JP2021057866A - Image reading device and control method of the same - Google Patents

Abstract

To make it possible to suppress degradation of image quality caused by misalignment of a reading position of a plurality of photosensitive element rows.SOLUTION: An image reading device has reading means having a plurality of rows of photosensitive elements lined up in a first direction and in a second direction orthogonal to the first direction, and generating reading data by reading an image of an object, control means for independently controlling a charge accumulation timing of the plurality of rows of photosensitive elements, and correction means for correcting a reading position shift in the reading data of the plurality of rows of photosensitive elements generated by the reading means.SELECTED DRAWING: Figure 4

Description

The present invention relates to an image reader and a control method for the image reader.

Copiers and multifunction printers are equipped with an image reader for reading an image from a document. As a reading method using an image reading device, there are known a pressure plate reading method in which a document is placed on a document table and the document is read while moving the scanning unit, and a scanning method in which the document is read while being transported by an automatic document transport mechanism.

The reading unit includes a light emitting unit that irradiates the document and a light receiving unit that receives the reflected light from the document. The image reader generates image data representing an image of the original based on the reflected light received by the light receiving unit.

A light source such as an LED (Light Emitting Diode) is used as the light emitting unit. The light receiving unit includes a plurality of line sensors for reading a color image, and for example, R (red), G (green), and B (blue) color filters are applied on the light receiving surface of each line sensor. .. The reading unit reads the document by receiving the diffused light of the light emitted from the light emitting unit to the document by the light receiving unit. The image reading device generates image data from luminance data (hereinafter, referred to as “reading data”) which is a light receiving result of a light receiving unit of a reading unit.

Hereinafter, an image reading device including a reading unit using a light emitting unit and a light receiving unit will be described as an example. In the reading unit of this image reading device, a plurality of light receiving elements are arranged in the main scanning direction, with the direction orthogonal to the direction in which the document is conveyed or the direction orthogonal to the direction in which the reading unit moves as the main scanning direction. In such an image reading device, when the scanning resolution in the sub-scanning direction is changed to increase the conveying speed of the automatic document conveying mechanism, or the conveying speed of the scanning unit is increased to perform high-speed scanning, R, G, and B are used. The amount of deviation is the amount of deviation for non-integer pixels such as 0.5 pixels.

Patent Document 1 discloses a method of generating pseudo pixels at integer pixel positions by performing interpolation processing.

Further, in Patent Document 2, a multicolor light source (for example, R light source, G light source, B light source) is used for the light emitting portion to control the lighting timing of each light source, so that the position of the image can be obtained by the alignment process for integer pixels. A method of matching is disclosed.

Japanese Unexamined Patent Publication No. 1-109966 Japanese Unexamined Patent Publication No. 2005-322990

However, in Patent Document 1, since interpolation processing is performed on a line sensor that is deviated by a non-integer pixel with respect to the position of the reference line sensor, pixels are generated in a pseudo manner, so that the signal level of the light receiving element has a light receiving area. It will be in the same state as the widened state, and blurring will occur and the image quality will deteriorate. Further, in Patent Document 1, when high-speed scanning is performed and a low-resolution image is generated, aliasing noise occurs when the original contains high-frequency components. For example, when the reading position of each line sensor is deviated by 0.5 pixel from R and B, the aliasing noise of the image generated by the G line sensor is the image generated by the R and B line sensors. It occurs at a position different from the aliasing noise of. Therefore, the RGB value at the position where the aliasing noise is generated does not become R = G = B, and chromatic pixels are generated. Therefore, when a monochrome original is read, false color occurs, and deterioration of image quality and erroneous determination of automatic color selection (ACS: Auto Color Select) (determining the monochrome original as a color original) occur.

Further, in Patent Document 2, the light source needs to be an RGB light source including an R light source, a G light source, and a B light source, and cannot be used for a white light source, and the usable light source is limited. With a white light source, multiple light sources are arranged in the main scanning direction to irradiate light, but if the RGB light source has the same configuration, it is necessary to triple the number of light sources in order to obtain the same illuminance, and the required area. Will increase. When the number of light sources is reduced and the amount of light is increased, unevenness of bright spots occurs and the arrangement of LEDs appears in the image data. For this reason, in the RGB light source, a method of diffusing and irradiating light using a light guide is adopted, but it is difficult to secure the amount of light when the reading speed is increased.

An object of the present invention is to make it possible to suppress deterioration of image quality due to misalignment of reading positions of a plurality of light receiving element rows.

The image reading device of the present invention has a plurality of light receiving element rows in which a plurality of light receiving elements are arranged in the first direction in a second direction orthogonal to the first direction, and reads an image of an object. The reading means for generating the read data, the control means for independently controlling the charge accumulation timing of the plurality of light receiving element trains, and the reading position deviation of the read data of the plurality of light receiving element trains generated by the reading means are corrected. It has a correction means to be used.

According to the present invention, deterioration of image quality due to misalignment of reading positions of a plurality of light receiving element rows can be suppressed.

It is a block diagram of an image reader. It is a block diagram of a CIS line sensor. It is a block diagram of a control part. It is a flowchart which shows the process at the time of image reading. It is a figure which shows an example of the light receiving timing. It is a figure which shows an example of the image at the time of reading 600 dpi. It is a figure which shows an example of the image at the time of reading 300 dpi. It is a figure which shows an example of the image at the time of reading 300 dpi. It is a figure which shows an example of the light receiving timing at the time of reading 300 dpi. It is a figure which shows an example of the image at the time of reading 300 dpi. It is a figure which shows an example of the image at the time of reading 300 dpi. It is a figure which shows an example of the light receiving timing at the time of reading 200 dpi. It is a figure which shows the arrangement of a line sensor. It is a block diagram of a control part. It is a flowchart which shows the process at the time of image reading. It is a figure which shows an example of gain adjustment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the following embodiments do not limit the invention according to the claims, and not all combinations of features described in the embodiments are essential for the means for solving the invention.

(First Embodiment)
FIG. 1 is a diagram showing an example of an image reading device 115 according to the first embodiment. The image reader 115 is, for example, a scanner, a copier, a multifunction printer, or the like. The image scanning device 115 is equipped with an automatic document feeding device 100, and reads images on both sides of the document 102 by the front surface scanning unit 121 and the back surface scanning unit 122 while transporting the document 102, which is an object to be image-read. Can be done.

The paper feed roller 103 is connected to the same drive source as the separate transport roller 104, and rotates as the separate transport roller 104 rotates to feed paper. The paper feed roller 103 is retracted to a position above FIG. 1, which is normally the home position, so as not to interfere with the document setting work. When the paper feeding operation is started, the paper feeding roller 103 descends and comes into contact with the upper surface of the document 102. The paper feed roller 103 is pivotally supported by an arm (not shown), and moves up and down as the arm swings.

A separation transfer driven roller 105 is arranged on the opposite side of the separation transfer roller 104 in a state of being pressed against the separation transfer roller 104 side. The separate transfer driven roller 105 is formed of a rubber material or the like having slightly less friction than the separate transfer roller 104, and is formed on a document tray 101 to be fed by the paper feed roller 103 in cooperation with the separate transfer roller 104. Documents 102 are separated one by one and fed.

Further, the automatic document feeding device 100 includes a resist roller 106, a resist driven roller 107, a lead roller 108, and a lead driven roller 109. The resist roller 106 and the resist driven roller 107 operate so as to align the tips of the documents fed at the separation unit.

The lead roller 108 and the lead driven roller 109 convey the document 102 toward the scanning glass 116. A platen roller 110 is arranged above the scanning glass 116. The document 102 is conveyed by the platen roller 110 to the lead discharge roller 111 and the lead discharge driven roller 112 after passing over the scanning glass 116 constituting the first reading unit.

At the end of the scanning glass 116 on the lead discharge roller 111 side, a jump table 117 for scooping up the document is provided in order to facilitate the transfer of the document to the lead discharge roller 111.

The surface of the document 102 is conveyed so that its surface is in contact with the scanning glass 116, and at this time, the surface reading unit 121 arranged in the image reading device 115 reads the surface of the document through the scanning glass 116. The surface reading unit 121 is composed of a CIS (Contact Image Sensor) line sensor. Details will be described later.

The lead ejection roller 111 and the lead ejection driven roller 112 convey the document that has passed over the scanning glass 116 to the scanning glass 120. A platen roller 119 is provided on one side of the scanning glass 120, and a back surface reading unit 122 is provided on the other side. Like the front surface reading unit 121, the back surface reading unit 122 is composed of a CIS (Contact Image Sensor) line sensor.

With this configuration, the back surface image of the document 102 passing between the scanning glass 120 and the platen roller 119 is read by the back surface reading unit 122. After that, the document 102 is conveyed to the paper ejection roller 113 and ejected to the paper ejection tray 114.

The image reading device 115 having the above configuration can read the original in two modes. The first mode is a document fixed scanning mode in which the document 102 placed on the platen glass 118 is read while the surface scanning unit 121 is moved in the sub-scanning direction (in the direction of the arrow in the drawing). The second mode is a scanning mode in which the document is read at the scanning glass 116 position while the document 102 is conveyed by the automatic document feeding device 100 with the surface scanning unit 121 stopped. In the second mode, by using the back surface reading unit 122 in addition to the front surface reading unit 121, the back surface image can be read in addition to the front surface image of the document.

FIG. 2 is a diagram showing a configuration example of a CIS line sensor of the front surface reading unit 121 and the back surface reading unit 122 of FIG. Since the front surface reading unit 121 and the back surface reading unit 122 have the same configuration, the configuration of the front surface reading unit 121 will be described here, and the description of the configuration of the back surface reading unit 122 will be omitted.

The surface reading unit 121 is a reading unit including white LEDs 201a and 201b which are light emitting units, a Selfock (registered trademark) lens array 202, and a light receiving element 203 which is a light receiving unit. The white LEDs 201a and 201b emit light when the document 102 passes through the casting glass 116 to illuminate the surface of the document 102. The surface of the document 102 reflects the light emitted by the white LEDs 201a and 201b. The light reflected by the surface of the document 102 is diffused light. The diffused light passes through the Selfock lens array 202 and is focused on the light receiving surface of the light receiving element 203. The light receiving element 203 is an image sensor, which photoelectrically converts the received light and outputs an analog electric signal according to the amount of received light.

FIG. 13 is a diagram showing an arrangement of CIS line sensors of the surface reading unit 121 of FIG. Since the front surface reading unit 121 and the back surface reading unit 122 have the same configuration, the configuration of the front surface reading unit 121 will be described here, and the description of the configuration of the back surface reading unit 122 will be omitted.

FIG. 13 shows the arrangement of the light receiving elements 203 of FIG. The line sensor is a row of light receiving elements in which the light receiving elements 203 are arranged in a row in the main scanning direction according to the resolution. The plurality of line sensors are arranged so as to be offset in the sub-scanning direction. The surface reading unit 121 has a plurality of light receiving element rows in which a plurality of light receiving elements 203 are arranged in the main scanning direction in a sub-operation direction orthogonal to the main scanning direction, and generates reading data by reading an image of an object. .. The back surface reading unit 122 is the same as the front surface reading unit 121.

FIG. 13 includes a line of the light receiving element 203 for reading the image of R (red), a line of the light receiving element 203 for reading the image of G (green), and a line of the light receiving element 203 for reading the image of B (blue). Therefore, R, G, and B color filters are applied to the light receiving surfaces of the three lines of the light receiving elements 203, respectively. As a result, the diffused light from the document 102 is color-separated, and each light receiving element 203 receives the light that has passed through the color filter.

Since the light receiving elements 203 of the three lines are arranged so as to be offset in the sub-scanning direction, the image reading device 115 does not read the images of each color of R, G, and B from the same position of the document at the same timing. Therefore, it is necessary to align the image signals output from the light receiving element 203 of each line. In the example of FIG. 13, RGB alignment can be performed by shifting G by one pixel and B by two pixels in the sub-scanning direction with respect to R.

As shown in FIG. 13, the line sensor includes a plurality of lines of light receiving elements 203 corresponding to the resolution in the main scanning direction of the document 102 in the sub scanning direction (conveying direction). For example, the line sensor includes three lines of light receiving elements 203 for 7,500 pixels in the main scanning direction in the sub scanning direction. The three-line light receiving element 203 is arranged in a state of being deviated by one pixel at 600 dpi in the sub-scanning direction. A color filter is applied on the light receiving element 203 of each line. A color filter that transmits R light is applied to the light receiving element 203 of the first line. A color filter that transmits G light is applied to the light receiving element 203 of the second line. A color filter that transmits the light of B is applied to the light receiving element 203 of the third line.

FIG. 3 is a diagram showing a configuration example of a control unit of the image reading device 115. The image reading device 115 includes a CPU (Central Processing Unit) 301, a non-volatile memory 302, an operation unit 303, an image processing unit 306, a parallel / serial conversion unit 310, and an image output controller 311. A front surface reading unit 121 and a back surface reading unit 122 are connected to the CPU 301 and the image processing unit 306.

The CPU 301 controls the operations of the automatic document feeding device 100 and the image reading device 115 by executing a program stored in the non-volatile memory 302. The operation unit 303 is a user interface for setting the double-sided scanning mode of the document 102, setting the scanning resolution, setting the transmission destination of image data representing the scanned image, and the like. The content input by the operation unit 303 is transmitted to the CPU 301.

The image processing unit 306 acquires the image data read by the front surface reading unit 121 and the back surface reading unit 122, performs predetermined image processing, and outputs the data. The image processing unit 306 includes A / D conversion units 304 and 305, a line memory 307, a shading correction unit 308, and a color shift correction unit 209.

The A / D conversion units 304 and 305 convert the analog electric signal read by the front surface reading unit 121 and the back surface reading unit 122 into image data which is a digital signal. The line memory 307 is a memory for storing the image data converted by the A / D conversion units 304 and 305.

The shading correction unit 308 performs shading correction processing for correcting the non-uniformity of the amount of light and the influence of the sensitivity difference for each light receiving element 203 on the read data of each color of R, G, and B stored in the line memory 307. .. In the shading correction process, the shading coefficient obtained by reading a white reference plate (not shown) is used for the shading correction process.

The color shift correction unit 309 performs color shift correction processing for aligning the read position with respect to the read image data of R, G, and B. In the color shift correction process, a process for correcting color shifts for integer pixels and a process for correcting color shifts for non-integer pixels are performed. Here, for example, the correction is performed by a filter process having a window size of 1 × 3 (main scan × sub scan). Here, when the image data for three pixels in the sub-scanning direction is PV1, PV2, PV3 and the weighting coefficients are w1, w2, w3, the pixel value PV2'after the filter processing is calculated by the equation (1).
PV2'= (PV1 x w1 + PV2 x w2 + PV3 x w3) / (w1 + w2 + w3) ... (1)

The parallel / serial conversion unit 310 converts the read data of each color into serial data and transmits it to the image output controller 311. The image output controller 311 outputs the scanned data converted into serial data as image data representing the image of the scanned document 102.

FIG. 4 is a flowchart illustrating a control method of the image reading device 115. The program that executes this flowchart is stored in the non-volatile memory 302 and executed by the CPU 301.

In step S401, the CPU 301 acquires the information set by the operation unit 303 and acquires the reading conditions. For example, the CPU 301 acquires information such as a resolution setting set by the operation unit 303.

In step S402, the CPU 301 determines the resolution information acquired in step S401. The CPU 301 proceeds to step S403 when the resolution information is 600 dpi (YES in S402), and proceeds to step S406 when the resolution information is 300 dpi (NO in S402).

In step S403, the CPU 301 instructs the automatic document feeding device 100 to start feeding documents in the transport speed setting (normal mode) for 600 dpi.

In step S404, the CPU 301 instructs the line sensors of the R, G, and B colors to start reading at the same time at the time Tn.

FIG. 5 shows a reset pulse instructing the start of scanning when scanning a document using the line sensor shown in FIG. 13 and a timing at which the reset pulse is detected and the light receiving elements 203 of R, G, and B store electricity. ing. The light receiving elements 203 of R, G, and B in the figure indicate a period in which electricity is stored at the high level and a period in which electricity is not stored at the low level. When the light receiving element 203 of R, G, and B detects the reset pulse at the time Tn, it resets the stored electric charge and starts storing the electric charge after a certain delay period. Therefore, as shown in FIG. 5, the light receiving elements 203 of R, G, and B detect the reset pulse at the time Tn, and a delay period occurs until the high level state in which electricity is stored. The interval from the time Tn to Tn + 1 shown in FIG. 5 is the charge of one sub-scanning pixel.

In step S405, the CPU 301 determines whether the reading of the document 102 has been completed. If the reading of the document 102 has not been completed, the CPU 301 returns to step S404 and instructs the reading of the next line. When the reading of the document 102 is completed, the CPU 301 ends the process of the flowchart of FIG.

The image data generated at the time of reading 600 dpi will be described with reference to FIGS. 6 (a) to 6 (c). FIG. 6A is a diagram showing an example of sampling positions at the time of reading 600 dpi when the document 102 reads a black line having a cycle of 600 dpi and 4 pixels. The arrow 601 indicates the position read by the line sensor of each color in the period from the time Tn to Tn + 1. As shown in FIG. 13, the line sensor is arranged so that G is 600 dpi 1 pixel with respect to R and B is 600 dpi 2 pixels with respect to R in the sub-scanning direction. Therefore, as shown by arrow 601, the image positions read at the same time are shifted.

FIG. 6B is a diagram showing signal values of each color of R, G, and B before color shift correction, in which the read signal values are converted into digital signals by the A / D conversion units 304 and 305. As for the signal value, the vertical axis represents the luminance value and the horizontal axis represents the sub-scanning position. The arrow 601 in FIG. 6 (b) indicates the image position read at the same time as the arrow 601 shown in FIG. 6 (a). It can be seen that the signal value obtained by reading the black line portion of the document 102 is delayed by 600 dpi and one pixel at a time. In the portion of arrow 601 in FIG. 6B, the signal value of R is low, the signal values of G and B are high, and R ≠ (G = B). Therefore, in the document 102, the portion that was the black line becomes chromatic, and the image quality is deteriorated.

FIG. 6 (c) is a diagram showing the result of performing color shift correction for an integer pixel by the color shift correction unit 309 with respect to the signal value of FIG. 6 (b). The signal value of FIG. 6 (c) is an image obtained by correcting the signal value of FIG. 6 (b) by one pixel of G and two pixels of B with reference to R, and the colors of the signals of R, G, and B. The deviation is corrected, and the black line original can be reproduced.

Next, when 300 dpi reading is performed using the line sensor shown in FIG. 13 using FIGS. 7 (a) to 7 (d) and 8 (a) to 8 (d), the colors of R, G, and B are displayed. An example of image data when reading is started simultaneously by the line sensor will be described.

FIG. 7A is a diagram showing an example of sampling positions for reading 300 dpi when the document 102 reads a black line having a cycle of 600 dpi and 4 pixels. The arrow 701 in FIG. 7A indicates the position read by the line sensor of each color from the time Tn to Tn + 1. For example, the line sensor is arranged so that G is 600 dpi 1 pixel with respect to R and B is 600 dpi 2 pixels with respect to R in the sub-scanning direction. When 300 dpi reading is performed by the line sensor having this configuration, the line sensor of G reads the position shifted by 0.5 pixel by 300 dpi with respect to R and B.

FIG. 7B is a diagram showing a signal value before color shift correction in which the read signal value is converted into a digital signal by the A / D conversion units 304 and 305. The arrow 701 in FIG. 7 (b) indicates the image position read at the same time as the arrow 701 shown in FIG. 7 (a). The signal value obtained by reading the black line portion of the document 102 is a signal with a deviation of 300 dpi and one pixel from R for B, but a deviation of 300 dpi and 0.5 pixels with respect to R.

FIG. 7 (c) is a diagram showing the result of performing color shift correction for an integer pixel by the color shift correction unit 309 with respect to FIG. 7 (b). The signal value of FIG. 7 (c) is corrected by 300 dpi for one pixel with respect to the signal value of FIG. 7 (b) with reference to R. In this state, since the signal value of G is 300 dpi and is deviated by 0.5 pixel, the portion of the arrow 701 becomes (R = B) ≠ G, and the color becomes chromatic.

FIG. 7 (d) is a diagram showing a state in which the color shift correction unit 309 performs color shift correction of 300 dpi and 0.5 pixels for the signal value of G with respect to FIG. 7 (c). When the equation (1) is used, the color shift correction of 0.5 pixels is performed by using the weighting coefficient of the following equation.
PV2'= (PV1 x 0 + PV2 x 64 + PV3 x 64) / 128

By the color shift correction process, the signal values of R, G, and B in the portion of arrow 701 become R = G = B, and the color shift of R, G, and B is corrected, but it is generated by the smoothing effect of the correction process. Blurring occurs in the image data, and the image quality deteriorates.

FIG. 8A is a diagram showing an example of a sampling position of 300 dpi reading when the document 102 reads a black line having a cycle of 600 dpi and 1.5 pixels. The arrow 801 in FIG. 8A indicates the position read by the line sensor of each color at the same time.

FIG. 8B is a diagram showing a signal value after the A / D conversion process. FIG. 8C is a diagram showing a signal value obtained by performing color shift correction for an integer pixel. FIG. 8D is a diagram showing a state in which the signal value of FIG. 8C is corrected for color shift by 0.5 pixels on the signal value of G.

A black line with a period of 600 dpi and a period of 1.5 pixels has a periodicity of 200 dpi. Since the Nyquist frequency at the time of reading 300 dpi is 150 dpi, the black line having a period of 200 dpi cannot be resolved, and aliasing noise is generated. Since G reads the positions shifted by 0.5 pixels from R and B at 300 dpi, the aliasing noise generated in G is generated as a signal shifted by half a cycle of the aliasing noise. Therefore, as shown in FIG. 8D, even if the color shift correction processing for 0.5 pixels is performed, R = G = B does not occur, and chromatic pixels are generated in the black line portion. For example, an image reader of a document reader or a copier has a function of determining whether a scanned document is color or monochrome, such as ACS (Auto Color Select). When 300 dpi reading is performed by an image reading device having this function, the ACS function may determine a monochrome original as a color original due to the generation of chromatic pixels due to aliasing noise.

In the present embodiment, the image reading device 115 that suppresses the above-mentioned deterioration of image quality and misdetermination of ACS is provided. Returning to the description of FIG.

In step S402, the CPU 301 proceeds to step S406 when the resolution information is 300 dpi (NO in S402).

In step S406, the CPU 301 instructs the automatic document feeding device 100 to start feeding documents at the transport speed setting (high-speed mode) for 300 dpi. For example, the CPU 301 feeds documents at double speed for 600 dpi.

In step S407, the CPU 301 starts reading the R and B line sensors at the same time at time Tn. In step S408, the CPU 301 starts reading the G line sensor at time Tn'.

In FIG. 9, the line sensor shown in FIG. 13 is used to detect a reset pulse for each of R, G, and B instructing the start of scanning when scanning a document at 300 dpi, and a reset pulse of R, G, and B. It is a figure which shows the timing which the light receiving element 203 stores electricity. The light receiving elements 203 of R, G, and B indicate a period in which electricity is stored at the high level and a period in which electricity is not stored at the low level. When the light receiving element 203 of R and B detects the reset pulse at the time Tn, it resets the stored electric charge and starts storing the electric charge after a certain delay period. On the other hand, when the light receiving element 203 of G detects the reset pulse at the time Tn', it resets the stored electric charge and starts storing the electric charge after a certain delay period. The interval from time Tn to Tn + 1 is the charge of one pixel of the sub-scanning of R and B. Further, in G, the section from Tn'to Tn + 1'is the charge of one sub-scanning pixel of G. In this way, the reset pulse is controlled independently for each color, and R and B are controlled to receive light for the first half 0.5 pixels of 300 dpi and G for the second half 0.5 pixels of 300 dpi.

The time Tn'is a time deviated from the time Tn by 300 dpi and a reading time of 0.5 pixels by tm, and Tn'= Tn + tm. Further, R and B are controlled to receive light for the first half 0.5 pixels of 300 dpi and G for the latter half 0.5 pixels of 300 dpi, but G is controlled to receive the first half 0.5 pixels and R and B are controlled to receive the second half 0.5 pixels. It may be controlled to receive light.

The CPU 301 is a control unit, and independently controls the charge accumulation timing of the light receiving element trains of R, G, and B by the reset pulse. The CPU 301 controls the charge accumulation timings of the light receiving element trains of R, G, and B when they are not the same. The light receiving element sequence of G has a different charge accumulation timing from that of the light receiving element rows of R and B. The CPU 301 controls the charge accumulation timing so that the light receiving element rows of R and B receive light for 0.5 pixels in the first half and the light receiving element rows of G receive light for 0.5 pixels in the second half.

In step S409, the CPU 301 determines whether or not the reading of the document 102 is completed. If the scanning of the document 102 has not been completed, the CPU 301 returns to step S407 and scans the next line. When the reading of the document 102 is completed, the CPU 301 ends the process of the flowchart of FIG.

Next, the image data generated at the time of reading 300 dpi will be described with reference to FIGS. 10 (a) to 10 (c) and FIGS. 11 (a) to 11 (c). FIG. 10A is a diagram showing an example of sampling positions for reading 300 dpi when the document 102 reads a black line having a cycle of 600 dpi and 4 pixels. Arrows 1001 indicate the positions of the light receiving elements 203 of R and B read from the time Tn to Tn + 1 shown in FIG. 9, and the light receiving elements 203 of G indicate the positions read from the time Tn'to Tn + 1'. As shown in FIG. 10A, R and G read the same position at the same time. B reads a position shifted by one pixel of 300 dpi.

In this way, the light received by the light receiving element 203 of R and B is set to 0.5 pixels in the first half of 300 dpi, and the light received by the light receiving element 203 of G is set to 0.5 pixels in the second half of 300 dpi. It is possible to perform color shift correction by correcting an integer amount. This makes it possible to suppress the blurring of the image caused by the color shift correction for 0.5 pixel.

FIG. 10B is a diagram showing a signal value after the A / D conversion process. FIG. 10C is a diagram showing a signal value obtained by performing color shift correction for an integer pixel, and it is possible to suppress deterioration due to color shift correction of 0.5 pixel.

As shown in FIG. 10C, the color shift correction unit 309 corrects the read position shift of the read data of the light receiving element trains of R, G, and B. At that time, the color shift correction unit 309 corrects the reading position shift for an integer pixel.

FIG. 11A is a diagram showing an example of a sampling position of 300 dpi reading when the document 102 reads a black line having a cycle of 600 dpi and 1.5 pixels. The arrow 1101 indicates the position of the light receiving element 203 of R and B to be read from the time Tn to Tn + 1 shown in FIG. 9, and the position of the light receiving element 203 of G to be read from the time Tn'to Tn + 1'.

FIG. 11B is a diagram showing a signal value after the A / D conversion process. FIG. 11C is a diagram showing a signal value obtained by performing color shift correction for an integer pixel. The black line with a cycle of 600 dpi and 1.5 pixels causes aliasing noise when reading at 300 dpi, but since the same positions are read at R, G, and B, aliasing noise also occurs at almost the same position. Therefore, as shown in FIG. 11C, it is possible to suppress the generation of chromatic color pixels and suppress the erroneous determination of ACS by performing the color shift correction for an integer.

In the present embodiment, the control at the time of reading 300 dpi has been described, but the present invention is not limited to this. FIG. 12 uses the line sensor shown in FIG. 13 to detect a reset pulse for each of R, G, and B instructing the start of scanning when scanning a document at 200 dpi, and a reset pulse for each of R, G, and B. It is a figure which shows the timing which the light receiving element 203 stores electricity. The light receiving elements 203 of R, G, and B indicate a period in which electricity is stored at the high level and a period in which electricity is not stored at the low level. When the light receiving element 203 of R detects the reset pulse at the time Tn, it resets the stored electric charge and starts storing the electric charge after a certain delay period. When the light receiving element 203 of G detects the reset pulse at the time Tn', it resets the stored electric charge and starts storing the electric charge after a certain delay period. When the light receiving element 203 of B detects the reset pulse at the time Tn'', it resets the stored electric charge and starts storing the electric charge after a certain delay period. The interval from time Tn to Tn + 1 is the charge of one pixel of the sub-scanning of R. Further, in G, the interval from the time Tn'to Tn + 1'is the charge of one sub-scanning pixel of G. In B, the interval from the time Tn'' to Tn + 1'' is the charge of one sub-scanning pixel of B. In this way, by controlling the reset pulse independently for each color, it is possible to correct the color shift of R, G, and B by the correction for an integer as in the case of 300 dpi.

As described above, according to the present embodiment, even with a white light source, the deviation of the image signals output from the plurality of line sensors can be corrected by the alignment of the integer pixels, and the deterioration of the image quality can be suppressed. It is possible to provide an image reading device capable of the above.

When the line sensor reads at a reading speed of 600 dpi, the CPU 301 controls the charge accumulation timings of the light receiving element trains of R, G, and B at the same timing. Further, when the line sensor reads at a reading speed of 300 dpi, the CPU 301 controls at a timing in which the charge accumulation timings of the light receiving element trains of R, G, and B are not the same.

(Second embodiment)
In the first embodiment, a method of individually controlling the light receiving timings of the R, G, and B line sensors so that the color shift correction can be corrected by an integer amount and the deterioration of the image quality is suppressed has been described. However, in the method of the first embodiment, the light receiving time of each line sensor at the time of reading 300 dpi is shorter than the light receiving time of 600 dpi, and the amount of light is insufficient.

FIG. 16 is a diagram showing an example of gain adjustment for adjusting the white level. When the amount of light is insufficient, the brightness value obtained when the document 102 is read becomes low, so that the shading correction unit 308 corrects the non-uniformity of the amount of light and the influence of the sensitivity difference for each light receiving element 203, and at the same time adjusts the white level. Adjust Gain Adjust.

When the shading correction unit 308 performs gain processing or the like as shown in FIG. 16 on the read signal, the difference between the output out1'and out2'after the processing is larger than the difference between the outputs out1 and out2 with respect to the inputs in1 and in2. growing. Therefore, S / N (Signal / Noise) deteriorates, and the image quality deteriorates.

In the second embodiment, when the amount of light is insufficient at the time of reading 300 dpi and the S / N deteriorates, a method of performing a smoothing process for noise removal will be described. Hereinafter, control of document scanning will be described with reference to FIGS. 14 and 15.

FIG. 14 is a diagram showing a configuration example of a control unit of the image reading device 115 according to the second embodiment. FIG. 14 shows a smoothing processing unit 1401 added to FIG. The smoothing processing unit 1401 is provided in the image processing unit 306. Hereinafter, the difference between the second embodiment and the first embodiment will be described.

The smoothing processing unit 1401 removes noise by filtering the data generated by the color shift correction unit 309. The smoothing processing unit 1401 uses a low-pass filter as a noise removing filter in order to suppress high-frequency noise. For example, the smoothing processing unit 1401 removes noise by using a bilateral filter. The bilateral filter is represented by the following equation (2).

Here, w is the kernel size, σ ₁ is the control value of the Gaussian filter, and σ ₂ is the control value of the luminance difference. The _{smaller σ 1} is, the smaller the smoothing effect is, _{and the larger σ 1} is, the larger the smoothing effect is. Further, when σ ₂ is increased, the smoothing effect on the edge is increased, and when σ ₂ is decreased, the smoothing effect on the edge is decreased, but the noise removal effect is also weakened.

FIG. 15 is a flowchart illustrating a control method of the image reading device 115 according to the second embodiment. The program that executes this flowchart is stored in the non-volatile memory 302 and executed by the CPU 301. FIG. 15 shows the addition of steps S1501 and S1502 to FIG. Hereinafter, the points that FIG. 15 differs from FIG. 4 will be described.

In step S402, if the resolution information is 600 dpi (YES in S402), the process proceeds to step S1501, and if the resolution information is 300 dpi (NO in S402), the process proceeds to step S1502.

In step S1501, the CPU 301 sets a weak smoothing processing coefficient for 600 dpi in the smoothing processing unit 1401 and ends the setting process.

In step S1502, the CPU 301 sets a strong smoothing processing coefficient for 300 dpi in the smoothing processing unit 1401 and ends the setting process.

The smoothing processing unit 1401 is a smoothing unit, and has different coefficients for the read data corrected by the color shift correction unit 309 depending on whether the line sensor reads at a reading speed of 600 dpi or a reading speed of 300 dpi. Smooth with. The smoothing processing unit 1401 performs smoothing using, for example, a bilateral filter.

Here, the coefficient for strong smoothing processing for 300 dpi is such that, for example, σ ₁ in the equation (2) is made larger than the weak smoothing processing coefficient for 600 dpi, or σ ₂ is made larger than the weak smoothing processing coefficient for 600 dpi. It should be set to. Further, _{both σ 1} and σ ₂ may be set to be changed.

Further, when it is desired to enhance the noise removing effect while maintaining the edge, a plurality of bilateral filters may be arranged, and the noise may be removed by repeatedly processing a plurality of bilateral filters at the time of reading 300 dpi.

As described above, according to the present embodiment, even if the amount of light is insufficient for 600 dpi reading during 300 dpi reading, noise can be appropriately reduced by changing the smoothing process according to the reading resolution. It can be removed and the deterioration of image quality can be suppressed.

According to the first and second embodiments, the image reader 115 makes it possible to correct the deviation of the image signals output from the plurality of line sensors by aligning the integer pixels even with a white light source, and the image quality. Deterioration can be suppressed.

(Other embodiments)
The present invention supplies a program that realizes one or more functions of the above-described embodiment to a system or device via a network or storage medium, and one or more processors in the computer of the system or device reads and executes the program. It can also be realized by the processing to be performed. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

It should be noted that all of the above embodiments merely show examples of embodiment in carrying out the present invention, and the technical scope of the present invention should not be construed in a limited manner by these. That is, the present invention can be implemented in various forms without departing from the technical idea or its main features.

121 Front surface reader, 122 Back surface reader, 301 CPU, 302 Non-volatile memory, 303 Operation unit, 308 Shading correction unit, 309 Color shift correction unit

Claims (11)

A reading means that has a plurality of light receiving element rows in which a plurality of light receiving elements are arranged in the first direction in a second direction orthogonal to the first direction, and reads an image of an object to generate reading data. ,
A control means for independently controlling the charge accumulation timing of the plurality of light receiving element sequences, and
An image reading device comprising a correction means for correcting a reading position deviation of reading data of the plurality of light receiving element trains generated by the reading means. The image reading device according to claim 1, wherein the correction means corrects the reading position deviation for an integer pixel. The image reading device according to claim 1 or 2, wherein the control means controls the charge accumulation timing by a reset pulse. The image reading device according to any one of claims 1 to 3, wherein the control means controls at timings when the charge accumulation timings of the plurality of light receiving element sequences are not the same. The plurality of light receiving element rows include a first light receiving element row, a second light receiving element row, and a third light receiving element row.
The image reading device according to any one of claims 1 to 4, wherein the second light receiving element row has a different charge accumulation timing from the first and third light receiving element rows. The control means controls the charge accumulation timing so that the first and third light receiving element trains receive light for 0.5 pixels in the first half and the second light receiving element train receives light for 0.5 pixels in the second half. The image reading device according to claim 5, wherein the image reading device is characterized by the above. A red color filter is applied to the first light receiving element row.
A green color filter is applied to the second light receiving element row.
The image reading device according to claim 5 or 6, wherein a blue color filter is applied to the third light receiving element row. The control means
When the reading means reads at the first reading speed, the charge accumulation timings of the plurality of light receiving element trains are controlled at the same timing.
The invention according to any one of claims 1 to 7, wherein when the reading means reads at a second reading speed, the charge accumulation timings of the plurality of light receiving element rows are controlled at timings that are not the same. Image reader. Further, the reading data corrected by the correction means is further provided with a smoothing means that smoothes the read data with different coefficients depending on whether the reading means reads at the first reading speed or the second reading speed. The image reading device according to any one of claims 1 to 8. The image reading device according to claim 9, wherein the smoothing means performs smoothing using a bilateral filter. A reading step in which a plurality of light receiving element rows in which a plurality of light receiving elements are arranged in the first direction are provided in a second direction orthogonal to the first direction, and reading data is generated by reading an image of an object. ,
A control step that independently controls the charge accumulation timing of the plurality of light receiving element sequences, and
A control method for an image reading device, which comprises a correction step for correcting a reading position deviation of reading data of the plurality of light receiving element trains generated in the reading step.

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