JPH04123668A - Image reader - Google Patents

Abstract

PURPOSE:To read the thin line whose density is low by selecting appropriately one of two comparing means whose thresholds are different at the time of reading an image of the next line, based on density history of an inputted image signal. CONSTITUTION:An analog image signal S1 from an image sensor 10 is inputted to a comparator 12 and a comparator 14, binarized by thresholds V1, V2 (V1>V2), respectively and image data S2, S4 are outputted. S2 is supplied to a line memory 18 and an arithmetic circuit 20, and S4 is inputted to the arithmetic circuit 20. The arithmetic circuit 20 is provided with a selector 24 and a 2-input OR circuit 26, outputs S4, when S3 from the line memory 18 is in a high level, and outputs S2, when S3 is in a low Level. On the other hand, the OR circuit 26 executes an OR operation of S5, and S6 from a line memory 22 and outputs S7. Both thin lines whose density is low or high on the document can be read without deteriorating the resolution.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image reading device used in facsimiles and the like. - In layer details, when selecting two comparison means with different threshold values, the resolution is determined by selecting an appropriate comparison means for reading the image of the next line based on the density history of the input image signal. This makes it possible to read thin lines with low density without decreasing the density.

[Conventional technology]

Conventionally, in image reading devices such as facsimiles, one line of a document in the main scanning direction is divided into two or more in the sub-scanning direction, and images such as characters and figures on the original stack are read using photoelectric conversion means. The so-called double scan method is adopted (Special Publication No. 60-22859, Special Publication No. 5).
5-=Refer to Publication No. 15316).

Image reading devices that use this double scan method
It is possible to read fine lines with relatively high density.

[Problem to be solved by the invention]

However, the conventional image reading apparatus employing the double scan method cannot read thin lines with low density. In this case, for example, a thin line with low density may be read by inserting an ND filter into the optical input section of the photoelectric conversion means, or by increasing the level of the reference voltage (threshold) in the binarization comparator to which the image signal is input. It is possible to do so. In this way, when the reading density of the image reading device is increased, the resolution of the image reading device is reduced, resulting in a problem that, for example, so-called image collapse occurs.

The present invention has been made in view of the above points, and an object of the present invention is to provide an excellent image reading device that can read thin lines with low density on a document without lowering the resolution. be.

[Means to solve the problem]

In order to solve the above-mentioned problems, the image reading device of the present invention includes a photoelectric conversion unit that main-scans a document image an integer number of two or more times within one sub-scanning period and outputs an image signal that is photoelectrically read; a first comparison means that compares the image signal with a first threshold value and outputs first binary data;
a second comparing means for outputting second binary data by comparing with a second threshold corresponding to a lower density than the threshold; and storing the first binary data for one line in the main scanning direction. a first memory means for reading the image of the next line;
In response to the first binary data output from the first memory means, the first binary data output from the first comparison means
a selection means for selecting and outputting either the value data or the second binary data output from the second comparison means; Number of main scans within a period - 1) A second memory means for storing lines and the above-mentioned selection means, and the output data of the selection means and the output data of the above-mentioned second memory means are calculated to calculate the number of lines. It is equipped with arithmetic means for outputting data.

[Effect]

In the image reading device of the present invention configured as described above, the threshold value set in the first comparison means is set to a threshold value that allows reading thin lines with low density, and the threshold value set in the second comparison means is set to a threshold value that allows reading thin lines with low density. is set to a threshold value that allows reading fine lines with an average density, and further, the first binary data of the first comparison means stored in the first memory means is used to read the image of the next line. Since the control data is used to determine which comparison means to use, the first comparison means or the second comparison means, the image of the next line is determined based on the density history of the input image signal. Appropriate comparison means for reading can be selected and both thin lines with low density and fine lines with high density can be read.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image reading apparatus according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a circuit block diagram showing the configuration of one embodiment, FIG. 2 is a circuit block diagram showing a detailed configuration of a part of the configuration of the one embodiment, and FIG. 3 is a circuit block diagram showing the operation of one embodiment. It is a waveform diagram provided for explanation.

In FIG. 1, 10 is an image sensor (photoelectric conversion means), and information about the image drawn on the original (hereinafter referred to as
In this system, light having image information) is input, and an analog image signal Sl proportional to the intensity of the light is output. Therefore, for example, when reflected light from a white original is input, a relatively high-level positive analog image signal S1 is output, and when the light receiving section is filtered, 0
An analog image signal SI of volts is output.

Analog image signal S output from the image sensor 10
1 is a comparator 12 (first comparison means) and a comparator 14 (
is input to the comparison input terminal of the second comparison means). A positive threshold value Vl (first threshold value) is supplied from a threshold value generation circuit 16 to a reference input terminal of the comparator 12. Threshold V1 is resistor 1
8 and the resistor 20, and is supplied to the reference input terminal of the comparator 14 as a threshold value V2 (second threshold value). In this way, the threshold value V1 is set as a threshold value for reading thin lines with low density, and the threshold value V2 is set as a threshold value for reading fine images with normal average density. .

These comparators 12.14 output low-level image data when the level of the analog image signal Sl supplied to the comparison input terminal is higher than the level of thresholds V1 and v2 supplied to the reference input terminal. , is low, high-level image data, that is, binary data is output.

The image data S2 (first binary data) output from the comparator 12 is in the main scanning direction! Line memory 18 (first memory means) capable of storing image data for lines
and is supplied to the arithmetic circuit 20 (arithmetic means). Image data S3 (first binary data) output from the line memory 18 is supplied to the arithmetic circuit 20. Image data S4 (second binary data) output from the comparator 14 is input to the arithmetic circuit 20. The image data S5 output from the arithmetic circuit 20 is stored in a line memory 22 (second memory means) that can store image data for one line in the main scanning direction.
The image data S6 output from the line memory 22 is supplied to the arithmetic circuit 20. Note that, as the line memory 18 and the line memory 22, a dual port memory capable of simultaneous write operation and read operation is selected.

As shown in FIG. 2, the arithmetic circuit 20 has a selector 24 (
selection means) and two-person Chaor circuit (hereinafter referred to as OR circuit)
26. As can be understood from the figure, the selector 24 is configured as a well-known logic circuit, and the selector 24 receives image data 53 (
When the level of the binary data (binary data) is high level, the comparator 14 outputs the image data S5 from the selector 24.
outputs the image data S4 supplied from the comparator 12 to one signal input terminal of the selector 24, and when the level is low, the image data S2 supplied from the comparator 12 to the other signal input terminal of the selector 24 as image data s5. Output. On the other hand, the OR circuit 26 inputs image data S5.
Image data S7, which is the output after performing a logical OR operation on the image data S6 outputted from the line memory 22, is output.

Next, the operation of the above embodiment will be explained.

Note that when reading an image from a document with the image reading device in this embodiment, one line of the document in the main scanning direction is divided into two in the sub-scanning direction, and the upper part (
(hereinafter referred to as 1/2 line) and the lower part (hereinafter referred to as 2/2 line)
2 lines) sequentially, and the I in 1 line is read.
By performing a predetermined calculation in the calculation circuit 20 every time the /2 line and the 2/2 line are read, the output image data S7 is
is to be determined.

First, when reading the Nth 2/2 line in the sub-scanning direction, the analog image signal S1 output from the image sensor 10 is compared by the comparator 12, and the comparison result signal is an image that is binary data. Data S2 is temporarily stored in the first memory area 18a of the line memory 18. In this way, the output image data S2 of the comparator 12 is input and stored in the line memory 18, or in other words, the data stored in the line memory 18 is updated after reading the 2/2 line. The stored image data S2 is 1/1 of the next line (N+1 line).
Arithmetic circuit as image data S3 both when reading 2 lines and when reading 2/2 lines. The signal is inputted to the control terminal C of No. 20.

Therefore, when reading the N+I+1st line/2nd line (see FIGS. 3(a) to 3(d)), the image data S2 and S4, which are the comparison result signals of the comparators 12 and 14, are transferred to the arithmetic circuit. It is input to a selector 24 that constitutes 20. In this case, since the control input terminal of the selector 24 is supplied with the image data S3 of the Nth 2/2 line from the first memory area 18a of the line memory 18, the control input terminal of the selector 24 Image data S2 or image data S4 is selected, and the selected image data is stored in the line memory 22 as image data S5.
The data is stored as determined data for the 1/2 line of the +1st line (hereinafter referred to as 1/2 line data). Note that this stored data is output with a delay of l line period.

Next, when reading the 272nd line (N+1) (
3(e) to (i)), the output image data S2 of the comparator 12 is stored in the line memory 18, and the comparator 12 and the comparator The image data S2 and S4, which are the 14 comparison result signals, are input to the selector 24 constituting the arithmetic circuit 20. In this case, since the control input terminal of the selector 24 is supplied with the image data S3 of the Nth line 2/2 line from the line memory 18, this image data S3
Image data S2 or image data S4 depending on the level of
is selected, and the image data S which is the selected image data
5 is temporarily stored in the line memory 22 as determined data of the 2/2 line of the N+1st line (hereinafter referred to as 2/2 line data).

In this case, 1/2 of the N+1st line is input from the line memory 22 in synchronization with the determined data of the N+l+1st line/2nd line being input to the line memory 22.
Line data is output, and this 1/2 line data and N
An OR circuit 26 performs a logical OR operation with the 2/2 line data of the +1st line, and the OR circuit 26 outputs image data S7, which is line data.

As described above, according to the embodiment described above, the second
/When the level of the image data S3 stored in the line memory 18 as read data of 2 lines is low level (the level of the analog image signal St is equal to or lower than the threshold value V1
), the next N+1th line analog image signal S1 is! Comparators with relatively high threshold levels for both /2 line and 2/2 line! Since the binarization process is performed at 2, even if the analog image signal 31 corresponds to a thin line with low density, it can be read (the comparator 12 is inverted).

On the other hand, when the document contains a series of fine images with high density on average, the level of the image data S3 stored in the line memory 18 as the read data of the 2/2 line of the Nth line is high. level (because the level of the analog image signal S1 becomes lower than the threshold value V1), the next N+1th line analog image signal Sl becomes 1/
Both lines 2 and 2/2 are binarized by a comparator 14 with a relatively low threshold level. Signal S1 can be read (comparator I4
(inverted), and the resolution does not decrease.

〔Effect of the invention〕

As described above, the image reading device of the present invention has two comparing means with different threshold values, and when selecting between these two comparing means, the next line is selected based on the density history of the input image signal. By selecting an appropriate comparison method for reading images, it is possible to read thin lines with low density on the document, and since the resolution does not decrease, it is possible to read any of the fine lines with high density. This has the effect that lines can also be read.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of an image reading device in one embodiment of the present invention, FIG. 2 is a detailed circuit diagram of an arithmetic circuit in the embodiment shown in FIG. 1, and FIG. 3 is an image reading device in one embodiment. FIG. 3 is a waveform diagram used to explain the operation of the device. lO...Image sensor, 12...Comparator, 14.
... Comparator, 16... Threshold generation circuit, 18... Line memory, 20... Arithmetic circuit, 22... Line memory, 24... Selector.

Claims (1)

[Claims] (1) A photoelectric conversion means that main-scans a document image an integer number of times of 2 or more within one sub-scanning period and outputs an image signal that is photoelectrically read; a first comparing means for outputting binary data; and a second comparing means for comparing the image signal using a second threshold value corresponding to a lower density side than the first threshold value and outputting second binary data. a first memory means for storing the first binary data for one line in the main scanning direction; and a first memory means for storing the first binary data for one line in the main scanning direction; According to the binary data of
a selection means for selecting and outputting either the first binary data output from the comparison means or the second binary data output from the second comparison means; and the selection means a second memory means for storing the output data for lines in the main scanning direction (the number of main scans in one sub-scanning period - 1), and the selection means, and the output data of the selection means and the second 1. An image reading device comprising: arithmetic means for calculating output data of a memory means and outputting line data.