JP3408480B2 - Image reading method and apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for reading an original image with a linear image sensor and converting it into digital data.

[0002]

2. Description of the Related Art In an image reading apparatus which is equipped with a linear image sensor as a photoelectric conversion element and uses it as a main scanning and combines it with a sub-scanning mechanism to capture a two-dimensional image, it is held on a stand, As an example of a stand-type image scanner in which a remote image reading means inputs a document, Japanese Patent Laid-Open No. 62-29125 is used.
9 is given. Generally, a stand-type image input device
This has the advantage that the user can digitize the image while checking the actual document. On the other hand, depending on the environment in which the apparatus is placed, ambient light with varying illuminance may be reflected on the document surface, which may affect the document reading characteristics. For example, when the light of the ceiling lamp illuminates the document surface, the reading signal is deteriorated because the normal ceiling lamp has a flicker phenomenon of brightness corresponding to the timing of the alternating current flowing through the power line. In particular, when the speed of capturing an image is high and the capturing time per line of the linear image sensor is shorter than the flicker cycle, even if an image having a uniform reflectance between capture lines is captured, The signal level of each signal varies depending on the flicker. This fluctuation is 2
When developed in a three-dimensional image, it appears as horizontal stripes and adversely affects the image. Therefore, as a technique disclosed as a method for solving this problem in a stand-type apparatus that uses a linear image sensor and that captures an image at high speed, flicker correction is performed by detecting light including flicker. In some cases, dedicated light without flicker is emitted more strongly than light including flicker.

As a conventional example of a method of detecting a pulsation contained in illumination light for performing flicker correction, a light guide path (prism) is provided on a part of a light receiving surface of a linear image sensor.
Is provided, and the light irradiated on the document surface is detected by a part of the light receiving pixels of the linear image sensor. Further, there is a method in which a marker portion (reference member) having a specific reflectance is provided on a part of the document surface, and this part is read by a part of pixels of the linear image sensor to detect the pulsation of the illumination light. An example of this is Japanese Patent Publication No. 1-19311. Further, in the conventional example of Japanese Patent Laid-Open No. 10-336404, in order to detect flicker, a marker area (reference area) is provided along the sub-scanning direction at the edge of the document surface, and a part of the image sensor on the image forming surface is provided. Is used as a dedicated sensor area to read the above marker area. Alternatively, instead of using some pixels of the linear image sensor as a sensor, a method of detecting the pulsation of light from the document surface using another optical sensor is also mentioned as a known example in the above patent example. The flicker correction method reduces the flicker component included in the image signal by analog signal processing, in which the detected flicker light is used as a divisor and the original image signal from the linear image sensor is divided as the dividend.

As a conventional example of a stand-type image reading device which irradiates a dedicated light without flicker, Japanese Patent Laid-Open No. 9-1
There is 53988. In this conventional example, a high-frequency lighting fluorescent lamp illumination with few flicker components is used as a dedicated light source. When the dedicated illumination is stronger than the ambient light having the flicker component in the surroundings, it is not necessary to perform the correction for reducing the flicker component from the image signal.

[0005]

Among the conventional methods for reducing flicker in an image reading apparatus, an environment including a flicker including a dedicated light guide path in a stand-type image reading apparatus that does not include a dedicated light source. In the method of capturing flicker by capturing light, the amount of flicker components and the shape of the flicker waveform (change in brightness change) that appears in the cycle are captured between the direction or region in which ambient light is captured and the region in which the image is captured. If there is a difference, there is a problem that flicker is not removed. Further, when the light source of the ambient light is directly above the image reading means and the influence thereof is strong, a shadow of the image reading means is generated in the document image area, and therefore, the ambient light and the reflected light from the image area. There is a difference between and, which causes a phenomenon that flicker correction is not performed correctly.

Further, even in a stand-type image reading apparatus equipped with a dedicated light source, if ambient light having a flicker component stronger than the light amount of the dedicated light source is present, the captured original image is adversely affected by flicker. Will occur. Further, when the irradiation ratio of the dedicated light source is not uniform on the original image surface, the mixing amount of the flicker component is not evenly distributed on the original image surface but is two-dimensionally distributed, and correction is performed for each line of the linear image sensor. In the method, the effect of reducing the flicker cannot be removed because the flicker cannot be completely removed, and the image quality of the read original image deteriorates.

[0007]

According to a first aspect of the present invention, there is provided an image reading method in which a read original document under illumination light including flicker is spread on a linear image sensor in a sub-scanning direction of the read original document. Image reading for forming an image data of the entire surface of the original by imaging and scanning a narrow partial image of the original and reading by a stand-type image scanner in which the original surface and the linear image sensor have a fixed fixed distance. And a two-dimensional image correction data obtained in advance by scanning a plain image original in synchronization with the flicker phase. , The flicker of the illumination light included in the image data of the read document is calculated by synchronizing with the phase of the flicker. Characterized by reducing the image noise due. Further, the image reading method of the invention according to claim 2 of the present invention is characterized in that the calculation according to claim 1 is division of the image data of the read document by the two-dimensional image correction data. The image reading device of the invention according to claim 3 of the present invention is an image reading device for reading an original document under illumination light including flicker, and a phase detection means for detecting the phase of the flicker and a linear image sensor. A partial image of the read original having a narrow width in the sub-scanning direction is image-scanned to generate image data of the entire surface of the original in synchronization with the output signal of the phase detecting means, and the original surface and the linear image are generated. An image reading means by a stand type image scanner having a fixed fixed distance from a sensor, and a plain image original is read in advance by an image reading means by the stand type image scanner in synchronization with an output signal of the phase detecting means. 2D image correction data holding means for holding image data, and original document intended for reading When reading, the image data read by the image reading means of the stand type image scanner in synchronization with the phase detector output signal is output from the two-dimensional image correction data holding means in synchronization with the output signal of the phase detecting means. The image data due to the flicker of the illumination light included in the image data of the original document to be read for the purpose of reading is reduced. To do. Further, in the image reading device of the invention according to claim 4 of the present invention, the phase detecting means for detecting the phase of the flicker according to claim 3 detects the phase of alternating current supplied to the illumination. And According to a fifth aspect of the present invention, in the image reading apparatus, the phase detection means for detecting the phase of the flicker according to the third aspect includes an optical sensor for detecting the flicker of illumination light. It is characterized in that the phase of the output pulsating flow signal is detected. An image reading apparatus according to a sixth aspect of the present invention is the image reading apparatus according to the third aspect.
In addition to the configuration of the image reading apparatus described above, the image reading unit has a dedicated light source for irradiating at least a portion which is being sub-scanned. In addition, claim 7 of the present invention
The image reading apparatus of the invention according to claim 1 is the image reading apparatus according to any one of claims 3 to 6, wherein when the original document intended for reading is read, the computing means is one of the image reading means by the stand-type image scanner. It is characterized in that the correction data is taken out from the two-dimensional image correction data holding means at least twice or more during the sub-scanning, and is calculated and output in synchronization with the output signal from the phase detection means.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration of a first embodiment of an image reading apparatus of the present invention. A linear image sensor 1 in which elements for performing photoelectric conversion are arranged in one row or a plurality of rows, a lens 2 for forming an original image on the surface of the linear image sensor, and a partial image 5 of the original image 4 are converted into the lens 2 A stand-type image scanner 10 including a sub-scanning mechanism 3 for projecting onto The output image data of the image scanner 10 is digital, and an A / D converter for A / D converting the analog image signal of the linear image sensor is not shown. In addition to the stand-type image scanner 10, the configuration of this embodiment further includes a two-dimensional image correction table 11, a phase detector 12 for detecting the phase of the AC power line 101 synchronized with the flicker of the ceiling light 100, The image data obtained from the linear image sensor 1 and the correction data from the two-dimensional image correction table 11 are synchronized with the signal from the phase detector 12 and arithmetic processing is performed by the arithmetic unit 13.
It is characterized by reducing flicker. The image signal output from the linear image sensor 1 includes a flicker component that is an influence of a power line ceiling light, and is captured as the strength of the signal when capturing the image signal. The strength of the signal adversely affects the image quality as horizontal stripes in a two-dimensional image. The cycle of the horizontal stripes matches the cycle of the intensity of flicker output from the linear image sensor 1, and the cycle is generally constant depending on the power supply engine. As a feature of the present invention, the trigger function and the two-dimensional shading correction based on the desired phase angle of the flicker cycle are used by utilizing the characteristics of the flicker having the same cycle and the characteristics of the constant cycle of the flicker emitted from the ceiling light fed from the commercial power line. By combining with the function, the adverse effect of flicker is reduced.

Next, the operation of this embodiment will be described. First,
A case will be described in which correction document image data for creating the two-dimensional image correction table 11 is acquired. A correction original having a desired reflectance, for example, a plain white paper is placed on the original surface, and the image data of the correction original obtained from the linear image sensor 1 is read into the two-dimensional image correction table 11. As described above, the correction calculation is performed by the calculator 13 by synchronizing the image data obtained from the linear image sensor 1 and the correction data from the two-dimensional image correction table 11 with the phase signal from the phase detector 12. Therefore, the desired phase angle of the ceiling light flicker is set in advance, and the address counter of the two-dimensional image correction table 11 is operated by the synchronization signal output from the phase detector 12 in synchronization with this phase angle to perform correction. The correction original image data as data is input.

2 for reducing the above flicker
The three-dimensional image correction table data is generated before inputting a document image. The two-dimensional image correction table is generated when the device is installed for the first time, when the light environment for illuminating the document surface is changed by moving peripheral devices, etc.
Alternatively, it is preferable to implement it when the lighting environment or the like changes such that the lighting device or the like is changed and the degree of mixing of flicker changes.

Next, the case of acquiring a document image will be described. In FIG. 1, a document is placed on the document surface of a stand-type image scanner 10 supported by a stand 6, and the image data obtained from the linear image sensor 1 is converted into the desired phase from the phase detector 12, that is, a two-dimensional image. The correction data is fetched at the same timing as when it was acquired, and is output to the calculator 13. At this time, the calculator 13 simultaneously calculates from the two-dimensional image correction table 11
The previously acquired correction data is loaded. And these 2
The arithmetic processing is performed between the two data, and the image data is output as flicker-corrected image data. The calculation process reduces flicker by performing a process of dividing the image data by the correction data from the two-dimensional image correction table, for example.

FIG. 2 is a diagram showing the configuration of the second embodiment of the image reading apparatus of the present invention. Instead of the phase detector of the AC power line in the apparatus of the first embodiment shown in FIG. ,
An image sensor obtained by the linear image sensor 1 and a two-dimensional image correction table are provided with an optical sensor 14 for detecting a flicker of a ceiling light and a phase detector 12 for generating a synchronization signal from a pulsating current signal photoelectrically converted by the optical sensor. The correction data from 1) is synchronized with the signal from the phase detector 12 to perform arithmetic processing to reduce flicker. Generally, the pulsating flow of the electric power line and the flicker of the ceiling light are synchronized, and the cycle is stable, so the flicker can be reduced by using the phase detection result based on the optical sensor. it can.

Next, as a third embodiment of the image reading apparatus of the present invention, in addition to the configuration of the image reading apparatus described above, an example of reducing flicker when a dedicated light source is also used is shown in FIG. It demonstrates using. As the dedicated light source 20, a low ripple and high frequency lighting type light source that does not include a flicker component is used. Original surface 4 illuminated by a dedicated light source
In the case of both the linear light source 20 of FIG. 3A and the total illumination 30 of FIG. 3B, the captured image data may be an image in which the brightness of the illumination is relatively bright in the center. Many. In this case, the peripheral portion is more likely to be affected by the environmental light, and the flicker component increases. Note that the center does not always become bright depending on the configuration of the dedicated light source, but in any case, it generally has a two-dimensional brightness distribution. When the dedicated light source is used, the image data is a mixture of the illumination of the dedicated light source and the illumination in which the flicker of ambient light is relatively large. To reduce the flicker from the image data of this flicker mixture Needs to be corrected by removing the two-dimensionally distributed flicker component 40.

In order to create the two-dimensional correction data in this embodiment, an original having a uniform reflectance (for example, a general blank sheet) is placed on the correction table provided in the stand-type image input device having a dedicated light source. Placed on the original surface, the image data is synchronized with the pulsating cycle of the power line or the cycle from the optical sensor that detects the flicker of the ceiling light at the desired phase, and is read into the correction table to distribute the flicker distribution state. Is input as two-dimensional correction data. After that, when the original image is input, the original image correction data is synchronized with the same phase as the correction data is input in the same manner as in the above-described embodiment, and the image is taken in. The flicker component is reduced by performing a process (for example, division) using data and as input. When the linear light source 20 is used, since the position of the linear light source 20 for illuminating the original document and the sub-scanning position of the original document projected by the sub-scanning mechanism 3 on the linear image sensor 1 coincide with each other, both rotation operations are performed. Needless to say, must be synchronized.

Next, a fourth embodiment for reducing the data storage capacity of the two-dimensional image correction table, which can be applied to the image reading apparatus of any of the embodiments of the present invention, will be described with reference to FIG. In FIG. 4, when reading an original image, correction data is repeatedly extracted from the above-mentioned two-dimensional image correction table two times or more (three times in the figure) during one sub-scan, and is synchronized with the signal from the phase detector. By using the image reading apparatus for reducing the flicker, the memory for storing the correction table data can be reduced. This is possible because the flicker has a characteristic that it periodically changes in response to the pulsating current of the power line in the determined light environment. In FIG. 4, A0 is a document image 50 to be read, B0 is a correction document 60 for creating a two-dimensional image correction table, and C is image data 70 after correction. A0 is read by a stand-type image scanner and becomes original image data 51 before correction shown in A1. In the data before correction, horizontal stripes are mixed due to the adverse effect of flicker. On the other hand, the correction document image 60 indicated by B0 is read when the two-dimensional correction data is acquired, and becomes the correction data 61 indicated by B1. B1
Indicates that the data capacity is smaller than the data capacity for one sub-scanning for one-side scanning of the original document, which is a feature of this embodiment.

As shown in FIG. 5, when the original image data is acquired from the linear image sensor in response to the synchronization signal from the phase detector 12 which detects the pulsating current phase of the power line, it is held in the two-dimensional image correction table 11. The B1 data being read is repeatedly read by the repetitive signal 80 and output to the arithmetic unit 13 to form two-dimensional image correction data for one sub-scan in a pseudo manner as shown by Bn in FIG. A
The image data from 1 and the correction data B1 that is repeatedly input are input to the arithmetic unit, and the division is executed. As a result, the division is performed between the image data of A1 and the two-dimensional image correction data Bn for all sub-scans, and as a result, as shown in FIG.
As indicated by C, the corrected original image data 70 with reduced flicker is obtained. In particular, this method in which the correction data is repeatedly used has a great effect of reducing the adverse effect of the flicker of the read original image when the influence of illumination including flicker in the sub-scanning direction on the original surface is small. Further, when a dedicated light source and a light source from the environment are combined and the influence of flicker increases or decreases in a direction perpendicular to the linear image sensor and parallel to the sub-scanning direction, this embodiment is relatively effective. is there.

Regarding the storage capacity of the two-dimensional image correction table 11, the two-dimensional image correction data repeatedly used for one sub-scanning stores the image data for at least one cycle of flicker. It must have the capacity to do it. One line of sub-scan is now 266
With 0 pixels, the flicker cycle is 100 Hz, and it takes 540 microseconds per main scanning line,
The correction table requires a memory capacity capable of accumulating data of 19 lines or more and 50540 pixels or more. The number of times the correction table is repeatedly read is a value obtained by dividing the number of sub-scanning lines by the number of lines that can be read by the correction table. If one sub-scan is 3000 lines, and if the correction table for 19 lines is used, 15
It is necessary to read 8 times.

[0018]

According to the image reading apparatus of the present invention, in the stand-type image scanner, in order to eliminate the adverse effect of flicker on the light irradiated on the original image, a two-dimensional correction table is used to determine the phase of the flicker cycle. By performing the correction in synchronism, it is possible to accurately remove the adverse effect of flicker even when there are variations in the flicker component on the document surface, and there is an effect of improving image quality. Also, by providing a function to create a correction table, it is possible to set the correction table according to the installation location and time even for adverse changes in flicker due to changes in the installation location and time of the device and changes in the brightness environment. This has the effect of expanding the range of adaptation to environmental changes. In addition, by detecting the phase of the flicker cycle with an optical sensor, flicker removal can be performed even when the ambient light is supplied by a power source different from the power line and the pulsating flow phase between the power line and the ambient light is not synchronized. Can be performed, and there is an effect of improving image quality. Further, by repeatedly using the two-dimensional correction table, the storage capacity of the correction table can be reduced,
There is an effect on the cost and space of the device.

[Brief description of drawings]

FIG. 1 is a perspective view including a block diagram showing a first embodiment of an image reading apparatus of the present invention.

FIG. 2 is a perspective view of an image reading apparatus according to a second embodiment of the present invention when the optical sensor is used.

FIG. 3 is a perspective view of an image scanner using a dedicated light source of a third embodiment of the image reading apparatus of the present invention.

FIG. 4 is a diagram showing an embodiment using a repetitive two-dimensional image correction table according to the present invention.

FIG. 5 is an explanatory diagram showing a state of creating a two-dimensional image correction table and a flow of data for reading a document image according to the embodiment of the present invention.

[Explanation of symbols]

1 Linear image sensor 2 lens 3 Sub-scanning mechanism 4 Original image 5 partial images 10 Stand type image scanner 11 Two-dimensional image correction table 12 Phase detector 13 arithmetic unit 14 Optical sensor 20 linear light source 30 overall lighting 40 Flicker component 50 original image 51 Original image data before correction 60 Correction original 61 Correction data 70 Corrected original image data 80 repeated signals 100 ceiling lights 101 AC power line

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Segawa 1-1-1, Shinurashima-cho, Kanagawa-ku, Yokohama-shi, Kanagawa Electric Robot Engineering Co., Ltd. (72) Inventor Takayuki Nishida 5-chome, Shiba 5-chome, Minato-ku, Tokyo No. 7 No. 1 within NEC Corporation (56) Reference JP-A-10-224636 (JP, A) JP-A-10-294891 (JP, A) JP-A-11-41424 (JP, A) 62-85063 (JP, U) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04N 1/19 G06T 1/00 H04N 1/409

Claims (7)

(57) [Claims] 1. A read original document under illumination light including flicker is image-scanned on a linear image sensor with a partial image having a narrow width in the sub-scanning direction of the read original document to generate image data of the entire surface of the original document. A method for reading an image by a stand-type image scanner having a fixed fixed distance between the document surface and the linear image sensor, wherein the read document obtained in synchronization with the flicker phase An image of the read original is obtained by calculating image data and two-dimensional image correction data obtained by scanning the plain image original in synchronization with the phase of the flicker in synchronization with the phase of the flicker. An image reading method comprising reducing image noise caused by flicker of the illumination light included in data. 2. The image reading method according to claim 1, wherein the calculation is division of image data of the read document by the two-dimensional image correction data. 3. An image reading device for reading an original document under illumination light including flicker, wherein phase detection means for detecting a phase of the flicker and a width of the read original document in a sub-scanning direction are provided on a linear image sensor. A narrow partial image is image-scanned to generate image data of the entire surface of the original document in synchronization with an output signal of the phase detecting means, and the original surface and the linear image sensor have a fixed fixed distance. Image reading means by a stand-type image scanner and two-dimensional image correction in which image data read by the image reading means by the stand-type image scanner is held in advance in synchronization with an output signal of the phase detecting means for a plain image original. Synchronize with the phase detector output signal when reading the original document for data holding means and reading Then, the image data read by the image reading means by the stand-type image scanner is divided by the correction data output from the two-dimensional image correction data holding means in synchronization with the output signal of the phase detection means, and the corrected image data is obtained. An image reading apparatus, comprising: an arithmetic unit for outputting the image data as an object to reduce the image noise due to the flicker of the illumination light included in the image data of the original document to be read. 4. The image reading apparatus according to claim 3, wherein the phase detection means for detecting the phase of the flicker detects the phase of an alternating current supplied to the illumination. 5. The phase detecting means for detecting the phase of the flicker includes an optical sensor for detecting the flicker of illumination light, and detects the phase of a pulsating flow signal output from the optical sensor. Item 3. The image reading device according to item 3. 6. The image reading apparatus according to any one of claims 3 to 5, further comprising a dedicated light source for illuminating at least a sub-scanning portion of the image reading unit. 7. The image reading apparatus according to claim 3, wherein when the original document intended to be read is read, the calculation means performs one sub-scan of the image reading means by the stand-type image scanner. Between the above 2
An image reading apparatus characterized in that the correction data is repeatedly taken out at least twice or more from the three-dimensional image correction data holding means, and is calculated and output in synchronization with the output signal from the phase detection means.