JPH10173920A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To read an original accurately even on the occurrence of a dirty original or a defective CCD sensor. SOLUTION: This image reader is provided with a CCD sensor that reads an original image optically and that binarizes dot image data obtained by reading the image with the CCD sensor based on a prescribed threshold level. The reader is provided with a memory device storing tentatively the dot image data obtained by reading the image with the CCD sensor, the dot image data from the memory device are binarized by setting at first the threshold level to be an initial value, a maximum number of consecutive same kinds of dots in the binarized data is detected and when the maximum number reaches a prescribed value or over, the threshold level is changed and the dot image data are again binarized based on the threshold level after the revision.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus for reading images such as handwritten characters and printed characters drawn on a document.

[0002]

2. Description of the Related Art An image reading apparatus of this type irradiates light while moving along a document set on a reading glass, and captures reflected light of the light by a CCD (Charge Coupled Device) sensor line by line. The image data composed of the dot data is converted into electronic image information (for example, halftone data in which the image density is represented by 256 bytes) by a CCD control circuit and stored in a memory device. Then, the image data is taken out from the memory device and is set to 2 by a predetermined threshold value.
The binarized data is transferred to the host computer.

However, the threshold for binarization is
The optimum value differs depending on the CCD sensor, the light emitting element which is a light source, the background color of the original, the type of pen for writing handwritten characters on the original, and the like. For this reason, conventionally, the maximum value of the read density has been detected for each line of image data from the memory device, and a half of the maximum value has been set as a threshold, and binarized using the threshold. .

The image reading control performed by an MPU (microprocessor unit) constituting the control section main body of such an image reading apparatus will be specifically described with reference to FIG. The MPU first controls the CCD sensor in ST (step) 1 to capture image data for one page of the document.
Then, the image data is successively converted into halftone data by the CCD control circuit and stored in the memory device.

Next, in ST2, one line of image data (halftone data that has already been converted) is extracted from the memory device, and in ST3, the maximum value of the read density is detected for the one line of image data. . Subsequently, in ST4, the image data is binarized using 1/2 of the maximum value of the read density as a threshold, and in ST5, the binarized data is transferred to the host computer. Then, in ST6, it is determined whether or not the binary data has been transferred for one page. At this time, if it is determined that one page has not been transferred yet, the process returns to ST2, and if it is determined that one page has been transferred, the image reading control ends.

[0006]

However, in such an image reading apparatus, a threshold value for detecting the maximum value of the read density of the image data for each line and binarizing it based on the maximum value is set. However, since the threshold value is always set to の of the maximum value, the background state of the character drawn on the document image (the background color difference of the document as shown in FIG. 7 or FIG. In some cases, the reading may be defective due to the contamination of the original as shown in FIG.

That is, as shown in FIG. 7, when there is no dirt on the original, the reading density of the line portion constituting the character is higher than its surroundings, so that the maximum reading density When the binarization is performed using 1/2 of the threshold value as a threshold value, only the line portion of the character becomes a black dot and a good image can be read. However, when the original is stained as shown in FIG. Since the reading density of the line portion constituting the reading density is not much different from the surrounding area, even if binarization is performed using 1/2 of the maximum value of the reading density as a threshold value, black dots are formed even in the stained portion, and the characters are not printed. Cannot be read well.

In other words, in the example shown in FIG. 8, the read density level between the characters "I" and "U" of the original image is higher than the threshold value, so that black dots continue. As a result, when such binary data is transferred to the host computer, the host computer cannot correctly recognize the character.

Accordingly, an object of the present invention is to provide an image reading apparatus capable of accurately reading a document image even if the document is stained or a CCD sensor is defective.

[0010]

According to a first aspect of the present invention, there is provided an optical reading means for optically reading an original image, and dot image data obtained by reading the original image is binarized by a predetermined threshold value. A dot image data storage unit for temporarily storing dot image data obtained by reading by an optical reading unit, and a dot image data from the dot image data storage unit.
Binarizing means for binarizing, continuous dot number detecting means for detecting the maximum number of continuous dots of the same kind in the binarized data obtained by the binarizing means; When the maximum number is equal to or greater than a predetermined value, a threshold value is changed, and binarization control means for binarizing the dot image data from the dot image data storage means by the binarization means with the changed threshold value is provided. It is a thing.

According to a second aspect of the present invention, the continuous dot number detecting means detects the maximum number of the same kind of dots continuous in the line direction read by the optical reading means among the binary data obtained by the binarizing means. The image reading device according to claim 1.

According to a third aspect of the present invention, in the continuous dot number detecting means, the maximum of the same kind of dots continuous in the direction perpendicular to the line direction read by the optical reading means is selected from the binarized data obtained by the binarizing means. 2. The image reading device according to claim 1, wherein the number is detected.

According to a fourth aspect of the present invention, the continuous dot number detecting means includes, in the binarized data obtained by the binarizing means, the maximum number in the line direction of the same kind of continuous dots in the line direction read by the optical reading means; Detecting the maximum number of the same kind of dots continuous in the direction perpendicular to the line direction in the perpendicular direction, and the binarization control means when the maximum number in the line direction detected by the continuous dot detection means is equal to or more than a predetermined value in the line direction, or 2. The method according to claim 1, wherein when the maximum number in the right-angle direction is equal to or more than a predetermined value in the right-angle direction, the threshold value is changed, and the binarized means binarizes the dot image data from the dot image data storage means with the changed threshold value. Image reading device.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a configuration of an image reading apparatus according to the present embodiment. Reference numeral 1 denotes an MPU (microprocessor unit) constituting a control unit main body of the apparatus, and 2 denotes a program for the MPU to control each unit. ROM 3 stores electronic image information (for example, when image density is 256) by applying so-called white correction or black correction to image data obtained when the original image is read by the CCD sensor 4 for optically reading the original image. CCD control circuit for converting into halftone data expressed in bytes)
A memory device 6 for temporarily storing image data from the control circuit 3 is an interface for connecting a host computer 7 and the like via a communication line. The above MPU1,
The ROM 2, the CCD control circuit 3, the memory device 5, and the interface 6 are electrically connected by a bus line 8 such as a data bus, a control bus, and an address bus. Also, MPU
1 is provided with an internal memory (not shown) so that image data can be extracted from an external memory device 3 and data processing such as binarization can be performed.

The CCD sensor 4 includes a CC (not shown).
Mounted on D unit. This CCD unit has, for example, an L in which a plurality of LEDs (light emitting diodes) are arranged in a line.
The CCD sensor 4 includes an ED array, a condensing lens that receives reflected light from the document irradiated by the LED array, and the like, and the CCD sensor 4 receives the reflected light from the document via the condensing lens. When the CCD unit reads a document placed on a reading glass (not shown), the CCD unit moves the position facing the document along the document. Note that the manuscript must be ADF
When reading is performed by an (automatic paper feeder), the conveyance of the document may be controlled such that the document is fed to the opposite surface of the CCD unit while the CCD unit is stopped at a predetermined position.

The MPU 1 performs an image reading control as shown in FIG. 2 when a document is placed on a reading glass of an image reading device and a command to start reading the document is received from the host computer 7. ing. That is, M
First, at step ST11, the PU 1 controls the movement of the CCD unit so as to face the original, and the CCD sensor 4 converts the original image into one.
Read each line. Then, the image data from the CCD sensor 4 is subjected to processing such as white correction and black correction by the CCD control circuit 3 and is converted as halftone data expressing the read density in 256 bytes, for example, and is successively sent to the memory controller 5. Is recorded.

Subsequently, in ST12, a threshold value for binarization is initialized as a predetermined ratio in the maximum value of the read density. For example, when the halftone data is composed of 256 bytes, it is initialized to a relatively low level of about 3/16 of the maximum value of the read density in one line. In ST13, one line of image data is extracted from the memory device 5, and ST1 is read.
In step 4, the maximum value of the read density of the image data is detected, binarized by a threshold obtained based on the maximum value, and converted into binary data of black dots and white dots (binarization means). .

In step ST15, the maximum value n of the number of continuous dots in the line direction read by the CCD sensor 4 is detected from the binary data, and it is determined in step ST16 whether the maximum value n is equal to or larger than a predetermined value. (Consecutive dot number detecting means). This predetermined value should be set to an optimum value according to the nature of the original image to be read. For example, in the case of an original image in which handwritten characters are drawn with a pencil or a ballpoint pen, the line width is within a certain range (dot width). ), The range (dot width) may be set as a predetermined value. In particular,
At a resolution of 300 DPI, when a character or the like is drawn with a 0.8 mm ball-point pen, it may be set to about 9 dots.

If it is determined in ST16 that the maximum value n of the number of consecutive black dots is not greater than a predetermined value, the process proceeds to ST16.
At 17, the binary data is transferred to the host computer 7, and the process proceeds to ST18. That is, in ST18, 1
It is determined whether or not the page of binary data has been transferred to the host computer 7. At this time, if it is determined that the one-page binary data has been transferred to the host computer 7, the image reading control is terminated and the one-page binary data has been transferred to the host computer 7. If it is determined that there is not, the process returns to ST14.

On the other hand, if it is determined in ST16 that the maximum value n of the number of consecutive black dots is equal to or greater than a predetermined value, the threshold for binarization is changed by a predetermined amount in ST19. To return to the process of ST13 (binary control means). This predetermined amount may be a ratio to the maximum value of the reading density, and may be determined in relation to the processing speed, reading accuracy, and the like. For example, the initial value of the threshold value is 3/1 of the maximum value of the read density described above.
In the case of 6, 1/16 of the maximum value of the reading density is added as a predetermined amount, and this is binarized as a new threshold value.

In the embodiment of the present invention having such a configuration, when reading an original image, the original image is captured by the CCD sensor 4 and the image data is transferred to the CCD control circuit 3.
The data is converted into halftone data and recorded in the memory device 5 for one page.

Image data is taken out from the memory device 5 line by line and binarized. At this time, first, as shown in FIG. 3, binarization is performed with the initial value of the threshold, and when the maximum value of the number of continuous black dots in the binarized data of the line is equal to or more than a predetermined value, the threshold is set to a predetermined And then binarize again. Then, the processing of changing the threshold value and binarizing is repeated until the maximum value of the number of black dots does not exceed the predetermined value. Thus, the binarized data binarized with the optimum threshold is transferred to the host computer 7.

Accordingly, as shown in FIG. 4A, when a handwritten character is drawn on a document to be read and there is a wide dirt A there, the threshold value at the time of first binarization is set to the threshold value. If the read density of the line is 3/16 of the maximum value, then the binarized data obtained at the threshold value will have continuous black dots at the stain A portion of the document.

In such a case, since the number of consecutive black dots is equal to or more than a predetermined value, the threshold value is reduced to 1/16 to 3/16.
The binarization is performed as 4/16 of the maximum value of the reading density obtained by adding 6 to the value. Even so, if the number of consecutive black dots is equal to or more than a predetermined value, the threshold value is set to 5/16, 6/16,.
And the binarization is performed, and this is repeated until the number of continuous black dots finally becomes smaller than a predetermined value. Then, binarized data is obtained such that only data of a line having a predetermined width becomes a black dot.

As described above, in the present embodiment, there is dirt or CCD sensor failure wider than the characters in the document image in the width direction of the document (the reading line direction of the CCD sensor 4), or the background color of the document is Even when the density is close to the density, the image can be binarized with an appropriate threshold value, so that the original image can be read accurately. This improves the accuracy of the host computer 7 in character recognition of handwritten characters and the like.

Next, a second embodiment of the present invention will be described with reference to FIGS. Note that the configuration of the control unit according to the present embodiment is the same as that shown in FIG. 1, and a detailed description thereof will be omitted.

The MPU 1 performs image reading control as shown in FIG. 5, for example, when an original is placed on a reading glass of an image reading apparatus and a command to start reading the original is received from the host computer 7. I have. That is, MPU
First, in ST21, the movement of the CCD unit is controlled so as to face the original, and the original image is read line by line by the CCD sensor 4. Then, the image data from the CCD sensor 4 is subjected to processing such as white correction and black correction by the CCD control circuit 3 and is converted as halftone data expressing the read density in 256 bytes, for example, and is successively sent to the memory controller 5. Is recorded. Subsequently, in ST22, a threshold value for binarization is initialized as a predetermined ratio of the maximum value of the read density. For example, when the halftone data is composed of 256 bytes, it is initialized to a relatively low level of about 3/16 of the maximum value of the read density in one line. In ST23, the image data is taken out from the memory device 5, the maximum value of the read density of the image data is detected, and one page is binarized with a threshold obtained based on the maximum value to obtain black dots and white dots. The data is converted into dot binary data (binarization means).

In step ST24, the maximum value m of the number of lines in which the black dots continue in the vertical direction of the document (in the direction perpendicular to the read line of the CCD sensor 4) is detected from the binary data (detection of the number of continuous dots). Means), this maximum value m in ST25
Is determined to be greater than or equal to a predetermined value. This predetermined value should be set to an optimal value depending on the nature of the original image to be read, such as dirt, but, for example, an original obtained by a copying machine or a facsimile may have long and thin line-shaped dirt in the vertical direction. In order to read such a dirty original, a dot length of about の of the vertical size of the original may be set as the predetermined value.

If it is determined in step ST25 that the maximum value m of the number of continuous lines of black dots is not greater than a predetermined value, the process proceeds to step ST25.
At 26, the binary data is transferred to the host computer 7, and the process proceeds to ST27. That is, in ST27, 1
It is determined whether or not the page of binary data has been transferred to the host computer 7. At this time, if it is determined that one page of the binary data has been transferred to the host computer 7, the image reading control ends.

On the other hand, if it is determined in ST25 that the maximum value m of the number of continuous lines of black dots is equal to or greater than a predetermined value, the threshold for binarization is changed by a predetermined amount in ST28. To return to the processing of ST23 (binary control means). This predetermined amount may be a ratio to the maximum value of the reading density, and may be determined in relation to the processing speed, reading accuracy, and the like. For example, the initial value of the threshold value is 3/1 of the maximum value of the read density described above.
In the case of 6, 1/16 of the maximum value of the reading density is added as a predetermined amount, and this is binarized as a new threshold value.

In the embodiment of the present invention having such a configuration, when reading an original image, the original image is captured by the CCD sensor 4 and the image data is transferred to the CCD control circuit 3.
The data is converted into halftone data and recorded in the memory device 5 for one page.

Image data is fetched from the memory device 5 and one page is binarized. At this time, if the maximum value of the number of lines in which the black dot continues in the vertical direction of the document is equal to or larger than a predetermined value in the one-page binary data, the threshold is changed and binarization is performed again. Then, the processing of changing the threshold value and binarizing is repeated until the maximum value of the number of lines of continuous black dots does not exceed the predetermined value. The binary data thus obtained is transferred to the host computer 7.

Therefore, as shown in FIG. 4A, when a handwritten character is drawn on a document to be read and there is a dirt A or a line-shaped dirt B elongated in the vertical direction of the document.
Assuming that the threshold value at the time of the first binarization is 3/16 of the maximum value of the read density of the line, the binarized data obtained at the threshold value is a black dot at the stains A and B of the original. Will be continuous.

In such a case, the number of lines of the continuous black dots is equal to or more than a predetermined value.
Is added to 1/16 and binarized as 4/16 of the maximum value of the reading density. Even so, if the number of consecutive black dots is equal to or greater than a predetermined value, the threshold is set to 5/16, 6 /
The binarization is performed by increasing the number of dots, and this process is repeated until the number of continuous black dots finally becomes smaller than a predetermined value. Then, as shown in FIG. 4B, an image within a predetermined range in the vertical direction of the document, for example, binary data in which only handwritten characters and printed characters are black dots is obtained.

As described above, in this embodiment, even if the CCD sensor is defective or the original image has a background color, binarization can be performed with an appropriate threshold value. Can be. Original length (CCD
If there is dirt longer than the characters of the original image in the direction perpendicular to the reading line of the sensor 4), the dirt may be narrow within a predetermined value of the number of consecutive black dots in the first embodiment. For example, in the first embodiment, black dots are formed in the first embodiment. However, even if such dirt is long in the vertical direction of the document, the threshold value is changed and binarization is performed again in the present embodiment. Especially effective. This improves the accuracy of the host computer 7 in character recognition of handwritten characters and the like.

It is to be noted that the second embodiment may be combined with the first embodiment. For example, only when the number of continuous black dots in the vertical direction of the document is equal to or more than a predetermined number of lines and the number of continuous black dots in the width direction of the document is equal to or more than the predetermined number of black dots in ST25 of FIG. The process may proceed to ST26, and the other process may proceed to ST28. Thus, even if both the dirt A in the width direction of the original and the dirt B long in the vertical direction of the original shown in FIG. 4A can be binarized with an appropriate threshold value, 2) where only the handwritten characters shown in ()) are extracted
The original image can be converted to value data, and the original image can be read more accurately. This improves the accuracy of the host computer 7 in character recognition of handwritten characters and the like.

Further, in the embodiment of the present invention, a C element in which reading elements are arranged in a line in the main scanning direction of a document.
Although the reading of the original image line by line by the CD sensor 4 has been described, the present invention is not limited to this, and a CCD sensor having reading elements arranged in the sub-scanning direction of the original is mounted on the carrier. The present invention may be applied to an apparatus in which a plurality of lines of an original image are read while being moved in the main scanning direction. In this case, the main scanning direction, that is, the moving direction of the carrier corresponds to the line direction.

In the first and second embodiments, the threshold value for binarization is set as a ratio with respect to the maximum value of the read density. However, in the present invention, the threshold value is changed. Therefore, accurate reading can be performed without necessarily setting the threshold as a ratio to the maximum value of the reading density.
For example, if the image data read by the CCD sensor 4 is 256
When the data is converted to byte halftone data, 3/16 of the 256 bytes is used as the initial value of the threshold value, and 1 /
The binarization may be performed using a threshold value added for every / 16.

[0039]

As described above in detail, according to the present invention, it is possible to provide an image reading apparatus capable of accurately reading an original image even if the original is dirty or the CCD sensor is defective.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an image reading apparatus according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing image reading control performed by the MPU shown in FIG.

FIG. 3 shows the reading density of a document image and 2 in the present embodiment.
The figure which shows the relationship with the threshold value for converting into a value.

FIG. 4 shows solid stains A and B in the vertical and horizontal directions of a document.
The figure which shows an example in the case where there is.

FIG. 5 is a flowchart illustrating image reading control performed by an MPU according to a second embodiment of the present invention.

FIG. 6 is a flowchart showing image reading control in a conventional image reading apparatus.

FIG. 7 is a diagram illustrating a relationship between a reading density and a threshold for binarization when a conventional image reading apparatus reads a document image with a white background color.

FIG. 8 is a diagram illustrating a relationship between a read density and a threshold for binarization when a conventional image reading apparatus reads a document image having a background color darker than the document illustrated in FIG. 7;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... MPU 3 ... CCD control circuit 4 ... CCD sensor (optical reading means) 5 ... Memory device (dot image data storage means)

Claims (4)

[Claims] An image reading device for optically reading a document image, and binarizing dot image data obtained by reading the image with a predetermined threshold value; Dot image data storage means for temporarily storing dot image data obtained by reading, binarization means for binarizing dot image data from the dot image data storage means, and binarization means A continuous dot number detecting means for detecting the maximum number of consecutive dots of the same type in the binarized data obtained by
When the maximum number detected by the continuous dot detection means is equal to or more than a predetermined value, the threshold value is changed, and the binarization means converts the dot image data from the dot image data storage means into binary data with the changed threshold value. An image reading apparatus, comprising: a binarization control unit for converting the image into a binary image. 2. The method according to claim 1, wherein the continuous dot number detecting means detects a maximum number of dots of the same type continuous in a line direction read by the optical reading means in the binarized data obtained by the binarizing means. The image reading device according to claim 1, wherein: 3. The continuous dot number detecting means detects the maximum number of dots of the same kind which are continuous in the direction perpendicular to the line direction read by the optical reading means in the binarized data obtained by the binarizing means. The image reading device according to claim 1, wherein 4. The continuous dot number detecting means, wherein the maximum number and the line direction of the same type of continuous dots in the line direction read by the optical reading means are included in the binarized data obtained by the binarizing means. Detecting the maximum number of the same kind of dots continuous in the direction perpendicular to the right angle direction, the binarization control means, when the maximum number of line directions detected by the continuous dot detection means is equal to or more than a predetermined value in the line direction, Alternatively, when the maximum number in the right-angle direction is equal to or more than a predetermined value in the right-angle direction, a threshold value is changed, and the binarization means binarizes the dot image data from the dot image data storage means with the changed threshold value. Item 2. The image reading device according to Item 1.