JP2910067B2 - Reader - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a document reading apparatus used for a facsimile or the like.

[Prior Art] In a document reading apparatus such as a facsimile,
At the time of reading, a thin line in the main scanning direction (hereinafter referred to as a horizontal thin line)
May be difficult to read. This occurs because, when scanning on a horizontal thin line, the read data or the threshold value, which is a reference when binarizing black and white, rises and falls. Therefore, the reproduced image may not be a horizontal thin line but a jagged crank shape. Therefore, at the time of reading a document, a fine reading mode in which the number of scanning lines per unit length in the sub-scanning direction is increased is adopted to secure the resolution of the horizontal fine lines.

[Problems to be Solved by the Invention] However, as described above, in the fine reading mode, the reading speed is slow, so that it takes a long time to read and is not suitable for transmitting a large amount of information. Therefore, when the normal reading mode is set to the normal speed and the density is increased to read the horizontal thin line, the resolution is further reduced and the entire image may be destroyed.

SUMMARY OF THE INVENTION The present invention solves the above-described problem. When a current line is read during photoelectric conversion, the threshold value is changed according to binary data of a previous line that is one line before the current line. Without lowering the resolution when scanning
An object of the present invention is to provide a reading device capable of reading horizontal thin lines.

Means for Solving the Problems In order to achieve the above object, according to an embodiment of the present invention, a light source for irradiating a document, an image sensor for photoelectrically converting reflected light from the document, and reading of the image sensor are controlled. A reading device including a reading control circuit, a comparator for binarizing a signal from an image sensor, and a threshold control circuit capable of arbitrarily changing a threshold level for binarization, the photoelectric conversion A memory for storing binary data of the previous line corresponding to the middle and one line before the current line, wherein the threshold value control circuit changes a threshold value according to the binary data of the previous line stored in the memory A thermal head for image reproduction having a shift register function for storing at least one line of binary data is used as a memory.

According to the above configuration, when the n-th dot (pixel) of the current line is read, the threshold output of the threshold control circuit changes within a predetermined range by the binary data of the n-th dot of the previous line. I do. Then, the comparator compares the read analog data of the current line of the n-th dot from the image sensor with the threshold output of the threshold control circuit. Further, the data of the n-th dot of the current line binarized by the comparator is stored in the shift register of the thermal head functioning as a memory, and is used when binarizing the next line. Thus, the threshold value of the current line can be changed by referring to the binarized data of the previous line without requiring a dedicated memory.

According to a second aspect of the present invention, in the first aspect, the threshold value set by the threshold value control circuit is a high-level threshold value if the read result of the previous line is white, If the result is black, the threshold value is set to a low level.

According to a third aspect of the present invention, in the first aspect, provided between the output end of the comparator and the input end of the thermal head,
A switch device for inhibiting transmission of data sent from the comparator side to the thermal head side for adjusting the communication speed when reading data is transmitted outside the apparatus and the timing of reading by the image sensor is provided. Further provisions.

[Embodiment] FIG. 1 shows the configuration of an embodiment of a reading apparatus according to the present invention.
This will be described with reference to FIGS.

As shown in the block diagram of FIG.
A microcomputer (hereinafter referred to as CPU) 1 for outputting a command for controlling the operation of the entire apparatus, a reading control circuit 2 for controlling reading by the command, and a drive pulse from the reading control circuit 2 An image sensor (hereinafter, referred to as CIS) 3 which photoelectrically converts the reflected light and outputs the analog light as analog image data. And CIS
A binarization circuit 4 for binarizing the analog image data read at 3; and storage data (2 of the line) output from the binarization circuit 4 as digital image data via the CPU 1.
D / A conversion to output an analog threshold value used for binarizing analog image data by a thermal head 5 having a shift register function for storing one line of value data) and a binarization circuit 4 And a container 6. Note that the thermal head 5 may also serve as a member used for image reproduction.

The base data of the analog threshold value is input from the read control circuit 2 to the D / A converter 6. Further, the transmission data output from the CPU 1 is converted into a signal via a buffer 10 and a modem 11 by a network control unit (NCU) 12 so as to be on a line. Also, the received data is input to the CPU 1 via the modem 11. Further, the CPU 1 has a ROM 13 and a RAM 14 as storage elements.

The binarizing circuit 4 includes a threshold control circuit 7 and a comparator 8, as shown in the functional block diagram of the reading unit in FIG. A new threshold value is determined from the analog-converted threshold value and the binary data of the previous line from the thermal head 5. The comparator 8 receives the analog image data output a from the CIS 3 as one input, and the output b of the threshold control circuit 7 as the other input. The switch 9 is connected between the output terminal of the comparator 8 and the input terminal of the thermal head 5, and the CPU 1 performs its function.

FIG. 3 shows a specific example of the threshold control circuit 7. The control circuit 7 includes an AND circuit 17 that performs a logical operation on the binary data (white: 0, black: 1) of the previous line from the thermal head 5 and the signal c of the threshold control instruction from the read control circuit 2. , AND circuit 17
And a resistor R1, which determines the level of the input b of the comparator 8 by dividing the threshold signal from the D / A converter 6 by turning the transistor Tr1 on and off by the output of the transistor Tr1. R2. Here, the threshold signal from the D / A converter 6 is divided by R2 / (R1 + R2) when the transistor Tr1 is turned on and the previous line data is determined to be black. When it is determined to be white, on the other hand, the transistor Tr1 is turned off, the threshold signal is not divided, and the threshold level is kept high. When the threshold control is not performed in the fine reading mode or the like, the signal c is dropped to “0” so that the output of the D / A converter 6 can be input to the comparator 8 without dividing the voltage. it can. The switch 9 is used to secure binary data of the previous line in the thermal head 5 when performing idle reading (reading operation is performed but data is not used) for adjusting timing of communication and reading. The switch 9 is turned off at the time of blank reading, and the comparator 8
Has the role of disconnecting data from

Next, the operation of this embodiment will be described with reference to the time charts of FIGS. 4 (a) and 4 (b). In FIG. 4, ST20, NT2
Reference numeral 1 denotes a high or low output level of the threshold value control circuit 7, ST20 is a threshold value set so that a horizontal thin line can be determined to be black when reading, and NT21 is a conventional normal line. This is a threshold level set in the mode, and one of the levels is selected. VID22 indicates the read analog output of CIS3. The dashed lines B1 and B2 indicate the selected and set thresholds (input b). FIG. 4A shows the reading operation of the first line, and FIG. 4B shows the reading operation of the second line. The level of NT21 is a value when the transistor Tr1 in FIG. 3 described above is turned on and the threshold value from the D / A converter 6 is divided by the resistors R1 and R2. The level of ST20 is This is the value when the transistor Tr1 is not turned on and the threshold from the D / A converter 6 is not divided. In this embodiment, at the time of normal reading, binarization is performed according to the level of ST20, and if the previous line data obtained from the thermal head 5, that is, the previous dot in the sub-scanning direction is black: 1, NT
Binarization is performed according to 21 levels. At the time of reading the first line, the level of NT21 is set to the threshold value B1 and binarized.

If the output of CIS3 by reading the first line becomes VID22 in FIG. 4 (a), the binary image signal D becomes as shown in FIG. 4 (a). 2
The threshold value of the line is as shown by the dashed line B2. Therefore, the output of CIS3 that has read the second line
In the case of the VID 22 shown in FIG. 3B, the binary image signal D is as shown in FIG. Here, it should be noted that, in the case where the previous line is determined to be white in the illustrated area E, the current line is determined to be black because the threshold value has become high. Corresponds to the reading when appears. Further, in the case where the previous line is determined to be black in the region F, the current line is determined to be white because the threshold value has become low (normal). This corresponds to reading when a thin line appears.

Next, the operation procedure of the present embodiment will be described with reference to the flowchart of FIG. 5. First, it is determined whether or not the communication reading is started (S1). In the start state, the threshold control circuit 7
The input signal c is set to "0" and the switch 9 is turned on (S2). Then, it detects whether the communication mode is normal or fine (S3). If the communication mode is the fine reading mode,
Reading is performed in the fine reading mode (S4), and the process ends.
In the normal reading mode, 8-bit threshold data is sent from the reading control circuit 2 to the threshold control circuit 7 (S
Five). At this time, since the signal c is “0”,
The output of the / A converter 6 is at the level of ST20 without being divided. Based on the threshold value, the first line of the document is read (S6) and binarized by the comparator 8. Now, as a result of reading the first line, when the VID 22 is output as shown in FIG. 4A, the binary image signal D as shown in FIG.
This data is stored in the thermal head 5. Next, the signal c is set to "1" (S7), and the threshold control circuit 7 is set to the threshold control state.

Next, the number n of lines is set to "2" (S8), and reading of the second line is started. At this time, it is determined whether or not the blank reading is performed for timing adjustment (S9). If the blank reading is performed, the switch 9 is turned off (S10), and the reading operation is performed (S11). Data is not destroyed. If it is not blank reading or if it is not blank reading, the switch 9 is turned on (S12), and reading of the second line is performed (S13). At this time, the threshold value B2 at the time of reading the second line is adjusted in accordance with the binary image signal D of the first line obtained from the data of the thermal head 5 as shown in FIG.
Is set to either ST20 or NT21.
Here, as the threshold value B2, if the read result of the previous line is white, a high level ST20 is set, and if the read result is black, a low level ST20 is set.
NT21 is selected. After the reading of the second line, it is determined whether or not the read line is the last line (S14). If it is not the last line, n is incremented by one (S1).
5) Read the next line. In this way, when the reading up to the last line is completed, the operation ends.

Next, referring to FIGS. 6 (a) to 6 (d), a description will be given of the difference between the read result and the read result according to the embodiment of the present invention. For the original shown in FIG. 11A, the result of reading at the conventional standard density is shown in FIG. 10B, and the result of reading at the conventional dark density is shown in FIG. The results are shown in FIG. In the conventional standard density shown in FIG. 6B, the horizontal thin line on the second line and each horizontal line between the second and third lines and between the fourth and fifth lines are used. The thin line cannot be reproduced, and at the conventional high density shown in FIG. 3C, the horizontal thin line between the second and third lines and the thin line between the fourth and fifth lines The white line portions between the horizontal thin lines are combined to cause image collapse. On the other hand, in the case of the embodiment of the present invention, by performing the operations shown in the above-mentioned time chart and flowchart, the horizontal thin line between the second and third lines and the fourth and fifth lines are formed. For example, if the horizontal thin line between the lines is determined to be black in the second line, the threshold value is reduced in the next third line and is determined to be white. This time, the threshold value increases and it is determined that the color is black. In this way, the horizontal line is faithfully reproduced.

[Effects of the Invention] As described above, according to the first aspect of the present invention, 2
Since the threshold value of the current line is changed with reference to the quantified data, the fine line mode, for example, a horizontal thin line in the main scanning direction can be faithfully reproduced without lowering the resolution without setting the fine reading mode. Can be reproduced and therefore
The resolution is not reduced, and the entire image is not collapsed, and reading does not take much time. Furthermore, since the memory also serves as a thermal head required for image reproduction having a shift register function, the cost can be reduced as compared with the case where a dedicated memory is provided.

According to the second aspect of the present invention, by changing the threshold value at the time of reading the current line data depending on whether the previous line data is white or black, for example, when the previous line data is determined to be black, The threshold is set lower than normal, so that even if the current line data is a little black, it will not be determined as black,
When the previous line data is determined to be white, the threshold value becomes a normal threshold value, the area where the current line data is determined to be white is reduced, and even if the blackness is slight, it is determined to be black. Therefore, when a thin horizontal line is written between the second and third lines, if the first line is determined to be white, the second line is determined to be black, the third line is determined to be white, and the second line is determined to be white. A horizontal line is reproduced at the line.

According to the third aspect of the present invention, in addition to the above effects, the present apparatus performs idle reading as necessary in order to adjust the communication speed for transmitting read data to the outside of the apparatus and the timing of reading. In this case, since the data is not sent to the thermal head during the idle reading by the control of the switch device, it is possible to prevent the data in the thermal head used as the memory from being destroyed.

[Brief description of the drawings]

FIG. 1 is a block diagram of a reading control device according to an embodiment of the present invention, FIG. 2 is a functional block diagram of a reading unit of the reading control device,
3 is a block diagram of a threshold control circuit, FIG. 4 is a time chart showing a reading operation of the apparatus, FIG. 5 is a flowchart showing a reading operation procedure, and FIGS. 6 (a) to 6 (d).
FIG. 9 is a diagram showing a comparison between a document and a reproduced image based on reading according to a conventional example and an example of the present invention. 2 ... read control circuit, 3 ... image sensor, 5 ... thermal head, 6 ... D / A converter, 7 ... threshold control circuit, 8 ... comparator, 9 ... switch, 17 ... … AND circuit, transistors Tr1, R1, R2 …… resistance

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04N 1/40-1/409 H04N 1/04-1/207

Claims (3)

(57) [Claims] A light source for irradiating a document, an image sensor for photoelectrically converting reflected light from the document, a reading control circuit for controlling reading of the image sensor, and a comparator for binarizing a signal from the image sensor. A threshold value control circuit capable of arbitrarily changing a threshold level for binarization, wherein binary data of a previous line which is one line before the current line undergoing photoelectric conversion is stored. A threshold value control circuit configured to change a threshold value in accordance with binary data of a previous line stored in the memory; A reading device using a thermal head for image reproduction having a shift register function for storing data. 2. The threshold value set by the threshold value control circuit is a high level threshold value if the read result of the previous line is white, and a low level threshold value if the read result of the previous line is black. 2. The reading device according to claim 1, wherein the threshold value is: 3. A communication device, which is provided between an output terminal of the comparator and an input terminal of the thermal head, for adjusting a communication speed when reading data is transmitted outside the apparatus and a timing of reading by the image sensor. 3. The reading device according to claim 1, further comprising a switch device for prohibiting transmission of data sent from the comparator side to the thermal head side.