JPS5824267A - Original reader - Google Patents

Abstract

PURPOSE:To prevent fogging at a front end by changing a time constant for integration according to the presence of an original in a reader which reads an original through changing into a binary-coded signal. CONSTITUTION:A detecting circuit 6 which detects whether an original is inserted or not is provided and according to the presence of the original, time constants of an integrator composed of a resistance 7 and a capacitor 8 are changed with a switch 10; a discharge time constant for the detection of ground lightness is increased by turning on the switch 10 when the original is not inserted, or decreased by turning off the switch 10 when the original is inserted and its read starts. Thus, fogging at the front end of the original which occurs when the ground of the original is dark is eliminated to perform secure reading and inspection.

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 threshold value for binarization in such a facsimile document reading device, there is a method of detecting a highlighted portion of the document by assuming that the ground color (the color of the background 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 this, 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 document instead of detecting the highlighted area.
Similarly, a threshold value was determined based on this and a binarized signal was obtained. In the former method, for example, if there are white areas in the document, they become noise in the document, and these white areas are detected as highlights, 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 incorrect binarized signal would be generated.

In addition, with the latter method, if there are various sizes of originals to be inserted, there is a risk that non-original areas may be mistakenly included as ground brightness information, so be sure to set the position range for detecting the ground brightness to the original. It will have to be limited to certain locations. 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 background color changes slowly from white to black.
On the other hand, the directionality is given to speed up the change from black to white.

In the method described above, the background color does not change suddenly, and the background color of one manuscript is almost the same, and there are at least 2 to 3
It is assumed that even if the lines are fixed at the same threshold value, it will be sufficient.

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 bright background color to a background color, the above-mentioned directionality may become a problem. , there was a drawback that the gray background was read as information from the binarized result point. 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 considered to be information, there is a risk that ``kabushi'' may occur. For normal documents, the background color is white and does not vary greatly, 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 for the back plate to be 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 a document is inserted or not detects a sudden change in the brightness of the background color when reading a document with a white background that is close to gray, and the direction of the change is 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 rapid changes in the brightness of the background, resulting in "fogging" especially at the leading edge.

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, errors such as fogging at the leading edge of the original are avoided. To provide a document reading device capable of accurately binarizing and reading a document without generating 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 ``edge'' that occurs when the background of the manuscript is dark.

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, and this reading device includes a document reading circuit 1 that sequentially reads a document in the main and sub-scanning directions and generates an analog signal.
is provided. 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 a non-inverting input of operational amplifier 4 and to one input of comparator 15 . Switch 3 is background (i.e. ground)
The background detection width control circuit 2 detects the brightness of the document and captures a predetermined portion (width) in the main scanning direction of the document as a signal. This control circuit 2 generates a signal having a waveform as shown in FIG. In this way, the operational amplifier 4 functions as a buffer that detects the brightness of the ground, and operates together with the diode 5, and only when a voltage higher than the voltage applied to the resistor 7 is input to the operational amplifier 4, the operational amplifier 4 performs the calculation. The amplifier is configured to operate. 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.

A resistor 12 is connected in parallel to the resistor 9 via a switch 10, and the switch 10 is controlled by the starting position detection circuit 6. As shown in C' in FIG. 2, this detection circuit 6 outputs a signal at a low level and turns on a switch 10 when a document is not detected, and when a document is detected, the signal becomes low level and the switch 10 is turned off. become.

11 is an operational amplifier, which is connected to 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 waveform becomes like D' in FIG. This becomes the other input of the comparator 15 and becomes a threshold value when the read signal A is compared and binarized by the comparator 15, and the comparator 15 outputs the binarized read signal.

In such a configuration, from the original reading circuit 1, A
A read signal such as 'B' in FIG.
The read signal is integrated for a period corresponding to the level period, and
A value (D) corresponding to the integral 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 at C'+ in FIG. 2, which turns on the switch 10 and connects the resistors 9 and 12 in parallel. Ru. 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. Yonitaru. On the other hand, when a document is detected, the switch 10 is turned off, and the integral value becomes large, and 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. I do. 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 whether or not a document has been inserted is provided, and its time constant is switched depending on the presence or absence of a document. The discharge time constant for brightness detection is switched quickly, while the discharge time constant is switched slowly when the document is inserted and reading begins, so the edge of the document that occurs when the document has a dark background can be eliminated without major changes to the circuit. A document reading device that can eliminate "fogging", obtain accurate binarized information, and perform reliable reading and scanning can be obtained.

[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. 1. l... Original reading circuit, 2... Background detection width control circuit, 6... Original beginning detection circuit, 15... Comparator.

Claims (2)

[Claims] (1) In a document reading device that converts a read output signal read from a document into a binary signal using a threshold determined by an integral value of the read signal in the main scanning direction, a detection means for detecting the presence or absence of a document is provided, and the A document reading device characterized in that the time constant of the document is switched depending on the presence or absence of a document. (2) The document reading device according to claim 1, wherein the time constant of the integration is made faster when there is no document.