white reference data Xi is displayed on the position 8 where the line sensor 12 can read the white reference plate 6 and the correction chart 16.
The second white reference data Yi is obtained by performing a reading operation in a state where
It is obtained by performing a reading operation in a state where the opening 7 and the correction chart 16 are superimposed on each other. Therefore, the first
Since the optical path length from the light source 9 to the line sensor 12 is different between when the white reference data Xi is obtained and when the second white reference data Yi is obtained, the image formation state on the line sensor 12 is different. As a result, as can be seen by comparing FIGS. 4A and 4B, the scale line position CXj detected based on the first white reference data Xi and the detection based on the second white reference data Yi are detected. Is shifted from the scale line position CYj.

Therefore, at this time, it is determined that the scale line position CXj does not match the scale line position CYj (NO in step S7), and the shift amount between the scale line position CXj and the scale line position CYj approaches zero. As described above, the drive of the zoom motor M3 is controlled to change the magnification of the lens 11 (step S8). That is, in step S8, the line sensor 1
The image forming state on the line sensor 12 when the opening 7 and the correction chart 16 are located on the readable position 8 by the second reference 2 indicates that the white reference plate 6 and the correction chart 16 are located on the readable position 8. The magnification of the lens 11 is adjusted so as to match the image formation state on the line sensor 12 at the time of operation. Therefore, in this embodiment, it can be said that steps S7 and S8 correspond to the function of the optical system adjusting unit.

Thereafter, returning to step S5, the reading operation is performed at the adjusted magnification ratio, and the second read operation after zoom adjustment is performed.
The white reference data Yi is stored in the memory 18. Then, the second white reference data after zoom adjustment stored in the memory 18
Based on Yi, detection of the scale line position CYj is executed again (step S6), and it is determined whether or not the detected scale line position CYj matches the scale line position CXj stored in the memory 18 (step S6). Step S7). If it is determined that the scale line position CYj does not match the scale line position CXj,
Proceeding to step S8, the magnification of the lens 11 is readjusted.

On the other hand, if it is determined that the scale line position CYj and the scale line position CXj match (see FIG. 4C), the scale factor or adjustment amount after this adjustment is set before the start of the shading correction processing. The original image is stored in the memory 18 in association with the reading magnification (magnification before adjustment) of the original image (step S9). Note that the processing of steps S5 to S8 does not necessarily need to be repeated until the scale line position CYj and the scale line position CXj completely match. For example, the scale line position CYj includes the scale line position CXj in step S7. A determination may be made as to whether or not it exists in the predetermined area, and if the determination is affirmative, the process may be changed to proceed to step S9.

Thereafter, the driving of the chart motor M2 is controlled, and the correction chart 16 is removed from the position readable by the line sensor 12 (step S10). Then, the reading operation is performed with the scaling ratio adjusted in steps S5 to S8 described above, and the obtained data is stored in the memory 18 as the third white reference data Wi (i = 1 to n) ( Step S11). The third stored in the memory 18
The white reference data Wi is used as white reference data when performing shading correction on the document image data in the processing described below. That is, steps S10 and S11
Corresponds to the function of the correction data acquisition means.

As described above, when the third white reference data Wi as the white reference data is obtained, as shown in FIG.
The reading operation is performed in a state where only the opening 7 formed in the document table 2 is located on the readable position 8. Thus, unlike the conventional method of arranging a white reference member having the same translucency as that of the document holder 3 on the readable position 8 and acquiring the white reference data, the acquired white reference data Wi is the white reference member. It is not affected by dust or the like adhering to the surface.

When the white reference data Wi is obtained, the reading operation is performed at the magnification adjusted in steps S5 to S8 described above. As a result, the image formation state on the line sensor 12 when the white reference data Wi is obtained matches the image formation state on the line sensor 12 when the document is read.
Therefore, the white reference data obtained as described above
In the shading correction based on Wi, the line sensor 12
Unlike the case where the shading correction is performed based on the white reference data obtained in a state where the image formed above is different from that when reading the original, the illumination unevenness of the light source 9 and the sensitivity variation between the CCD elements are correctly compensated. can do.

When the white reference data Wi is obtained, the black reference data Bi (i = 1 to n) used for performing shading correction on the document image data is obtained and stored in the memory 18. (Step S12). Black reference data Bi
Is, for example, a black reference plate 5 arranged on the original table 2.
Is moved to the position 8 where the line sensor 12 can read, and the reading operation is performed in a state where the light from the light source 9 is blocked by the black reference plate 5.

Thereafter, the driving of the lens motor M3 is controlled, and the magnification of the lens 11 is returned to the state before being adjusted in step S8 (step S13). Then, the drive of the table motor M1 is controlled, and FIG.
As shown in (e), the original 1 held in the original holder 3
Is moved to the readable position 8, and the original image on the readable position 8 is read by the line sensor 12 (Step S14). An output signal of the line sensor 12 is supplied to an A / D converter 14 via an amplifier 13 and is converted into digital original image data Si (i = 1 to n).

The original image data Si after A / D conversion is DS
P15, the shading correction is performed based on the white reference data Wi and the black reference data Bi stored in the memory 18 (step S15). Specifically, as described above, the function of the DSP 15 can be realized by software processing executed by the CPU 17, and the original image data Si
Is achieved by the CPU 17 executing arithmetic processing according to the following arithmetic expression.

SDi = k · (Si−Bi) / (Wi−Bi) (arithmetic expression) where SDi (i = 1 to n) is
Represents the image data after shading correction. Also, k
Represents a predetermined shading correction coefficient. That is, the image data SDi after the shading correction is obtained by multiplying the value obtained by subtracting the black reference data Bi from the original image data Si by the shading correction coefficient k and the white reference data Wi.
And a value obtained by subtracting the black reference data Bi from. Then, when all the document images within the preset reading range are read and the obtained all image data is subjected to the shading correction, the shading correction processing ends.

As described above, in the shading correction processing according to the present embodiment, the image formation state on the line sensor 12 when the opening 7 and the correction chart 16 are arranged on the readable position 8 by the line sensor 12 is determined. The magnification of the lens 11 is determined so as to match the state of image formation on the line sensor 12 when the white reference plate 6 and the correction chart 16 are arranged on the readable position 8. After that, the correction chart 16 is removed, and the reading operation at the obtained magnification is performed in a state where only the opening 7 is disposed on the readable position 8. The data acquired by this reading operation is used as white reference data Wi, and shading correction based on the white reference data Wi is performed on the document image data Si.

As a result, a problem that occurs when shading correction is performed based on white reference data obtained by disposing a white reference member having the same translucency as that of the original holder 3 on the readable position 8, It is possible to avoid a problem that occurs when shading correction is performed based on white reference data obtained in a state where an image formed on the sensor 12 is different from that at the time of document reading, and perform good shading correction on document image data. Can be.

The magnification of the lens 11 obtained as described above is associated with a preset image reading magnification (magnification before zoom adjustment) in the memory before the shading correction processing is executed. 18 is stored. Thereby, when a new shading correction process is performed,
If the shading correction processing and the image reading magnification are the same, the variable magnification is read from the memory 18 using the image reading magnification as an address, and the read magnification is set to the lens 11.
The white reference data Wi may be obtained by adjusting the zoom mechanism described above, and the processing in steps S1 to S8 described above can be omitted. Therefore, in this case, the time required for the shading correction processing can be significantly reduced.

In the above-described shading correction processing, the amount of deviation between the scale line position CXj detected based on the first white reference data Xi and the scale line position CYj detected based on the second white reference data Yi is calculated. The scaling factor that becomes zero is determined by trial and error. However, the scale line position CXj
And a scale factor at which the shift amount between the scale line position CXj and the scale line position CYj becomes zero based on the shift amount between the scale line position CYj and the first detected scale line position CYj. Since the processing of steps S5 to S8 can be omitted, the time required for the shading correction processing can be further reduced.

The black reference data Bi is stored in the document table 2
Is obtained by performing a reading operation in a state where the light from the light source 9 is shielded by the black reference plate 5 provided in the above, but is obtained by performing a reading operation in a state where the light source 9 is turned off. Is also good. Alternatively, the information may be obtained by adjusting a squeezing mechanism built in the lens 11 and performing a reading operation in a state where light to the line sensor 12 is shielded. When the black reference data Bi is obtained as described above, it is not necessary to provide the black reference plate 5 on the document table 2, and the manufacturing cost of the apparatus can be reduced.

Further, in the above description, the function of the DSP 15 is realized by software processing, and the shading correction is achieved by the arithmetic processing executed by the CPU 17, but for example, a subtractor,
A shading correction circuit including a divider and a multiplier may be provided, and the shading correction may be performed on the document image data Si by supplying the document image data Si to the shading correction circuit.

FIG. 5 is a flowchart showing the flow of the scale line detection processing. The graduation line detection process is a process executed in steps S3 and S6 in the above-described shading correction process.
This is a process for detecting a CCD element that has read the graduation line C of the correction chart 16 when the first white reference data Xi or the second white reference data Yi is obtained from the CD element. Hereinafter, the flow of the scale line detection process in the case where the scale line position CXj is detected from the first white reference data Xi will be described with reference to FIG.

When the n pieces of first white reference data Xi are stored in the memory 18 in the above-described shading correction processing and the scale line detection processing is started, for example, the counter i and the counter j provided in the memory 18 are provided. Is reset (step T1). The count value of the counter i represents the number of the first white reference data Xi checked after the start of the scale line detection processing. The count value of the counter j indicates the number of detected scale line positions CXj.

Next, it is determined whether or not the count value of the counter i is equal to the number n of CCD elements included in the line sensor 12 (step T2). At this time, the counter i
Is zero, the determination as to whether the count value is n is negated (NO in step T2) and the counter i
Is incremented by +1 (step T
3). Then, the first white reference data Xi corresponding to the value of the counter i at this time is read from the memory 18. Specifically, at this time, the value of the counter i has been rewritten to 1, so that the first white reference data X1
Is read.

Next, the first
It is determined whether the white reference data X1 is equal to or less than a predetermined threshold value Vth (step T4). If the first white reference data X1 is larger than the threshold value Vth, the process returns from step T4 to step T2, and it is determined again whether or not the count value of the counter i is n. At this time, since the count value of the counter i is 1, it is determined that the count value is not n, and the count value of the counter i is rewritten to 2 (step T3). X2
Is read. Then, it is determined whether the read first white reference data X2 is equal to or less than the threshold value Vth (step T4).

As described above, the processing of steps T2 to T4 is repeatedly performed, and the n stored in the memory 18
The magnitudes of the first white reference data Xi and the threshold Vth are sequentially examined. When the first white reference data Xi that is equal to or less than the threshold value Vth is found (YES in step T5), the counter j is incremented (step T6), and the count value of the counter i is set to the scale line position CXj (step T6). T7). Next, the detected scale line position CX1 is stored in the memory 1.
8, the process returns to step T2, and the processing after step T2 is executed.

The processing of steps T2 to T7 is repeatedly executed, and the scale line positions CXj are detected one after another.
When it is determined in step 2 that the count value of the counter i is n, the counter j is checked to determine whether the value of the counter j is m (step T8). If the value of the counter j is m, it is determined that all the scale line positions CXj have been detected, and the scale line detection processing ends. On the other hand, if the value of the counter j is not m, it is determined that all the scale line positions CXj have not been detected, and a notification that the scale line position CXj has not been properly detected is given. The scale line detection processing ends.

When the first white reference data Xi is obtained, it is assumed that one scale line C formed on the correction chart 16 is read by a plurality of CCD elements adjacent to each other. In this case, there is a possibility that a plurality of first white reference data Xi equal to or less than the threshold value Vth are continuous. Therefore, one graduation line C is read by a plurality of CCD elements adjacent to each other, and in this graduation line detection processing, it is detected that the plurality of first white reference data Xi are continuously equal to or less than the threshold value Vth. , The CCD element near the center of the plurality of CCD elements adjacent to each other is set as the scale line position CXj.
For example, when the first white reference data X4, X5, X6, X7 are detected to be equal to or less than the threshold value Vth, i = 5 is set to the scale line position CX.
j. Thereby, the possibility that the scale line positions CXj equal to or larger than the number of the scale lines C formed on the correction chart 16 can be reduced.

Although the description of one embodiment of the present invention is as described above, the present invention is not limited to the above-described embodiment. For example, in the above-described embodiment, in order to match the image formation state on the line sensor when acquiring the second white reference data with the image formation state on the line sensor when acquiring the first white reference data. The zoom mechanism (zoom motor) built in the lens is controlled to adjust the magnification of the lens. However, when a fixed focus lens system is applied instead of the zoom lens having a built-in zoom mechanism, the image formation state on the line sensor at the time of acquiring the second white reference data is changed to the first white reference data. The position of the fixed-focus lens system with respect to the line sensor may be adjusted so as to match the image formation state on the line sensor at the time of acquisition of. In this case, in step S9 of the shading correction processing shown in FIG. 2, the moving amount and the moving direction of the fixed focus lens system are associated with the lens position before adjustment (the lens position corresponding to the reading magnification of the original image) in the memory. 18 may be stored.

The fixed-focus lens system forms an original image on a line sensor at a predetermined reading magnification. That is, the fixed-focus lens system does not have a zoom mechanism for greatly changing the reading magnification of the document unlike the zoom lens, and cannot change the reading magnification of the document positively. Therefore, when a fixed focus lens system is applied instead of the zoom lens, the lens position adjustment mechanism provided for focusing is manually operated to change the lens position by a very small amount. What is necessary is just to adjust the above-mentioned imaging state. Then, by reading the scale of a micrometer or the like provided in the lens position adjusting mechanism, in the shading correction processing to be performed thereafter, the image formation state on the line sensor at the time of acquiring the second white reference data and the first In order to match the image formation state on the line sensor at the time of acquiring the white reference data, it is not necessary to perform trial and error adjustment of the lens position.

In the above-described embodiment, the method of acquiring the white reference data using the correction chart has been described. However, it is not always necessary to use a correction chart, and it is possible to obtain white reference data that can perform good shading correction without using a correction chart. This method will be briefly described with reference to FIG.

By performing a reading operation by the line sensor in a state where the white reference plate provided on the original table is arranged at the reading position, the first white reference data Xi (i = 1 to n) is obtained.
(See FIG. 7A). Then, the obtained first white reference data Xi is stored in the memory. Next, the document table is moved, and the opening provided in the document table is arranged at the reading position. By performing the reading operation by the line sensor in this state, the second white reference data Yi
(I = 1 to n) is acquired (see FIG. 7B). The lens is adjusted so that the acquired second white reference data Yi substantially matches the first white reference data Xi stored in the memory, and the data acquired when the first white reference data Xi substantially matches the first white reference data Xi. What is necessary is just to make it white reference data. Even with such a method, similarly to the method according to the above-described embodiment, it is possible to obtain white reference data that can perform a good correction in which the influence of dust or the like attached to the white reference member is eliminated.

Further, in the above-described embodiment, the case where the present invention is applied to an image reading apparatus of a type in which the original table moves is described as an example. However, the present invention is applied to a case where the original table is fixed. The present invention can also be applied to an image reading apparatus in which an optical system such as a light source and a lens moves. In addition, various changes can be made within the scope of the technical matters described in the claims.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an electrical configuration of an image reading apparatus to which an embodiment of the present invention has been applied.

FIG. 2 is a flowchart illustrating a flow of a shading correction process.

FIG. 3 is a flowchart illustrating a flow of a shading correction process.

FIG. 4 is a diagram for explaining positions of a document table and a correction chart during a shading correction process, and an output state of a line sensor.

FIG. 5 is a flowchart illustrating a flow of a scale line detection process.

FIG. 6 is a diagram for explaining a difference between an optical path when acquiring white reference data and an optical path when reading a document held in a document holder.

FIG. 7 is a diagram for explaining a method of acquiring white reference data without using a correction chart.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 document 2 document table (document holding member) 3 document holder (document holding member) 6 white reference plate (white reference member) 8 readable position 11 lens 12 line sensor 15 DSP 16 correction chart 17 CPU 18 memory (storage means) C Scale line

Claims (10)

[Claims] 1. A shading correction for performing correction based on correction data on document image data obtained by reading a document held by a transparent document holding member with a line sensor having a plurality of photoelectric conversion elements. A light source for illuminating a predetermined position readable by a line sensor; an imaging optical system interposed between the light source and the line sensor; and a light transmissivity equivalent to that of the document holding member. A first data acquisition unit that acquires first white reference data by performing a reading operation with the white reference member advanced to the predetermined position, and a white reference member that moves the white reference member from the predetermined position. A second data acquisition unit for acquiring the second white reference data by performing a reading operation in a retracted state; Optical system adjusting means for adjusting the image forming optical system so that the image forming state on the line sensor coincides with the image forming state at the time of obtaining the first white reference data; and And a correction data acquiring means for acquiring the correction data by performing a reading operation with the white reference member retracted from the predetermined position after adjusting the image optical system. Correction device. 2. A shading correction for performing correction based on correction data on document image data obtained by reading a document held by a transparent document holding member with a line sensor having a plurality of photoelectric conversion elements. A light source for illuminating a predetermined position readable by a line sensor; an imaging optical system interposed between the light source and the line sensor; and a light transmissivity equivalent to that of the document holding member. A white reference member, a correction chart in which a predetermined image is formed on a transparent film-like member, and a first white by performing a reading operation with the white reference member and the correction chart advanced to the predetermined position. First data acquisition means for acquiring reference data; and a plurality of photoelectric elements included in the line sensor based on the acquired first white reference data. Means for identifying the photoelectric conversion element that has read the image formed on the correction chart; and retreating the white reference member from the predetermined position, and performing a reading operation with the correction chart advanced to the predetermined position. A second data acquisition unit for acquiring the second white reference data by performing the operation; and an image formed on the correction chart from the plurality of photoelectric elements included in the line sensor based on the acquired second white reference data. Means for specifying the photoelectric conversion element that has read the first and second white reference data; and a deviation amount between the position of the photoelectric conversion element specified based on the first white reference data and the position of the photoelectric conversion element specified based on the second white reference data. Based on this, the image formation state on the line sensor when the second white reference data is obtained matches the image formation state on the line sensor when the first white reference data is obtained. An optical system adjusting unit for adjusting the imaging optical system, and a reading operation in a state where the white reference member and the correction chart are retracted from the predetermined position after adjusting the imaging optical system by the optical system adjusting unit. And a correction data acquisition means for acquiring the correction data by performing the correction. 3. The image forming apparatus according to claim 1, further comprising a storage unit configured to store an adjustment amount of the imaging optical system by the optical system adjustment unit in association with a state of the imaging optical system before adjustment. The shading correction device according to the above. 4. The imaging system according to claim 1, wherein said imaging optical system is a zoom lens, and said optical system adjusting means adjusts a magnification of said zoom lens. Shading correction device. 5. The apparatus according to claim 1, wherein said imaging optical system is a fixed focus lens system, and said optical system adjusting means adjusts a position of said fixed focus lens system with respect to said line sensor. 4. The shading correction device according to any one of 1 to 3. 6. A shading correction for performing correction based on correction data on document image data obtained by reading a document held by a transparent document holding member with a line sensor having a plurality of photoelectric conversion elements. A first white reference data is obtained by performing a reading operation in a state in which a white reference member having the same translucency as the document holding member has advanced to a predetermined position readable by the line sensor. Acquiring a second white reference data by performing a reading operation in a state where the white reference member is retracted from the predetermined position; and forming an image on a line sensor at the time of acquiring the second white reference data. Is formed between the light source and the line sensor so as to match the image formation state on the line sensor when the first white reference data is obtained. Adjusting the optical system, and after adjusting the imaging optical system, performing a reading operation with the white reference member retracted from the predetermined position to obtain the correction data. A shading correction method comprising: 7. A shading correction for performing correction based on correction data on document image data obtained by reading a document held by a transparent document holding member with a line sensor having a plurality of photoelectric conversion elements. A method in which a correction chart in which a predetermined image is formed on a white reference member and a transparent film-like member having the same transparency as the document holding member is advanced to a predetermined position readable by the line sensor. By performing the reading operation in the state, the first
Acquiring white reference data; and identifying, from the plurality of photoelectric elements included in the line sensor, a photoelectric conversion element that has read an image formed on the correction chart, based on the acquired first white reference data. Step of retrieving the second reference data by retracting the white reference member from the predetermined position and performing a reading operation with the correction chart advanced to the predetermined position. (2) identifying a photoelectric conversion element that reads an image formed on the correction chart from a plurality of photoelectric elements included in the line sensor based on the white reference data; and identifying based on the first white reference data. The second white reference data is calculated based on the amount of deviation between the specified position of the photoelectric conversion element and the position of the photoelectric conversion element specified based on the second white reference data. Imaging optics provided between the light source and the line sensor so that the image formation state on the line sensor at the time of data acquisition matches the image formation state on the line sensor at the time of obtaining the first white reference data. Adjusting the system, and adjusting the imaging optical system by the optical system adjusting means, and then performing a reading operation in a state where the white reference member and the correction chart are retracted from the predetermined position, whereby the correction for the correction is performed. Obtaining a data. 8. The method according to claim 6, further comprising the step of storing the adjustment amount of the imaging optical system by the optical system adjustment unit in the storage unit in association with the state of the imaging optical system before adjustment. Or the shading correction method according to 7. 9. The image forming apparatus according to claim 6, wherein said image forming optical system is a zoom lens, and said step of adjusting said image forming optical system is a step of adjusting a magnification of said zoom lens. The shading correction method according to any one of the above. 10. The imaging optical system is a fixed-focus lens system, and the step of adjusting the imaging optical system is a step of adjusting a position of the fixed-focus lens system with respect to the line sensor. The shading correction method according to any one of claims 6 to 8, wherein