JP2019029838A - Document reader - Google Patents

Abstract

To provide a document reader capable of correcting image unevenness caused by a difference in illumination luminance distribution due to a difference in position between a white reference plate position and a document reading position without enlarging a backup area.SOLUTION: By holding correlation data between reading data corresponding to one color of RGB reading data of a shading white board and reading data corresponding to one color of the read RGB reading data with a reference member placed on an original reading position, shading correction of each color of RGB is performed on the basis of the correlation data for each reading.SELECTED DRAWING: Figure 5

Description

    The present invention relates to a document reading device that reads image information recorded on a document.

  As an image reading device applied to image forming devices such as copiers and facsimiles, the purpose of increasing the document reading throughput, or the possibility of damage or breakage of the document being transported without complicating the transport path In order to reduce this, an apparatus capable of reading images on both sides of a document at once has been developed.

  In order to make the apparatus compact, the image reading apparatus described in Patent Document 1 has a configuration in which a front side reading unit and a back side reading unit are arranged close to each other and face each other on a translucent original table surface on the side where the front side reading unit is arranged. A technique is described in which a reference white plate for correcting the optical system of the back surface reading unit is provided at a position where the front surface reading unit does not obstruct the optical path when the original is optically read, so that the reference white plate is hardly soiled.

JP 2002-335380 A

  In the above-mentioned prior art, in Patent Document 1, the reference white plate arrangement of the back surface reading unit is at a position farther from the document reading position on the conveyance surface. As the distance from the light source increases, the light distribution becomes darker and more diffuse. For this reason, when shading is performed with a white reference plate far from the reading position, the luminance at both ends of the main scan is lower than that at the center of the main scan, so that the shading coefficient at both ends of the main scan is higher than that at the center of the main scan. If the image is read and the shading correction is performed with the shading coefficients at both ends of the main scanning being high, the reading position is closer to the white reference plate, so that the luminance at both ends of the main scanning is higher than the central portion.

  In the vicinity of the center of the main scanning, the luminance distribution in the main scanning direction on the white reference plate and the luminance distribution in the main scanning direction at the document reading position on the conveyance surface are not the same because the degree of illumination diffusion is different. That is, when a document is read using a shading coefficient generated on a distant white reference plate, unevenness occurs in the read image. With respect to the unevenness of the image, the luminance distribution for each of the three RGB colors of the substitute reference plate located in the back in advance, and the luminance distribution for each of the three RGB colors on the document reading surface acquired with a member having a uniform density in the main scanning direction, The correlation for each of the three RGB colors is calculated.

  The calculated correlation for each of the three RGB colors is backed up, and before reading, a shading correction coefficient for each of the three RGB colors is generated based on the correlation for each of the three RGB colors, and shading correction for each of the three RGB colors is performed. At this time, the correlation calculated based on the luminance distribution of the white reference plate and the luminance distribution on the original reading surface is backed up. However, since it is necessary to back up the correlation data for each color of RGB, the backup area becomes large. There is a problem.

  An object of the present invention is to provide a document reading apparatus capable of correcting image unevenness due to a difference in illumination luminance distribution due to a difference in position between a white reference plate position and a document reading position without increasing a backup area. It is.

  In order to achieve the above object, a document reading apparatus according to the present invention includes a document stacking unit that loads a document, a document transport unit that transports a document, a document reading unit that reads the transported document, and the document reading unit. An original reading glass disposed between the original reading position, an original platen glass disposed opposite to the original reading glass with the original reading position interposed therebetween, and opposed to the original reading position with the original table glass interposed therebetween. A white reference plate for generating the arranged shading data, a shading data generation unit for reading the white reference plate by the document reading unit to generate shading data, and the shading data generated by the shading data generation unit. A shading data holding means for holding, and a correction coefficient generator for correcting the shading data. In the original reading apparatus having the means, the read data corresponding to one color in the RGB read data of the self-reference plate and the RGB read data acquired by using a member having a uniform density at the original read position in advance. Correlation data between read data corresponding to one color is held in the shading data holding means, and a shading coefficient is generated and read from the read data of the white reference plate obtained before reading and the correlation data. It is characterized by that.

  According to the present invention, it is possible to correct image unevenness caused by a difference in illumination luminance distribution due to a difference in position between the white reference plate position and the document reading position without increasing the backup area.

It is a block diagram of a document conveyance reading apparatus. FIG. 6 is a control configuration diagram of the document conveyance reading device. It is a block diagram at the time of a white reference board and a reference member reading. It is a figure which shows an illumination intensity distribution characteristic. It is a flowchart when backing up the backup value Z (n) in the first embodiment. It is a figure which shows the waveform of the main scanning direction of Z (n) to back up. It is a flowchart at the time of the reading in 1st Embodiment. It is the figure shown about the correction effect at the time of reading.

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

(First embodiment)
FIG. 1 shows a configuration of a document conveyance reading device 120 equipped with an automatic document conveyance mechanism. In FIG. 1, reference numeral 101 denotes a document tray on which documents 102 are stacked. (The original 102 is hereinafter referred to as a blank sheet). 2 drives the document pick roller 121, the document separation roller 122, the document transport roller 123, and the document offset roller 124. The document transport motor 105 shown in the block diagram of FIG. A document 102 placed on the document tray 101 is fed.

  The document reading unit 106 reads the document 102 conveyed between the document reading glass 119 and the document table glass 126.

  There is also a white reference plate 125 for generating shading data arranged opposite to the document reading position 107 with the document table glass 126 interposed therebetween.

  When the image reading of the document 102 by the document reading unit 106 is completed, the document 102 is discharged onto the discharge tray 108. The document reading unit 106 includes a light guide 202, a CIS line sensor 203, and a lens 204 that irradiates the document 102 with light from an LED light source 201 (not shown) on the document surface at the document reading position 107. The CIS line sensor 203 photoelectrically converts the reflected light from the document 102 guided by the lens 204 with a light receiving element, and outputs an electrical signal corresponding to the amount of incident light.

  The original 102 is read at the original reading position 107 while the original 102 is conveyed by the original reading apparatus having the above-described configuration.

  FIG. 2 is a diagram illustrating a control configuration of the document reading apparatus according to the embodiment of the present invention. 401 is a main CPU for controlling the document reading apparatus, and includes an LED light source 201, a CIS line sensor 203, and a document transport motor 105. Then, control is performed to read the original image by controlling the backup memory 402.

  Next, the flow of the image signal will be described. The RGB three-color electrical signals corresponding to the original density read by the CIS line sensor 203 are converted from analog electrical signals to RGB three-color digital image signals by the A / D conversion circuit 403.

  Next, the shading correction circuit 404 corrects the influence of the non-uniformity of the light amount of the LED light source 201 and the influence of the sensitivity variation for each pixel of RGB of the CIS line sensor 203.

  The CPU 401 receives the digital image signal from the shading correction circuit 404, transmits / receives data to / from a calculation temporary SRAM 405 and a backup memory 402 described later, and performs correction described later.

  The backup memory 402 stores correlation data calculated from the luminance distribution data of the white reference plate 125 and the luminance distribution data obtained by reading the reference member 500 that is a member having a uniform density at the original reading position 107. This is a non-volatile RAM. Then, data can be read / written from / to the shading correction circuit 404 via the CPU 401. The reference member 500 is a member having a uniform density in the main scanning direction. The density is not limited as long as the density is uniform, but in the present embodiment, it is white (hereinafter referred to as a white reference member).

  The temporary calculation RAM 405 is a RAM used by the CPU 401 when temporarily storing data of the backup memory 402 and the shading correction circuit 404, and is configured to be able to transmit and receive data under the control of the CPU 401. ing.

Next, details of the shading correction performed by the shading correction circuit 404 will be described. The shading correction is performed for each pixel in each RGB color in order to correct the influence of the non-uniformity of the light quantity of the LED light source 201, the sensitivity variation of each pixel of the CIS line sensor 203, and the sensitivity variation of each color of RGB. I do.
The shading-corrected data is defined as a shading correction output value (n).

Shading correction output value (n)
= Original reading value (n) x target reading value / shading data (n)
n: Pixel position original reading value of the CIS line sensor 203 (n): Data reading target value when reading the original at the original reading position 107: Target of reading value when reading the white reference original on the white reference plate 125 Value shading data: Data obtained when a white reference original on the white reference plate 125 is read. The shading correction circuit 404 can output the original read value (n) as it is without shading correction by communication with the CPU 401. is there.
That is, shading correction output value (n) = document reading value (n),
n = pixel position of the CIS line sensor 203.
This operation is hereinafter defined as “shading correction off”.

  The shading correction is performed by the CPU 401 calculating shading data for each color of RGB based on the luminance distribution data of the white reference plate 125 stored in the backup memory 402 and setting it in the shading correction circuit 404.

  The shading data in this embodiment includes the luminance distribution data of the white reference plate 125 stored in the backup memory 402 and the luminance distribution obtained by reading the reference member 500 that is a member having a uniform density at the document reading position 107. The shading data for each color of RGB is calculated based on the correlation data calculated from the data. A method for calculating the shading data Q corrected with the correlation data will be described later.

  FIG. 3 is a diagram illustrating a reading state of the reading unit 106. FIG. 3A is a diagram showing that nothing is placed at the document reading position 107 and the reading unit 106 is in an arrangement relationship so that the white reference plate 125 can be read. FIG. 3B is a diagram showing that the reference member 500 is placed at the document reading position 107 and the reading unit 106 is in an arrangement relationship in which the reference member 500 can be read. In the embodiment, the state of FIG. 3B is realized by the operator's hand in the backup data generation method described below.

  A method for generating data to be stored in the backup memory 402 will be described with reference to the flowcharts of FIGS. 3, 4, and 5. As shown in FIG. 3A, in a state where the original reading unit 106 is in contact with the original platen glass 126 (FIG. 3A), in S1401, the CPU 401 reads from an operation panel (not shown) by a service person or the like. Manipulate the start signal, detect the read start signal, and set the reading. Specifically, the LED light source 201 is turned on, the CIS line sensor 203 is read and controlled, and the shoeing correction is turned off (S1401).

  In step S1402, the CPU 401 samples the data of the white reference plate 125. Specifically, the read data X (n) (where n is the pixel position) of the white reference plate 125 is stored in the temporary calculation SRAM 405 (S1402).

  Next, the operator places the reference member 500 at the document reading position 107 as shown in FIG. (FIG. 3 (b)) After placing the reference member 500 at the document reading position 107, the operator makes a setting to start reading from an operation panel (not shown).

  In step S1403, the CPU 401 detects the above-described reading start signal and samples the data of the reference member 500. Specifically, the read data Y (n) (where n is the pixel position) of the reference member 500 is stored in another area in the temporary calculation SRAM 405 (S1403). In the present embodiment, the read data Y (n) of the reference member 500 stores G data of RGB color data.

In step S1404, the CPU 401 calculates correlation data Z (n). In particular,
The CPU 401 reads the G reading data X (n) of the white reference plate 125 and the G reading data Y (n) of the reference member 500 from the temporary calculation SRAM 405, and performs the following calculation (S1404).

Since G data is used in this embodiment, the read data X (n) and the G read data Y (n) of the reference member 500 are XG (n) and YG (n), respectively.
Z (n) = YG (n) / XG (n)
n: Pixel Position In S1405, the CPU 401 backs up the correlation data Z (n) calculated from the read data XG (n) and YG (n) described above to the backup memory 402 (S1405). In this embodiment, the correlation data Z (n) is calculated using G data of RGB data, but may be calculated using either R data or B data. Data backup of the correlation data Z (n) to the backup memory 402 is performed at the time of shipment from the factory, when the reading unit 106 is replaced, or when the control board itself on which the backup memory 402 is mounted is failed or replaced. It is carried out at the timing.

  The shape of the luminance distribution of the read data X (n) of the white reference plate 125 and the read data Y (n) of the reference member 500 in the flowchart of FIG. 5 will be supplemented using FIG. 4A shows the main scanning luminance distribution at different reading positions when a point light source is assumed, and FIG. 4B shows the illumination luminance distribution by the LED 201 and the light guide 202 at different reading positions. It is. A dotted line shows the illumination luminance distribution when the white reference plate 125 is read. A solid line indicates an illumination luminance distribution when reading is performed with the reference member 500 placed at the reading position 107.

  The light guide 202 is configured so that the irradiation light from the LED 201 is directed to the document reading position 107 and the white reference plate 125 by a reflection plate (not shown) (for example, a white printing reflection plate) that is configured in the light guide 201. Yes. Although the irradiation plate (not shown) is configured uniformly, unevenness in the brightness distribution occurs due to variations in printing position, density, etc., but the unevenness in the brightness distribution is corrected by shading.

  In the present embodiment, there is illumination unevenness at different positions of the reading position 107 and the white reference plate 125. The illumination unevenness at the different positions will be described below.

  The read data X (n) of the white reference plate 125 has the following two characteristics. The first point is data with low brightness because the distance from the reading unit 106 is as much as the thickness of the platen glass 126 relative to the reading position 107 as shown by the dotted line in FIG. 4B (FIG. 4B). ).

  The second point is that, as indicated by the dotted line in FIG. 4B, the read data at the end becomes lower than the main scanning center. When the illumination luminance distribution 4b by the light guide shown in FIG. 4B is an array of point light sources (FIG. 4A) as shown in FIG. 4A, the white reference plate 125 is read. The data is data whose end is darker than the main scanning center.

  Although described as data in which the end portion becomes dark, when the light guide 202 and the white reference plate 125 are sufficiently long in the main scanning direction with respect to the effective area of the CIS line sensor 203, the data in which the end portion becomes dark as described above. However, it becomes flat data similar to the central part of the main scanning.

  In the configuration of the present embodiment, since the light guide 202 and the white reference plate 125 are the shortest in the main scanning direction in order to reduce the size of the document conveying / reading device 120, the data becomes dark at the end.

  The read data Y (n) of the reference member 500 reads the reference member 500 at the reading position 107 close to the reading unit 106, and has the following two characteristics. The first point is closer to the reading unit 106 as shown by the solid line in FIG. 4B, and therefore the data is higher in luminance than X (n) (FIG. 4B).

  The second point is that the read data at the end is substantially flat with respect to the main scanning center as shown by the solid line in FIG.

  When the illumination luminance distribution (4 (b)) by the light guide as shown by the solid line in FIG. 4 (b) is considered to be an array of point light sources (solid line in FIG. 4 (a)) shown in FIG. 4 (a). The read data of the reference member 500 is read data in which the main scanning center portion and the end portion are substantially flat.

  The correlation data Z (n) to be backed up will be supplemented using FIG. FIG. 6 is a diagram showing a waveform shape with respect to the main scanning position of the correlation data Z (n) to be backed up. Since Z (n) = Y (n) / X (n), the correlation data at the main scanning end is larger than the correlation data at the main scanning center. The read data X (n) of the white reference plate 125 has a lower luminance value and a longer optical path length than the read data Y (n) of the reference member 500, so that the light irradiated from the light guide 202 is sufficiently diffused and the main scanning direction. Flat data X (n). For this reason, the correlation data at the main scanning end is larger than that at the center of the main scanning from the correlation data calculation formula Z (n) = Y (n) / X (n) (FIG. 6).

  In the above-described embodiment, the correlation data Z (n) is calculated using G data. However, the correlation data Z (n) similar to the G data as described above can be acquired for other R data and B data. In the above embodiment, the correlation data Z (n) is calculated from the G data. However, the correlation data Z (n) corresponding to one color may be acquired from the average value of the R data, the G data, and the B data. .

  A document reading operation in the image reading apparatus having the above configuration will be described with reference to the flowchart of FIG. When the operator sets reading start from an operation panel (not shown) and the CPU 401 detects a reading start signal, the CPU 401 sets the reading operation in S1501. Specifically, the CPU 401 turns on the LED light source 201, reads and controls the CIS line sensor 203, and turns off the shoeing correction (S1501).

  In step S1502, the CPU 401 performs data sampling on the white reference plate 125. Specifically, read data P (n) (where n is a pixel position) (FIG. 8A) of the white reference plate 125 is acquired. The above-mentioned data P (n) exists for each color of RGB, and R data is stored in PR (n), G data is stored in PG (n), B data is stored in PB (n) in the temporary SRAM 405 for calculation (S1502). ).

In step S1503, shading data Q (n) at the document reading position 107 is calculated. Specifically, the CPU 401 stores the read data PR (n), PG (n), and PB (n) of each color of the white reference plate 125 stored in the temporary calculation SRAM 405 and the backup memory 402 in advance. The following calculation is performed from the correlation data Z (n).
R data QR (n) = Z (n) × PR (n)
G data QG (n) = Z (n) × PG (n)
B data QB (n) = Z (n) × PB (n)
n: Pixel position The shading data Q (n) is stored in the temporary calculation SRAM 405 (S1503, S1504).

  QR (n), QG (n), and QB (n) are read data corresponding to reading of the reference member 500 at the original reading position 107, and PR (n), PG (n), and PB (n). Compared with, the end portion read data is corrected to be large.

In step S1505, the CPU 401 sets shading data. Specifically, the CPU 401 sets shading data QR (n), which is R data, in the shading correction circuit 404.
Similarly, shading data QG (n) and QB (n) which are G data and B data are also set in the shading correction circuit 404. The shading correction circuit 404 performs the following calculation on the original reading value.
R data R shading correction output value (n)
= R original reading value (n) x reading target value / shading data QR (n)
G data G shading correction output value (n)
= G original read value (n) × read target value / shading data QG (n)
B data B shading correction output value (n)
= B original reading value (n) x reading target value / shading data QB (n)
n = represents the pixel position of the CIS line sensor 203 Document read value (n): data obtained when the document is read at the document read position 107 Read target value: arbitrary value obtained when the white reference document on the white reference plate 125 is read Reading target value Shading data Q: Data obtained by reading a white reference document on the white reference plate 125 and multiplying it by correlation data Z In step S1506, the CPU 401 reads the document. Specifically, the CPU 401 turns on the LED light source 201, reads and controls the CIS line sensor 203, drives the document transport motor 105, transports the document 102 so as to pass the reading position 107, and reads the document 102.

  In the document reading operation described with reference to the flowchart of FIG. 7, the read data acquired by the CPU 401 is supplemented with reference to FIG. FIG. 8 is a diagram showing a luminance distribution in the main scanning direction that can be acquired by the CPU 401 in the form according to the flowchart of FIG. FIG. 8A shows the main scanning luminance distribution of the read data P (n) of the white reference plate 125 acquired in S1502. Since P (n) is RGB data, the RGB data is PR (n), RG (n), and PB (n), respectively, as described above. The horizontal axis is the main scanning position, and the vertical axis is the reading value. Since the shading correction is turned off, it is synonymous with sampling the illumination luminance distribution itself.

FIG. 8B shows the main scanning luminance distribution of Q (n) acquired in S1503. This means that the read data corresponds to reading the reference member 500 at the original reading position 107.
Since Q (n) is RGB data, as described above, the RGB data are QR (n), QG (n), and QB (n), respectively.
Since the R data is QR (n) = Z (n) × PR (n), compared to PR (n), the end portion has a luminance distribution that is corrected so that the read data becomes larger.
Similarly, G and B data are as follows: QG (n) = Z (n) × PG (n)
QB (n) = Z (n) × PB (n)
The G and B data also have a luminance distribution that is corrected so that the read data becomes larger than PG (n) and PB (n).

  FIG. 8D shows the luminance distribution in the main scanning direction of the shading correction output value of the document 102 read in S1506. The shading data Q (n) is divided for each pixel with respect to the read value of the document 102, and a flat image can be read in the main scanning direction.

  Correlation data corresponding to one color calculated based on the read value for each of the three RGB colors of the white reference plate and the read value for each of the three RGB colors of the reference member at the original reading position is backed up in advance. By performing shading correction for three colors of RGB based on correlation data corresponding to one color when reading a document, image unevenness due to a difference in illumination luminance distribution due to a difference in position between the white reference plate position and the document reading position is corrected. can do. Thus, the backup area can be reduced by providing a backup area corresponding to one color instead of the three-color backup area.

101 Document tray 102 Document 105 Document transport motor 106 Document reading unit 107 Document reading position 108 Paper discharge tray 119 Document reading glass 120 Document transport reading device 121 Document pick roller 122 Document separation roller 123 Document transport roller 124 Document offset roller 125 White reference plate 126 Document platen glass 150 Document reading device 201 LED light source 202 Light guide 203 CIS line sensor 204 Lens 401 CPU
402 Backup Memory 403 A / D Conversion Circuit 404 Shading Correction Circuit 405 Temporary SRAM for Calculation
500 Reference material

Claims (1)

A document loading means for loading a document;
A document transport section for transporting a document;
An original reading unit for reading the original to be conveyed;
A document reading glass disposed between the document reading unit and a document reading position;
An original platen glass disposed opposite to the original reading glass across the original reading position;
A white reference plate for generating shading data arranged opposite to the original reading position across the original table glass;
A shading data generating means for reading the white reference plate at the document reading unit and generating shading data;
Shading data holding means for holding the shading data generated by the shading data generation means;
Correction coefficient generating means for correcting the shading data;
In a document reading apparatus having
Read data corresponding to one color in the RGB read data of the self-reference plate and read data corresponding to one color in the RGB read data acquired with a member having a uniform density at the original reading position in advance. An image reading apparatus, wherein correlation data is held in the shading data holding unit, and a shading coefficient is generated and read from the reading data of the white reference plate obtained before reading and the correlation data.