JP2000244739A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an excellent image by applying gamma correction to image data read with a correction characteristic corresponding to an attribute of a gamma characteristic for each light receiving element after shading correction to eliminate nonuniformity of an image caused by dispersion in the characteristic of each light receiving element. SOLUTION: A ROM is provided with gamma correction tables A (8a), B (8b) that stores inverse characteristics of a gamma characteristic A of a light receiving element with a large downward projection and of a gamma characteristic B of the light receiving element with a small downward projection. The light receiving element reads an original image, the resulting signal is A/D- converted and corrected for shading, and the result is given to an image data gamma correction automatically 5. A selection flag Fs corresponding to the image data from an n-th light receiving element under processing at present is read from a selection table in the ROM, the gamma correction table A 8a or B 8b is selected in response to the value of the selection flag Fs and collated with the input value from the correction table for gamma correction.

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, and more particularly to an image reading apparatus for performing gamma correction.

[0002]

2. Description of the Related Art In a device including an image reading device as a configuration of a scanner device, a facsimile device, or the like, a contact image sensor is often used as a photoelectric conversion unit in a photoelectric conversion unit. The photoelectric conversion characteristics of the elements cannot be completely the same, and the light receiving sensitivity characteristics of each light receiving element vary widely, and the output characteristics of the read image vary. Even in a CCD image sensor, a similar variation occurs in output characteristics even though it is not as great as in a contact image sensor.

FIG. 3 shows light receiving elements A and B in the same sensor.
Shows an example of the variation of the light receiving sensitivity characteristic for each of the above, where the original characteristic A shows the relationship between the amount of received light in the sensor A and the output voltage level, and the original characteristic B shows the same relationship in the sensor B. ing. Original characteristic A shown in FIG.
When the image data obtained by A / D conversion of the voltage signals respectively obtained from the light receiving elements A and B having the respective characteristics of A and B are subjected to shading correction, the received light amount proportional to the reflectance of the document and the image data after shading correction are obtained. Relationship, that is,
The gamma characteristics are as shown in gamma characteristics A and B in FIG. 4. The signal level is normalized, and the gamma characteristic A is compared with the ideal characteristic in which the amount of received light and the data after shading correction are proportional. And B both have downward convex characteristics, but the degree of downward convex is different.

[0004]

As a result, the difference in gamma characteristics becomes large especially near the intermediate density. Because of such a difference in gamma characteristics of each light receiving element in the same sensor, a single gamma correction characteristic could not sufficiently correct the gamma characteristic of each light receiving element, and a halftone image was read. There has been a problem that image defects such as vertical streaks appear in the obtained image in some cases.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an image reading apparatus capable of performing gamma correction optimal for a gamma characteristic of each light receiving element of a photoelectric conversion unit.

[0006]

According to a first aspect of the present invention, there is provided an image reading apparatus comprising the steps of: subjecting an image signal obtained by reading an image by a photoelectric conversion unit to A / D conversion and performing shading correction; An image reading device that gamma-corrects and outputs the obtained image data, for each light-receiving element constituting the photoelectric conversion unit, an element-specific gamma characteristic attribute storage unit that stores in advance a gamma characteristic attribute of each light-receiving element; Element-specific gamma correction in which image data for each light-receiving element after shading correction is gamma-corrected with a correction characteristic corresponding to an attribute stored corresponding to each light-receiving element by the element-specific gamma characteristic attribute storage means, and output. Means.

According to a second aspect of the present invention, there is provided an image reading apparatus for subjecting an image signal obtained by reading an image by a photoelectric conversion unit to A / D conversion, performing shading correction, and performing gamma correction on the obtained image data for output. In the apparatus, for each light receiving element constituting the photoelectric conversion unit, an element-specific gamma characteristic attribute storage unit for storing an attribute of a gamma characteristic of each light receiving element, and when reading a white reference plate by the photoelectric conversion unit. Element-specific gamma correction attribute setting means for setting an attribute of each of the light-receiving elements stored in the element-specific gamma characteristic attribute storage means in accordance with an output voltage of an image signal for each of the light-receiving elements; and The image data for each light receiving element is gamma-corrected with the correction characteristic corresponding to the attribute stored for each light receiving element by the element-specific gamma characteristic attribute storage means and output. Characterized by comprising a that device by the gamma correction means.

According to a third aspect of the present invention, there is provided an image reading apparatus for subjecting an image signal obtained by reading an image by a photoelectric conversion unit to A / D conversion, performing shading correction, and performing gamma correction on the obtained image data for output. In the device, for each light receiving element constituting the photoelectric conversion unit, an element-specific gamma characteristic attribute storage unit for storing an attribute of a gamma characteristic of each light receiving element, and the photoelectric conversion unit for shading correction. The light-receiving element stored by the element-specific gamma characteristic attribute storage means according to each value of shading correction data obtained by A / D converting an image signal for each light-receiving element obtained by reading a white reference plate. Element-specific gamma characteristic attribute setting means for setting each attribute; and image data for each light-receiving element after shading correction, Storage means, characterized in that a device-specific gamma correction means for gamma correction and outputs the correction characteristic corresponding to the attribute stored in correspondence with each light receiving element.

According to a fourth aspect of the present invention, in the image reading apparatus according to the third aspect, the element-specific gamma characteristic attribute setting means uses a white reference plate by the photoelectric conversion unit for shading correction. The light receiving means stores the gamma characteristic attribute storing means for each element in accordance with a high-order specific bit of each value of shading correction data obtained by A / D converting an image signal for each light receiving element obtained by reading. It is characterized by setting the attribute of each element.

According to a fifth aspect of the present invention, in the image reading apparatus according to any one of the first, second, third and fourth aspects, the gamma correction means for each element comprises a plurality of gamma correction sections having different characteristics. A table storage unit for storing a table, wherein the gamma characteristic attribute storage unit for each of the light-receiving elements after shading correction matches the attribute stored in the gamma characteristic attribute storage unit corresponding to each light-receiving element. A correction table is sequentially selected from a plurality of gamma correction tables stored in the table storage means, and gamma correction is performed with reference to the selected gamma correction table.

According to a sixth aspect of the present invention, in the image reading apparatus according to any one of the first, second, third and fourth aspects, the gamma correction means for each element performs gamma correction having different characteristics. While having a plurality of gamma calculating means, the gamma calculating means adapted to the image data for each of the light receiving elements after shading correction and adapted to the attribute stored by the element-specific gamma characteristic attribute storing means corresponding to each light receiving element. Sequentially selecting from a plurality of gamma calculation means,
The gamma correction is performed by a calculation by the selected gamma calculation means.

[0012]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment of the present invention will be described in detail.

FIG. 1 shows a block configuration of an image reading apparatus 1 according to the present embodiment.

In FIG. 1, an image reading apparatus 1 includes a photoelectric conversion unit 2, an A / D conversion unit 3, a shading correction unit 4, a gamma correction unit 5, an output unit 6, a control unit 7, a ROM 8, a RAM.
9, an operation unit 10, and a system bus 11.

The photoelectric conversion unit 2 includes a CCD image sensor,
It is composed of a CIS (contact) image sensor or the like, and generates an analog image signal corresponding to the amount of light received from the reading surface for each light receiving element. The A / D converter 3 converts an analog image signal from each light receiving element input from the photoelectric converter 2 into multi-valued image data as a digital signal. The shading correction unit 4 corrects distortion due to a difference in light receiving element sensitivity, and normalizes multi-valued image data. The gamma correction unit 5 performs gamma correction on the multi-valued image data after the shading correction, and converts a characteristic of the output image data with respect to the document reflectance into a desired output characteristic.

The output unit 6 differs depending on the apparatus to which the image reading apparatus 1 is applied. If the apparatus to which the image reading apparatus 1 is applied is an image scanner, it is an external interface to a PC or the like, and may be a digital copying machine or a facsimile machine. For example, it is an internal interface to the image processing unit, and outputs multi-valued image data after gamma correction. The control unit 7 is a microcomputer that controls the entire device. ROM8
Is a read-only memory that is read by the control unit 7, and stores various control programs and various data tables performed by the control unit 7. The RAM 9 is a random access memory serving as a work area of the control unit 7.
The contents of the RAM 9 are retained by a backup circuit (not shown) even when the power of the apparatus is turned off. Operation unit 10
Is provided with various keys for accepting an operation input by a user. The system bus 11 is a signal line through which the above-described units exchange data. Note that the analog image signal from the photoelectric conversion unit 2 is directly input to the A /
It is directly input to the D conversion unit 3.

FIG. 2 shows a flow of processing of image data in the image reading apparatus 1.

In FIG. 1, a photoelectric converter 2 outputs a voltage for each light receiving element according to the amount of received light as an analog image signal. In that case, the relationship between the amount of received light and the output voltage for each light receiving element should ideally be proportional, but in practice,
The amount of received light and the output voltage are not proportional and have distorted characteristics.
The light receiving sensitivity characteristic of each light receiving element of the photoelectric conversion unit 2 is represented by an original characteristic A corresponding to the light receiving element A and an original characteristic B corresponding to the light receiving element B shown in FIG. Different. The original characteristic A includes a downwardly convex gamma characteristic and has relatively high overall light receiving sensitivity. Original characteristic B
Includes a gamma characteristic in which the degree of downward projection is greater than the original characteristic A, and the overall light receiving sensitivity is relatively low.

The analog image signal from the photoelectric conversion unit 2 is
The A / D converter 3 performs A / D conversion at a predetermined bit resolution.
Although converted and output as digital image data, in the present embodiment, it is assumed that the A / D conversion unit 3 performs A / D conversion with a resolution of 256 gradations from 0 to 255 in 8 bits.

Even after A / D conversion, the original characteristic A shown in FIG.
Although the variation in the characteristics of B and B is not improved, the overall variation in the light receiving sensitivity is corrected by normalization as shown by the gamma characteristics A and B in FIG. And only the variation of the gamma characteristic remains.

In the shading correction in the shading correction section 4, the shading correction data 9a
Is referred to. The shading correction data 9a is
Prior to the reading of the original image, a white reference plate (not shown) is read by the photoelectric conversion unit 2, and A / D conversion is performed by the A / D conversion unit 3. As shown, it is stored in the storage area 9a of the RAM 9.

The image data subjected to shading correction by the shading correction unit 4 is gamma-corrected by the gamma correction unit 5. The gamma correction unit 5 performs gamma correction on the input image data by table conversion with reference to the gamma correction table and outputs the gamma correction to the output unit 6. Therefore, the gamma correction table has a range of possible values of the input image data, that is, , 0 to 255 are stored.

There are two gamma correction tables that can be referred to by the gamma correction section 5, that is, gamma correction tables 8 a and 8 b. These tables are determined by a selection flag Fs stored in an element-specific gamma characteristic selection table 8 c described later. The switching is sequentially performed according to the light receiving element being processed by the controlled SW1.

In FIG. 4, in order to correct the gamma characteristic A to make it an ideal characteristic, the characteristic inverse to the gamma characteristic A, as shown in FIG.
Needs to be stored and referred to as a gamma correction table. Further, in order to correct the gamma characteristic B, it is necessary to store and refer to a table corresponding to the gamma correction characteristic B as a gamma correction table. It goes without saying that the ideal characteristics after gamma correction are not limited to linear characteristics.

Ideally, all the gamma correction tables optimal for the gamma characteristics of the respective light receiving elements are stored, and the gamma correction tables corresponding to the light receiving elements that output the image data being processed are sequentially switched and referred to. However, since the memory capacity consumed for storing the gamma correction table is enormous, as shown in FIG. 7, the gamma correction table 8a and the gamma correction table 8b
Only the two types of gamma correction tables are stored in the ROM 8 in advance.

The gamma correction table 8a is a table having a characteristic opposite to the gamma characteristic A shown in FIG.
The relationship between input and output is as shown in FIG. The gamma correction table 8b is a table having a characteristic opposite to that of the gamma characteristic B shown in FIG. 4, and has a specific relationship between input and output as shown in FIG. 8B.

The gamma correction characteristic selection table 8c for each element is stored in the ROM 8. The table 8c has a specific configuration shown in FIG. 9, in which the element number (maximum N) corresponding to each light receiving element constituting the photoelectric conversion unit 2 is associated with the value of the selection flag Fs. It is. When the value of the selection flag Fs is 0, it indicates that SW1 is switched on the gamma correction table A side in FIG. 2, and when the value of the selection flag Fs is 1, SW1 is switched on the gamma correction table B side in FIG. This indicates that it can be switched.

The light receiving elements corresponding to each element number actually show various gamma characteristics, and the corresponding selection is made according to which of the gamma characteristics A or B shown in FIG. The value of the flag Fs is set. That is,
The value of the selection flag Fs corresponding to each element number indicates an attribute that is closer to the gamma characteristic A or B of the gamma characteristic of each light receiving element.

Whether each gamma characteristic is closer to the gamma characteristic A or B is determined, for example, by determining that the level of the data after shading correction at the light receiving amount corresponding to the intermediate density at which the difference between the gamma characteristics is most likely to appear. The comparison can be made by comparing which one of the characteristics A and B is closer to the corresponding level. The element-specific gamma correction characteristic selection table 8c is created in advance by such a comparison, and is stored in the ROM.
8 is stored. Needless to say, the table 8c may be stored in the RAM 9.

Then, the image reading apparatus 1 performs a reading process shown in FIG.

Referring to FIG. 1, the image reading apparatus 1 first
Perform shading correction data collection processing (processing 10
1).

FIG. 11 shows a specific processing procedure of the shading correction data collection processing in the processing 101.

In the figure, first, one line of a white reference plate (not shown) is read by the photoelectric conversion unit 2 (step 20).
1) A / D conversion is performed by the A / D conversion unit 3 (processing 20).
2) The obtained image data for each light receiving element is stored in the storage area 9a of the RAM 9 (process 203).

FIG. 12 shows the specific contents of the shading correction data stored in the storage area 9a of the RAM 9 by the process 203. In the figure, the shading correction data is obtained by associating the element number (maximum N) corresponding to each light receiving element constituting the photoelectric conversion unit 2 with the image data value Vs. In the figure, the shading correction data is stored in 8 bits. However, in shading correction, shading correction is rarely performed at the same resolution as the number of bits of image data. Is 8 bits, shading correction is performed using only the upper 4 bits as shading correction data, and the lower 4 bits are allowed to remain uncorrected, thereby simplifying the shading correction processing. It goes without saying that only the upper characteristic bits may be stored as the value Vs.

Returning to FIG. 10, after the shading correction data collection processing of processing 101 is performed, the counter n is initialized to 1 (processing 102), and the n-th pixel corresponding to the element number n constituting the photoelectric conversion unit 2 is processed. The image of the minute is read by the photoelectric conversion unit 2 (process 103), and the A / D
D conversion is performed (process 104), and shading correction is performed by the shading correction unit 4 (process 105). In the shading correction in the process 105, the shading correction data 9a collected in the process 101 is referred to.

The image data from the n-th light receiving element, which has been subjected to shading correction in step 105, is gamma-corrected by the gamma correction section 5 and output to the output section 6 (step 106).

After the process 106, it is determined whether or not the counter n has reached N, that is, the total number of pixels constituting the photoelectric conversion unit 2 (decision 107).
s) to determine whether there is a next line to be read (determination 1)
09) If not (No in decision 109), the reading process is terminated. If the counter n has not yet reached N in the judgment 107 (No in the judgment 107), the counter n
Is incremented, and the processing returns to the processing 103. Also, judgment 1
09, if there is a next line (Ye in decision 109)
s), and return to processing 102;

As a result, the original image is read, subjected to shading correction, and output after being subjected to gamma correction.
Regarding a specific procedure of the gamma correction processing of the processing 106,
This will be described with reference to FIG.

In the figure, first, a selection flag F corresponding to the image data from the n-th light receiving element currently being processed.
The value of s (n) is set in the gamma correction characteristic selection table 8c for each element.
And judges its value (decision 301). Fs
If the value of (n) is 0, the gamma correction table A is selected (step 302), and the value of the image data from the n-th light receiving element is compared with the input value of the selected gamma correction table A. Then, gamma correction for outputting a corresponding output value is performed (process 304). If the value of Fs (n) is 1, the gamma correction table B is selected (step 303), and the value of the image data from the n-th light receiving element is determined by the input value of the selected gamma correction table B. The collation is performed, and gamma correction for outputting a corresponding output value is performed (process 304).

Thus, gamma correction can be performed with a correction characteristic that is optimal for the attribute of the gamma characteristic of the n-th light receiving element to be processed. Needless to say, three or more gamma correction tables may be prepared to increase the accuracy of gamma correction.

As shown in FIG. 7, the element-specific gamma correction characteristic selection table 8c in which the value of the selection flag Fs corresponding to each element number is set in advance is not stored in the ROM 8, but is shown in FIG. As described above, only the gamma correction tables A and B are stored in the ROM 8 in advance, and the element-specific gamma correction characteristic selection table 9b having the same configuration as the element-specific gamma correction characteristic selection table 8c as shown in FIG.
As shown in FIG. 15, the reading process shown in FIG. 10 may be performed by storing it in the RAM 9 together with the shading correction data 9a.

In this case, however, the processing shown in FIG. 16 is performed instead of the processing shown in FIG. 11 as the shading correction data collection processing in processing 101, and the gamma correction processing in processing 106 specifically shown in FIG. Then, the gamma correction characteristic selection table 9b for each element is referred to.

The procedure of the shading correction data collection process shown in FIG. 16 will be described.

In the figure, first, one line of a white reference plate (not shown) is read by the photoelectric conversion unit 2 (step 40).
1) A / D conversion is performed by the A / D conversion unit 3 (processing 40).
2) The obtained image data for each light receiving element is stored in the storage area 9a of the RAM 9 (process 403).

Then, the counter n is initialized to 1 (step 404).
Element number n of the shading correction data stored in No. 9
It is determined whether or not the data value Vs (n) corresponding to is greater than the threshold level Lth (decision 405).

The data value Vs (n) has a threshold level Lth
If it is larger (Yes in decision 405), the selection flag Fs corresponding to the element number n in the element-specific gamma correction characteristic selection table 9b stored in the RAM 9 with the configuration shown in FIG.
The value of (n) is set to a value 0 corresponding to the gamma correction table A (process 406). If the data value Vs (n) is smaller than the threshold level Lth (No in decision 405),
The value of the selection flag Fs (n) corresponding to the element number n in the element-specific gamma correction characteristic selection table 9b is set to the value 1 corresponding to the gamma correction table B (process 407).

Then, judgment 405, processing 406, processing 4
07 is repeated until the counter n reaches the maximum element number N (Yes in decision 408) (No in decision 408, process 409).

Thus, the shading correction data is collected, and the gamma characteristic attribute of each light receiving element is set using the shading correction data.

Here, in the judgment 405, the data value Vs corresponding to the element number n of the shading correction data
As shown in FIG. 3, the threshold level Lth to be compared with (n) is a substantially intermediate value between the voltage levels of the original characteristics A and B corresponding to the amount of received light when the white reference plate is read.

Due to the influence of the output voltage loss due to the load inside the circuit of the photoelectric conversion unit 2 and the like, the lower the sensitivity (the output voltage level with respect to a given amount) of each light receiving element constituting the photoelectric conversion unit 2, the lower the gamma characteristic. Tend to be more convex downward. That is, there is a correlation between the sensitivity of each light receiving element and the gamma characteristic, and the gamma characteristic of the light receiving element that outputs a data value Vs larger than the threshold level Lth is closer to the gamma characteristic A shown in FIG. It can be said that the gamma characteristic of the light receiving element that outputs the data value Vs smaller than the level Lth is closer to the gamma characteristic B shown in FIG.

Therefore, the gamma characteristic attribute for each light receiving element can be set by using the data collected for shading correction, and the gamma characteristic attribute can be set by measuring the gamma characteristic itself for each light receiving element. This is much simpler than the above, and can be executed for each reading process. Therefore, it is possible to flexibly cope with a temporal change in the gamma characteristic of the light receiving element. Needless to say, the accuracy of gamma correction may be improved by setting a plurality of threshold levels Lth and preparing three or more corresponding gamma correction tables. Also, instead of comparing the shading correction data, which is data obtained by A / D converting the image signal obtained by reading the white reference plate with the A / D conversion unit 3, with the threshold level Lth, the white reference plate is used. The gamma characteristic attribute of each light receiving element may be determined by comparing the read image signal with a predetermined threshold level signal at the stage of an analog signal.

Further, in place of the configuration shown in FIG.
The original image may be read by the configuration shown in FIG.

The configuration shown in FIG. 17 is different from the configuration shown in FIG. 2 in that the gamma correction section 5 replaces the gamma correction data A with the gamma correction coefficient table A, and replaces the gamma correction data B with the gamma correction coefficient table B. Is switched and referenced by a switch SW1 controlled by a selection flag Fs, and gamma correction is performed not by table conversion but by a broken line approximation calculation.

Therefore, as shown in FIG. 18, the gamma correction coefficient tables A and B are stored in the ROM 8 together with the gamma correction characteristic selection table 8c for each element having the structure shown in FIG.

FIG. 19 shows the contents of the coefficient table stored as the gamma correction coefficient table A or B. In the figure, coefficients T0, T1, and T2 are values serving as breaks for dividing the range of 0 to 255 that can be taken by the data after shading correction into four. Coefficients T0, T1 and T2
May be set to a value that divides the range of 0 to 255 at equal intervals, or may be set so that a range where the change in the gamma correction characteristic is large is narrow and a range where the change is small is wide. In addition, in order to increase the accuracy of the polygonal line approximation, it may be divided into five or more divisions.

The coefficients a0 and b0 are values for determining a straight line (a0x + b0) that approximates the gamma correction characteristic in the range of 0 ≦ x <T0, where x is the data after shading correction. Similarly, the coefficients a1 and b1 are given by T0 ≦ x <T
This is a value for determining the straight line (a1.x + b1) in the range of 1. Similarly, the coefficients a2 and b2 are T1 ≦ x <T2
Is a value for determining the straight line (a2.x + b2) in the range of. Similarly, the coefficients a3 and b3 are T2 ≦ x <256
Is a value for determining the straight line (a3.x + b3) in the range of.

The gamma correction coefficient table A is obtained by approximating the gamma correction characteristic A of FIG. 5 with a polygonal line, and the gamma correction coefficient table B is obtained by approximating the gamma correction characteristic B of FIG. 5 with a polygonal line.

With the above configuration, the reading process shown in FIG. 10 is performed, the process shown in FIG. 11 is performed as process 101 in FIG. 10, and the process shown in FIG. 13 is performed as process 106 in FIG. Gamma correction can be performed with a correction characteristic that is optimal for the attribute of the gamma characteristic of the target n-th light receiving element. In this case, the gamma correction coefficient table A is selected in the processing 302 of FIG. 13, and the gamma correction coefficient table B is selected in the processing 303 of FIG. Needless to say, three or more gamma correction coefficient tables may be prepared to improve the accuracy of gamma correction.

In the processing 304 of FIG.
Alternatively, the procedure of gamma correction in the gamma correction unit 5 performed with reference to the gamma correction coefficient table A or B selected in the process 303 will be described with reference to FIG.

In the figure, a gamma correction coefficient table A
Alternatively, when the data x after shading correction is input from the shading correction unit 4, the gamma correction unit 5 that performs the gamma correction operation while
If it is less than 0 (Yes in decision 501), a0.
x + b0 is output to the output unit 6 (process 502), and the data x
Is not greater than 0 and less than T0 (N of decision 501)
o), if the data x is equal to or greater than T0 and less than T1 (Yes in decision 503), a1.x + b1 is output to the output unit 6 (process 504), and if the data x is not greater than T0 and less than T1 ( No in decision 503), data x
Is greater than or equal to T1 and less than T2 (Ye in decision 505).
s), and outputs a2 × x + b2 to the output unit 6 (process 50).
6) Further, when the data x is not equal to or more than T1 and less than T2 (No in decision 505), that is, when the data x is equal to or more than T2 and less than 256, a3 · x + b3 is output to the output unit 6.
(Step 507).

As a result, it is possible to perform a gamma correction operation by broken line approximation. It is needless to say that the gamma correction calculation is not limited to the polygonal line approximation, and that other calculation methods such as curve approximation can be applied.

Also, as shown in FIG. 18, the element-specific gamma correction characteristic selection table 8c in which the value of the selection flag Fs corresponding to each element number is set in advance is not stored in the ROM 8, but is shown in FIG. As described above, only the gamma correction coefficient tables A and B are stored in the ROM 8 in advance,
An element-specific gamma correction characteristic selection table 9 having the same configuration as the element-specific gamma correction characteristic selection table 8c as shown in FIG.
15 may be stored in the RAM 9 together with the shading correction data 9a, as shown in FIG. 15, and the reading process shown in FIG. 10 may be performed.

In this case, however, the processing shown in FIG. 16 is performed instead of the processing shown in FIG. 11 as the shading correction data collection processing in the processing 101, and the gamma correction in the processing 106 specifically shown in FIG. In the processing, the gamma correction characteristic selection table 9b for each element is referred to.

As a result, the gamma characteristic attribute of each light receiving element can be set using the data collected for shading correction, and the setting is performed by measuring the gamma characteristic itself of each light receiving element. Since the setting is much simpler than the setting and can be executed for each reading process, it is possible to flexibly cope with a change with time in the gamma characteristic of the light receiving element.

[0065]

According to the first aspect of the invention, the gamma characteristic attribute of each light receiving element constituting the photoelectric conversion unit is stored in advance, and the image from each light receiving element after shading correction is stored. Since the data is gamma-corrected with the correction characteristics corresponding to the attributes of the respective gamma characteristics, even if there is a difference in the gamma characteristics between the respective light-receiving elements constituting the photoelectric conversion unit, the gamma corresponding to the gamma characteristics of the respective light-receiving elements is obtained. Correction can be performed, and an effect that an image with uniform output characteristics can be obtained without vertical stripes or the like can be obtained.

According to the second aspect of the present invention, the white reference plate is obtained by reading the white reference plate in view of the correlation between the magnitude of the output voltage from the light receiving element for a given amount of received light and the gamma characteristic. Since the attribute of the gamma characteristic for each light receiving element is set according to the output voltage of the image signal for each light receiving element, the gamma characteristic for each light receiving element is set in addition to the same effect as the invention according to claim 1. It saves the trouble of measuring and examining the attributes. In addition, since the gamma characteristic of each light receiving element is determined only by the output voltage when reading the white reference plate, the circuit can be simplified and the cost can be reduced.

According to the third aspect of the present invention, similarly to the second aspect of the present invention, in view of the fact that there is a correlation between the magnitude of the output voltage from the light receiving element for a given amount of received light and the gamma characteristic. Setting an attribute of a gamma characteristic for each light receiving element according to each value of the shading correction data equivalent to an output voltage of an image signal for each light receiving element obtained by reading the white reference plate. In addition to the same effect as that of the invention according to the first aspect, it is possible to eliminate the trouble of measuring the gamma characteristic of each light receiving element and examining the attribute, and further, each light receiving element can be obtained only by the output voltage when reading the white reference plate. Since the gamma characteristic is determined, the circuit can be simplified and the cost can be reduced. Further, since the shading correction data which is originally required for shading correction can be used for determining the attribute of the gamma characteristic of each light receiving element, there is an advantage that the reading process can be simplified.

According to the fourth aspect of the invention, in addition to the same effect as the third aspect of the invention, the gamma characteristic attribute of each light receiving element is determined by referring to all bits of each value of the shading correction data. Instead of judging, for example, the top 4
Since the determination is made by using a specific bit such as a bit, it is not necessary to refer to data having a large number of bits unnecessarily, and an effect that the circuit can be further simplified can be obtained.

According to the fifth aspect of the present invention, since the gamma correction is performed by the gamma correction table corresponding to the gamma characteristic attribute of each light receiving element, any light receiving sensitivity characteristic can be handled, and any gamma correction can be performed. The effect that the characteristic can be set is obtained.

According to the sixth aspect of the present invention, since gamma correction is performed by gamma calculation corresponding to the gamma characteristic attribute of each light receiving element, a memory for storing a gamma correction table corresponding to each gamma characteristic attribute is unnecessary. Thus, the effect that the cost can be reduced is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a block configuration of an image reading apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a flow of processing of image data.

FIG. 3 is a diagram illustrating a relationship between a light receiving amount and an output voltage level in a photoelectric conversion unit.

FIG. 4 is a diagram illustrating a relationship between a light receiving amount in a photoelectric conversion unit and data after shading correction.

FIG. 5 is a diagram illustrating a relationship between an input and an output in gamma correction.

FIG. 6 illustrates an RA of the image reading apparatus according to the embodiment of the present invention.
It is a figure showing about the storage contents of M.

FIG. 7 illustrates an RO of the image reading apparatus according to the embodiment of the present invention.
It is a figure showing about the storage contents of M.

FIG. 8 is a diagram showing specific contents of gamma correction tables A and B.

FIG. 9 is a diagram showing specific contents of a gamma correction characteristic selection table for each element.

FIG. 10 is a flowchart showing a reading processing procedure in the image reading apparatus according to the embodiment of the present invention.

FIG. 11 is a flowchart illustrating a specific processing procedure of shading correction data collection processing.

FIG. 12 is a diagram showing specific contents of shading correction data.

FIG. 13 is a flowchart illustrating a specific processing procedure of gamma correction processing.

FIG. 14 illustrates an image reading apparatus according to an embodiment of the present invention.
FIG. 8 is a diagram showing the storage contents of the OM, which is different from FIG. 7.

FIG. 15 illustrates an image reading apparatus according to an embodiment of the present invention;
FIG. 7 is a diagram showing the storage contents of the AM, which is different from FIG. 6.

FIG. 16 is a diagram showing a specific processing procedure of shading correction data collection processing, which is different from FIG. 11;

FIG. 17 shows the flow of processing of image data,
FIG.

FIG. 18 illustrates an image reading apparatus according to an embodiment of the present invention.
FIG. 15 is a diagram showing the storage contents of the OM, which is different from FIG. 7 or FIG. 14.

FIG. 19 is a diagram showing the contents of a gamma correction coefficient table.

FIG. 20 is a flowchart illustrating a specific processing procedure of gamma correction by polygonal line approximation.

FIG. 21 illustrates an image reading apparatus according to an embodiment of the present invention;
FIG. 7, FIG. 14, or FIG. 1 showing the stored contents of the OM
FIG. 8 is a diagram different from FIG.

[Explanation of symbols]

 Reference Signs List 1 image reading device 2 photoelectric conversion unit 3 A / D conversion unit 4 shading correction unit 5 gamma correction unit 6 output unit 7 control unit 8 ROM 8a gamma correction table A 8b gamma correction table B 8c gamma correction characteristic selection table for each element 8d gamma Correction coefficient table A 8e Gamma correction coefficient table B 9 RAM 9a Shading correction data 9b Gamma correction characteristic selection table for each element 10 Operation unit 11 System bus SW1 switch

Claims (6)

[Claims] 1. An image reading apparatus for A / D converting an image signal obtained by reading an image by a photoelectric conversion unit, performing gamma correction on image data obtained by performing shading correction, and outputting the image data, wherein the photoelectric conversion unit is configured. Gamma characteristic attribute storing means for each element in which an attribute of a gamma characteristic of each light receiving element is stored in advance for each light receiving element, and image data for each light receiving element after shading correction are stored in the gamma characteristic attribute for each element. An image reading device, comprising: an element-specific gamma correction unit for performing gamma correction with a correction characteristic corresponding to an attribute stored corresponding to each light receiving element and outputting the corrected gamma. 2. An image reading apparatus for A / D converting an image signal obtained by reading an image by a photoelectric conversion unit and performing gamma correction on image data obtained by performing shading correction and outputting the image data, wherein the photoelectric conversion unit is configured. Gamma characteristic attribute storage means for storing the gamma characteristic attribute of each light receiving element, and an image signal for each light receiving element at the time of reading the white reference plate by the photoelectric conversion unit Element-specific gamma correction attribute setting means for setting the attribute of each of the light-receiving elements stored in the element-specific gamma characteristic attribute storage means according to the output voltage of the element, and image data for each light-receiving element after shading correction, Element-specific gamma correction means for performing gamma correction with the correction characteristic corresponding to the attribute stored for each light-receiving element by the element-specific gamma characteristic attribute storage means and outputting the result; Image reading apparatus characterized by a. 3. An image reading apparatus for A / D converting an image signal obtained by reading an image by a photoelectric conversion unit and performing gamma correction on image data obtained by shading correction, and outputting the image data, wherein the photoelectric conversion unit is configured. For each light receiving element to be obtained, a gamma characteristic attribute storing means for each element for storing an attribute of a gamma characteristic of each light receiving element, and a white reference plate is read by the photoelectric conversion unit for shading correction. An element-specific gamma for setting an attribute of each of the light-receiving elements stored in the element-specific gamma characteristic attribute storage means according to each value of shading correction data obtained by A / D converting the image signal for each of the light-receiving elements. The characteristic attribute setting means and the gamma characteristic attribute storing means for each element correspond to each light receiving element. Image reading apparatus characterized by the correction characteristic corresponding to the stored attribute and a device-specific gamma correction means for gamma correction and outputs. 4. The element-specific gamma characteristic attribute setting means,
For shading correction, an image signal for each light receiving element obtained by reading a white reference plate by the photoelectric conversion unit is A / D converted to a higher specific bit of each value of shading correction data obtained. 4. The image reading apparatus according to claim 3, wherein the attribute of each of the light receiving elements stored in the element-specific gamma characteristic attribute storage unit is set in accordance with the attribute. 5. The device-specific gamma correction unit includes a table storage unit that stores a plurality of gamma correction tables having different characteristics, and the device-dependent gamma correction unit stores the image data of each of the light receiving elements after shading correction. The gamma correction table matching the attribute stored by the separate gamma characteristic attribute storage means corresponding to each light receiving element is sequentially selected from the plurality of gamma correction tables stored in the table storage means, and the selected gamma correction is performed. 5. The image reading apparatus according to claim 1, wherein gamma correction is performed with reference to a table. 6. The element-specific gamma correction means includes a plurality of gamma calculation means for performing gamma corrections having different characteristics, and converts the image data for each light-receiving element after shading correction into the element-specific gamma characteristic attribute. The storage means sequentially selects gamma calculation means suitable for the attribute stored corresponding to each light receiving element from the plurality of gamma calculation means, and performs gamma correction by calculation by the selected gamma calculation means. Claim 1, characterized in that:
The image reading device according to any one of 2, 3, and 4.