JP2025118004A - Reading device - Google Patents

Abstract

To provide a reading device capable of improving detection accuracy of a position and a size of a foreign substance while suppressing an increase in time required to detect the position and the size of the foreign substance.SOLUTION: A first reading range and a second reading range are read while a reading device is reciprocated in a sub-scanning direction. It is determined whether each of first blocks is a block without foreign substance or a block with foreign substance based on a histogram of luminance values created for each of a plurality of first blocks obtained by dividing a read image of the first reading range (S207 to S209). Further, it is determined whether each of second blocks is a block without foreign substance or a block with foreign substance based on a histogram of luminance values created for each of a plurality of second blocks obtained by dividing the read image of a second reading range (S207 to S209). The second reading range is set to be narrower than the first reading range (S213).SELECTED DRAWING: Figure 6A

Description

The present invention relates to a reading device.

Traditionally, reading devices have been provided that optically read an object to be read and generate image data of the object.

In one example of a reading device, a reading device equipped with a light source and an image sensor is placed opposite the object to be read across a transparent plate. The image sensor has multiple light-receiving elements arranged in the main scanning direction. In addition, a white background member is placed opposite the transparent plate across the object to be read.

When light from the reading device's light source is reflected by the object to be read and the background material, and this reflected light enters the reading device's image sensor, photoelectric conversion is performed in each light-receiving element, and an electrical signal (voltage) corresponding to the amount of light received is output from each light-receiving element. The electrical signal output from each light-receiving element is A/D converted into a digital brightness value (image data), thereby achieving reading of one line in the main scanning direction by the reading device. When reading the object to be read, the reading device is moved in the sub-scanning direction perpendicular to the main scanning direction, and reading of one line in the main scanning direction is repeated, reading a reading range that includes the entire object to be read. The image of the object to be read is then identified from the read image of the reading range, and image data of the object to be read is generated.

For example, if dust or other foreign matter is attached to the area of the transparent plate facing the object to be read, the foreign matter may appear in the read image of the object to be read. Furthermore, if foreign matter is attached to an area of the transparent plate or background member that does not face the object to be read, the foreign matter may appear in the read image of the background member, potentially interfering with the identification of the read image of the object to be read.

In response, a technology has been proposed in which a predetermined reading range is read when the object to be read is not facing a transparent plate, and the read image of that reading range is analyzed to detect the presence or absence of a foreign object, and if a foreign object is present, its position and size are detected (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2015-211307

The object of the present invention is to provide a reading device that can improve the accuracy of detecting the position and size of a foreign object while minimizing the increase in the time required to detect the position and size of the foreign object.

In order to achieve the above-mentioned object, a reading device according to one aspect of the present invention comprises a transparent plate, a reading device provided on one side of the transparent plate and having a light source that emits light toward the transparent plate and a plurality of light receiving elements arranged in a main scanning direction, a movement mechanism that moves the reading device in a sub-scanning direction that intersects the main scanning direction and follows the transparent plate, a white background member that is provided on the other side of the transparent plate and is arranged opposite the transparent plate, and a control unit. The control unit performs a first reading process that reads a first reading range by emitting light from the light source of the reading device and converting electrical signals output from the light receiving elements into brightness values while moving the reading device in one side of the sub-scanning direction, and a histogram of brightness values created for each of a plurality of first blocks into which the read image of the first reading range is divided. a first determination process that determines whether each of the first blocks is a foreign substance-containing block that includes a read image different from the read image of the background member based on the result of the first determination process; a setting process that sets a second read range that is narrower than the first read range and includes the first blocks determined to be foreign substance-containing blocks based on the determination result of the first determination process; a second read process that reads the second read range by emitting light from the light source of the read device while moving the read device in the other direction of the sub-scanning direction and converting the electrical signal output from the light receiving element into a brightness value; and a second determination process that determines whether each of the second blocks is a foreign substance-containing block based on a brightness value histogram created for each of the multiple second blocks obtained by dividing the read image of the second read range.

With this configuration, the first reading range is read. The read image of the first reading range is then divided into multiple first blocks, and a brightness histogram is created for each first block. Based on the histogram, it is determined whether each first block is a foreign object block that contains a read image that differs from the read image of the background member.

Then, a second reading range is set and the second reading range is read. The read image of the second reading range is then divided into multiple second blocks, and a histogram of brightness values is created for each second block. Based on this histogram, it is determined whether each second block contains a foreign object.

To read the first reading range, the reading device is moved to one side in the sub-scanning direction. After reading the first reading range, the reading device must be returned to its original position (the position before reading the first reading range), and the movement of the reading device at that time is used to read the second reading range. This makes it possible to read both the first reading range and the second reading range while the reading device is reciprocated in the sub-scanning direction.

The second reading range is set to a range that includes the first block determined to be a block containing foreign matter, and is narrower than the first reading range.

As a result, when the size of the second blocks is set to the same as the size of the first blocks, the number of second blocks is reduced compared to the number of first blocks, and the time required to determine whether each second block is a foreign object block can be reduced compared to the time required to determine whether each first block is a foreign object block. Furthermore, because the second read range is narrower than the first read range, the position of the second block is shifted from the position of the first block. Therefore, if a portion of a first block determined to be a foreign object block overlaps with a portion of a second block determined to be a foreign object block, the position and size of the overlapping portion can be detected as the position and size of the foreign object. As a result, the position and size of the foreign object can be detected with high accuracy.

On the other hand, if the size of the second blocks is set smaller than the size of the first blocks, the position and size of the foreign object can be detected in more detail (with greater accuracy) from the results of determining whether the second blocks are foreign object blocks. Even in this case, by making the second reading range narrower than the first reading range, an increase in the number of second blocks can be suppressed, and an increase in the time required to determine whether each second block is a foreign object block can be suppressed.

This makes it possible to improve the accuracy of detecting the position and size of a foreign object while minimizing the increase in the time required to detect the position and size of the foreign object.

A reading device according to another aspect of the present invention includes a transparent plate, a reading device provided on one side of the transparent plate and having a light source that emits light toward the transparent plate and a plurality of light receiving elements arranged in a main scanning direction, a movement mechanism that moves the reading device in a sub-scanning direction that intersects the main scanning direction and follows the transparent plate, a white background member that is provided on the other side of the transparent plate and is arranged opposite the transparent plate, and a control unit. The control unit performs a first reading process that reads a first reading range by emitting light from the light source of the reading device and converting electrical signals output from the light receiving elements into brightness values while moving the reading device in one side of the sub-scanning direction, and a second reading process that reads a first reading range into a plurality of first blocks into which the read image of the first reading range is divided. A first determination process is performed to determine whether each of the first blocks is a foreign substance-containing block containing a read image different from the read image of the background member based on a histogram of brightness values created in the first determination process. A second determination process is performed to read the first read range by moving the reading device in the other direction of the sub-scanning direction, emitting light from the light source of the reading device, and converting the electrical signal output from the light-receiving element into a brightness value. A second determination process is performed to determine whether each of the second blocks is a foreign substance-containing block based on a histogram of brightness values created for each of multiple second blocks obtained by dividing the read image of the first read range, and the positions of the first blocks and the second blocks are shifted and set.

With this configuration, the reading device is moved to one side in the sub-scanning direction and the first reading range is read. The read image of the first reading range is then divided into multiple first blocks, and a brightness histogram is created for each first block. Based on the histogram, it is determined for each first block whether it is a foreign object block that contains a read image that differs from the read image of the background member.

The reading device then needs to be returned to its original position (the position before reading the first reading range), and the movement of the reading device at that time is used to read the first reading range. This allows the first reading range to be read twice while the reading device is moved back and forth in the sub-scanning direction.

Then, the image read from the second reading of the first reading range is divided into multiple second blocks, and a histogram of brightness values is created for each second block. Based on this histogram, it is determined whether each second block contains a foreign object.

The position of the second block is set to be offset from the position of the first block. As a result, if a portion of the first block determined to be a foreign object block overlaps with a portion of the second block determined to be a foreign object block, the position and size of the overlapping portion can be detected as the position and size of the foreign object.

This makes it possible to improve the accuracy of detecting the position and size of a foreign object while minimizing the increase in the time required to detect the position and size of the foreign object.

This invention makes it possible to improve the accuracy of detecting the position and size of a foreign object while minimizing the increase in the time required to detect the position and size of the foreign object.

1 is a perspective view of a reading device according to an embodiment of the present invention; FIG. 2 is a diagram showing a part of the top surface of the housing of the reading device. FIG. 2 is a cross-sectional view illustrating the configuration of a reading device. FIG. 2 is a block diagram showing the electrical configuration of the reading device. 10 is a flowchart showing the flow of a process for determining when to execute a foreign object detection process. 10 is a flowchart (part 1) showing the flow of a foreign object detection process. 10 is a flowchart (part 2) illustrating the flow of a foreign object detection process. FIG. 4 is a diagram for explaining a first reading range and a first block. FIG. 10 is a diagram showing an example of a histogram of luminance values of all pixels in a target block (an example in the case where the target block is a block containing a foreign substance); FIG. 10 is a diagram showing another example of a histogram of luminance values of all pixels in a target block (an example in the case where the target block is a block without a foreign object). FIG. 10 is a diagram for explaining a second reading range and a second block. 10 is a flowchart illustrating another example of a process for determining when to execute a foreign object detection process. 10 is a flowchart illustrating another example of the foreign object detection process. 10A and 10B are diagrams for explaining the setting positions of a first reading range and a second block;

The following describes in detail an embodiment of the present invention with reference to the accompanying drawings.

<Reading device>
The reading device 1 shown in Fig. 1 is a device that optically reads an object to be read OB (see Fig. 2) using a flatbed (FB) method and generates image data of the object to be read OB. The object to be read OB includes originals such as text documents and photographic documents that are read for reproduction by printing or the like, documents that are read for digital documentation using OCR (Optical Character Recognition) technology, and media such as paper on which a barcode (one-dimensional barcode or two-dimensional code) is displayed that is read for decoding.

The front, rear, top, bottom, left, and right directions of the reading device 1 have been defined, and these directions will be used appropriately in the following explanation. In Figure 1, the front, rear, top, bottom, left, and right directions of the reading device 1 are indicated by arrows, in Figure 2, the front, rear, left, and right directions of the reading device 1 are indicated by arrows, and in Figure 3, the top, bottom, left, and right directions of the reading device 1 are indicated by arrows.

The reading device 1 comprises a housing 11 having a substantially rectangular parallelepiped shape and a cover 12 that opens and closes the top surface of the housing 11. The rear end of the cover 12 is connected to the upper rear end of the housing 11 so that it can swing about an axis extending in the left-right direction. The cover 12 swings between an open position in which the front end is raised relative to the top surface of the housing 11, exposing the top surface of the housing 11, and a closed position in which it is folded down relative to the top surface of the housing 11, covering the top surface of the housing 11.

A rectangular opening 13 that is long in the left-right direction is formed on the top surface of the housing 11. The opening 13 is closed from below by a transparent plate 14. The transparent plate 14 is made of a transparent plate such as a transparent glass plate or resin plate.

The object to be read OB is placed at a specified position on the transparent plate 14 with the surface to be read facing downward. The specified position is based on the left rear corner where the rear edge 15 and left edge 16 of the opening 13 intersect. For example, as shown in FIG. 2, if the object to be read OB is rectangular, this is the position where one corner of the object to be read OB abuts the left rear corner of the opening 13 and the two edges of the object to be read OB abut against the rear edge 15 and left edge 16 of the opening 13. After the object to be read OB has been placed at the specified position on the transparent plate 14, the cover 12 is closed, and the object to be read OB is covered from above by the cover 12.

As shown in Figure 3, a background member 17 made of a sheet of white resin is elastically supported on the inner surface of the cover 12. The background member 17 is formed in a roughly rectangular shape that is smaller than the opening 13. When the cover 12 is closed, the background member 17 does not rest on the peripheral edge of the opening 13 in the housing 11, but is positioned within the opening 13 with a gap between it and each edge of the opening 13, pressing the object to be read OB against the transparent plate 14.

A reading device 18 and a moving mechanism 19 are provided below the transparent plate 14.

The reading device 18 is in the form of a CIS (Contact Image Sensor) unit and includes a light source 21, a rod lens array 22, and an image sensor 23. The light source 21 includes three LEDs (Light Emitting Diodes): R (red), G (green), and B (blue). The rod lens array 22 includes a large number of rod lenses aligned in the main scanning direction, which coincides with the left-right direction of the reading device 1. The rod lenses are gradient index lenses with a fixed magnification. The image sensor 23 is a linear image sensor configured with multiple light-receiving elements arranged at equal intervals in the main scanning direction. Each light-receiving element includes, for example, R (red), G (green), and B (blue) color filters and photodiodes, and outputs an electrical signal (voltage) corresponding to the intensity of each RGB color component contained in the received light.

The movement mechanism 19 moves the reading device 18 in a sub-scanning direction that is perpendicular to the main scanning direction. The sub-scanning direction coincides with the left-right direction of the reading device 1. The movement mechanism 19 includes a CIS carriage 24 that carries the reading device 18, and a scanner motor 25 that generates a driving force to move the CIS carriage 24 back and forth in the left-right direction.

Note that the reading device 1 is not limited to a configuration that uses a CIS system, which is a 1x optical system, as its reading method, but may also use a reduced optical system, i.e., a CCD (Charge Coupled Devices) system.

<Electrical configuration>
4, the reading device 1 includes an ASIC (Application Specific Integrated Circuit) 31. The ASIC 31 incorporates a CPU (Central Processing Unit) 32 and a memory 33. The memory 33 includes a nonvolatile memory that allows data to be rewritten, such as a flash memory or an E2PROM, and a volatile memory, such as a DRAM (Dynamic Random Access Memory).

The ASIC 31 is connected to a bus 34 for data communication. The reading device 18 and the movement mechanism 19 are also connected to the bus 34.

The CPU 32 (an example of a control unit) of the ASIC 31 executes a program stored in the non-volatile memory of the memory 33 and controls the operation of the reading device 18 and the movement mechanism 19. When executing the program, the CPU 32 uses the volatile memory of the memory 33 as a work area.

For example, an external terminal such as a PC (Personal Computer) connected to the reading device 1 so that it can communicate with the reading device 1 is operated, and the external terminal instructs the reading device 1 to start reading. When the instruction to start reading is given, the CPU 32 sets a reading range and starts the reading process to read that reading range.

During the reading process, the reading device 18 is moved from its home position to a reading start position. The reading start position is set, for example, to the leftmost position of the maximum reading range of the reading device 18. The reading device 18 is then moved from the reading start position in one direction in the sub-scanning direction, i.e., to the right, at a constant speed.

Meanwhile, the light source 21 of the reading device 18 is turned on, and light from the light source 21 passes through the transparent plate 14. When an object to be read OB is placed on the transparent plate 14, the light passing through the transparent plate 14 is mainly reflected by the object to be read OB or the background member 17. When an object to be read OB is not placed on the transparent plate 14, the light passing through the transparent plate 14 is mainly reflected by the background member 17. When this reflected light passes through the rod lens array 22 and enters the image sensor 23, photoelectric conversion is performed in each light-receiving element of the image sensor 23, and a voltage (electrical signal) corresponding to the amount of light received is output from each light-receiving element.

The ASIC 31 is equipped with an A/D conversion circuit. The A/D conversion circuit has, for example, 8-bit (0-255) resolution and converts the voltage (electrical signal) output from the image sensor 23 for each RGB color into a digital brightness value (image data). For example, voltages below the lower limit reference voltage (lower limit value) are uniformly converted to a brightness value of "0," voltages above the upper limit reference voltage (upper limit value) are uniformly converted to a brightness value of "255," and voltages between the lower limit and upper limit values are converted to a brightness value corresponding to the magnitude of the voltage. By converting the voltage output from each light-receiving element into a brightness value, the reading device 18 can read one line in the main scanning direction.

While the reading device 18 is moved to the right at a constant speed, the reading device 18 repeatedly reads one line at a time, thereby reading the entire reading range and generating image data of the reading range. When the object to be read OB is placed on the transparent plate 14, the reading range is set to a range corresponding to the size of the object to be read OB, and image data of the object to be read OB is generated. Once reading of the reading range is complete, the direction of movement of the reading device 18 is reversed, and the reading device 18 moves in the other direction in the sub-scanning direction, i.e., to the left, toward the home position (return operation).

<Foreign object detection processing>
In the reading device 1, foreign matter such as dust may adhere to the transparent plate 14 and the background member 17. For example, if foreign matter adheres to an area on the transparent plate 14 where the object to be read OB is placed, the foreign matter will appear in the read image of the object to be read OB when the object to be read OB is read. Therefore, in the reading device 1, the CPU 32 of the ASIC 31 executes foreign matter detection processing to detect the presence or absence of foreign matter attached to the transparent plate 14 or the background member 17 and to detect the position and size of the foreign matter.

To determine whether to execute the foreign object detection process, the CPU 32 determines whether it is currently time to execute the foreign object detection process (S1), as shown in FIG. 5.

To accurately detect the presence or absence of a foreign object, as well as the position and size of the foreign object, the foreign object detection process is preferably performed when the cover 12 is in the closed position and no object to be read OB is present between the transparent plate 14 and the background member 17; in other words, when the transparent plate 14 and the background member 17 are facing each other without the object to be read OB sandwiched between them. Since the power to the reading device 1 is often turned on when the transparent plate 14 and the background member 17 are facing each other without the object to be read OB sandwiched between them, the CPU 32 determines, for example, when the power to the reading device 1 is turned on that it is now time to perform the foreign object detection process.

Furthermore, when a user operates an external terminal communicatively connected to the reading device 1 to set the reading device 1 to foreign object detection mode, the reading object OB is not usually placed on the transparent plate 14. Therefore, the CPU 32 may determine that it is now time to perform the foreign object detection process in response to the reading device 1 being notified by the external terminal that the foreign object detection mode has been set. In a configuration in which the reading device 1 is equipped with operation keys, the CPU 32 may determine that it is now time to perform the foreign object detection process in response to the foreign object detection mode being set (selected) by operating the operation keys.

If the CPU 32 determines that the current time is the time to execute the foreign object detection process (S1: YES), it executes the foreign object detection process (S2). On the other hand, if the CPU 32 determines that the original time is not the time to execute the foreign object detection process (S1: NO), it does not execute the foreign object detection process, waits a predetermined time, and then again determines whether the current time is the time to execute the foreign object detection process (S1).

The flow of the foreign object detection process is shown in Figures 6A and 6B. In the foreign object detection process, as shown in Figure 7, the CPU 32 sets a size X1 x Y1 determined by the length X1 in the main scanning direction and the length Y1 in the sub-scanning direction of the first block so that the read image read in the first reading process described below (an image related to the image data obtained in the reading process) is divided into multiple first blocks based on the left rear edge of the read image (S201). The size X1 x Y1 may be set to a predetermined fixed value, or may be set each time to a value corresponding to the first reading range described below, for example.

The CPU 32 sets the first reading range (S202). The first reading range is set, for example, to the range in which a rectangular sheet of the largest size that can be read by the reading device 1 can be placed, as shown by the two-dot chain line in Figure 7.

Then, the CPU 32 controls the operation of the reading device 18 and the movement mechanism 19 to start the first reading process, which reads the first reading range (S203). In the first reading process, the reading device 18 is moved at a constant speed from the reading start position to the right in the sub-scanning direction, while repeatedly reading one line in the main scanning direction by the reading device 18, until the entire first reading range is read. When reading of the entire first reading range has been completed, the CPU 32 ends the first reading process.

After the first reading process begins, the CPU 32 designates a target block from among the multiple first blocks as the target for attribute determination as to whether it is a block with foreign matter or a block without foreign matter (S204). A block with foreign matter is a block that includes a read image that differs from the read image of the background member 17, such as a read image of foreign matter attached to the transparent plate 14 or the background member 17. On the other hand, a block without foreign matter is a block that does not include a read image that differs from the read image of the background member 17, or a block that includes almost no read image that differs from the read image of the background member 17. The first target block is designated as the first block that includes a read image of the area facing the left rear end of the transparent plate 14 within the opening 13.

Then, the CPU 32 obtains a histogram of the luminance values of all pixels in the target block, for example, from a histogram creation circuit provided in the ASIC 31 (S205). The ASIC 31 converts the luminance values of each RGB color into grayscale luminance values (e.g., 256 levels) for each pixel in the target block using a known conversion method, and the histogram creation circuit creates a histogram of the luminance values (horizontal axis: luminance value, vertical axis: frequency) as shown in Figures 8 and 9.

The CPU 32 calculates the sum A of the frequency of brightness values equal to or greater than a predetermined brightness threshold THL based on a histogram of the brightness values of all pixels in the target block (S206). When the background member 17 is read, the brightness value of each pixel in the read image of the background member 17 indicates a value near "255." The brightness threshold THL is defined as the lower limit of the brightness value corresponding to the background member 17 (the brightness value corresponding to the voltage output from the light receiving element that receives light reflected from the background member 17).

The CPU 32 then determines whether the sum A is greater than a predetermined frequency threshold THF (S207). Brightness values corresponding to objects other than the background member 17, such as foreign matter adhering to the transparent plate 14 or the background member 17, (brightness values corresponding to the voltage output from the light-receiving element receiving the light reflected by the object other than the background member 17) tend to be lower than brightness values corresponding to the background member 17. Therefore, if the target block includes a scanned image different from the scanned image of the background member 17, as shown in FIG. 8, the frequency (number of pixels) of brightness values lower than the brightness threshold THL will be relatively high, and the frequency of brightness values equal to or greater than the brightness threshold THL will be relatively low. Conversely, if the target block does not include a scanned image different from the scanned image of the background member 17, the frequency of brightness values equal to or greater than the brightness threshold THL will be relatively high, and the frequency of brightness values lower than the brightness threshold THL will be relatively low, as shown in FIG. 9. Therefore, if the sum A is greater than the frequency threshold THF (S207: YES), the CPU 32 determines that the target block is a foreign substance-free block that does not contain a scanned image different from the scanned image of the background member 17 (S208). On the other hand, if the sum A is equal to or less than the frequency threshold THF (S207: NO), the CPU 32 determines that the target block is a foreign substance-containing block that contains a scanned image different from the scanned image of the background member 17 (S209).

The CPU 32 then determines whether attribute determination has been performed for all first blocks (S210).

If there are any remaining first blocks for which attribute determination has not been performed and the CPU 32 determines that attribute determination has not been performed for all first blocks (S201: NO), it updates the target block to another first block (S204). If there is a first block adjacent to the previous target block for attribute determination on the front side, that first block is designated as the target block, and the target block is updated. If there is no first block adjacent to the previous target block for attribute determination on the front side, the rearmost first block of the first blocks adjacent to the previous target block for attribute determination on the right side and forming a row in the main scanning direction is designated as the target block, and the target block is updated.

As described above, the CPU 32 then obtains a histogram of the brightness values of all pixels in the target block (S205), calculates the sum A of the frequencies of brightness values equal to or greater than the brightness threshold THL (S206), and determines whether the target block is a block without a foreign object or a block with a foreign object based on the magnitude relationship between the sum A and the frequency threshold THF (S207, S208, S209). The CPU 32 then determines whether attribute determination has been performed for all first blocks (S210).

Steps S204 to S210 are repeated until attribute determination for all first blocks is complete. When attribute determination for all first blocks is complete, the CPU 32 determines that attribute determination for all first blocks has been performed (S210: YES). The CPU 32 then determines whether the completed attribute determination was the first week's attribute determination, i.e., whether it was the attribute determination for the first block (S211).

If the CPU 32 determines that the completed attribute determination was the first week's attribute determination (S211: YES), it determines whether the number of first blocks determined to be blocks containing foreign matter in the first week's attribute determination (the number of blocks containing foreign matter) is 1 or greater (S212).

If the CPU 32 determines that the number of blocks containing foreign matter is one or more (S212: YES), it sets a second read range that includes the blocks containing foreign matter (S213). In Figures 7 and 10, foreign matter is indicated by an "x." For example, as shown in Figure 7, if the first block in the second row from the rear end in the main scanning direction and the second column from the leftmost column in the sub-scanning direction, the first block in the third row from the rear end in the main scanning direction and the fourth column from the leftmost column in the sub-scanning direction, the first block in the second row from the rear end in the main scanning direction and the fifth column from the leftmost column in the sub-scanning direction, and the first block in the fourth row from the rear end in the main scanning direction and the fifth column from the leftmost column in the sub-scanning direction are all blocks containing foreign matter, the second read range is set to include all of the first blocks in the second to fourth rows from the rear end in the main scanning direction and the second to fifth columns from the leftmost column in the sub-scanning direction. In Figure 10, the set second reading range is shown by a two-dot chain line.

Thereafter, the CPU 32 sets a size X2×Y2, which is determined by the length X2 in the main scanning direction and the length Y2 in the sub-scanning direction of each second block, so that the image read in the second reading process (described later) is divided into a plurality of second blocks based on the right rear edge of the read image (S214). The size X2×Y2 may be set by reducing the size X1×Y1 of the first block in accordance with the reduction ratio of the second reading range relative to the first reading range, or may be set to a fixed value that satisfies the relationships X2<X1 and Y2<Y1.
The CPU 32 controls the operation of the reading device 18 and the moving mechanism 19 to start a second reading process for reading the second reading range (S215). In the second reading process, the reading device 18 moves (returns) at a constant speed to the left in the sub-scanning direction from the position at the end of one reading process, while repeatedly reading one line in the main scanning direction by the reading device 18, until the entire second reading range is read. When reading of the entire second reading range is completed, the CPU 32 ends the second reading process.

After the second reading process begins, the CPU 32 designates a target block from among the multiple second blocks to be subjected to attribute determination as to whether it is a block with foreign matter or a block without foreign matter (S204). The first target block is designated as the second block located at the rear right edge of the read image in the second reading range.

Then, as in the case of determining the attributes of the first block, the CPU 32 obtains a histogram of the brightness values of all pixels in the target block (S205), and calculates the sum A of the frequencies of brightness values equal to or greater than a predetermined brightness threshold THL based on that histogram (S206). If the sum A is greater than the frequency threshold THF (S207: YES), the CPU 32 determines that the target block is a block without foreign matter (S208). If the sum A is equal to or less than the frequency threshold THF (S207: NO), the CPU 32 determines that the target block is a block with foreign matter (S209).

The CPU 32 then determines whether attribute determination has been performed for all second blocks (S210).

If there are remaining second blocks for which attribute determination has not been performed and the CPU 32 determines that attribute determination has not been performed for all second blocks (S201: NO), it updates the target block to another second block (S204). If there is a second block adjacent to the previous target block for attribute determination on the front side, that second block is designated as the target block, and the target block is updated. If there is no second block adjacent to the previous target block for attribute determination on the front side, the rearmost second block of the second blocks adjacent to the previous target block for attribute determination on the left side and forming a row in the main scanning direction is designated as the target block, and the target block is updated.

Then, as with the attribute determination for the first block, steps S204 to S210 are repeated until attribute determination for all second blocks is completed. When attribute determination for all second blocks is completed, the CPU 32 determines that attribute determination for all second blocks has been completed (S210: YES). The CPU 32 then determines whether the completed attribute determination was the attribute determination for the first week, that is, whether it was the attribute determination for the first block (S211).

If the CPU 32 determines that the completed attribute determination is not the first-week attribute determination (S211: NO), it confirms the result of the attribute determination for the second block as the result of the foreign object detection process (S216) and ends the foreign object detection process. In this case, the CPU 32 detects the position and size X2 x Y2 of the second block that has been confirmed to be a block containing a foreign object as the position and size of a foreign object attached to the transparent plate 14 or background member 17, respectively.

Furthermore, if the CPU 32 determines that the number of first blocks determined to be foreign object blocks in the first week's attribute determination (number of foreign object blocks) is not 1 or greater, i.e., is 0 (S211: NO), it confirms the result of the attribute determination of the first blocks as the result of the foreign object detection process (S216) and terminates the foreign object detection process. In this case, the CPU 32 detects that no foreign object is attached to the transparent plate 14 or background member 17.

<Action and effect>
As described above, in the foreign object detection process, the first read range is read. Then, the read image of the first read range is divided into a plurality of first blocks, and a brightness histogram is created for each first block. Based on the histogram, it is determined whether each first block is a foreign object block containing a read image of a foreign object other than the read object OB.

Then, a second reading range is set and the second reading range is read. The read image of the second reading range is then divided into multiple second blocks, and a histogram of brightness values is created for each second block. Based on this histogram, it is determined whether each second block contains a foreign object.

To read the first reading range, the reading device 18 is moved to one side in the sub-scanning direction, i.e., to the right. After reading the first reading range, the reading device 18 must be returned to its home position, and this movement of the reading device 18 is used to read the second reading range. This makes it possible to read both the first reading range and the second reading range while the reading device 18 is reciprocated in the sub-scanning direction.

The second read range is a range that includes the first block determined to be a foreign substance block, and is set to be narrower than the first read range. The size of the second block is also set to be smaller than the first block. This allows the position and size of the foreign substance to be detected in more detail (detected with greater accuracy) based on the determination result of whether the second block is a foreign substance block. Even if the size of the second block is set smaller than the size of the first block, by making the second read range narrower than the first read range, an increase in the number of second blocks can be suppressed, and an increase in the time required to determine whether each second block is a foreign substance block can be suppressed.

This makes it possible to improve the accuracy of detecting the position and size of a foreign object while minimizing the increase in the time required to detect the position and size of the foreign object.

Furthermore, if the number of first blocks determined to be foreign object blocks in the first week's attribute determination is zero, the result of the attribute determination for the first blocks is determined as the result of the foreign object detection process, and attribute determination for the second blocks is not performed. This reduces the time required for the foreign object determination process.

<Another Example of Processing for Determining Timing for Executing Foreign Object Detection Processing>
Instead of the process shown in FIG. 5, the process shown in FIG. 11 may be executed.

In the process shown in FIG. 11, the CPU 32 determines whether or not a read object OB is present between the transparent plate 14 and the background member 17 (S1'). The CPU 32 controls the operation of the reading device 18 and the movement mechanism 19, for example, by moving the reading device 18 a fixed distance to the right in the sub-scanning direction from the reading start position while the reading device 18 performs a reading. If the edge of the read object OB is detected by analyzing the read image, it is determined that the read object OB is present between the transparent plate 14 and the background member 17. If the edge of the read object OB is not detected, it is determined that the read object OB is not present between the transparent plate 14 and the background member 17. Techniques for detecting the edge of the read object OB are well known, so their description will be omitted.

In a configuration in which the foreign object detection mode is set in the reading device 1 by operating an external terminal communicatively connected to the reading device 1 or an operation key provided on the reading device 1, a query such as "Has the object to be read been removed from the transparent plate?" may be displayed on the display of the external terminal or on an indicator provided on the reading device 1 in response to the setting of the foreign object detection mode. If the user selects "YES" in response to the query, the CPU 32 may determine that there is no object to be read OB between the transparent plate 14 and the background member 17, and if the user selects "NO", the CPU 32 may determine that there is no object to be read OB between the transparent plate 14 and the background member 17.

If the CPU 32 determines that there is no object to be read OB between the transparent plate 14 and the background member 17 (S1': YES), it executes a foreign object detection process (S2). On the other hand, if the CPU 32 determines that there is an object to be read OB between the transparent plate 14 and the background member 17 (S1': NO), it does not execute a foreign object detection process, and after completing the reading process to read the object to be read OB, it again determines whether there is an object to be read OB between the transparent plate 14 and the background member 17 (S1').

Furthermore, as shown by the two-dot chain line in Figure 4, for example, if the light-emitting unit and light-receiving unit of the document sensor 41, which is a transmission sensor, are positioned opposite the left rear end of the transparent plate 14 within the opening 13, with the transparent plate 14 sandwiched between them, and if the document sensor 41 detects the object to be read OB, the CPU 32 may determine that the object to be read OB is between the transparent plate 14 and the background member 17, and if the document sensor 41 does not detect the object to be read OB, it may determine that the object to be read OB is not between the transparent plate 14 and the background member 17.

By performing the process shown in Figure 11, the foreign object detection process can be performed while ensuring that the object to be read OB is not present between the transparent plate 14 and the background member 17.

<Another Example of Foreign Object Detection Processing>
Instead of the process shown in Fig. 6B, the process shown in Fig. 12 may be executed. The process shown in Fig. 12 will be described by focusing on the differences from the process shown in Fig. 6B.

In the process shown in FIG. 6B, if the number of first blocks determined to be foreign substance blocks in the attribute determination in the first week is one or more (S212: YES), a second read range is set that includes the foreign substance blocks (S212). In contrast, in the process shown in FIG. 12, if the number of first blocks determined to be foreign substance blocks in the attribute determination in the first week is one or more (S212: YES), the CPU 32 does not set a second read range, and maintains the read range for the second read process as the first read range for the first read process.

The CPU 32 then sets a size X2 x Y2, determined by the length X2 in the main scanning direction and the length Y2 in the sub-scanning direction of the second block, so that the image read in the second reading process is divided into multiple second blocks (S214). The size X2 x Y2 may be set to a fixed value that satisfies the relationships X2 < X1 and Y2 < Y1, or may be set to a value that satisfies X2 = X1 and Y2 = Y1. In the latter case, however, the basis for dividing the second blocks is set so that the first and second blocks are shifted in at least one of the main scanning direction and the sub-scanning direction. For example, as shown in FIG. 13, the positions of the second blocks are set so that the image read in the second reading process is divided into multiple second blocks based on the right rear edge of the image.

Furthermore, in the process shown in FIG. 6B, if the number of first blocks determined to be foreign substance blocks in the attribute determination in the first week (number of blocks with foreign substance) is 0 (S212: NO), attribute determination of the second blocks is not performed. In contrast, in the process shown in FIG. 12, if the CPU 32 determines that the number of first blocks determined to be foreign substance blocks in the attribute determination in the first week is not 1 or more (S212: NO), the reading resolution is increased from that of the first reading process (S217) and the second reading process is performed. For example, the reading resolution in the first reading process is set to 300 dpi x 300 dpi, while the reading resolution in the second reading process is set to 600 dpi x 600 dpi.

If the CPU 32 determines that the completed attribute determination is not the first week's attribute determination (S211: NO), it confirms the result of the attribute determination for the first block and the result of the attribute determination for the second block as the result of the foreign object detection process (S216), and ends the foreign object detection process. In this case, if a portion of the first block determined to be a foreign object block overlaps with a portion of the second block determined to be a foreign object block, the CPU 32 detects the position and size of the overlapping portion as the position and size of the foreign object.

By executing the process shown in FIG. 12, similar to when the process shown in FIG. 6B is executed, after the first reading range is read by the first reading process, the movement of the reading device 18 to return the reading device 18 to its home position is utilized to read the first reading range again by the second reading process, so that the first reading range can be read twice while the reading device 18 is moved back and forth in the sub-scanning direction.

Furthermore, if a portion of a first block determined to be a foreign object block overlaps with a portion of a second block determined to be a foreign object block, the position and size of the overlapping portion are detected as the position and size of the foreign object.

This makes it possible to improve the accuracy of detecting the position and size of a foreign object while minimizing the increase in the time required to detect the position and size of the foreign object.

<Modification>
Although the embodiment of the present invention has been described above, the present invention can be embodied in other forms.

For example, in the process shown in FIG. 6B, if the CPU 32 determines that the completed attribute determination is not the first week's attribute determination (S211: NO), it may confirm the result of the attribute determination for the first block and the result of the attribute determination for the second block as the result of the foreign object detection process (S216), and terminate the foreign object detection process. In this case, if a portion of the first block determined to be a foreign object block overlaps with a portion of the second block determined to be a foreign object block, the CPU 32 preferably detects the position and size of the overlapping portion as the position and size of the foreign object. This can further improve the accuracy of detecting the position and size of the foreign object.

In the above-described embodiment, for example, a histogram of brightness values quantized to 256 levels (8 bits) is created, but a histogram of brightness values quantized to 64 levels (4 bits) may also be created.

In the process shown in FIG. 6A, the sum A of the frequency of brightness values equal to or greater than the brightness threshold THL is calculated based on a histogram of the brightness values of all pixels in the target block (S206). If the sum A is greater than the frequency threshold THF (S207: YES), the target block is determined to be a block without a foreign object (S208). Alternatively, the sum of the frequency of brightness values less than a predetermined brightness threshold THL' is calculated based on a histogram of the brightness values of all pixels in the target block. If this sum is less than the frequency threshold THF', the target block is determined to be a block without a foreign object, and if this sum is greater than or equal to the frequency threshold THF', the target block is determined to be a block with a foreign object.

Note that brightness values corresponding to objects other than the background member 17 (brightness values corresponding to the voltage output from the light-receiving element that receives light reflected from an object other than the background member 17) tend to be lower than the brightness values corresponding to the background member 17, and the brightness threshold THL' is defined as the upper limit of brightness values corresponding to objects other than the background member 17.

In the above embodiment, the CPU 32 executes each process, but the reading device 1 may be provided with multiple CPUs, and the multiple CPUs may cooperate to execute each process.

The reading device 1 may be used alone, or together with a printing device (not shown) that prints an image based on image data on paper, it may also be used in a multi-function peripheral (MFP) that has multiple functions, such as reading and printing.

In addition, various design modifications may be made to the above-described configuration within the scope of the claims.

1: Reading device 14: Transparent plate 17: Background member 18: Reading device 19: Moving mechanism 32: CPU
OB: Object to be read

Claims (8)

A transparent plate and
a reading device provided on one side of the transparent plate, the reading device having a light source that emits light toward the transparent plate and a plurality of light receiving elements arranged in a main scanning direction;
a moving mechanism that moves the reading device in a sub-scanning direction that intersects with the main scanning direction and that is along the transparent plate;
a white background member provided on the other side of the transparent plate and arranged opposite the transparent plate;
a control unit,
The control unit
a first reading process in which the reading device is moved in one direction of the sub-scanning direction, the light source of the reading device is caused to emit light, and an electrical signal output from the light receiving element is converted into a luminance value, thereby reading a first reading range;
a first determination process for determining whether each of the first blocks is a foreign substance block including a read image different from the read image of the background member, based on the histogram of the luminance values created for each of a plurality of first blocks obtained by dividing the read image of the first read range;
a setting process for setting a second read range that is narrower than the first read range and includes the first block determined to be the foreign substance block based on the determination result of the first determination process;
a second reading process in which the reading device is moved in the other direction in the sub-scanning direction, the light source of the reading device is caused to emit light, and the electrical signal output from the light receiving element is converted into a luminance value, thereby reading the second reading range;
and a second determination process for determining whether each of the second blocks is a foreign matter block based on a histogram of the brightness values created for each of a plurality of second blocks obtained by dividing the read image of the second reading range. 2. The reading device according to claim 1,
The control unit sets the size of the second block to be smaller than the size of the first block. 3. The reading device according to claim 2,
The control unit sets the size of the first block and the size of the second block to fixed values. 3. The reading device according to claim 2,
The control unit sets a size of the second block reduced relative to a size of the first block in accordance with a reduction ratio of the second read range to the first read range. A transparent plate and
a reading device provided on one side of the transparent plate, the reading device having a light source that emits light toward the transparent plate and a plurality of light receiving elements arranged in a main scanning direction;
a moving mechanism that moves the reading device in a sub-scanning direction that intersects with the main scanning direction and that is along the transparent plate;
a white background member provided on the other side of the transparent plate and arranged opposite the transparent plate;
a control unit,
The control unit
a first reading process in which the reading device is moved in one direction of the sub-scanning direction, the light source of the reading device is caused to emit light, and an electrical signal output from the light receiving element is converted into a luminance value, thereby reading a first reading range;
a first determination process for determining whether each of the first blocks is a foreign substance block including a read image different from the read image of the background member, based on the histogram of the luminance values created for each of a plurality of first blocks obtained by dividing the read image of the first read range;
a second reading process in which the reading device is moved in the other direction in the sub-scanning direction, the light source of the reading device is caused to emit light, and the electrical signal output from the light receiving element is converted into a luminance value, thereby reading the first reading range;
a second determination process for determining whether each of the second blocks is a foreign substance-containing block based on the histogram of brightness values created for each of the second blocks obtained by dividing the read image of the first read range;
A reading device that sets the position of the first block and the position of the second block to be shifted from each other. The reading device according to any one of claims 1 to 5,
When the control unit determines in the first determination process that none of the first blocks are blocks containing foreign matter, the control unit omits execution of the second reading process and the second determination process. The reading device according to any one of claims 1 to 5,
A reading device in which, when the control unit determines in the first determination process that all of the first blocks are not foreign substance blocks, the control unit executes the second reading process at a reading resolution higher than the reading resolution in the first reading process. The reading device according to any one of claims 1 to 5,
a sensor that detects whether the object to be read is placed between the transparent plate and the background member,
The control unit executes the first reading process when the sensor detects that the object to be read is not placed.