JPH0626437B2 - Image reader - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Field of Application> The present invention is used for reading an image including characters written on a paper surface or a board surface in a facsimile machine, an electronic blackboard, etc., and converting it into a binary signal. The present invention relates to an image reading device.

<Prior Art> A conventional general image reading apparatus of this type reads an original image described on a paper surface or a board surface by using a photoelectric conversion device such as a CCD image sensor and outputs an output voltage of the photoelectric conversion device. The level is compared with a preset specific level, that is, a slice level, and the level is converted into a binarized signal. When the level is higher than the slice level, the signal is processed as white, and when it is smaller, the signal is processed as black. ing.

<Problems to be solved by the invention> However, when the above-mentioned slice level is set to a fixed value, when the information in characters is printed, the light and shade of the signal is discriminated only by the binary value of black and white. As a result, it is possible to print clear characters, but on the other hand, information such as pictures and photographs cannot be displayed in the intermediate gradation, resulting in an unnatural print display. Therefore, when the slice level is changed for each pixel by using a method such as a dither method in order to express an intermediate gradation, fine information in the character information portion is lost, and an unclear character is printed. There is a problem that will be done.

<Object of the Invention> The present invention solves these two contradictory problems and provides an image reading binary signal capable of clearly printing both picture information and character information mixed in an image signal. It is a technical object to provide an image reading apparatus capable of performing the image reading.

<Means for Solving Problems> The image reading apparatus of the present invention, as shown in FIG. 1 corresponding to the embodiment, includes a differentiating circuit 2 for differentiating an image signal obtained by photoelectric conversion from an original image to be read. , Two positive and negative levels of the amplitude of the rate-of-change signal after differentiation are respectively compared with a set value, and two comparators CP1 and CP2 which output a signal when the level is equal to or more than the set value, and the comparators A holding circuit 4 that holds an output signal for a certain period of time to generate a pulse signal of a predetermined width, and one of a fixed slice level and a dither method slice level depending on whether the pulse signal is generated or not. It is characterized by including a switching circuit 8 for selecting and a converter (comparator) 9 for comparing the slice level selected by this circuit with the above-mentioned image signal and converting it into a binarized signal. Be kicked.

<Operation> With the above configuration, when the rate of change of the image signal in which characters and pictures are mixed is obtained, the image signal of information such as a picture usually has a gentle waveform change, and conversely Since the signal changes drastically in its waveform, the rate of change is large only in the area of the character information, resulting in a large rate of change signal. Therefore, in the present invention, the rate-of-change signal is guided to a comparator and compared with a set value, and when the amplitude level is equal to or higher than the set value, binarization processing of the image signal is performed based on the fixed slice level. When the amplitude level is less than the set value, the binarization processing of the image signal is performed based on the dither method slice level.

Here, since the rate of change (differential value) of the character information signal in the image signal is an edge-shaped signal, the signal output by the comparator when this signal is input takes into consideration the character size. It is held for a certain period of time, and the character information section is set by this.

<Examples> Hereinafter, preferred examples of the present invention will be described in detail with reference to the drawings.

In FIG. 1 showing an embodiment of the present invention, an image signal output from an image sensor 1 is input to a rate-of-change detecting circuit 2 composed of a differentiating circuit to be differentiated. A rate of change signal corresponding to the rate is output. The character area discrimination circuit 3 extracts the character information area of the image signal depending on whether or not the amplitude of the change rate signal is equal to or higher than a certain level. Two comparators CP1 and CP2 for detection,
The voltage of the reference power source + B, -B is divided to divide each comparator CP1,
It is composed of resistors R1 to R4 for setting the reference voltage of CP2.

Since the character area detection signal from the character area determination circuit 3 is the detection signal of the edge of the character area, the signal holding circuit 4
The size of the characters is taken into consideration for holding for a certain period of time, and the signal is kept for a predetermined number of pulses based on the sampling pulse input from the control unit (not shown) to the sampling pulse input terminal 5. Hold. It is composed of a counter 4A for counting sampling pulses and a D flip-flop 4B.

The dither method slice level producing circuit 6 and the fixed slice level producing circuit 7 respectively output the well-known dither method slice level and fixed slice level, and both slice levels are selectively switched by the slice level switching circuit 8. . This slice level switching circuit 8 is
The first analog switch SW1 which is turned on through the inverter by the output low level of the signal holding circuit 4 and allows the passage of the dither method slice level, and the high analog output SW1 which is turned on by the output high level of the signal holding circuit 4 is fixed slice level. Second analog switch SW that allows passage of
2 and. The slice level from the slice level switching circuit 8 and the image signal from the image sensor 1 are compared by a comparator 9 to convert the image signal into a binarized signal.

Next, the operation of the above embodiment will be described with reference to FIGS. 2 and 3.

FIG. 2 (a) shows an image signal output from the image sensor 1. T1, T2 and T3 are picture information areas, and t1 and t2 are character information areas. As is clear from the figure, since character information is usually represented in black and white, it becomes an image signal with a sharp waveform change, whereas picture information is generally expressed in gradation, so it is an image signal with a smooth waveform change. Become. Therefore, when the change rate of the waveform of the image signal is obtained, it is possible to distinguish between the character information area and the picture information area.

Therefore, when the image signal is differentiated by the change rate detection circuit 2, the differential waveform output from the change rate detection circuit 2 is shown in FIG.
The change rate signal of the image signal as shown in (b) is obtained.
The amplitude is larger than the constant level on the positive and negative sides indicated by the dotted line. That is, in the character information area of the image signal, a change rate signal having a certain amplitude or more is obtained due to a large change. Therefore, in the character area discrimination circuit 3, the reference voltages of the comparators CP1 and CP2 are set to the predetermined levels on the positive side and the-side indicated by the one-dot chain line and the two-dot chain line in FIG. 2 (b), respectively. From the character area discrimination circuit 3,
A character area detection signal indicating an edge of character information as shown in FIG. 2 (c) is output. It should be noted that the + side of the character information shown in FIG. 2 (b) is a change from black to white, and the-side is a change from white to black. Both of these detection signals cause a black character on a white background and a white character on a black background. Both cases are detected, and the character area discrimination circuit 3 outputs a mixture of both detection signals. Since the character area detection signal output from the character area determination circuit 3 is a signal indicating the edge of the character information as described above, this signal is kept constant in the signal holding circuit 4 as shown in FIG. 2 (d). The time A is held and converted into a pulse signal having a predetermined pulse width. Therefore, the high level of the output signal of the signal holding circuit 4 is the character information area, and the other low levels are the picture information area.

The slice level switching circuit 8 is generated by the output pulse of the signal holding circuit 4 separated into the character information area and the picture information area.
The slice level for binarization is switched via. FIG. 3 (a) shows the slice level used in the known dither method. In this embodiment, the slice level is changed from 4 →
It is shown that the gradation is changed to 2 → 3 → 1 to express halftone. However, 4 is white, 3 is light gray, 2 is intermediate gray, and 1 is dark gray. On the other hand, the fixed slice level producing circuit 7 outputs two fixed slice levels in the middle of white and black. Then, when the signal holding circuit 4 outputs a pulse signal designating the character information area as shown in FIG. 3 (b) similar to that shown in FIG.
As shown in FIG. 3C, the second analog switch SW2 is turned on by this pulse signal, the fixed slice level is input to the comparator 9, and the signal holding circuit 4
When the output signal of is low level, this is the inverter IN
Inverted by V, the first analog switch SW1 is turned on, the dither method slice level is input to the comparator 9, the character information is compared with the dither method slice level, and the picture information is compared with the dither method slice level. Image signal is 2
Valued. Incidentally, FIG. 3 (d) shows a sampling pulse, and this one pulse corresponds to one pixel, and the above-mentioned dither method slice level is also produced based on this sampling pulse.

<Effects of the Invention> As described above, according to the image reading apparatus of the present invention, the image signal is differentiated in an analog manner, the amplitude level of the change rate signal obtained by this differentiation is compared with the set value, and the amplitude thereof is compared. When the level is equal to or higher than the set value, the image signal is binarized based on the fixed slice level, and when the amplitude level is equal to or lower than the set value, the image signal is binarized based on the dither method slice level. Since the image information is printed, for example, when printing the image information, the picture information can be printed in gradation display, and the character information can be printed clearly.

Further, according to the present invention, basically, the pixel type (character information or picture information) is judged by processing the image signal in an analog manner, so that the circuit configuration is extremely simple, and it is described above at a low cost. The effect can be achieved.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a timing chart of means for separating a character information area and a picture information area in FIG. 1, and FIG. 3 is a slice level of FIG. It is a timing chart of the means for switching and setting. 2 ... Change rate detection circuit 3 ... Character area discrimination circuit 4 ... Signal holding circuit 6 ... Dither method slice level preparation circuit 7 ... Fixed slice level preparation circuit 8 ... Slice level switching circuit 9 ... Comparator

Claims (1)

[Claims] 1. A differentiating circuit for differentiating an image signal obtained by photoelectric conversion from an original image to be read, and the positive and negative levels of the amplitude of the change rate signal after the differentiating are respectively compared with set values, and the levels are compared. Is a set value or more, two comparators that output a signal, and a holding circuit that holds the output signal of each comparator for a certain period of time to generate a pulse signal of a predetermined width,
A switching circuit that selects either one of the fixed slice level and the dither method slice level according to the presence or absence of the generation of the pulse signal, and the slice level selected by this circuit and the above image signal are compared. An image reading apparatus including a converter for converting a binary signal into a binary signal.