JP7099146B2 - Image reader, image forming device and program - Google Patents

Description

The present invention relates to an image reader, an image forming apparatus and a program.

Generally, in an image reading device called a scanner, it is required to accurately quantize a document image and convert it into data into gradation values. On the other hand, it is known that an image reading device causes a reading gradation value error called a flare phenomenon. The reading gradation value error is an error that occurs in the reading gradation value in the attention image region of the captured image due to the difference in the peripheral image density.

Conventionally, there is a technique for correcting such a reading gradation value error by image processing. Patent Document 1 discloses a technique of detecting a flare state near the original surface of an image reader and using the detected flare state (function) to correct an error due to the flare phenomenon.

According to the conventional technique, it is effective as a means for correcting the white flare phenomenon affected by the white image of the original image by software. However, according to the conventional technique, there is a problem that it takes time and effort to acquire the flare distribution required for correction, and further, it is not possible to correct the black flare phenomenon which is affected when the density of the scanned image is high.

The present invention has been made in view of the above, and an object of the present invention is to correct for a white flare phenomenon and a black flare phenomenon, and to read the image density of a document with higher accuracy.

In order to solve the above-mentioned problems and achieve the object, the present invention is an image reading device that irradiates a document to be imaged with illumination light and photographs it with an image pickup element, and a peripheral image with respect to a region of interest of the photographed image. The influence of the density of the above-mentioned attention image is measured by using the cumulative calculation value of the peripheral image reading value and the first function as a coefficient and the addition value of the peripheral image reading value and the cumulative calculation value of the second function. The first function corrects the read image signal of the region, and is characterized in that the first function represents an increase in the amount of illumination light due to the density of the peripheral image with respect to the region of interest .

According to the present invention, it is possible to correct the white flare phenomenon and the black flare phenomenon and to read the image density of the original with higher accuracy.

FIG. 1 is a diagram schematically showing a configuration of an image forming apparatus according to an embodiment. FIG. 2 is a diagram schematically showing the configuration of an image reader. FIG. 3 is an explanatory diagram showing a black flare phenomenon in an image reader. FIG. 4 is a diagram schematically showing a scanned image in which a flare phenomenon occurs. FIG. 5 is a block diagram showing a configuration of a control unit of an image reader. FIG. 6 is a diagram illustrating basic terms in an image reader. FIG. 7 is a graph showing data for white flare correction. FIG. 8 is a graph showing data for black flare correction. FIG. 9 is a diagram showing an example of a reference chart used for black flare correction data acquisition and white flare correction data acquisition. FIG. 10 is a graph showing the evaluation area reading distribution. FIG. 11 is a diagram showing an example of a reference chart used for black flare correction data acquisition and white flare correction data acquisition. FIG. 12 is a diagram showing an outline of the correction calculation.

Hereinafter, embodiments of an image reading device, an image forming device, and a program will be described in detail with reference to the accompanying drawings.

FIG. 1 is a diagram schematically showing a configuration of an image forming apparatus 1 according to an embodiment. In FIG. 1, the image forming apparatus 1 is generally referred to as a multifunction device (MFP: Multifunction Peripheral / Printer / Product) having at least two functions of a copy function, a printer function, a scanner function, and a facsimile function.

As shown in FIG. 1, the image forming apparatus 1 includes a main body 2 and an automatic document feeder (hereinafter referred to as ADF) 3. The main body 2 has an image reading device 5 for reading an image of a document, and an image forming unit 9 including a writing unit 6, an engine unit 7, and a paper feeding unit 8. The ADF 3 sends the document to be read to the image reading device 5, and collects the document read by the image reading device 5. The image forming unit 9 forms an image of the captured image read by the image reading device 5.

Next, the image reading device 5 will be described.

FIG. 2 is a diagram schematically showing the configuration of the image reading device 5. As shown in FIG. 2, the image reading device 5 is an image reading device of a flatbed type. As shown in FIG. 2, the image reading device 5 includes a first traveling body 15, a second traveling body 17, a lens 20, and a line sensor 21.

The first traveling body 15 has a light source 12, a reflector 13, and a first mirror 14 that irradiate a document 11 placed on a contact glass 10 with light for reading.

The second traveling body 17 has a second mirror 16a and a third mirror 16b. The reading lens 20 collects the light from the third mirror 16b of the second traveling body 17. The line sensor 21 incidents the light collected by the reading lens 20. A CMOS (Complementary MOS) or a CCD (Charge Coupled Device) is used as an image pickup element in the line sensor 21.

The first traveling body 15 and the second traveling body 17 move in parallel with the contact glass 10 due to the rotation of the drive motor.

The flatbed type image reading device 5 is roughly classified into two reading methods. The first method is a method in which the line sensor 21 reads the document image two-dimensionally while the ADF3 moves the document 11 to be read in one direction. The second method is a method in which the document 11 is placed on the contact glass 10 and the document image is read two-dimensionally by the reading system including the line sensor 21 moving in one direction. Further, two types of optical systems are known: a reduction optical system and a 1x magnification optical system. Each of these types of image readers has a built-in light source 12 that illuminates the surface of the document. The present embodiment is intended for an image reader including any of these methods.

In the image reading device, it is required to accurately quantize the original image and convert it into a gradation value. On the other hand, it is known that an image reading device causes a reading gradation value error called a flare phenomenon. The reading gradation value error is an error that occurs in the reading gradation value in the attention image area of the captured image due to the difference in the peripheral image density. This phenomenon is caused by the following two physical phenomena.
(1) Fluctuation of illumination light amount in the image area of interest due to reflection of illumination light on the original surface (2) Fluctuation of imaging light due to diffusion of imaging light inside the image sensor

As shown in FIG. 2, the physical phenomenon of (1) is that the light illuminating the document 11 (primary illumination light) is reflected again by the light reflected according to the reflectance of the document 11 (secondary illumination light). It occurs due to the relighting phenomenon that illuminates the document 11. The higher the reflectance of the image area of interest, the greater the effect of this fluctuation in the amount of illumination light. As a correction method for this phenomenon, a correction by software shown in Patent Document 1 (Patent No. 4159867) and the like has been proposed.

The physical phenomenon of white flare will be described below together with the explanation of FIG.

The light source 12 irradiates the document 11 directly as primary illumination light or via the reflector 13, and a part of the reflected light in the reading area follows the reading optical axis to the first mirror 14, the second mirror 16a, and the third mirror 16b. The image is formed on the image pickup element surface of the line sensor 21 by the reading lens 20 via the above. A part of the primary illumination light reflected on the surface of the document 11 is reflected by a component of the image reading device 5 to illuminate the reading area again, which is called a secondary illumination light. The intensity of this secondary illumination light changes greatly depending on the reflectance (image density) on the surface of the document 11. That is, in this phenomenon, the amount of illumination light changes depending on the peripheral image density of the attention image region, and the higher the reflectance of the attention image region (the lower the density), the more affected it. Since such a phenomenon is strongly influenced by the white image of the document 11, it is called a white flare phenomenon.

Next, the black flare phenomenon, which is the physical phenomenon of (2), will be described. FIG. 3 is an explanatory diagram showing a black flare phenomenon in the image reader 5.

As shown in FIG. 3, the physical phenomenon of (2) is that the imaged light generated by the reading lens 20 from the image of the document 11 reaches the image pickup element 21b of the line sensor 21 and reaches the glass 21a of the line sensor 21. A part of it is reflected and reaches the image pickup element 21b of the line sensor 21 again as diffusely reflected light.

In the case of this phenomenon, it is determined only by the amount of incident light on the part where the diffusely reflected light is generated, regardless of the amount of incident light of the imaged light on the part where the diffusely reflected light is incident. Further, it is known that the reading fluctuation caused by this phenomenon is relatively small as compared with the one caused by the white flare phenomenon. Further, it is caused by the difference in the density of the surrounding original regardless of the density of the image area of interest.

The image sensor 21b of the line sensor 21 mounted on the image reader 5 basically outputs a signal value in proportion to the amount of incident light, whereas human recognition recognizes the amount of light as there are indicators such as density and brightness. It is said to be proportional to the logarithm of and the 1/3 power. Therefore, the human eye is particularly sensitive to images on the dark side (high density), and a slight difference in the image reading value linear in the amount of light causes a large difference when converted to a density value. That is, this phenomenon is called a black flare phenomenon because it has a large effect when the scanned image is black (when the density is high).

What is common to the two flare phenomena as described above is that the reading value fluctuates depending on the peripheral density of the image to be read, and an image inspection device that requires particularly accurate image reading. It is known that such a case causes a large shooting error.

FIG. 4 is a diagram schematically showing a scanned image in which a flare phenomenon occurs.

As shown in FIG. 4, with respect to the original image, the white flare generation portion is darkened in the center, and the black flare generation portion is slightly whitish. The white flare phenomenon in which the periphery is black and the central portion is darkened is because the image reading device 5 performs shading processing on the reference image whose entire surface is white. In this shading state, white flare is maximized. Since this state is used as a reference, the central portion of the document whose both sides are black becomes dark due to almost no secondary illumination light, and becomes darkened. On the contrary, a black flare phenomenon occurs in the lower black patch portion, and the illumination light in the peripheral white portion is repeatedly reflected inside the image sensor of the line sensor 21 to read the black patch slightly white.

Next, the control system included in the image reading device 5 will be described.

FIG. 5 is a block diagram showing the configuration of the control unit 41 of the image reading device 5. As shown in FIG. 5, the control unit 41 of the image reader 5 includes a central control unit 42, an A / D conversion unit 43, a shading correction unit 44, an image signal generation unit 45, an arithmetic processing unit 46, and a program. It has a storage unit 47, a data storage unit 48, a correction data storage unit 49, an image processing unit 50, an external output unit 51, and an external storage medium control unit 52.

The central control unit 42 has a CPU that controls the operation of the entire image reading device 5, and manages the operation of the entire device under various printing conditions input from the operation display unit 53 when reading and printing the image of the document 11.

The A / D conversion unit 43 converts the signal transmitted from the line sensor 21 into a digital signal, and sends the converted digital signal to the shading correction unit 44.

The shading correction unit 44 executes shading correction on the digital signal converted by the A / D conversion unit 43.

The image signal generation unit 45 stores the image data in the data storage unit 48.

The arithmetic processing unit 46 executes a predetermined arithmetic processing on the image data stored in the data storage unit 48.

The program storage unit 47 stores, for example, a measurement of flare correction data and a processing program for flare correction.

The flare correction data measurement and flare correction processing program executed by the image forming apparatus 1 of the present embodiment is a file in an installable format or an executable format, and is a CD-ROM, a flexible disk (FD), or a CD-. It is recorded and provided on a computer-readable recording medium such as R or DVD (Digital Versatile Disk).

Further, the measurement of flare correction data and the processing program of flare correction executed by the image forming apparatus 1 of the present embodiment are stored on a computer connected to a network such as the Internet and provided by downloading via the network. It may be configured to do so. Further, the measurement of flare correction data and the processing program for flare correction executed by the image forming apparatus 1 of the present embodiment may be provided or distributed via a network such as the Internet.

The flare correction data measurement and flare correction processing program executed by the image forming apparatus 1 of the present embodiment may be configured to be provided by incorporating it into a ROM or the like in advance.

The data storage unit 48 stores image data and the like. The correction data storage unit 49 stores, for example, flare correction data.

The image processing unit 50 includes an image recognition unit 54, a scaling unit 55, a filter unit 56, a gamma correction unit 57, and a gradation processing unit 58.

The external storage medium control unit 52 controls input / output from an external storage medium 59 such as a flexible disk or an optical disk.

Next, the process for correcting the white flare and the black flare described above will be described.

The arithmetic processing unit 46 operates in accordance with the processing program for measuring flare correction data stored in the program storage unit 47, thereby measuring flare correction data for correcting white flare and black flare in advance, and the correction data storage unit. Store in 49. Further, the arithmetic processing unit 46 operates according to the flare correction processing program stored in the program storage unit 47 to correct white flare and black flare based on the flare correction data stored in the correction data storage unit 49. ..

First, the concept of basic correction for white flare and black flare is shown below. FIG. 6 is a diagram illustrating basic terms in the image reader 5. The image reading area of the image reading device 5 is defined in two directions, a "main scanning" for line reading and a "secondary scanning" for the line reading operation. The light source 12 built in the image reading device 5 illuminates only the line reading area, and the light source 12 moves as it is scanned to maintain the positional relationship.

Next, a method for correcting white flare will be described. FIG. 7 is a graph showing data for white flare correction. FIG. 7A shows the distribution of the white flare function range, and FIG. 7B shows the distribution of the white flare function intensity value. In FIG. 7, Hw indicates a flare range in the main scanning direction. A indicates the rear flare range in the sub-scanning direction, and B indicates the front flare range in the sub-scanning direction.

The horizontal axis of the graph shown in FIG. 7A indicates the sub-scanning direction, and the vertical axis indicates the main scanning direction. The center of the rhombus in FIG. 7 (a) is set as the attention reading position. The graph shown in FIG. 7A is a flare distribution graph showing the degree of influence (%) of flare on the attention reading position in gradation (black has a higher degree of influence).

The degree of influence of flare indicates the amount of fluctuation in the amount of illumination light with respect to the reading position, and the original reading value at each point inside the rhombus affects the reading value according to the degree of influence with respect to the central attention reading position. Will be done. This rhombus shape is generally symmetrical in the main scanning direction, but is different in the sub-scanning direction because the optical system that affects flare is not the target, as in A and B in FIG. 7 (a).

Further, the total volume (Wmax) shown in the graph shown in FIG. 7B is the total amount of influence of white flare.

Next, a method for correcting black flare will be described. FIG. 8 is a graph showing data for black flare correction. FIG. 8A shows the distribution of the black flare function range, and FIG. 8B shows the distribution of the black flare function intensity value. In FIG. 8, Hb indicates a flare range in the main scanning direction. C indicates the front flare range in the sub-scanning direction, and D indicates the rear flare range in the sub-scanning direction.

The horizontal axis of the graph shown in FIG. 8A indicates the sub-scanning direction, and the vertical axis indicates the main scanning direction. The center of the rhombus in FIG. 8 (a) is set as the attention reading position. It is a flare distribution graph showing the degree of influence (%) of flare on the attention reading position by gradation (black has a higher degree of influence).

The degree of influence of flare indicates the amount of incident light from the periphery with respect to the reading position, and the original reading value at each point inside the rhombus becomes the reading value according to the degree of influence with respect to the central attention reading position. It will affect you. This rhombus shape is generally symmetrical in the main scanning direction, but is different in the sub-scanning direction because the optical system that affects flare is not the target, as in C and D in FIG. 8 (a).

Further, the total volume (Bmax) shown in the graph shown in FIG. 8B is the total amount of influence of the black flare.

As mentioned above, the white flare phenomenon is "multiplication" and the black flare phenomenon is "addition", so that the two flare phenomena cannot be processed in a unified manner. A simple calculation model formula for the read image signal value based on this phenomenon is shown below.
Scanned image signal = (white flare influence +1.0) x true read image signal + black flare influence value True read image signal = (read image signal-black flare influence value) / (white flare influence +1.0)

The white flare influence degree (white flare function: first function) is the flare illumination light ratio reflected around the document reading position. That is, the degree of influence of white flare (white flare function: first function) is a function representing an increase in the amount of illumination light due to the peripheral image density.

The black flare influence value (black flare function: second function) is an added value due to the flare light reflected around the reading image sensor. That is, the black flare influence value (black flare function: second function) is a function representing the amount of light read by the peripheral image density for the image sensor corresponding to the image region of interest.

The above-mentioned white flare influence degree and black flare influence value are the sum of peripheral data. Since the range (image range in the main scanning direction) differs between the white flare phenomenon and the black flare phenomenon in this peripheral range, the calculation formula (1) for correcting each flare by integrating these is as follows. Become.

Next, a method of acquiring each flare correction data for white flare and black flare will be described below.

FIG. 9 is a diagram showing an example of a reference chart used for black flare correction data acquisition and white flare correction data acquisition. Although the dimensions are shown in FIG. 9, it is an example using an A3 image as an example.

As shown in FIG. 9, the reference chart X1 for the main scanning flare distribution and the reference chart Y for the sub-scanning flare distribution are used for acquiring the white flare correction data. The reference chart X1 for the main scan flare distribution is a white triangle pattern that opens in the sub scan direction. The reference chart Y for the sub-scan flare distribution is a black-and-white band pattern that appears alternately with respect to the sub-scan direction.

On the other hand, as shown in FIG. 9, the reference chart X2 for the main scanning flare distribution and the reference chart Y for the sub-scanning flare distribution are used for acquiring the black flare correction data. The reference chart X2 for the main scan flare distribution is a black triangle pattern that opens in the sub scan direction. The reference chart Y for the subscan flare distribution is the same as that used for the white flare.

The arithmetic processing unit 46 uses the image data obtained by reading these charts X1, Y, and X2 to Hw / A / B shown in FIG. 7A and Hb / C / D shown in FIG. 8A. Calculate the value of.

The operator causes the image reader 5 for which the flare distribution is to be acquired to read the charts X1, Y, and X2. The arithmetic processing unit 46 takes out the data of the evaluation area O from the read image data and calculates the evaluation area reading value.

Here, FIG. 10 is a graph showing the evaluation area reading distribution. The arithmetic processing unit 46 derives the white flare-related characteristic value Hw / A / B and the black flare-related characteristic value Hb / C / D within the range shown in FIG.

Specifically, the main scanning flare range (Hw) of the white flare is the main scanning size corresponding to the width of the inclined portion (white flare influence range in the sub-scanning direction) of the evaluation area reading distribution shown in FIG. Further, the sub-scanning flare range (A, B) of the white flare corresponds to the width of the inclined portion (white flare influence range in the main scanning direction) of the portion where the image signal of the evaluation region reading distribution shown in FIG. 10 is high. Scan size.

The main scanning flare range (Hb) of the black flare is the main scanning size corresponding to the width of the inclined portion (black flare influence range in the sub-scanning direction) of the evaluation area reading distribution shown in FIG. Further, the sub-scanning flare range (C, D) of the black flare corresponds to the width of the inclined portion (white flare influence range in the main scanning direction) of the portion where the image signal of the evaluation region reading distribution shown in FIG. 10 is low. Scan size.

Subsequently, a method for calculating Wmax and Bmax will be described.

FIG. 11 is a diagram showing an example of a reference chart used for black flare correction data acquisition and white flare correction data acquisition.

As shown in FIG. 11, the reference chart Z is used for acquiring Wmax and Bmax data. The reference chart Z is a pattern in which the white area Z1 and the black area Z2 are separately formed in the sub-scanning direction (transportation direction). As shown in FIG. 11, a small black area J is provided in the black flare evaluation region, which is the white area Z1. The area H is a predetermined area of the white area Z1. Further, as shown in FIG. 11, a small area I on a white background is provided in the white flare evaluation area which is the black area Z2. The area K is a predetermined area of the black area Z2.

The operator causes the image reading device 5 that wants to acquire the flare distribution to read the chart Z. Since Wmax and Bmax can be considered as the maximum flare amount, the arithmetic processing unit 46 obtains Wmax and Bmax by the following formula using the readings of the points H, I, J, and K in the reference chart Z. ..
Wmax = H / I
Bmax = JK

By the above processing, flare correction data of white flare and black flare is calculated.

It should be noted that this calculation process may be performed for each image reading device (scanner) to be produced, but if the quality of the image reading device is stable, it is not necessary to perform this calculation process for each unit. The average value of several representatives is sufficient.

Further, this correction function has a correction function for each RGB image when the image reading device to be corrected is a color image reading device for RGB reading.

The outline of the actual correction calculation is shown in FIG. FIG. 12 is a diagram showing an outline of the correction calculation. As shown in FIG. 12, the true read image signal can be expressed by the following equation.
V'= (V-B) / (W + 1.0)
V': True scanned image signal V: Scanned image signal B: Black flare influence value W: White flare influence degree

If the pixel of interest is at the end and there is no image data within the function range, the image data is complemented with a gray value (60/255, etc.). Originally, the outside of the shooting range is not illuminated, and in many cases, it is a metal frame or the like, so it is possible to deal with this degree.

As described above, according to the present embodiment, the influence of flare on the low image density and the high image density can be corrected at the same time, so that all the gradations of the image can be corrected. It can be applied even under conditions with different causes. As a result, the flare phenomenon near the original surface is corrected and the flare phenomenon generated in the image sensor is corrected by one formula using two different functions, and the image density of the original is read with higher accuracy. Can be done.

In the above embodiment, an example in which the image forming apparatus 1 of the present invention is applied to a multifunction device having at least two of a copy function, a printer function, a scanner function, and a facsimile function will be described. It can be applied to any image forming apparatus such as a machine, a printer, a scanner apparatus, and a facsimile apparatus.

1 Image forming device 5 Image reading device 9 Image forming unit

Japanese Patent No. 4159867

Claims (6)

In an image reader that irradiates a document to be photographed with illumination light and photographs it with an image sensor.
The effect of the density of the peripheral image on the area of interest of the captured image is defined by the cumulative calculated value of the peripheral image reading value and the first function as a coefficient, and the cumulative calculated value of the peripheral image reading value and the second function. And is used as an additional value to correct the read image signal in the image region of interest .
The first function is a function representing an increase in the amount of illumination light due to the density of the peripheral image with respect to the attention image region.
An image reader characterized by this. In an image reader that irradiates a document to be photographed with illumination light and photographs it with an image sensor.
The influence of the density of the peripheral image on the area of interest of the captured image is defined by the cumulative calculated value of the reading value of the peripheral image and the first function as a coefficient, and the reading value of the peripheral image and the cumulative calculated value of the second function. And is used as an additional value to correct the read image signal in the area of interest.
The second function is a function representing the amount of light read by the density of the peripheral image with respect to the image sensor corresponding to the image region of interest.
An image reader characterized by this. The first function is
It is a function representing an increase in the amount of illumination light due to the density of the peripheral image with respect to the attention image region.
The image reading device according to claim 2 . The image reading device according to any one of claims 1 to 3 and the image reading device.
An image forming unit that forms an image of a captured image read by the image reader, and an image forming unit.
An image forming apparatus comprising. A computer that controls an image reader that irradiates the document to be photographed with illumination light and photographs it with an image sensor.
The effect of the density of the peripheral image on the area of interest of the captured image is defined by the cumulative calculated value of the reading value of the peripheral image and the first function as a coefficient, and the reading value of the peripheral image and the cumulative calculated value of the second function. And are used as an additional value to function as a means for correcting the read image signal in the image region of interest .
The first function is a function representing an increase in the amount of illumination light due to the density of the peripheral image with respect to the attention image region.
program. A computer that controls an image reader that irradiates the document to be photographed with illumination light and photographs it with an image sensor.
The influence of the density of the peripheral image on the area of interest of the captured image is defined by the cumulative calculated value of the reading value of the peripheral image and the first function as a coefficient, and the reading value of the peripheral image and the cumulative calculated value of the second function. And are used as an additional value to function as a means for correcting the read image signal in the image region of interest.
The second function is a function representing the amount of light read by the density of the peripheral image with respect to the image sensor corresponding to the image region of interest.
program.

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