JP5849041B2 - Image forming apparatus and image reading apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus and an image reading apparatus.

  The image forming apparatus includes an image reading device that reads an original image using a CCD sensor, which is an image sensor. This image reading apparatus corrects high-frequency distortion, low-frequency distortion, and light emission characteristic distortion in an image signal. The high-frequency distortion is a distortion caused by variation in sensitivity of the photoelectric conversion sensor corresponding to each pixel constituting the CCD sensor. Low-frequency distortion is distortion generated by an optical system until light from an original is guided to a CCD sensor. The distortion of the light emission characteristic is distortion (light emission unevenness) of light irradiated on the document from the light source. In order to correct these distortions and unevenness, the image reading apparatus generally performs shading correction on the output signal of the CCD sensor.

  On the other hand, as a means for illuminating a document, there is known an image reading apparatus using three color LEDs of a red LED, a blue LED and a green LED as a light source. The LED has a large variation in light intensity compared to other light sources such as a xenon lamp. In view of this, a technique has been proposed that can prevent the occurrence of problems caused by variations in illumination light from the light source.

JP-A-9-294207

  By using the technique described in Patent Document 1, it is possible to prevent the occurrence of problems caused by variations in illumination light from the light source. By the way, the need to improve the quality of a read image is a problem to be solved at all times, and further quality improvement is required. Therefore, not only the above-described distortion and unevenness caused in the light source and the optical system, but also the corresponding distortion and unevenness caused by the characteristics of the CCD sensor is required.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an image forming apparatus and an image reading apparatus that can cope with distortion and unevenness caused by characteristics of an image sensor.

  According to an embodiment for solving the above-described problem, a plurality of light sources that irradiate a document surface that is a reading target, and an imaging unit that images light emitted from the plurality of light sources and reflected from the document surface; The black reference value is subtracted from a first memory that stores a black reference value that is an output of the imaging unit in a state where the imaging unit is not irradiated with light, and an imaging signal obtained by imaging the document surface by the imaging unit. The maximum value of the output of the first subtracter when a predetermined reference plane is irradiated only by the reference light source, using any one of the first subtractor and the plurality of light sources as a reference light source is predetermined. An image reading apparatus is provided that includes a control unit that adjusts the amount of light of the reference light source so as to have a value of.

1 is a diagram illustrating a configuration of an image forming apparatus according to an exemplary embodiment. 1 is a diagram illustrating a configuration of a CIS in an image forming apparatus according to an embodiment. FIG. 3 is a diagram illustrating a configuration of a control system related to image reading of the image forming apparatus of the present embodiment. It is a figure for demonstrating the shading correction | amendment and light quantity adjustment control in the conventional image forming apparatus. 10 is a flowchart illustrating a processing procedure of light amount adjustment control in a conventional image forming apparatus. It is a figure for demonstrating the problem in the light quantity adjustment control in the conventional image forming apparatus. It is a figure which shows the structure of the circuit regarding light quantity adjustment in the image forming apparatus of this Embodiment. It is a figure for demonstrating light quantity adjustment control in the image forming apparatus of this Embodiment. It is a figure which shows the structure of the circuit regarding the light quantity adjustment in the image forming apparatus of the form of the variation of this Embodiment.

  Hereinafter, as an image forming apparatus according to an embodiment of the present invention, an MFP (Multi Function Peripheral) which is an electrophotographic image forming apparatus will be described as an example.

  The MFP not only scans and scans images with the specified resolution and paper size, but also functions of various office devices such as an image receiving function by FAX, an image receiving function by e-mail, and a print image receiving function by a network. It is a digital multi-function machine that can be used in a comprehensive manner.

  FIG. 1 is a diagram illustrating a configuration of an image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 includes an image reading device 1 and an image forming unit 2.

  The image reading device 1 reads image information of a document for each line in units of pixels corresponding to the resolution, and generates image data. A CIS (Contact Image Sensor) 120 is used for reading a document. The CIS 120 includes a light source that illuminates a document, an optical system that captures reflected light from a document surface illuminated by the light source, and an imaging unit.

  The image reading apparatus 1 is configured to be capable of both ADF reading and manual placement reading.

  In ADF reading, an image of a document sent in the F direction by an automatic document feeder (ADF) is read by the CIS 120 at a predetermined position P. In manual placement reading, an image of a document placed on the platen glass 109 is read by the CIS 120 that moves in a predetermined direction R.

  The image forming unit 2 executes processing (printing, copying, etc.) for forming an image on a medium based on image data read from an original by the image reading device 1 or image data received from an external device.

  Further, the image forming apparatus 100 includes a CPU 801 and a memory 802 that collectively control operations of the image reading apparatus 1 and the image forming unit 2. Details of the configuration of these control systems will be described later.

  FIG. 2 is a diagram illustrating a configuration of the CIS 120 in the image forming apparatus according to the present embodiment.

  The CIS 120 includes a first illumination unit 121, a second illumination unit 122, an optical system 125, and an imaging unit 126.

  The first illumination unit 121 is composed of a white type light guide tube having three red LEDs, green LEDs, and blue LEDs as a light source, and illuminates the document surface from a direction inclined by a predetermined angle with respect to the document surface. To do. The second illumination unit 122 includes an LED array including yellow-green LEDs as a light source, has a spectral characteristic different from that of the first illumination unit, and is a first illumination unit with respect to a normal to the document surface. The original surface is illuminated from a substantially symmetrical direction.

  In this way, by illuminating from two positions that are in line contrast with the original surface by illumination lights of different colors, a read image without a shadow can be obtained regardless of the presence or absence of unevenness on the original surface. Can do. The plurality of light sources used in the image forming apparatus according to the present embodiment includes at least one of a red LED, a green LED, a blue LED, and a yellow-green LED.

  The optical system 125 is composed of a SELFOC (registered trademark) lens or the like, and guides the light emitted from the first illumination unit 121 and the second illumination unit 122 and reflected by the document surface to a predetermined imaging position. . The imaging unit 126 captures a light image that is guided by the optical system 125 and forms an image at a predetermined position. The imaging unit 126 includes, for example, a photoelectric conversion element (imaging element) 127 such as a CCD or a photodiode. An image of a document imaged by the imaging unit 126 is formed as an image on a medium or transmitted to an external device capable of communication.

  Further, the CIS 120 is driven in the R direction by the drive belt 108. That is, as described above, in the ADF reading, the CIS 120 is moved to a predetermined reading position by the driving belt 108 and stopped, and reads the image of the original 9 moving on the original platen glass 109. In manual placement reading, the CIS 120 reads an image of the document 9 placed on the document table glass 109 while being driven by the drive belt 108.

  The image reading apparatus 1 is provided with a white reference plate 107 for performing shading correction. At a predetermined timing, the CIS 120 is driven to the position of the white reference plate 107 and reads an image of the white reference plate. The CIS 120 described on the left side of FIG. 2 represents a state in which an image of a white reference plate is read.

  FIG. 3 is a diagram illustrating a configuration of a control system related to image reading of the image forming apparatus according to the present embodiment.

  The image reading apparatus 1 includes a CIS module 130 and a control board 131. The CIS module 130 is provided with a plurality of LEDs 128 that constitute the first and second illumination units 121 and 122, and an imaging element 127 that constitutes the imaging unit 126. The control board 131 is provided with various circuits for controlling the image sensor 127 and processing an image signal, and a circuit for controlling the light quantity of the LED 128. A signal line between the CIS module 130 and the control board 131 is connected via a harness 132.

  In the image sensor 127 of the CIS module 130, three sensor chips are connected to form one channel. Accordingly, 18 sensor chips are configured as 6-channel outputs. When the resolution is 600 dpi, the image sensor 127 is generally configured by 7300 to 7600 elements. In the present embodiment, one sensor chip is about 400 elements, and one channel is composed of about 1200 elements. Note that the configuration of the image sensor 127 is determined based on the resolution and reading speed required for the image reading apparatus 1, and is not limited to the form shown in FIG.

  In order to simplify the description, the LED 128 shown in FIG. 3 is described as a light source including a red LED, a green LED, and a blue LED. However, as described above, it should be noted that in the present embodiment, the light source may include at least one of a red LED, a green LED, a blue LED, and a yellow-green LED.

  The control board 131 is provided with an analog front end unit 141, an LED driver 142, a buffer 143, and a control circuit ASIC. The control circuit ASIC includes a CPU 801, a memory 802, an I / O unit 803, a printer unit 804, an image input I / O unit 810, a peak detection unit 811, a shading correction unit 812, an image processing unit 813, and an LED control unit 814. , And a clock generator 815.

  The analog front end unit 141 performs gain adjustment and offset adjustment on the analog signal output from the image sensor 127 to adjust the signal level, converts the analog signal to a digital signal, and outputs the digital signal to the image input I / O unit 810. To do. The image input I / O unit 810 distributes the digital signal to the peak detection unit 811 and the shading correction unit 812 and outputs them.

  The peak detection unit 811 calculates parameters for the analog front end unit 141 to execute gain adjustment and offset adjustment, and outputs the parameters to the analog front end unit 141. In the offset adjustment, the potential of a portion that is not an effective pixel included in the output signal from the image sensor 127 input to the analog front end unit 141 is adjusted to a desired voltage. In gain adjustment, the amplitude of the signal after offset is adjusted to match the input range of analog-digital conversion.

  Further, the peak detection unit 811 acquires a peak detection value from the output of the image sensor 127 when the LEDs 128 are individually emitted. The LED control unit 814 outputs the light amount adjustment amount of the LED 128 to the LED driver 142 based on the peak detection value, and controls the light amount of the LED. This light quantity adjustment operation will be described later.

  The shading correction unit 812 performs shading correction calculation on the signal for each pixel output from the image input I / O unit 810 using the white level reference value and the black level reference value stored in the memory 802. . Details of the shading correction processing will be described later. The image processing unit 813 executes processing such as image density calibration and γ conversion for obtaining desired gradation characteristics.

  The clock generator 815 generates a reference clock signal for driving the imaging operation of the imaging device 127 and the A / D conversion operation of the analog front end unit 141. The memory 802 stores data necessary for the operation of the image reading apparatus 1. The I / O unit 803 is an interface for exchanging information with an external device. A printer unit 804 is an interface for outputting image data subjected to image processing to a printer. The CPU 801 controls the overall operation of the image reading apparatus 1.

  Subsequently, before describing the light amount adjustment operation in the image forming apparatus of the present embodiment, the light amount adjustment operation in the conventional image forming apparatus will be described.

  FIG. 4 is a diagram for explaining shading correction and light amount adjustment control in a conventional image forming apparatus.

  The digital signal of the document image output from the analog front end unit (AFE) 141 is input to the shading correction unit 812, and shading correction using the white level reference value and the black level reference value stored in the memory 802 is executed. The In the light amount adjustment control, the digital signal of the reference image output from the analog front end unit (AFE) 141 is input to the peak detection unit 811 and the peak detection unit A and the bottom detection unit A operate to operate the analog front end. Parameters for gain adjustment and offset adjustment of the unit (AFE) 141 are calculated. Further, the LED control unit 814 controls the light quantity of the LED 128 based on the operations of the peak detection unit A and the bottom detection unit A.

[Shading correction]
The operation of the shading correction process will be described. In the shading correction process, the output signal of the image sensor 127 that is an image signal read by the document reading process using the black level reference value obtained by the black reference reading process and the white level reference value obtained by the white reference reading process. First, in the black reference reading process, a black reference image for a plurality of lines is read in a state in which the light source is turned off, that is, in a state in which light is not applied to the image sensor 127. The signal processed by the analog front end unit (AFE) 141 is stored in the memory 802 as the black level reference value Dbk. This black level reference value Dbk is a value calculated for each pixel.

  Next, in the white reference reading process, the image of the white reference plate 107 (white reference image) is read with the light source turned on. The signal processed by the analog front end unit (AFE) 141 is stored in the memory 802 as the white level reference value Dwt. The white level reference value Dwt is a value calculated for each pixel.

  In the document image reading process, the CIS 120 performs a document image reading process as described above. The image sensor 127 of the CIS 120 sequentially reads a document for each line in the main scanning direction. That is, the image sensor 127 sequentially outputs the image signal Dim for each line in the main scanning direction to the analog front end unit (AFE) 141.

  The shading correction unit 812 performs shading correction on the image signal Dim sequentially supplied from the image sensor 127. This shading correction is executed using the black level reference value Dbk and the white level reference value Dwt stored in the memory 802.

For example, when the number of effective bits of the image signal is 8, the shading correction unit 812 calculates the image signal Dout after the shading correction by the following calculation formula.
Dout = (Dim−Dbk) / (Dwt−Dbk) × 255
[Peak detection operation]
When an LED is used as an illumination means, the light quantity of the LED may change due to variations in the characteristics of each LED product, deterioration due to aging, and the like. Such a change in the light amount of the LED causes a difference in image reading density in each image reading apparatus. Therefore, by optimizing the light quantity of each LED when starting up the image reading apparatus 1 and adjusting the image, occurrence of a density difference in image reading is prevented.

  FIG. 5 is a flowchart showing a processing procedure of light amount adjustment control in the conventional image forming apparatus.

  In Act 01, when the image forming apparatus 100 is activated, the CIS 120 is moved to the white reference detection position. Here, first, operations of gain adjustment and offset adjustment of the analog front end unit 141 are performed. Subsequently, light amount adjustment control is performed. In Act 02, first, only the reference light source (for example, the green LED) is turned on, and the LEDs other than the green LED are turned off. In Act 03, peak detection is performed. The peak detection is an operation for optimizing the output of the image sensor 127 at the white reference detection position. In the peak detection operation, the peak detection unit A extracts the maximum output value of the image sensor 127 for each channel (1 to 6 channels).

  In Act 04 to Act 05, the LED control unit 814 adjusts the gain of the green LED until the maximum value among the peak detection data Max1 to Max6 reaches a predetermined value. If the maximum value of Max1 to Max6 does not become a predetermined value (NO in Act 06), this operation is repeated, and if the maximum value of Max1 to Max6 becomes a predetermined value (Yes in Act 06), green The light amount adjustment control with the LED is finished.

  This light amount adjustment control is executed for each LED. The predetermined value in the light amount adjustment control described above is a value determined for each LED of each color.

  Here, the reason why the maximum value of Max1 to Max6 is set to the predetermined value is to adjust the light amount to an appropriate value when the light amount of the LED changes due to aging deterioration, etc. Thus, the output of the image sensor 127 can be made as large as possible and not saturated.

  FIG. 6 is a diagram for explaining a problem in the light amount adjustment control in the conventional image forming apparatus.

  FIG. 6 shows the output when the white reference plate is read after the peak detection control is performed by the conventional light amount adjustment control. The horizontal axis represents the number of main scanning pixels, and the vertical axis represents the output of the image sensor 127. According to FIG. 6, it can be seen that the final pixel of channel 6 shows the maximum output.

  However, the image sensor 127 has a different black level for each element. For this reason, even if offset correction is performed in the analog front end unit 141, the influence of the black level is not removed. That is, the maximum value obtained in the conventional peak detection process is a value obtained without correcting the black level, and is different from the value obtained by correcting the black level used in image processing. Therefore, it is desirable to perform light amount adjustment control so as to maximize the same value as that used in image processing.

  FIG. 7 is a diagram illustrating a circuit configuration relating to light amount adjustment in the image forming apparatus according to the present embodiment.

  In FIG. 7, unlike the conventional circuit configuration, a subtraction circuit 820, a peak detection unit B, and a bottom detection unit B are newly provided. The subtraction circuit 820 subtracts the black level reference value for each element from the output of the image sensor 127 output from the analog front end unit 141 via the image input I / O unit 810. As a result, the signal input to the peak detector B is a signal from which the influence of the black level is removed.

  FIG. 8 is a diagram for explaining light amount adjustment control in the image forming apparatus of the present embodiment. FIG. 8 is a diagram illustrating a result of correcting the output of the image sensor 127 with the black level for each element. Comparing FIG. 8 with FIG. 6, the first pixel of channel 5 shows the actual maximum output. The peak detection unit B extracts the maximum value based on the output signal of the subtraction circuit 820, and the LED control unit 814 adjusts the light amount of the LED based on the maximum value. As a result, accurate light quantity adjustment can be performed.

[Variations of this embodiment]
FIG. 9 is a diagram illustrating a circuit configuration relating to light amount adjustment in an image forming apparatus according to a variation of the present embodiment.

  In the variation, the configuration of the shading correction unit 812 is different from the above-described configuration. That is, the shading correction unit 812 includes a subtraction circuit 820, a subtraction circuit 822, and a correction unit 823.

  The subtraction circuit 820 calculates the image signal Dim−black level reference value Dbk. The subtraction circuit 822 calculates the white level reference value Dwt−the black level reference value Dbk. For example, when the number of effective bits of the image signal Dim is 8, the correction unit 823 calculates the image signal Dout after shading correction using the following calculation formula.

Dout = (Dim−Dbk) / (Dwt−Dbk) × 255
= (Output value of subtraction circuit 820 / Output value of subtraction circuit 822) × 255
By using the subtraction circuit 820 used in this embodiment mode, the calculation of shading correction can be configured only by multiplication and division, so that the circuit can be simplified and the processing time can be shortened for the shading correction.

  Each function described in the above embodiment may be configured using hardware, or may be realized by reading a program describing each function into a computer using software. Each function may be configured by appropriately selecting either software or hardware.

  Furthermore, each function can be realized by causing a computer to read a program stored in a recording medium (not shown). Here, as long as the recording medium in the present embodiment can record a program and can be read by a computer, the recording format may be any form.

Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage.
Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

  DESCRIPTION OF SYMBOLS 1 ... Image reading apparatus, 2 ... Image forming part, 9 ... Original, 100 ... Image forming apparatus, 107 ... White reference board, 108 ... Drive belt, 109 ... Original plate glass, 120 ... CIS, 121 ... 1st illumination part 122 ... second illumination unit, 125 ... optical system, 126 ... imaging unit, 127 ... imaging device, 128 ... LED, 130 ... CIS module, 131 ... control board, 141 ... analog front end unit, 142 ... LED driver, 801 ... CPU, 802 ... memory, 811 ... peak detection unit, 812 ... shading correction unit, 813 ... image processing unit, 814 ... LED control unit, 820 ... subtraction circuit, 822 ... subtraction circuit, 823 ... correction unit

Claims (5)

A plurality of light sources for illuminating the document surface to be read;
An imaging unit that images light emitted from the plurality of light sources and reflected by the document surface;
A first memory that stores a black reference value that is an output of the imaging unit in a state in which the imaging unit is not irradiated with light;
A first subtracter for subtracting the black reference value for each element of the imaging unit for each element of the imaging unit from an imaging signal obtained by imaging the document surface by the imaging unit;
Among the plurality of light sources, as the reference light source of any one, the reference light source only by the from the imaging signal from the first subtractor when irradiated with predetermined reference plane for each element of the image pickup unit An image reading apparatus comprising: a control unit that adjusts a light amount of the reference light source so that a maximum value of an output signal obtained by subtracting the black reference value for each element of the imaging unit becomes a predetermined value.   The image reading apparatus according to claim 1, wherein the plurality of light sources include at least one of a red LED, a green LED, a blue LED, and a yellow-green LED. A second memory for storing a white reference value obtained by imaging light emitted from the plurality of light sources and reflected by a white reference plate surface;
A second subtracter for subtracting a black reference value from the white reference value;
The image reading apparatus according to claim 2, further comprising: a correction unit that performs shading correction on the imaging signal based on a value obtained by dividing the output of the second subtractor by the output of the first subtractor. A plurality of light sources for illuminating the document surface to be read;
An imaging unit that images light emitted from the plurality of light sources and reflected by the document surface;
A first memory that stores a black reference value that is an output of the imaging unit in a state in which the imaging unit is not irradiated with light;
A first subtracter for subtracting the black reference value for each element of the imaging unit for each element of the imaging unit from an imaging signal obtained by imaging the document surface by the imaging unit;
Among the plurality of light sources, as the reference light source of any one, the reference light source only by the from the imaging signal from the first subtractor when irradiated with predetermined reference plane for each element of the image pickup unit A control unit that adjusts the light amount of the reference light source so that the maximum value of the output signal obtained by subtracting the black reference value for each element of the imaging unit becomes a predetermined value;
An image forming apparatus comprising: an image forming unit that forms an image on a medium based on image data of the original surface imaged by the imaging unit.   The image forming apparatus according to claim 4, wherein the plurality of light sources include at least one of a red LED, a green LED, a blue LED, and a yellow-green LED.

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