JP2012222520A - Image reading apparatus, image forming apparatus and image reading method - Google Patents

Abstract

An accurate black level correction value is obtained even when the amount of stray light changes with time.
A light source for irradiating a document with light and an image sensor for acquiring light reflected by the document are obtained, and the image sensor is made to acquire a first output (Xn) by stray light in advance (S103). The light amount of the light source is stored as the first light amount (Y) (S106), the light amount of the light source is acquired as the second light amount (Y ′) before the reading of the document is started (S204), and the first light amount is obtained. The output of the image sensor is corrected based on the ratio (Y ′ / Y) of (Y) and the second light quantity (Y ′) and the first output (Xn) acquired in advance (S206).
[Selection] Figure 5

Description

  The present invention relates to an image reading apparatus, an image forming apparatus, and an image reading apparatus, and in particular, an image reading apparatus that performs black level correction in response to a light amount variation with time, a copying machine including the image reading apparatus, a printer, a facsimile, The present invention relates to an image forming apparatus such as a digital multifunction peripheral and an image reading method executed by each of these apparatuses.

  In an image reading apparatus, light from a light source is applied to an original and an image is read by an image sensor using a light receiving element such as a CMOS or CCD.

In an original conveyance type reading apparatus using such an image sensor, it is desirable that the output of the image sensor is 0 when a black original (ideally reflectance 0) is read. However,
・ Dark output due to noise ・ Image sensor output does not become 0 because there is image sensor output due to stray light (directly or light reflected on contact glass or the like and incident on the light receiving element). In addition, since this value has a different value depending on the position in the main scanning direction, the image quality is deteriorated.

  The values of dark output and stray light due to this noise are equal to the image sensor output when a black document is read with the light source turned on. However, there is usually a white reference plate or white roller for white shading on the optical path for reading, and it is difficult to obtain dark output and stray light values by reading an ideal black original before starting original reading. It is. For this reason, conventionally, the output of the image sensor when the light source is turned off is subtracted as a black level.

  However, in the conventional subtraction method, since the stray light output is not included in the black level, if the stray light output increases, the image quality is adversely affected.

  For example, in the case of a method of conveying and reading a document, the document easily flutters up and down when passing through the document, and the focus position shifts from the document. As a countermeasure, there is a method of reducing the influence on the read image due to the fluttering of the original by diffusing light by providing a diffusion plate between the light source and the original and widening the focus position. However, in this case, stray light output is increased due to the effect of the diffusion plate, which adversely affects image quality. For example, in FIG. 28, the light emitted from the light source 6 is divided into components of light passing through the contact glass 2 (solid line) and light reflected by the contact glass 2 (broken line). At that time, as shown in FIG. 28A, when there is no diffusing plate 40, the light reflected by the contact glass 2 hardly enters the light receiving portion 5a of the image sensor 5, but as shown in FIG. If 40 is present, light is diffused by the diffusion plate 40, so that the light reflected by the contact glass 2 is more likely to enter the light receiving portion 5 a of the image sensor 5. In such a case, the stray light output becomes large, which adversely affects the image quality.

  Therefore, in Patent Document 1 (Japanese Patent Laid-Open No. 8-98017), the difference between the black document reading data when the light source is turned on and the image sensor output data when the light source is turned off is held in advance, and the light source is turned off immediately before reading the document. A technique has been proposed in which output data of image data is acquired, and shading processing is performed using black data as the sum of the held difference and the output data when the light source is turned off immediately before reading a document.

  However, even if processing is performed as described in Patent Document 1, if the amount of light from the light source changes over time, the difference between the black original reading data when the light source is turned on and the image sensor output data when the light source is turned off, in which the reference is held in advance. Therefore, if the light amount of the light source immediately before reading the document is changed from that when the light source is turned on, the comparison reference is different. Therefore, an accurate black level correction value cannot be obtained when the amount of stray light changes with such a change in the amount of light from the light source.

  Therefore, the problem to be solved by the present invention is to obtain an accurate black level correction value even when the amount of stray light changes with time.

  In order to solve the above problems, the first means includes a light source that irradiates light on the document, a light receiving element that acquires light reflected by the document, and a light sensor that previously acquires the first output due to stray light. First storage means for storing the light amount of the light source as a first light amount, and acquiring the light amount of the light source as a second light amount before starting reading of the document, and the first light amount and the first light amount The image reading apparatus includes a correction unit that corrects the output of the light receiving element based on the ratio of the amount of light of 2 and the first output acquired in advance.

  According to a second means, in the first means, the correction means obtains a second output of the light receiving element in a light-off state of the light source immediately before starting reading of the document, and the first light quantity and the first light quantity are obtained. A black level correction value is obtained by adding the second output to a value obtained by multiplying the ratio of the light quantity of 2 by the first value.

  According to a third means, in the first means, the first light amount is the averaged value for each preset reading range within the effective reading range, and the second light amount is immediately before the start. It is the averaged value for each of the preset reading ranges.

  A fourth means is characterized in that, in the first means, the correction means acquires the black level correction value for each of the preset ranges over the entire reading range.

  A fifth means is characterized in that, in the first means, the first and second light quantities are values obtained by averaging output values of a preset region.

  A sixth means is characterized in that, in the fifth means, one or more of the preset areas are set.

  The seventh means is characterized in that, in the sixth means, the reference plate is installed on a reading optical path of the light receiving element corresponding to one of the preset areas.

  According to an eighth means, in the seventh means, one of the preset areas is outside the effective reading range on the product and within the effective reading range of the light receiving element, and is a partial area of the one area And a reflecting member for blocking the reading optical path of the light receiving element.

  A ninth means is characterized in that, in the eighth means, the reflecting member has a reflectivity such that an output of the light receiving element is not saturated.

  A tenth means includes a photoelectric conversion means for generating an electrical output corresponding to a light amount directly incident from the light source instead of the reference plate in the first means, and the correction means replaces the reference plate. The first and second light amounts are obtained based on output values from the photoelectric conversion means, and the outputs of the light receiving elements are corrected using the obtained first and second light amounts.

  The eleventh means is the non-volatile first and second storage means for storing the first output and the first light quantity, respectively, and the second output and the second light quantity in the second means. Volatile third and fourth storage means respectively for storing the first output and the first light quantity immediately before the start of reading, including the time of manufacture of the image reading apparatus before the reading. The second output and the second light amount are acquired at an arbitrary timing earlier than before, and are acquired for each operation of reading a document immediately before the reading is started.

  A twelfth means is characterized in that the image forming apparatus includes the image reading apparatus according to any one of the first to eleventh aspects.

  A thirteenth means is an image reading method comprising: a light source that irradiates light on a document; and a light receiving element that acquires light reflected by the document, and reads an image of the document with the light receiving element. A step of causing the light receiving element to acquire a first output due to stray light and storing the light amount of the light source at that time in the storage means as a first light amount; And correcting the output of the light receiving element based on the ratio of the first light quantity and the second light quantity and the first output obtained in advance. .

  In an embodiment described later, the document is denoted by G, the light source is denoted by 6, the reference plate is denoted by the white reference plate 4, the light receiving element is denoted by the image sensor 5, the image reading device is denoted by 1, and the first output is X (n), the first light quantity is Y, the second light quantity is Y ', the second output is Z' (n), and the preset range is in each of the blocks 1 to b. The entire reading range is the effective reading range F, the preset area is the number of K pixels in the averaging area D, the partial area is the averaging area D, the reflecting member is 2a, and the photoelectric conversion means is a photoelectric sensor. 10, the first storage means corresponds to the memory 1, the second storage means corresponds to the memory 2, the third storage means corresponds to the memory 3, and the fourth storage means corresponds to the memory 4.

  According to the present invention, an accurate black level correction value can be obtained even when the amount of stray light changes with time.

It is the figure which looked at the mechanical structure of the image reading part in Example 1 of this invention from the subscanning direction. It is the figure which looked at FIG. 1 from the main scanning direction. In Example 1, it is a figure which shows the data previously acquired in order to remove a black level, and hold | maintained in memory. It is a figure which shows the data acquired and hold | maintained before the reading start. 6 is a flowchart showing a processing procedure for storing data shown in FIG. 3 in a memory, and a processing procedure for data calculation processing and black level correction value calculation shown in FIG. 5. FIG. 3 is a block diagram illustrating a signal processing configuration of the image reading apparatus according to the first exemplary embodiment. FIG. 6 is a diagram illustrating a mechanical configuration of a reading unit according to a second embodiment when viewed from a sub-scanning direction. It is a figure which shows the example which provided the reflection member in the lower surface of the contact glass of FIG. It is a figure which shows the example which made the reflective member of FIG. 8 the intermediate color. In Example 2, it is a figure which shows the data previously acquired in order to remove a black level, and hold | maintained in memory. In Example 2, it is a figure which shows the data acquired and hold | maintained before the reading start. FIG. 10 is a diagram illustrating a mechanical configuration of a reading unit according to a third embodiment when viewed from a sub-scanning direction. FIG. 9 is a diagram illustrating a mechanical configuration of a reading unit according to a fourth embodiment when viewed from the sub-scanning direction. It is the figure which looked at FIG. 13 from the main scanning direction. In Example 4, it is a figure which shows the data previously acquired in order to remove a black level, and hold | maintained in memory. In Example 4, it is a figure which shows the data acquired and hold | maintained before the reading start. 17 is a flowchart showing a processing procedure for storing data shown in FIG. 15 in a memory, and a processing procedure for data calculation processing and black level correction value calculation shown in FIG. 16. FIG. 10 is a block diagram illustrating a signal processing configuration of an image reading apparatus according to Embodiment 4. FIG. 19 is a circuit diagram illustrating details of a circuit configuration of a light amount detection unit illustrated in FIG. 18. 10 is a flowchart showing a processing procedure until updating a black level correction value applied in the cases of Embodiments 2 and 3. FIG. 10 is a diagram illustrating a mechanical configuration of a reading unit according to a fifth embodiment when viewed from the main scanning direction. It is the figure which looked at the LED array used as a light source from the subscanning direction. It is the figure which showed the light quantity distribution at the time of using the LED array shown in FIG. In Example 5, it is a figure which shows the data previously acquired in order to remove a black level, and hold | maintained in memory. It is a figure which shows the data acquired and hold | maintained before the reading start. It is a figure which shows the calculation method of a stray light output. FIG. 26 is a flowchart showing a processing procedure for storing data shown in FIG. 24 in a memory, and a processing procedure for data calculation processing and black level correction value calculation shown in FIG. 25. It is a figure which shows the state of reflection of the illumination light by the presence or absence of the diffusion plate in a prior art.

  Hereinafter, embodiments of the present invention will be described in detail based on the following examples. Note that, in each of the following embodiments, the same reference numerals are assigned to the equivalent parts, and overlapping descriptions are omitted as appropriate.

In the first embodiment, when the black level correction value is removed by the document conveyance type image reading apparatus,
1) Image sensor output X (n) (n: main scanning pixel) and stray light Y at that time are acquired in advance.
2) Next, the image sensor output data Z ′ (n) and the light amount Y ′ when the light source is turned off are acquired immediately before the start of document reading.
3) The correction value X ′ (n) = Y ′ / Y * X (n) of the stray light component is calculated from the ratio Y ′ / Y of the both light amounts, and X ′ (n) and Z ′ ( The sum of n) is removed from the original reading value as the black level correction value.
It is a feature.

  This is particularly effective when using an optical system in which the amount of light varies uniformly in the main scanning direction. The optical system in which the amount of light uniformly varies in the main scanning direction is, for example, a method (light guide method) in which light is irradiated to all main scans using a light guide with one light source. The amount of light corresponds to the image sensor output.

  FIG. 1 is a diagram of the mechanical configuration of the reading unit of the image reading apparatus viewed from the sub-scanning direction, and FIG. 2 is a diagram viewed from the main scanning direction. In these drawings, the image reading apparatus 1 includes a contact glass 2, a main body cover 3, a white reference plate 4, and an image sensor 5. A light source 6 is further provided on the side of the image sensor 5, and a reading unit 7 is configured by both. The main body cover 3 is disposed on the upper surface side of the contact glass 2, and a white reference plate 4 is provided between the main body cover 3 and the contact glass 2. Further, the image sensor 5 is arranged on the lower surface side of the contact glass 2 so that the surface to be read of the document placed on the upper surface of the contact glass 2 faces the light receiving unit 5a. The image sensor 5 has a plurality of photoelectric conversion elements (CMOS or CCD sensor chips) arranged in a row or a staggered pattern in the main scanning direction. A white reference plate (or white plate roller) 4 is provided on the optical path of the light source 6 provided in the vicinity of the image sensor 5. The white reference plate 4 is a reference plate for obtaining shading correction data for correcting image unevenness due to light amount unevenness in the main scanning direction and sensor sensitivity unevenness. The contact glass 2 also has a protection function for the image sensor 5. The original passes through the space A between the white reference plate 4 and the contact glass 2 when reading.

  With the above configuration, the light emitted from the light source 6 passes through the contact glass 2, reflects off the document surface, passes through the contact glass 2 again, and enters each pixel (element) element of the image sensor 5. The density of the original is read by changing the output (voltage) of the photoelectric conversion element in accordance with the amount of incident light. Also, here, assuming that there is one light source and the light guide is used to irradiate the entire region in the main scanning direction, the variation in the amount of light occurs uniformly in the entire main scanning direction.

  FIG. 3 is a diagram showing data acquired in advance to remove the black level and held in a memory described later. The term “predetermined” here is acquired at the time of manufacturing the image reading apparatus or when it is determined to be necessary in the market, and is a preset timing before document reading. The horizontal axis represents main scanning pixels (all N pixels), and the vertical axis represents image sensor output. FIG. 5A is a flowchart showing a processing procedure for holding the data shown in FIG. 3 in the memory.

  In this process, first, the light source 6 is turned off and the image sensor output Z (n) is acquired for all main scanning pixels (n is the nth pixel in all N pixels, and n ≦ N, n, and N are positive integers) ( Step S101). Next, the light source 6 is turned on, and the image sensor output V (n) when the black image is read is obtained for all main scanning pixels (step S102). For example, the black image may be read by reading a black document or may be acquired without using a black document. When a black document is used, a black document that is uniform and has no gloss (diffuse degree of 100%) is used in order to eliminate the influence of the document. When the original is not used, the main body cover 3 and the white reference plate 4 are removed in a space where light other than the light source 6 for reading does not enter the image sensor light receiving portion 5a (such as covering a dark room or apparatus with a dark curtain). The image sensor output when the reading light source 6 is turned on is obtained.

The stray light output X (n) when the black original reading output V (n) is acquired in this way is
X (n) = V (n) -Z (n) (1)
And is stored in the memory 1 (step S103). The stray light output X (n) in equation (1) is the change in the black level when the light source is turned on. The memory generally corresponds to the first to fourth storage means, and the memory 1, the memory 2, the memory 3, and the memory 4 are provided in the memory 32 described later. The memories 1 and 2 are nonvolatile memories, and the memories 3 and 4 are volatile memories.

Thereafter, the light source 6 is turned on, and the image sensor output W (n) when the white reference plate 4 is read is acquired for all main scanning pixels (step S104). The image sensor output Z (n) acquired earlier is Y (n) = W (n) −Z (n) (2)
Is calculated (subtracted) to calculate the light quantity component Y (n) (step S105). Further, an average light amount Y that is an average value in a partial region (elements for K pixels) of the light amount component Y (n) is expressed as Y = 1 / K * ΣY (n) (3)
And the average light amount Y is stored in the memory 2 as an initial light amount (step S106).

  The data shown in FIG. 3 includes Z (n), X (n) = V (n) −Z (n), V (n), Y (n) = W (n) −Z (n) and This is data obtained with W (n).

  FIG. 4 is a diagram showing data acquired and held before the start of reading. The horizontal axis represents main scanning pixels (all N pixels), and the vertical axis represents image sensor output. FIG. 5B is a flowchart showing the data calculation process and the black level correction value calculation process procedure shown in FIG. This process is performed every time the reading operation is performed immediately before the start of the reading operation.

  In this process, first, the light source 6 is turned off, and the image sensor output Z ′ (n) is acquired for all main scanning pixels and held in the memory 3 (step S201).

Next, the light source 6 is turned on, and the image sensor output W ′ (n) when the white reference plate 4 is read is acquired (step S202). The image sensor output Z ′ (n) acquired earlier is Y ′ (n) = W ′ (n) −Z ′ (n) (4)
Is calculated (subtracted) to calculate the light amount component Y ′ (n) (step S203). Further, an average value Y ′ in a partial region corresponding to the elements for K pixels in Y ′ (n) is expressed as Y ′ = 1 / K * ΣY ′ (n) (5)
And the average value Y ′ is held in the memory 4 as the amount of light before the start of reading (step S204).

Accordingly, if the apparatus has an optical system in which the stray light amount is proportional to the fluctuation amount of the light amount, the stray light component X ′ (n) before the start of reading from the data held in the memories 1, 2, 4
X ′ (n) = X (n) * Y ′ / Y (6)
(Step S205), and the sum of the stray light component X ′ (n) and the image sensor output Z ′ (n) held in the memory 3 is the black level correction value Vc.
Vc = X ′ (n) + Z ′ (n) (7)
(Step S206).

  In the processing procedure of FIG. 5, for example, it is not necessary to move a blackboard (a black original: an original with no glossiness and a reflectance of 0), and thus the black level correction value Vc can be obtained without reducing productivity. The blackboard is moved by, for example, installing a movable blackboard, moving the blackboard so as to block the optical path of the image sensor light source immediately before reading the document, and reading the blackboard to obtain a black level correction value. This method is executed in the case of a method of removing.

  Note that the data shown in FIG. 4 includes the above Z ′ (n), X ′ (n) = X (n) × Y ′ / Y, Y ′ (n) = W ′ (n) −Z ′ (n ) And W ′ (n). In FIGS. 3 and 4, the data indicated by the dotted line is the data used for the dark subtraction in step S206.

  FIG. 6 is a functional block diagram illustrating a signal processing configuration of the image reading apparatus according to the first embodiment. The signal processing unit according to the first embodiment basically includes the reading unit 7, the CPU 20, and the signal processing unit 30, and exchanges signals between the three parties. The reading unit 7 includes an image sensor 5 and an A / D converter 8, the signal processing unit 30 includes a black level calculation unit 31 and a black subtraction unit 35, and the black level calculation unit 31 includes a memory 32 and a calculator 33. The memory 32 includes the first to fourth memories 1, 2, 3, and 4 described above.

  The output from the image sensor 5 is converted into a digital signal by the A / D converter 8. The converted digital signal is sent to the black level calculation unit 31 when the black level correction value is calculated, that is, when the values shown in FIGS. 3 and 4 are obtained, and to the black subtraction unit 35 when the original is read. Sent. The black level calculation unit 31 performs an operation for calculating the black level correction value shown in FIGS. 3 and 4 from various data held in the memory 32. The black subtractor 35 performs a process of subtracting the black level correction value Vc calculated by the black level calculator 31 from the image signal sent from the A / D converter 11. The CPU 20 performs various controls on the reading unit 7 and the signal processing unit 30. The CPU 20 executes the control set by the program by expanding the program code stored in the ROM (not shown) in the RAM (not shown) and processing the RAM according to the program code while using the RAM as a work area and a data buffer. . Further, the black level calculation unit 31 executes arithmetic processing, and a logical circuit such as ASIC is used for the arithmetic processing.

  FIG. 7 is a view of the main part of the reading unit according to the second embodiment as viewed from the sub-scanning direction. The reflection member 2a is provided on a part of the lower surface of the contact lens 2 according to the first embodiment. The configuration is the same as that of the first embodiment.

  In Example 2, the effective reading range on the product is E, the effective reading range of the image sensor 5 is F, and the contact is within the effective reading range F of the image sensor 5 and outside the effective reading range E on the product. A reflecting member 2 a is installed in a predetermined region (hereinafter referred to as an averaged region) D on the lower surface of the glass 2. This reflecting member is provided to measure the light quantity of the light source, and blocks the optical path from the light source 6 within the averaging region D. In the second embodiment, the average read value (output value) of a part of the reflected light reflected in the averaging area D is stored in the memories 2 and 4 as the light quantity value, thereby correcting the black level correction value Vc. Is calculated. In addition, a space corresponding to a region (hereinafter referred to as a buffer region) C is opened between the averaging region D and the range E. This is because the reflected light from the reflecting member is effective reading range E due to the influence of flare. This is in order not to get inside. Incidentally, the buffer region C may have a distance of about 2 × B, where B is the distance from the lower surface of the white reference plate 4 to the light receiving surface 5a of the image sensor 5. Thereby, the influence of flare can be avoided.

  In the second embodiment, a reflection member 2a is provided on the lower surface of the contact glass 2, and the amount of light is monitored at the portion where the reflection member 2a is provided. There is an advantage that the portion is hardly damaged and the amount of light can be monitored accurately as compared with the first embodiment. The effective reading range E on the product is smaller than the effective reading range F of the image sensor 5. However, in the case of a configuration in which the image sensor 5 is arranged in a staggered manner in the main scanning direction for reading, a reflecting member is provided on the overlapping portion of the staggered arrangement. When 2a is provided, the effective reading range E is not particularly affected.

  FIG. 8 is a view showing the lower surface of the contact glass 2 of FIG. As shown in the figure, a white reflecting member 2 a is provided in the averaged region D on the lower surface of the contact glass 2. In this way, when the reflecting member 2a is white, the amount of reflected light is large, and thus the light quantity ratio is easily obtained accurately.

  In FIG. 9, the reflecting member 2 a is an intermediate color. Since the reflecting member 2 a is closer to the light source than the white reference plate 4, the amount of reflection increases. Therefore, in this example, an intermediate color having a reflectance lower than the white density is used so that the output of the image sensor is not easily saturated.

  FIG. 10 is a diagram showing data acquired in advance to remove the black level and held in the memory 32 in the second embodiment, and corresponds to FIG. 3 in the first embodiment. The second embodiment is the same as the first embodiment until X (n) is stored in the memory 1. Thereafter, the image sensor output W (n) when the light source is turned on is obtained, and the difference Y (n) from Z (n) is calculated based on the formula (2). Data only. Therefore, the average amount of light Y for K pixels in the averaging area D (a part in the D area) is calculated based on the equation (3) and is stored in the memory 2. The processing procedure is the same as the flowchart shown in FIG. 4 except that the reflecting member 2a is read instead of reading the white reference plate 4.

  FIG. 11 is a diagram illustrating data acquired and held before reading is started in the second embodiment. This processing procedure is also basically the same as that shown in FIG. However, the data in the averaging area D is used for calculating the light amount Y ′.

  Then, using the data shown in FIGS. 11 and 12, the black level correction value Vc can be obtained by the above equation (7).

  In addition, each part and the process of each part not specifically described are configured in the same manner as in the first embodiment, and are processed in the same manner.

  FIG. 12 is a diagram of the mechanical configuration of the reading unit according to the third embodiment viewed from the sub-scanning direction. In the third embodiment, third and fourth regions D ′ and C ′ similar to the first and second regions D and C are provided on the downstream side in the main scanning direction with respect to the second embodiment shown in FIG. The configuration is provided. That is, the reflection members 2a and 2a 'are provided on both sides of the image sensor 5. Therefore, the effective reading range E on the product is reduced only to the inside of the second and fourth regions C and C ′, but other parts are the same as those in the second embodiment.

  In the third embodiment, the amount of light is monitored using the average of the reading values of the first and third regions D and D '. Processing and calculation for obtaining the black level correction value Vc are the same as those in the first and second embodiments.

  When the reflection members 2a and 2a 'are provided at two locations on both sides in this way to obtain the black level correction value Vc, the effective reading range E is smaller than that in the second embodiment, but measurement is performed at both ends of the image sensor 5. Even when the light quantity fluctuations differ between the two ends of the image sensor 5, the influence can be reduced. Further, even when the effective reading range E is further smaller than that of the second embodiment as in the third embodiment, the image sensor 5 is arranged in a staggered manner in the main scanning direction in the same manner as in the second embodiment. Since the overlap portion of each image sensor 5 can be used as the first and third regions D and D ′, there is no problem.

  Also in the case of the third embodiment, the black level correction value Vc can be obtained by the above equation (7) using data calculated in the same manner as the data shown in FIGS. 10 and 11 of the second embodiment. .

  In addition, each part and the process of each part not specifically described are configured in the same manner as in the second embodiment, and are processed in the same manner.

  FIG. 13 is a diagram of the mechanical configuration of the reading unit according to the fourth embodiment viewed from the sub-scanning direction, and FIG. 14 is a diagram of FIG. 13 viewed from the main scanning direction. In the fourth embodiment, a light amount sensor 10 is provided in the vicinity of the light source 6 in the first embodiment. In the first embodiment, the light amount is monitored by the reading value of the white reference plate 4, but in the fourth embodiment, the light amount of the light source 6 is measured by a light amount sensor 10 provided separately. With this configuration, the light quantity cannot be accurately monitored when the white reference plate 4 or the reflecting members 2a and 2a 'to be monitored is damaged in other embodiments. However, in this embodiment, the light source is directly monitored. Because there is no effect from scratches.

  In the fourth embodiment, as shown in FIG. 13, the light amount sensor 10 is a position slightly overlapping with the upstream end of the contact glass 2 in the main scanning direction when viewed from the sub scanning direction. 14 is arranged at a position corresponding to the center of the light source 6 as shown in FIG. 14, and the light quantity from the light source is detected at the position.

FIG. 15 is a diagram showing data acquired in advance and stored in the memory for removing the black level, and FIG. 17A is a flowchart showing a processing procedure for storing the data shown in FIG. 15 in the memory. Steps S301 to S303 are the same as steps S101 to S103 of the first embodiment. Next, the light source 6 is turned on, and the light quantity P at that time is measured by the light quantity sensor (step S304). However, unlike the first to third embodiments, when the light amount sensor 10 is used, it cannot cope with a change in gain.
Y = P * G (8)
Is stored in the memory 2 (step S306). However, it is assumed that the gain G does not change during processing in the flowchart of FIG.

  FIG. 15 is a diagram showing data acquired and held before the start of reading, and FIG. 17B is a flowchart showing a data calculation process and a black level correction value calculation process procedure shown in FIG.

In FIG. 17B, first, the light source 6 is turned off, and the image sensor output Z ′ (n) is acquired for all main scanning pixels and held in the memory 3 (step S401). Next, the light source 6 is turned on, and the light amount P ′ at that time is measured by the light amount sensor 10 (step S402), and the gain G ′ at this time is obtained (step S403). Furthermore, the amount of light Y is obtained from the gain G ′ at this time. Y = P ′ * G ′ (9)
And is stored in the memory 4 (step S404).

Thus, if the stray light amount is proportional to the light amount fluctuation amount, the stray light component X ′ (n) before the reading is started from the data stored in the memories 1, 2, 3, and 4 and the current gain value. X ′ (n) = X (n) * Y ′ / Y * G ′ / G (10)
(Step S405).

In step S406, the calculated stray light component X ′ is added to the sensor output Z ′ (n) acquired in step S401, and as a black level correction value Vc, Vc = X ′ (n) + Z ′ (n) (11)
The black level can be removed by the black subtracting unit 35 by subtracting the black level correction value Vc from the image signal data. However, it is assumed that the gain G ′ does not change during processing in the flowchart of FIG.

  FIG. 18 is a block diagram illustrating a signal processing configuration of the image reading apparatus according to the fourth embodiment. This signal processing configuration is the same as the configuration of the first embodiment shown in FIG. 7 except that the light amount detector 15 is provided, and the other configurations are the same. The light quantity detection unit 15 has a function of detecting the light quantity from the light source 6 based on the output of the light quantity sensor 10, and is connected to the CPU 20 and the arithmetic unit 33 of the black level SN French part 31 so that signals can be transmitted and received mutually. It has become.

FIG. 21 is a circuit diagram showing details of the circuit configuration of the light quantity detector 15 shown in FIG. A photodiode 16 is used as the light quantity sensor 10 of the light quantity detection unit 15, and when the image reading apparatus is a color scanner, photodiodes having effective sensitivity in all of Red, Green, and Blue are used. That is, a photodiode having an effective sensitivity according to the light source 6 is used. In the photodiode, the incident light is changed to the current value I and amplified by the OP amplifier 17,
Vin = IR
To obtain the input voltage.

  This is converted into a digital signal by the A / D converter 8. In this embodiment, a 10-bit output from b0 to b9 is used. Note that the number of output bits can be changed according to the desired accuracy. Since the photodiode 16 has a proportional relationship between the light amount and the current value, a digital signal proportional to the light amount is input to the black level calculation unit 30. The black level calculation unit 30 calculates the ratio of the light amount after AD conversion acquired in advance and the light amount after AD conversion acquired before the start of reading, and detects the fluctuation amount of the light amount.

  Other parts not specifically described are configured in the same manner as in the first embodiment and function in the same manner.

  When configured as in the second to fourth embodiments, the light amount value of the light source can be obtained even during document reading. For this reason, even when the amount of light changes due to a temperature change or the like during document reading, correction can be made each time. FIG. 19 is a flowchart showing a processing procedure up to the update of the black level correction value applied in the second and third embodiments.

  In the figure, when reading is started, T (ms) is waited (step S501). This waiting is for performing the black level correction value update operation every T (ms). When reading is still in progress after T (ms) (step S502: Yes), the black level correction value update operation is performed from step S503 to step S507.

  The processing procedure from step S503 to step S506 is the same as the processing procedure from step S202 to step S205 shown in FIG. In step S505 and step S506, Y ′ (n) and X ′ (n) are calculated. When the black level correction value Vc is obtained in step S507, the black level correction value Vc is updated, and the process returns to step S501. And wait for T (ms). This is repeated until the reading is completed (step S502: No). In the black subtraction, when the black level correction value Vc is updated, the black subtraction is continued using the updated value.

In the first to fourth embodiments, in order to obtain the black level correction value Vc and remove the black level,
・ Stray light output (for all main scans)
・ Light quantity Y at that time
Is acquired and held, the dark output and the light amount Y ′ are acquired before the reading is started, the stray light output is corrected from the ratio Y ′ / Y, and the sum of the dark output and the corrected stray light output is removed as a black level. Is configured to do.

  However, in the above embodiment, since the light amount fluctuation amount Y ′ / Y is constant in the main scanning direction, the light amount as in the LED side light method, for example, the method in which the high-intensity LED is irradiated to the entire main scanning region with the light guide. It is good if the fluctuations in the main scanning direction are almost constant, but it is accurate if the light quantity fluctuations differ in the main scanning direction, such as when multiple LEDs are arranged in the main scanning direction, or when an Xe lamp is used. Cannot be corrected.

  The fifth embodiment is an example corresponding to such a case. By correcting the stray light output by acquiring the light amount fluctuation for each reading range, it is accurate even if the light amount fluctuation is different in the main scanning direction. The stray light output is calculated and the black level can be removed.

That is, in the fifth embodiment, when removing the black level correction value of the image reading apparatus,
1) First, all main scans are divided into blocks (number of blocks b).
2) Next, stray light output X (n) (n: main scanning pixel) is acquired in advance (for example, when the reading apparatus is manufactured), and the light quantity Y (a) (a: 1 to 1) in each block at that time is acquired. b) Obtain it.
3) The image sensor output data Z (n) and the light amount Y ′ (a) for each block when the light source is turned off are acquired immediately before the document reading is started.
4) The correction value X ′ (n) = Y ′ (a) / Y (a) * X (n) of the stray light component in each block is calculated from the ratio Y ′ (a) / Y (a) of the light amounts of the two. Then, when reading the original, the sum of X ′ (n) and Z ′ (n) is removed from the original read value as a black level correction value.
It is characterized by that.

  Hereinafter, it will be described in detail with reference to the drawings.

  FIG. 21 is a diagram of the mechanical configuration of the reading unit according to the fifth embodiment viewed from the main scanning direction, and corresponds to FIG. 1 (see the first embodiment) when viewed from the sub scanning direction. The signal processing configuration of the image reading apparatus is the same as that of the first embodiment.

  As can be seen from FIG. 21, the fifth embodiment is obtained by replacing the light source 6 of the first embodiment with an LED array 12, and the LED array 12 includes a plurality of LEDs 13 and a substrate 14 on which these LEDs 13 are mounted. Other parts are the same as those in the first embodiment.

  FIG. 22 is a view of an LED array serving as a light source viewed from the sub-scanning direction. The light source 6 shown in this embodiment has a configuration in which a plurality of LEDs 13 are arranged in an array in the main scanning direction. Further, the document reading area H is divided into a plurality of blocks at predetermined intervals in the main scanning direction. This block division is a division when calculating the average light quantity for each block later. In the fifth embodiment, the blocks are divided according to the arrangement interval of the LEDs 13, but other blocks may be used. In the figure, the block division is set as 1, 2,..., B−1, b (b: a positive integer of 2 or more).

  FIG. 23 is a diagram showing a light amount distribution when the LED array 12 shown in FIG. 22 is used. In the figure, a solid line indicates an initial light amount distribution (such as when an image reading apparatus is manufactured), and a dotted line indicates a light amount distribution after a certain period from the initial time (before reading starts). The light amount distribution varies over time, and the variation varies for each LED 13. For this reason, fluctuations in the amount of light have variations in the main scanning as a whole. When there is such variation, accurate black level correction cannot be performed by the method described in Patent Document 1 described above.

Therefore, in the fifth embodiment, first, the black level is calculated as follows.
FIG. 24 is a diagram showing data acquired in advance and stored in the memory in order to remove the black level. Here, “preliminarily” is acquired in the same way as in the first embodiment when the image reading apparatus is manufactured or when it is determined necessary in the market. The horizontal axis represents main scanning pixels (all N pixels: N is a positive integer), and the vertical axis represents image sensor output. FIG. 27A is a flowchart showing a processing procedure for holding the data shown in FIG. 24 in the memory.

  In FIG. 27A, first, the LED 13 of the light source 6 is turned off, and the image sensor output Z (n) is acquired for all main scanning pixels N (n is the nth pixel among all N pixels) (step S601). Next, the LED 13 of the light source 6 is turned on, and the image sensor output V (n) when the black image is read is acquired for all main scanning pixels (step S602). Reading a black image is the same as in the first embodiment.

The image sensor output V (n) when the black image is read is acquired, and the stray light output X (n) is
X (n) = V (n) -Z (n) (1)
And is stored in the memory 1 (step S603).

Next, the LED 13 of the light source 6 is turned on, and the image sensor output W (n) when the white reference plate 4 of FIG. Subtract the image sensor output Z (n) obtained when the light source is extinguished.
W (n) -Z (n) (2)
Is obtained (step S605). Further, this W (n) −Z (n) is averaged in each block, the average light amounts Y (1) to Y (b) are calculated, and stored in the memory 2 (step S606).

  FIG. 25 is a diagram showing data acquired before the start of reading, FIG. 26 is a diagram showing a method for calculating stray light output, and FIG. 27B shows a processing procedure of data calculation processing and black level correction value calculation shown in FIG. It is a flowchart. Note that the light amounts Y (1) to Y (b) and the initial stray light output X (n) for each block before reading the document shown in FIG. 24 are acquired by the processing of FIG. 27A.

  In FIG. 27B, first, the LED 13 of the light source 6 is turned off, and the image sensor output Z ′ (n) is acquired for all the main scanning pixels N and held in the memory 3 (step S701). Next, the light source 6 is turned on, and the image sensor output W ′ (n) when the white reference plate 4 is read is acquired (step S702). This result is the sensor output (dark output) Z ′ (n) when the light source is turned off and the white reference plate reading output W ′ (n) when the light source is turned on in FIG.

The light amount distribution before the start of reading by subtracting the previously obtained image sensor output Z ′ (n),
W ′ (n) −Z ′ (n) (4) ′
Is calculated (step S703). Next, an average value is calculated for each block with respect to the light amount distribution W ′ (n) −Z ′ (n), and average light amounts Y ′ (1) to Y ′ (b) for each block are calculated. Thereby, the light quantity fluctuation amount for each block from the initial state Y ′ (1) / Y (1) to Y ′ (b) / Y (b) (12)
Is calculated. Since the stray light output X ′ (n) is proportional to the light quantity fluctuation amount, X ′ (n) = X (n) * Y ′ (a) / Y (a) from the initial stray light output X (n) (13)
Where a = 1, 2,..., B
(Step S705). The a value at this time indicates a block No including the nth pixel. For example, when the block width is 300,
When n = 1 to 300 a = 1,
When n = 301 to 600, a = 2
・
・
・
It becomes.

Since the sum of the stray light output X ′ (n) calculated in step S705 and the dark output Z ′ (n) acquired before the start of reading becomes a black level,
X ′ (n) + Z ′ (n) (14)
7 to the black subtracting unit 35 shown in FIG. 7, and the black subtracting unit 35 subtracts the sum calculated by the equation (14) from the original reading value sent from the A / D converter 8. Can be corrected.

  As described above, in the fifth embodiment, as shown in FIG. 22, the light amount variation is calculated for each arbitrary or predetermined block 1 to b, but the width of this block can be changed. That is, if the block width is narrowed, it is possible to calculate the light amount variation with high accuracy, and if the block width is widened, the amount of retained data decreases accordingly. In addition, when there is dust on the contact glass 2 or the white reference plate 4, it may not be possible to accurately acquire the light amount fluctuation at the location where the dust exists. In such a case, the block width is set to one pixel. By doing so, it is also possible to perform black level correction by fluctuation of the amount of light in units of pixels. Furthermore, the block width of each block is not fixed, and the width may be changed for each block.

  In the fifth embodiment, the LED array 12 has been described as an example. However, a configuration in which light is diffused by a light guide instead of an arrayed light source, or when reading is performed using an Xe lamp, a fluorescent lamp, or the like. Applicable.

  In each of the above embodiments, the image reading apparatus has been described in detail. However, such an image reading apparatus is not only used as a PC (personal computer) color image input apparatus, but also a copying machine, a facsimile, It is used as an image input apparatus of an image forming apparatus such as a digital multifunction peripheral (MFP) having various functions. In this case, the image reading apparatus is configured integrally or separately from the image forming apparatus.

  As described above, according to the present embodiment, the image sensor output by stray light is acquired in advance, and the ratio between the initial light amount that is the light amount of the light source at that time and the light amount of the light source before reading is measured, and the light amount Since the output of the image sensor is corrected based on the ratio and the output of stray light measured in advance, stray light caused by environmental changes / time-dependent fluctuations in the dark output and fluctuations in the amount of light without reducing productivity with a simple device configuration Even if the image sensor output fluctuates due to the above, it is possible to accurately obtain and remove the black level correction value.

  The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention, and all technical matters included in the technical idea described in the claims are included. The subject of the present invention. Each of the above examples shows a preferred embodiment, but those skilled in the art will realize various alternatives, modifications, variations, and improvements from the contents disclosed in this specification. Which fall within the scope defined by the appended claims.

DESCRIPTION OF SYMBOLS 1 Image reader 2 Contact glass 2a Reflective member 4 White reference board 5 Image sensor 6 Light source 10 Photoelectric sensor 31 Black level correction value acquisition means D Averaging area F Effective reading range G Original

JP-A-8-98017

Claims (13)

A light source for illuminating the document;
A light receiving element for acquiring light reflected by the document;
First storage means for causing the light receiving element to acquire a first output by stray light in advance and storing the light amount of the light source at that time as a first light amount;
Before the reading of the document, the light amount of the light source is acquired as a second light amount, and the light receiving element is based on the ratio of the first light amount and the second light amount and the first output acquired in advance. Correction means for correcting the output of
An image reading apparatus comprising: The image reading apparatus according to claim 1,
The correction means includes
Obtaining a second output of the light receiving element in a light-off state of the light source immediately before starting reading of the document;
Image reading, wherein a black level correction value is obtained by adding the second output to a value obtained by multiplying the ratio of the first light quantity and the second light quantity by the first value. apparatus. The image reading apparatus according to claim 1,
The first light amount is the averaged value for each preset reading range within the effective reading range;
2. The image reading apparatus according to claim 1, wherein the second light amount is the averaged value for each of the preset reading ranges immediately before the start. The image reading apparatus according to claim 1,
The image reading apparatus, wherein the correction unit acquires the black level correction value for each of the preset ranges over the entire reading range. The image reading apparatus according to claim 1,
The image reading apparatus according to claim 1, wherein the first and second light amounts are values obtained by averaging output values of predetermined areas. The image reading apparatus according to claim 5,
An image reading apparatus characterized in that one or more of the preset areas are set. The image reading apparatus according to claim 6,
The image reading apparatus, wherein the reference plate is installed on a reading optical path of the light receiving element corresponding to one of the preset areas. The image reading apparatus according to claim 7,
One of the preset regions is outside the effective reading range on the product and within the effective reading range of the light receiving element, and a reflecting member that blocks the reading light path of the light receiving element in a partial region of the one region. An image reading apparatus comprising: The image reading apparatus according to claim 8, wherein
The image reading apparatus according to claim 1, wherein the reflection member has a reflectance that does not saturate the output of the light receiving element. The image reading apparatus according to claim 1,
Photoelectric conversion means for generating an electrical output according to the amount of light directly incident from the light source instead of the reference plate,
The correction means obtains the first and second light amounts based on an output value from the photoelectric conversion means instead of the reference plate, and uses the obtained first and second light amounts to receive the light receiving element. An image reading apparatus that corrects the output of the image. The image reading apparatus according to claim 2,
Nonvolatile first and second storage means for storing the first output and the first light amount, respectively;
Volatile third and fourth storage means for storing the second output and the second light amount, respectively;
With
The first output and the first light amount are acquired at an arbitrary timing before immediately before the start of reading, including the time of manufacturing the image reading apparatus before the reading,
2. The image reading apparatus according to claim 1, wherein the second output and the second light quantity are acquired for each operation of reading a document immediately before the start of reading.   An image forming apparatus comprising the image reading apparatus according to claim 1. A light source for illuminating the document;
A light receiving element for acquiring light reflected by the document;
An image reading method for reading an image of the document by the light receiving element,
A step of causing the light receiving element to acquire a first output by stray light in advance and storing the light amount of the light source at that time as a first light amount in a storage unit;
Before the reading of the document, the light amount of the light source is acquired as a second light amount, and the light receiving element is based on the ratio of the first light amount and the second light amount and the first output acquired in advance. Correcting the output of
An image reading method comprising: