JP2002199218A - Image reader and image processing method, and storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reader that can correct shading with high accuracy even when no dust or dirt exists at a position of a reference white board equivalent to a position of a target pixel. SOLUTION: The image reader has a maximum value detection circuit 19 that calculates a maximum value among a data value of a target pixel of an image sensor (CCD) 15 and data values of surrounding pixels of the target pixel among image data by one line obtained by the image sensor 15 that reads a white board read, a differential circuit 20 that calculates a difference between the maximum value and the data value of the target pixel, a comparator circuit 22 that compares the difference with a prescribed value, and a shading correction circuit 24 that uses the maximum value for a reference white level of the target pixel when the difference is greater than a specified value on the basis of the comparison result by the comparator circuit 22 or uses the data value of the target pixel as it is for the reference white level of the target pixel when the difference is the specified value or below and uses the reference white level to conduct shading correction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image reading apparatus, an image processing method, and a storage medium for scanning a document surface with a linear image sensor such as a CCD and reading a document image.

[0002]

2. Description of the Related Art Conventionally, in an image reading apparatus that scans a document surface and reads a document image using a linear image sensor in which a plurality of pixels such as CCDs are arranged in a line, variations in pixel sensitivity of the linear image sensor, light sources, and optical Shading correction is performed based on white data obtained by reading a reference white plate in order to correct variations in brightness due to the characteristics of the system.

As shown in FIG. 6, when reference white data can be read without dust or dirt on the reference white plate, shading correction can be performed normally. However, as shown in FIG. If there is dust at the corresponding position, as shown in FIG. 7, the signal level (data value) of the corresponding pixel drops due to the influence of dust, and when this signal level is used as reference white data to perform shading correction, A portion read by the pixel is formed as a vertical streak on a document image obtained by reading, thereby causing image deterioration.

[0004] In order to eliminate the influence of dust or dirt which causes the image deterioration, the white data of an arbitrary target pixel (the data value of the target pixel obtained by reading the reference white plate) and the white data of the pixels in the vicinity thereof are compared with the white data of the target pixel. There has been proposed a method of calculating an average value or a maximum value of, and using this value as a reference white (reference white value) of a target pixel to perform shading correction.

[0005]

However, as described above, in the method of calculating the maximum value of the white data of the target pixel and the white data of the pixels in the vicinity of the target pixel, dust or dirt is present at the position of the reference white plate corresponding to the target pixel. And even if the read white data is ideal as a white reference, it will be replaced with the maximum value of the white data of the neighboring pixels, and conversely, the correction accuracy will deteriorate and image deterioration may occur. There was a problem.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and it is possible to accurately perform shading correction even when there is no dust or dirt at a position corresponding to a target pixel on a reference white plate. It is an object to provide an image reading device, an image processing method, and a storage medium.

[0007]

An image reading apparatus, an image processing method, and a storage medium according to the present invention are configured as follows.

(1) In an image reading apparatus, an image sensor in which a plurality of pixels are arranged in a line, a white plate, and the image data of one line obtained by reading the white plate by the image sensor. Detecting means for detecting a data value of an arbitrary pixel of interest of the image sensor and a maximum value among data values of pixels in the vicinity thereof; calculating means for calculating a difference between the maximum value and a data value of the pixel of interest; And a shading correction unit for performing shading correction on the document image data read by the image sensor, wherein the comparison result indicates that the difference value is equal to or greater than the predetermined value. The maximum value is used as the reference white value of the pixel of interest, and when the difference value is smaller than the predetermined value, the data value of the pixel of interest is A reference white value of Mamakono target pixel, the shading correction means is to perform the shading correction using the reference white value.

(2) In the image reading device of the above (1), the range of peripheral pixels used for detecting the maximum value can be changed.

(3) In the image reading apparatus of (1) or (2), a plurality of predetermined values to be compared with the difference value can be selected.

(4) In the image processing method, data of an arbitrary pixel of interest of the image sensor out of one line of image data obtained by reading the white plate by an image sensor in which a plurality of pixels are arranged in a line. The value and the maximum value of the data values of the peripheral pixels are detected, the difference between the maximum value and the data value of the pixel of interest is calculated, and the difference value is compared with a predetermined value. If the difference value is equal to or larger than the predetermined value, the maximum value is set as a reference white value of the target pixel. If the difference value is smaller than the predetermined value, the data value of the target pixel is used as a reference for the target pixel. A white value is set, and shading correction is performed on the document image data read by the image sensor using the reference white value.

(5) 1 is obtained by reading the white plate with an image sensor in which a plurality of pixels are arranged in a line.
Detect the maximum value of the data value of an arbitrary pixel of interest of the image sensor of the image data for the line and the data value of the pixels around this, and calculate the difference between the maximum value and the data value of the pixel of interest. Comparing the difference value with a predetermined value, and as a result of the comparison, when the difference value is equal to or more than the predetermined value, the maximum value is set as a reference white value of the pixel of interest, and the difference value is larger than the predetermined value. If the value is smaller, the data value of the target pixel is used as it is as the reference white value of the target pixel, and a program for realizing shading correction on the document image data read by the image sensor using the reference white value is executed. Stored in a storage medium.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 4 is a sectional view showing a schematic structure of an image reading apparatus according to the present invention, and FIG. 5 is a sectional view showing an internal structure of the optical carriage 1 of FIG. FIG.
The schematic structure of the image reading apparatus according to the present invention will be described with reference to FIG.

In FIGS. 4 and 5, reference numeral 1 denotes an optical carriage (hereinafter, simply referred to as a carriage) 1, which has an integrated optical system. 7 is a light source for irradiating the original surface, 8
Reference numeral denotes a reflector for increasing the illuminance of the document surface, and irradiates the document surface of the document 5 placed on the document table 4 with the irradiation light from the light source 7 and the reflected light reflected by the reflection plate 8. Light reflected from the original 5 is reflected by mirrors 9 to 13 respectively, and is imaged by a lens 14 on an image sensor (CCD) 15 in which a plurality of pixels are arranged in a line. can get.

The carriage 1 is mounted on a rail 6 so as to be movable left and right, and is driven by a motor (not shown) to sequentially read line image information on the original surface while moving in the direction of the arrow in FIG. Obtain two-dimensional image information of the surface.

Next, the general operation will be described.

First, when a reading start instruction is received,
The carriage 1 is moved to the home position. next,
The light source 7 is turned on, and the carriage 1 waits at the home position until the light amount becomes stable.

Thereafter, the reference white plate 2 attached to the home position of the document table 4 is read, and reference white data (reference white value) W for shading correction described later is used.
(N) is created. Here, n is a positive integer and represents a pixel number in the main scanning direction. When the number of effective pixels in the main scanning direction is 7,000, n is up to 7,000.

After creating the reference white data W (n),
While moving the carriage 1, the document image information (document image data) Di (n) of each line is read, and the following formula is calculated to perform shading correction of the document image data Do.
(N) is obtained.

Do (n) = Di (n) × Wref / W (n) Here, Wref is a fixed reference value of the white level, and 8
When quantizing with bits, it becomes FFh.

FIG. 1 is a block diagram showing the configuration of the first embodiment, and a method of creating the above-described reference white data will be described with reference to FIG.

In FIG. 1, reference numeral 16 denotes a preprocessing circuit.
After the analog image data (image signal) of the reference white plate 2 read by the CCD 15 is clamped to an appropriate level, it is clamped for each pixel and amplified. The amplified analog image data is input to the A / D converter 17 and is converted into a digital image signal. Image data digitized by the A / D converter 17 is input to the delay circuit 18.

In the following, the range in which the maximum value is detected is described as a target pixel and one pixel before and after the target pixel as shown in FIG.

FIG. 10 is a circuit diagram showing the configuration of the delay circuit. In the figure, 181 and 182 are flip-flops, and input image data is delayed in two stages by the flip-flops 181 and 182, and data Di (n) of a target pixel n and a pixel (n− The data value of a total of three pixels, i.e., the data value Di (n-1) of 1) and the data value Di (n + 1) of the pixel (n + 1) immediately after the target pixel, are sent to the maximum value detection circuit 19, the selector 21, and the shading correction circuit 24. Output.

In the maximum value detection circuit 19, the data Di (n
-1), maximum value Dmax of Di (n), Di (n + 1)
(N) is calculated and output to the difference circuit 20 and the selector 21 at the subsequent stage.

In the difference circuit 20, the maximum value Dmax (n)
Difference (Diff (n) = Dmax (n) −Di (n)) between the data value Di (n) and the data value Di (n) of the nth pixel is calculated.

The comparison circuit 22 compares the output Diff (n) from the difference circuit 20 with a specified value (predetermined value) C, and outputs the comparison result to the S terminal of the selector 21.

If the comparison result is Diff (n) ≦ C, the selector 21 selects the input of the A terminal, that is, the data value Di (n) of the pixel of interest and stores the data value Di (n) in the reference white storage memory 23 for shading correction. The data is output from the Y terminal and stored in the memory 23 as the reference white data value W (n) of the n-th pixel.

When Diff (n)> C, the selector 21 selects the input of the terminal B, that is, selects the maximum value Dmax (n) and outputs it to the memory 23 from the terminal Y.
The reference white data value W (n) of the n-th pixel is stored in the memory 23.

FIG. 11 shows reference white data (reference white value) when the above-described processing of this embodiment is performed when dust is present at a position corresponding to the nth pixel (pixel of interest) as shown in FIG. FIG. 12 shows reference white data (reference data) when only the maximum value detection processing is performed when dust is present at the position corresponding to the n-th pixel (pixel of interest) as shown in FIG. FIG. 11 and 12, C =
It is assumed to be 10.

In FIG. 12, the reference white data of the n-th pixel affected by dust is corrected to a level close to the data when there is no dust, but the reference white data of the (n-3) -th pixel not affected by dust is corrected. Although the data and the reference white data of the (n + 3) th pixel have an error due to a side effect of the maximum value detection processing, the processing described above is performed in FIG. Reference white data in which only the influence is corrected can be obtained.

At the time of reading the original image, the analog image data read by the CCD 15 is processed by the pre-processing unit 16 in the same manner as described above, and then the A / D converter 1
At 7, the data is converted into digital value data Di (n), and is input to a shading correction circuit (shading correction means) 24 via a delay circuit 18.

Further, the reference white data W (n) previously stored in the memory 23 is read out and input to the shading correction circuit 24, and the above-mentioned calculation Do (n) = Di (n) × Wref / W (n), and the original image data Do after shading correction
(N) is output.

In the configuration shown in FIG. 1, the maximum value detection circuit 19 determines the data value Di (n) of the target pixel of the CCD 15 and the data value Di (n) of one line of image data obtained by reading the white plate 2 by the CCD 15. Maximum value Dma of data values Di (n-1) and Di (n + 1) of one pixel before and after
x (n) is detected by the difference circuit 20.
The comparing circuit 22 calculates the difference between the data value Max (n) and the data value Di (n) of the target pixel, and the comparison circuit 22 calculates the difference value Diff.
Comparing means for comparing (n) with the specified value C is provided.

As described above, in the first embodiment, the difference value Di
When ff (n) is larger than the specified value C, the maximum value Dma
x (n) is set as a reference white value of the pixel of interest, and a difference value Diff
When (n) is equal to or smaller than the specified value C, the data value of the target pixel is used as it is as the reference white value of the target pixel, and the shading correction circuit 24 performs shading correction using this reference white value. If there is dirt or dust on the plate 2, these effects are removed, and even if there is no dust or dirt at the position corresponding to the target pixel of the reference white plate 2,
A shading correction can be performed with high accuracy, and an image reading apparatus with excellent image quality can be provided.

(Second Embodiment) FIG. 2 is a block diagram showing a configuration of a second embodiment. The same components as those in FIG. 1 are denoted by the same reference numerals and described.

In the figure, reference numeral 16 denotes a preprocessing circuit.
After the analog image data (image signal) of the reference white plate 2 read by the CCD 15 is clamped to an appropriate level, it is clamped for each pixel and amplified. The amplified analog image data is input to the A / D converter 17 and is converted into a digital image signal.

The data value Di (n) digitized by the A / D converter 17 is input to and stored in a memory 23 for storing a reference white for shading correction.

After one line of data is stored, the CP
U (detection means, calculation means, comparison means) 25 calculates the data value Di (n) of the pixel of interest n and the pixel (n-1) immediately before it.
, And the maximum value Dmax (n) of the data values of a total of three pixels, that is, the data value Di (n−1) of the immediately following pixel (n + 1) and the data value Di (n + 1) of the immediately succeeding pixel (n + 1).

Further, the calculated maximum value Dmax
The difference Diff (n) = Dmax (n) −Di (n) between (n) and the data value Di (n) of the n-th pixel is calculated.

The calculated Diff (n) is compared with a specified value C. If Diff (n)> C, Dmax (n) is replaced with the n-th reference white data W
As (n), the address of the data value Di (n) in the memory 23 is overwritten.

Thus, processing for one line is performed.

At the time of reading the original image, the analog image data read by the CCD 15 is processed by the pre-processing unit 16 in the same manner as described above, and then the A / D converter 1
At 7, the data is converted into digital value data Di (n) and input to a shading correction circuit (shading correction means) 24.

The reference white data W (n) previously stored in the memory 23 is read out and input to the shading correction circuit 24, and the above-mentioned calculation Do (n) = Di (n) × Wref / W (n), and the original image data Do after shading correction.
(N) is output.

FIG. 3 is a flowchart showing the operation of the reference white data creating process according to one embodiment. The above-described process will be described with reference to FIG. This operation is executed based on a program stored in a ROM (not shown) in accordance with an instruction from the CPU 25.

First, the white plate 2 is read by the CCD 15 (step S101), and the data value Di (n) of the pixel of interest and the data values Di (n-1) of the pixels before and after this pixel in the obtained one line of image data. ) And Di (n + 1) are detected (step S102). Next, the difference between the maximum value Dmax (n) and the data value Di (n) of the pixel of interest is calculated (step S103), and the difference value Diff (n) is compared with the specified value C (step S104).

Based on the result of this comparison, the difference value Diff
When (n) is larger than the specified value C, the maximum value Dmax
(N) is stored in the memory 23 as the reference white value (reference white data) of the target pixel (step S105). When the difference value Diff (n) is equal to or less than the specified value C, the data value Di (n) of the target pixel is stored in the memory 23 as the reference white value of the target pixel as it is (step S).
106).

As described above, in the second embodiment, the maximum value detection circuit 19, the difference circuit 20,
Since the processing of the selector 21 and the comparison circuit 22 is performed by the CPU 25, the same effect as that of the first embodiment can be obtained with a simple circuit configuration.

In the first and second embodiments, the range in which the maximum value is detected is described as three pixels. However, by expanding this range, it is possible to remove the influence of larger dust.

Further, it is also possible to change the specified value C and switch the dust detection sensitivity according to the type of image to be read, such as a photograph or a character.

The present invention can also be implemented as a storage medium storing a program for realizing the above-described processing (image processing).

[0053]

As described above, according to the present invention,
Even when there is no dust or dirt at the position corresponding to the target pixel on the reference white plate, the shading correction can be performed with high accuracy, so that there is an effect that the image quality can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment.

FIG. 2 is a block diagram showing a configuration of a second embodiment.

FIG. 3 is a flowchart illustrating a reference white data creation processing operation according to an embodiment;

FIG. 4 is a sectional view showing a schematic structure of an image reading apparatus according to the present invention.

FIG. 5 is a sectional view showing the internal structure of the optical carriage shown in FIG. 4;

FIG. 6 is a waveform diagram showing an output signal of the image sensor when a reference white plate without dust is read.

FIG. 7 is a waveform diagram showing an output signal of an image sensor when a reference white plate having dust is read.

FIG. 8 is a diagram showing a relationship between dust and pixels of an image sensor.

FIG. 9 is a diagram showing a maximum value detection range according to one embodiment;

FIG. 10 is a circuit diagram showing the configuration of the delay circuit shown in FIG. 1;

FIG. 11 is a diagram showing reference white data of one embodiment.

FIG. 12 is a diagram showing reference white data of one embodiment in which only a maximum value detection process is performed.

[Explanation of symbols]

2 reference white plate 15 image sensor (CCD) 18 delay circuit 19 maximum value detection circuit (detection means) 20 difference circuit (calculation means) 21 selector 22 comparison circuit (comparison means) 23 memory 24 shading correction circuit (shading correction means) 25 CPU (detection means, calculation means, comparison means)

Claims (5)

[Claims] 1. An image sensor in which a plurality of pixels are arranged in a line, a white plate, and arbitrary attention of the image sensor in one line of image data obtained by reading the white plate by the image sensor. Detecting means for detecting the data value of the pixel and the maximum value of the data values of the peripheral pixels; calculating means for calculating the difference between the maximum value and the data value of the pixel of interest; and comparing the difference value with a predetermined value Comparing means, and shading correction means for performing shading correction on the document image data read by the image sensor, wherein the comparison result by the comparing means indicates that the maximum value is set when the difference value is equal to or greater than the predetermined value. When the difference value is smaller than the predetermined value, the data value of the target pixel is used as the reference white value of the target pixel. An image reading device, wherein the shading correction means performs shading correction using the reference white value. 2. The image reading apparatus according to claim 1, wherein a range of peripheral pixels used for detecting the maximum value is variable. 3. The image reading apparatus according to claim 1, wherein a predetermined value to be compared with the difference value can be selected from a plurality of values. 4. A data value of an arbitrary pixel of interest of the image sensor in one line of image data obtained by reading the white plate by an image sensor in which a plurality of pixels are arranged in a line and pixels in the vicinity thereof. Of the data value of the target pixel is calculated, the difference between the maximum value and the data value of the pixel of interest is calculated, and the difference value is compared with a predetermined value. In the above case, the maximum value is used as the reference white value of the pixel of interest, and when the difference value is smaller than the predetermined value, the data value of the pixel of interest is used as the reference white value of the pixel of interest, An image processing method, wherein shading correction is performed on document image data read by the image sensor using a white value. 5. A data value of an arbitrary pixel of interest of an image sensor of one line of image data obtained by reading the white plate by an image sensor in which a plurality of pixels are arranged in a line, and pixels in the vicinity thereof. Of the data value of the target pixel is calculated, the difference between the maximum value and the data value of the pixel of interest is calculated, and the difference value is compared with a predetermined value. In the above case, the maximum value is used as the reference white value of the pixel of interest, and when the difference value is smaller than the predetermined value, the data value of the pixel of interest is used as the reference white value of the pixel of interest, A storage medium storing a program for implementing shading correction on document image data read by the image sensor using a white value.