JPS6361552A - Image reader - Google Patents

Abstract

PURPOSE:To prevent the generation of a pseudo signal in case of reading a dot original whose density approximates that of grating points, by providing a filter, which cuts the space frequency higher than the half of the space frequency of read grating points, and an adding means which adds and averages original information at four read points close to one another. CONSTITUTION:A Selfoc lens array (rod lens array) 11 has the internal refractive index changed in a radial direction and is constituted to have such modulation transfer function value (MTF)-spatial frequency characteristic that MTF is 0, that is, white and black cannot be distinguished for the spatial frequency higher than the half of the spatial frequency of a photodetector. Results from addition and averaging of image data of four grating points are successively outputted by adding average circuits 107 and 109. In such a constitution, components having the frequency lower than the half of the spatial frequency of read grating points are surely read by the theorem of sampling and are added and averaged and are corrected, and components having the frequency higher than the half are read as a uniform contrast, and an image sensor 12 does not generate the pseudo signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image reading device that is used in facsimiles, digital copying machines, etc. and is capable of reading image data of a document in multiple gradations.

Conventional technology A conventional image reading device will be described below.

FIG. 8 is a block diagram of a conventional image reading device.
is a document, 2 is a light source, 3 is a lens, 4 is a self-scanning image sensor, 5 is a light source 2, a lens 3, and an image sensor 4
This is a carriage that holds a 3D image and is movable in the sub-scanning direction shown by arrow A. FIG. 9 is a perspective view of main parts of a conventional image reading device, in which 6 is a heald that drives the carriage 5, 7 is a fixing member that fixes the belt 6 to the carriage 5, 8 is a driven roller, 9 is a driving roller, 10 is a motor that drives the drive roller 9 and drives the carriage 5 via the belt 6.

FIG. 10 is a circuit block diagram of a conventional image reading device, in which 101 is a driver that provides a scan start signal and a scan clock to the image sensor 4, 102 is an amplifier that amplifies the output of the image sensor 4 to an appropriate voltage, and 103 is a circuit block diagram of a conventional image reading device. This is an A/D converter that converts the output of an amplifier into a digital value.

Regarding the conventional image reading device configured as described above,
The operation will be explained below.

First, light is irradiated onto the original 1 from the light source 2, and the reflected light is collected by the lens 3 and guided to the light receiving section (not shown in the figure) of the image sensor 4. The driver 101 provides the image sensor 4 with a scan start signal and a scan clock signal. A row of light-receiving elements (not shown in the figure) are arranged in the light-receiving part of the image sensor 4 in the main scanning direction of the original, and each light-receiving element has a light-receiving element that is proportional to the black and white gradation at each position on the original. Output voltage.

A case will be described in which the document 1 shown in Figure 11 is read.

The document 1 has C1 to C8, b1 to b8, and C1 of each line in the main scanning direction (hereinafter abbreviated as main scanning line).
~C8, information on points d1 to d8 is read. First, the carriage 5 is moved by the motor 10 and points a1 to a
It is located in the position to read the information of 8. Here, as shown in FIG. 12, when the driver 101 outputs a scanning start signal to the image sensor 4, the image sensor 4 generates a voltage proportional to the brightness of each pixel at points a1 to a8 on the document in synchronization with the scanning clock. Output sequentially. Next, when the scanning of each pixel at points a1 to a8 is completed, the carriage 5 moves to the position to read the information at points b1 to b8 (.After that, the driver 101 outputs a scan start signal and a scan clock to the image sensor 4. , each pixel at points b1 to b8 on the document is scanned, and image data is sequentially output.

By repeating the above operations, the image data of the document is read. The voltage, which is image data, is amplified by an amplifier 102 and converted by an A/D converter 103 into a digital value proportional to the brightness level of each pixel. The operation described above reads the original in multiple gradations.

Problems to be Solved by the Invention However, in the above-mentioned conventional configuration, the image data of the document is read by an image sensor in which a finite number of light receiving elements are arranged in a row in the main scanning direction of the document, so the reading linear density is In the main scanning direction and in the sub-scanning direction perpendicular to the main scanning direction, the value is about 4 lines/fence, and when reading a document using halftone dot printing used for printing photographs of magazines etc. at this linear density, As shown in Fig. 13, there are halftone dots and
Since all of the reading lines of the image sensor 4 are discrete, there is a problem in that interference occurs and a false signal generally called a moiré phenomenon is generated, which significantly deteriorates the reading quality of halftone printed matter. was.

Conventionally, as a countermeasure to this problem, it has been considered to widen the aperture width, which is the effective reading width of the image sensor 4, with respect to the linear density in the main scanning direction and the sub-scanning direction.

As another countermeasure, it has been considered to set the reading linear density in the main scanning direction and the sub-scanning direction to a value sufficiently larger than the spatial frequency of the read and printed document.

However, in the former case, no matter how wide the aperture width is, if the reading line density is 4 lines/mm, the generation of false signals cannot be prevented if the spatial frequency of the input signal is greater than 2 lines/mm. In addition, in the latter method, if the density of halftone dots increases,
The required reading linear density increases proportionally, and the number of elements in a self-scanning image scanner increases accordingly.The amount of image data also increases, so the scanning clock speed increases and the processing system needs a high-speed one. This results in the problem of increased costs.

Means for Solving the Problems The present invention is equipped with a filter that cuts a spatial frequency that is more than half of the spatial frequency of a reading grid point, and an adding means that adds and averages the document information of four adjacent reading points. It is.

Operation With the above configuration, components with a frequency less than half of the spatial frequency of the reading grid point are reliably read according to the sampling theorem and corrected by averaging, and components with a frequency more than half the spatial frequency are read as a --like contrast. .

Embodiment FIG. 1 is a block diagram of an image reading apparatus according to an embodiment of the present invention, in which 1 is a document, 2 is a light source, and 5 is a carriage, which have the same structure as the conventional example. 11 is a SELFOC lens array (trademark of Nippon Sheet Glass Co., Ltd., hereinafter abbreviated as rod lens array) in which the internal refractive index changes in the radial direction.

) and 12 are contact type image sensors, which correspond to the conventional lens 3 and self-scanning image sensor 4, respectively.

FIG. 2 is a perspective view of the main parts of the image reading device of this embodiment,
6 is a belt, 7 is a fixing member for fixing the belt 6 to the carriage 5, 8 is a driven roller, 9 is a driving roller, 10 is a motor, and the above structure is the same as that of the conventional example.

FIG. 3 is a circuit diagram of the image reading device of this embodiment, where 101 is a driver, 1'O'2 is an amplifier, and 103
is an A/D converter, and has the same configuration as the conventional example. 1
04 is a line memory that stores and outputs output data from the A/D converter 103. Reference numeral 105 denotes an address counter that is reset by the scan start signal output from the driver 101 and counts up by the scan clock. 106 is a line memory 10 in response to a scan start signal from the driver 101.
4 is a flip-flop that switches between write and read operations; 107 is an averaging circuit that adds and averages the output from the A/D converter 103 and the data stored in the line memory 104; 108 is an averaging circuit that adds and averages the output from the A/D converter 103; , a delay circuit that delays the scanning clock of the driver 101 by one clock, and 109 an averaging circuit that adds and averages the output of the averaging circuit 107 and the output of the delay circuit 108.

The operation of the image reading apparatus of this embodiment configured as described above will be described when reading the original 1 shown in FIG. 5(a).

As in the conventional example, the original 1 has points a1 to a 8 and b 1 to b.
8, information of C1 to C8 and d1 to d8 is read. First, the carriage 5 is moved by the motor 10 to a position where image information at points a1 to a8 is read. Here the fourth
As shown in the figure, when the driver 101 outputs a scan start signal to the image sensor 12, the image sensor 12 outputs image data as a voltage proportional to the brightness of each pixel at points a1 to a8 on the document in synchronization with the scan clock. .

Next, when scanning of each pixel at points a1 to a8 is completed, the carriage 5 moves to a position where image information at points b1 to b8 is read. Thereafter, the scan start signal and the scan clock are again output from the driver 101 to the image sensor 12, each pixel at points b1 to b8 on the document is read, and image data is sequentially output. At this time, the image data is transmitted to the amplifier 10.
2, the voltage is amplified by the A/D converter 103, and converted into a digital value proportional to the brightness level of each pixel. Similarly, image data reading of points C1 to C8 and points d1 to d8 is performed.

Points a1 to a sequentially output by the first scan start signal
The image data of No. 8 is written into the line memory 104. The image data of points b1 to b8 are sequentially output together with the next scanning start signal, but at this time the line memory 104 is in the read mode, and in synchronization with the output of the image data of points b1 to b8, the image data of points a1 to b8 are output. The image data of a8 is also output and input to the averaging circuit 107, where averaging is performed. At this time, the image data of each point is A1 to A8, 81 to B8,
When expressed as C1 to C8 and D1 to D8, the averaging is performed in the positional relationship as shown in FIG. 5(b). Next, the output data of this averaging circuit 107 is sent to a delay circuit 108.
The data is held for one scanning clock. By averaging this held data and the data next output from the averaging circuit 107 in the averaging circuit 109, the image data of the four grid points are added in the positional relationship shown in FIG. 5(C). The average sloppy patterns are output one after another as shown in FIG.

Next, the case of reading a halftone original will be described.

The density of the light receiving elements of the image sensor 12 is 16 per 1 mm, and the rod lens array 11 has a modulation transfer function value (hereinafter abbreviated as MTF)-spatial frequency characteristic as shown in FIG. , the spatial frequency of the photodetector (16
half the spatial frequency (8 Line Bear/Sir) of Line Bear/Sir).
+nm) or more, the MTF is 0, that is, black and white cannot be distinguished.For this reason, the image components of 8 line bare/dark or more have a negative contrast, and the image sensor 12 detects a false image. No signal is generated.

In this way, the image sensor 12 reads only the spatial frequency components of 8 line pairs/M or less, and
Components exceeding the limit are output as uniform concentrations. Figure 7 shows the case of reading a halftone original. It is assumed that the outputs of the first main scanning line and the second main scanning line are the same, and the results of averaging the outputs are shown in Figure 7. (c)
It is shown in

In this embodiment, a rod lens array was used as a filter, but a quartz birefringence filter or a lens with low resolution may be used instead.

Effects of the Invention The present invention includes a filter that cuts a spatial frequency that is more than half of the spatial frequency of a reading grid point, and an adding means that adds and averages the document information of four adjacent reading points.
Components with frequencies less than half of the spatial frequency of the reading grid points are reliably read according to the sampling theorem and corrected by averaging, and components with frequencies more than half are read as a -like contrast, so the density of the grid points Even when reading halftone dot documents with density close to 1, false signals are not generated (and stable reading can be performed).

[Brief explanation of drawings]

FIG. 1 is a block diagram of an image reading device according to an embodiment of the present invention, FIG. 2 is a perspective view of the main parts, FIG. 3 is a circuit block diagram, FIG. 4 is a timing chart, and FIG. ) ~
(c) is a plan view showing the positional relationship during addition; FIG. 6 is a graph showing the characteristics of the rod lens array; FIG. 7(a)
7(b) is a graph showing the output of the image sensor, and FIG. 7(c) and (d) are the averaged data. FIG. 8 is a block diagram of the conventional image reading device, FIG. 9 is a perspective view of the main parts, FIG. 10 is a circuit block diagram of the same, and FIG. 11 is the position of the original and the reading point. FIG. 12 is a plan view showing the relationship, FIG. 12 is a timing chart, FIG. 13 (a) is a plan view showing the positional relationship between the image sensor and the halftone document, and FIG. 13 (b) is the output of the image sensor. The graph in FIG. 13(c) is a plan view showing the positional relationship of the same image data. 1... Original 2... Light source 5... Carriage 6... Belt 7... Fixing member
8... Driven roller 9... Drive roller
10...Motor 11...Rod lens array 12...Image sensor 101...Driver 102...Amplifier 1
03...A/D converter 104...Line memory 105...Address counter 106...Flip-flop 107...Averaging circuit 108...Delay circuit 109...・Name of the averaging circuit agent Patent attorney Toshio Nakao 1 person Figure 1 f Figure 2 Figure 5 Figure 6
:ir/rnn, Figure 7 '3-t/Wazda-i 1-Sidan 7 5--Ichigo Ari, ShiE---Gilt γ---Gold support 7 houses Figure 10 Figure 11 Figure 13 figure

Claims (4)

[Claims] (1) A sensor that reads document information for each grid point, and a sensor that is provided between the sensor and the document and has a characteristic that the modulation transfer function value becomes zero for a spatial frequency that is half or more of the spatial frequency of the grid point. An image reading device comprising: a filter; and an adding means for averaging document information of four points forming the vertices of the smallest square among the grid points and outputting the average. (2) The image reading device according to claim 1, wherein the filter uses a rod lens array in which a plurality of cylindrical lenses whose refractive index changes in the radial direction are arranged. (3) The image reading device according to claim 1, wherein the filter is a quartz birefringence filter. (4) The image reading device according to claim 1, wherein the filter is a lens with low resolution.