JPH0230626B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a document reading device, and particularly to a document reading device that converts information written on a document into a binary signal and reads the signal in a facsimile machine or the like.

Conventionally, when determining a binarization threshold in such a facsimile document reading device, there is a method of detecting a highlighted portion of a document by assuming that the ground color (background color of the document) is white. In this method, a highlighted portion of one to several lines of a document is detected, a threshold value is determined based on the detected highlight portion, and the threshold value is changed in accordance with changes in the brightness of the highlighted portion to obtain a binarized signal. Another method is to detect the average brightness of the background of the original document, and similarly set a threshold value based on that value to obtain a binary signal. In the former method, for example, if there is a white spot in the document, it becomes noise in the document, and this white spot is detected as a highlight part, and the threshold value is set to a value that corresponds to a direction that contains more white information. There was a possibility that an erroneous binarized signal would be generated.

In addition, in the latter method, if there are various sizes of inserted originals, there is a risk that non-original areas may be mistakenly included as background brightness information.
The position range for detecting the background brightness must be limited to the location where the document is located. However, if this is done, it is possible that information such as letters written at the position where the brightness of the ground is detected may be detected and the detected content may be incorrect. Therefore, in order to accurately detect the brightness of the background, the influence of the information written on that part is reduced by integrating the read signal in the main scanning direction for several lines of that part of the document.

Furthermore, in this method, the influence of noise information on detection of the ground color is removed by changing the speed of response to a change in the binarization threshold in the direction in which the brightness of the ground color changes as the background color changes during scanning. ing. For example, if the background color is white, the directionality is such that the background color changes slowly from white to black, and conversely, changes from black to white faster.

The method described above assumes that the background color does not change suddenly, that the background color of one document is almost the same, and that it is sufficient to fix at least 2 to 3 lines with the same threshold value. ing.

However, if the background color of the original changes toward the background color where the threshold response changes slowly, that is, if the background color changes from a light background color to a dark background color, the above-mentioned directionality becomes a problem. However, when a gray background is binarized, it is read as black information. If this kind of phenomenon occurs in other parts of the original except for the peripheral areas, there is usually not a big change in the brightness of the background of a single document, so it is not a problem, but if the background color changes from white to black in the original, it is not a problem. If the background color information is reversed and black is read as information, but white is now considered as information, ``fogging'' may occur. For normal documents, the background color is white and does not change significantly, and the information is black, so the brightness of the background of the document is always detected in the main scanning direction and there is no problem, but in the sub-scanning direction In this case, the brightness of the back plate is detected until the document is inserted. When a document is inserted in a facsimile machine, the back plate must be scanned depending on the width of the document in the main scanning direction. In this case, it is convenient to make the back plate the same color as the background color of the document, that is, generally white, so the color of the back plate is usually white. Therefore, the circuit that detects the background color depending on whether or not a document is inserted detects a sudden change in the brightness of the background color when reading a document with a white background close to gray, and the direction changes from white to black. It is detected as the direction of change. For this reason, for originals with relatively dark backgrounds, the threshold value does not respond to sudden changes in the brightness of the background, resulting in "fogging", especially at the leading edge.
occurs.

Therefore, the present invention solves such conventional drawbacks, and when determining the threshold value for integrating the main scanning read signal and binarizing it based on the integrated value, it is necessary to avoid fogging or the like on the leading edge of the document. To provide a document reading device capable of accurately binarizing and reading a document without generating erroneous information.

According to the present invention, in order to achieve this objective, the time constant of integration is switched depending on the presence or absence of a document. Specifically, when there is no original, the threshold value for binarization is changed to judge gray information as white, and when there is an original, the threshold is changed to judge gray information as black. The time constant of integration is changed to change the time constant of the integral. This makes it possible to eliminate the "fogging" at the leading edge that occurs when the background of the document is dark.

That is, the present invention provides a document reading device that binarizes a read signal generated by reading a document by comparing it with a threshold value, including a charging/discharging means that performs charging/discharging according to the read signal, and a charge/discharge means for performing charging/discharging according to the read signal; forming means for forming a threshold for binarizing the read signal based on the amount of charge of the means; and comparing means for binarizing the read signal by comparing the threshold formed by the forming means and the read signal. , a detection means for detecting the presence or absence of a document, and a detection output of the detection means so that the discharge of the charging/discharging means is faster when there is no document than when there is a document, according to the detection output of the detection means. The present invention provides a document reading device characterized in that it has a switching means for switching the discharge time constant of the charging and discharging means accordingly.

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows a document reading device according to the present invention.
A document reading circuit 1 is provided that sequentially reads documents in the sub-scanning direction and generates analog signals. At the output A of the original reading circuit 1, a reading signal appears for each line as shown at A' in FIG. This read signal is input via switch 3 to the non-inverting input of operational amplifier 4 and to one input of comparator 15. The switch 3 is turned on and off by a background detection width control circuit 2 which detects the brightness of the background (ground) and captures a predetermined portion (width) of the document in the main scanning direction as a signal. This control circuit 2 is shown in FIG.
A signal having a waveform as shown in B' is generated, and while this signal is at a high level, the switch 3 is closed and the read signal A' is input to the operational amplifier 4. In this way, the operational amplifier 4 serves as a buffer for detecting the brightness of the ground, and operates together with the diode 5.
The operational amplifier is configured to operate only when a voltage higher than the voltage applied to the resistor 7 is input to the operational amplifier 4. The resistor 7 and the capacitor 8 constitute an integrator, and the brightness of the ground is detected as the amount of charge of the capacitor 8. In this case, the charging time constant of the capacitor 8 is determined by the resistor 7 and the capacitance of the capacitor 8, and the discharging time constant is determined by the resistor 9. The configuration consisting of these resistor 7, capacitor 8, and resistor 9 corresponds to the charging/discharging means of the present invention.

Resistor 1 is connected in parallel to resistor 9 via switch 10.
2 is connected, and the switch 10 is controlled by the document cue detection circuit 6. This detection circuit 6
As shown in C' of FIG. 2, when a document is not detected, a high level signal is output to turn on the switch 10, and when a document is detected, the signal becomes low level and the switch 10 is turned off.

This detection circuit 6 corresponds to the detection means of the present invention,
Further, the configuration consisting of the resistor 12 and the switch 10 corresponds to the switching means of the present invention.

Reference numeral 11 denotes an operational amplifier, which serves as a buffer for connecting a circuit that determines a threshold value for a signal that detects the brightness of the ground.The threshold value is determined by the division ratio of resistors 13 and 14, and its output The waveform will look like D' in Figure 2. The configuration consisting of these resistors 13 and 14 corresponds to the forming means of the present invention. This becomes the other input of the comparator 15 and becomes a threshold when the read signal A is compared and binarized by the comparator 15, and the comparator 15 outputs the binarized read signal.

This comparator 15 corresponds to the comparison means of the present invention.

In such a configuration, the document reading circuit 1
A read signal like A' is generated from , and the read signal is integrated through the switch 3 which is turned on and off by the control circuit 2 during a period corresponding to the high level period of B' in FIG. A value (D) corresponding to the value is input to the other input section of the comparator 15.
In this case, if there is no original, a high level signal is generated from the detection circuit 6 as shown in C'1 of FIG. ₂ , and the switch 10 is turned on.
Resistors 9 and 12 are connected in parallel. As a result, the integrator discharges faster and the integral value entering the non-inverting input of operational amplifier 11 becomes smaller. As a result, the threshold value of the comparator 15 is lowered, and when the background of the document is dark and gray information appears, it is determined to be white. On the other hand, when a document is detected, the switch 10 is turned off, and the integral value becomes larger, so that the threshold value of the comparator 15 becomes larger than before, so that the normal integral operation and the binarization reading based on the integral value are performed. conduct. That is, a read signal A' smaller than the threshold value D' in FIG. 2 is determined to be black, and a read signal is generated.

As explained above, according to the present invention, a means for detecting the presence or absence of a document is provided, and its time constant is switched depending on the presence or absence of a document. The discharge time constant for detection is made faster, while the discharge time constant is switched to a slower value when the original is inserted and reading begins. This eliminates "fogging" at the leading edge of the original, which occurs when the original is dark, without making major changes to the circuit. ” can be eliminated, accurate binarized information can be obtained, and a document reading device can be obtained that can perform reliable reading scanning.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram showing the configuration of a document reading apparatus according to the present invention, and FIG. 2 is a waveform diagram showing signal waveforms generated in each part of FIG. DESCRIPTION OF SYMBOLS 1... Original reading circuit, 2... Background detection width control circuit, 6... Original beginning detection circuit, 15... Comparator.

Claims (1)

[Scope of Claims] 1. A document reading device that binarizes a read signal generated by reading a document by comparing it with a threshold value, comprising: a charging/discharging means that performs charging/discharging according to the read signal; forming means for forming a threshold value for binarizing the read signal based on the amount of charge of the discharging means; and a comparing means for binarizing the read signal by comparing the threshold value formed by the forming means and the read signal. and a detection means for detecting the presence or absence of a document, and a detection output of the detection means such that the discharge of the charging/discharging means is faster when there is no document than when there is a document, according to the detection output of the detection means. a switching device for switching a discharge time constant of the charging and discharging device according to the switching device.