JPS5875376A - Picture reader - Google Patents

Abstract

PURPOSE:To regenerate pictures including half tones, by setting plural reference voltages for detection of the densities of pictures and switching the reference voltages for each scanning line to obtain a binary picture output. CONSTITUTION:A reference voltage generating circuit 13 for the reference voltage VTH2 is set in parallel to a reference voltage generating circuit 12 for the reference voltage VTH1. The outputs of these two circuits are fed to binary coding circuits 14 and 22 along with the output of a photoelectric converting circuit 10. The outputs of the circuits 14 and 22 are fed to a multiplexer 24. The voltages VTH1 and VTH2 are delivered to the multiplexer 24 when the output of a binary counter 26 is set at a high level and a low level respectively. In such constitution of circuit, the binary picture signals binary coded by the VTH1 and VTH2 respectively are delivered alternately every time when the reading start signals of a line are supplied.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image reading device, and more particularly to an image reading device capable of scanning an image including halftones for each main scanning line to obtain a binary image output. It is something.

A conventional image reading device will be explained below with reference to FIGS. 1 to 3.

The first position is the image data to be read by the image reading device, and the hatched portion is the 1st-foottone portion. FIG. 1B shows an output voltage waveform when an image as shown in the first image is read by a conventional image reading device and photoelectrically converted.

) in Figure 1 corresponds to the first rotation, and the white part of the uniform has a high reflectance, so an output of about 1 volt is obtained, and conversely, the black part has an output of 0.1 volt. voltage can be obtained in both directions. On the other hand, it is assumed that approximately 0.5 volts can be obtained from the 8-ftone portion. For these output voltages, conventional reading and decoding devices perform binarization using one reference voltage VTH as shown in FIG. 1 (Bl). In the case shown in FIG. 1 (B), Since this reference voltage VTR is smaller than the output voltage of the halftone part, the white level is output as the binary image output.As a result, the binary image output from the conventional reading device When an image is recorded using this method, the halftone portion is recorded as white, as shown in FIG. 1(C), and is not reproduced as a halftone.

By the way, FIG. 2 is a block circuit diagram of a conventional image reading device. In the figure, reference numeral 10 indicates a photoelectric conversion circuit, which is a block composed of, for example, a CCD, and includes a drive circuit and a pulse generator for driving the CCD. , and a differential amplifier for converting the output of the CCD to an appropriate level. The photoelectric conversion circuit 10 receives optical information indicated by reference numeral 1 based on reflected light from a document, and a reading start signal 2 for each scanning line. An output 11 from the photoelectric conversion circuit 10 is input to a reference voltage generation circuit 12 and a binarization circuit 14 composed of a comparator and the like.

The reference voltage generation circuit 12 generates an appropriate reference voltage (2) from the output 11 from the photoelectric conversion circuit 10. It has the function of generating H. Conventionally, as a method of generating this reference voltage, for example, image reading output 11 of multiple scanning lines has been used.
Find the average value of the image reading output 11 for multiple scanning lines, calculate the proportional value from this average value (method of generating the reference voltage from two points, and calculate the peak value in the image reading output 11 for multiple scanning lines, and calculate the peak value from this peak value. Two methods are used: one method generates the reference voltage VTH by proportional calculation.

On the other hand, the binarization circuit 14 compares the output from the photoelectric conversion circuit 10 and the reference voltage VTH, and generates a binarized image signal 1.
Outputs 5. That is, if the output value of the output signal 11 from the photoelectric conversion circuit 10 is larger than the reference voltage VTH, a high level is output as the binary image signal 15, and if not, a low level is output.

FIG. 3 is a time chart for driving the image reading device shown in FIG. 2, and the third prisoner is a one-line reading start signal indicated by reference numeral 2 in FIG. 2, which is input externally for each scanning line. be done. Further, FIG. 3(B) shows a binary image signal output from the binarization circuit 14, which is an output signal obtained when the original shown in FIG. 1(A) is scanned.

By the way, normally, in addition to the circuit shown in FIG. 2, a mechanism is required to move the document by one scanning line when the image reading of one scanning line is completed, but this is not directly related to the present invention. Since there is no such circuit, that circuit is omitted.

In this way, the conventional image reading apparatus has the disadvantage that it cannot satisfactorily reproduce halftone image signals.

The present invention has been made in order to eliminate the above-mentioned conventional drawbacks, and an object of the present invention is to provide an image reading device with a simple structure that can reliably reproduce even a 1-ftone. .

In order to achieve the above object, in the present invention, a plurality of reference voltages are set for identifying the shading of an image, and these reference voltages are switched every scan to repeatedly select and use them. ＼-We adopted a configuration that can reliably read and reproduce even foottones.

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

4 to 6 illustrate an embodiment of the present invention,
In each figure, the same or corresponding parts as in FIGS. 1 to 3 are denoted by the same reference numerals, and the explanation thereof will be omitted.

In this example, as shown in FIG. 4 CB) (=, 2
Set the different reference voltages VTHI and Vtua, and set the Vt
H+) Vryz. Furthermore, in the case of an image containing halftones as shown in Figure 1 (8), an output of 1 volt is obtained for the white part of the document, an output of 0.5 volts for the halftone part, and an output of 0.05 volts for the halftone part, and an output of 0.5 volts for the halftone part. 0.2 for parts
Assume that an output voltage of volts is obtained.

Two types of reference voltages VTHI and V7H shown in Figure 4(B)
2 is switched and used repeatedly for each scanning line to detect light and shade.

Figure 4(C) shows the reference voltage VT)I shown in Figure 4(B).
A binary image signal as a result of binarizing an image including halftones is shown by I. 4) shows an image signal that has been binarized using the reference voltage V7H1. As is clear from Fig. 4 fcl, (D), when the reference voltage vTH1 is used, the halftone part is detected as black, and when V7Hz is used, the halftone part is detected as white. I understand.

By using the reference voltages VTHI and VTH2 and switching them for each scanning line in this manner, it is possible to reproduce even the eight-tone portion as shown in FIG. 4(E). That is, as shown in the enlarged view in FIG. 4 (F'), the halftone part is divided into VTHI and VTHI
Since the reference voltage is switched alternately for each scanning line, the halftone part is expressed every other scanning line (: the image output as black is obtained, and the black part is expressed by all scanning lines. Note: Image output as two points can be obtained, and halftone parts can be reliably reproduced.

FIG. 5 shows a block circuit diagram for performing image reading control as described above, and FIG. 6 shows its timing chart.

As is clear from FIG. 5, in this embodiment, the reference voltage generation circuit 12 that generates the reference voltage VTHI mentioned above is used.
A reference voltage generation circuit 13 for generating another reference voltage vTH2 is provided in parallel with the photoelectric conversion circuit 10. The analog multiplexer 24 outputs the reference voltage V7Ht when the output from the binary counter 26 (to be described later) is at the 71 level, and outputs the reference voltage VTH2 when the output from the binary counter 26 is at the low pull.

On the other hand, the reference numeral 26 is a binary counter, and the circuit is set so that the output is inverted every time the scan start signal for the previous line is input.

By the way, Figure 6) to (E) show the output waveforms and their timings oscillated from each of the circuits shown in Figure 5, and they are shown on the right side of the symbols (3) to (E). Certain numbers indicate the respective circuits shown in FIG. 5 or their output signals.

With the circuit configuration shown in FIG. 5, when a one-line reading start signal is generated as shown in FIG. 6, the output of the binary counter 26 is at a high level as shown in FIG. 6(B). Therefore, one line of image information is output, and outputs from the binarization circuits 14 and 22 are generated as shown in FIG. 6 (DJ, (E)). Since the output of the counter 26 is at a high level, the output 15 from the binarization circuit 14 is selected and outputted to the output 24a of the multiplexer 24. When the reading of one line is completed, the original is divided by one sub-scanning line. After the movement, the one-line reading start signal 2 is generated again, and the output of the binary counter 26 is inverted and becomes a low level as shown by ■ in FIG.

The analog multiplexer 24 is connected to the binarization circuit 22.
Select and output the output. Thereafter, in the same way, every time the reading start signal for one line is input (two reference voltages vTH1
Binary image signals binarized with and vTH8 are output alternately.

By the way, in the above embodiment, two reference signals vTH
! and V7Hz are used, but the present invention is not limited thereto, and it goes without saying that a plurality of types of reference signals may be used.

FIG. 7 explains another embodiment which is a modification of the circuit shown in FIG.
If TH11Vy+u is selected, the number of binarization circuits required in the embodiment shown in the fifth diagram can be reduced to one, whereas two are required in the embodiment shown in FIG.

Even if such a structure is employed, the same effects as those of the above-mentioned embodiments can be obtained.

By the way, the above-mentioned image reading device may be used, for example, in a reading circuit on the sending side of a digital facsimile, but in this case, the receiver does not need a means to record a halftone image, and the transmitter Since there is no need to specially encode halftone information on the side,
Conventionally used encoding methods, such as CCITT
■Recommendation.

(2) There is an advantage that halftone images can be transmitted electronically using codes and the like as they are.

As is clear from the above description, according to the present invention, in order to detect the shading of an image, a plurality of ζ reference voltages are set,
Since this reference voltage value is switched for each scanning line to obtain a binary image output, it has the excellent effect of being able to reproduce images including halftones.

Furthermore, the structure is extremely simple and easy to manufacture, and an inexpensive image reading device capable of outputting a binary image containing halftone information can be provided.

[Brief explanation of drawings]

1 to 3 explain conventional image reading devices, and the first device is an explanatory diagram of an image to be read, and FIG.
) is a diagram showing the relationship between the output of the photoelectric conversion circuit and the reference voltage value, FIG. 1(C) is an explanatory diagram of a recorded image obtained by the conventional device, FIG. 2 is a block circuit diagram of the conventional device, Figures 3 (A) and (B) are timing charts of the conventional device,
4 to 6 illustrate an embodiment of the present invention,
Figure 4 (8) is an explanatory diagram of the image to be read, Figure 4 (B
) is a diagram explaining the relationship between the output of the photoelectric conversion circuit and two types of reference voltage values, FIG. 4(C) is a diagram of the output signal binarized by the reference voltage of VTHs, and FIG. DJ is a diagram of a signal binarized by the reference voltage VtH, Figure 4 @) is an explanatory diagram of a recorded image, Figure 4 F) is an enlarged diagram of a recorded image, and Figure 5 is a block circuit of a reading device. 6) to (E) illustrate the operation of the image reading apparatus according to the present invention. Reading start signal 2... Optical information input 10... Photoelectric conversion circuit 12, 20... Reference voltage generation circuit 14...Binarization circuit 24...Multiplexer 26...Binary counter Fig. 1 Fig. 2 Fig. 3 WA (A) (B) Fig. 4 Fig. 5 "-"

Claims (1)

[Claims] In an image reading device that reads a document containing grayscale information and obtains a binary image output, multiple reference voltages are set for reading the grayscale of the image, and these reference voltages are switched for each scanning line to obtain a binary image output. An image reading device characterized in that it is configured to be able to obtain a halftone image signal from a binary image signal for each scanning line.゛