JPH07312689A - Image reader - Google Patents

Abstract

PURPOSE:To provide an image reader capable of reading a halftone with high resolution. CONSTITUTION:A switch circuit 24 switches a first contact 24a and a second contact 24b to sides (b) replying to an instruction of half-tone from a binary/ halftone switching circuit, and potential difference between a reference voltage RefH on a white level side and a reference voltage RefL on a black level side to be applied to an analog/digital converter 16 can be narrowed. In this way, since the analog/digital converter 16 quantizes a picture signal between narrowed reference voltage RefH on the white level side and reference voltage RefL on the black level side, the halftone can be quantized with high resolution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus for reading an image of a document in a facsimile machine or the like.

[0002]

2. Description of the Related Art Image reading devices such as facsimile machines
In order to send an image with two types of data, white or black, to the destination facsimile machine, an image scanner reads a halftone image with light and shade, obtains a voltage value according to the density of the image, and outputs it as an analog signal. / The digital signal is converted by the digital converter, and the ratio of white and black in the image is determined by the dither circuit or the error diffusion circuit based on the digital signal to transmit the halftone (gray) image. Is going.

FIG. 9 shows a mode of quantization by a conventional analog / digital converter. In the figure, a line W indicates a voltage value serving as a white reference, and a line B indicates a voltage value serving as a black reference. Further, the shaded portion G indicates a halftone, that is, a voltage value when gray is read by the image scanner. The analog-to-digital converter, for example, outputs a picture signal input between the applied white reference voltage Vref H and the black reference voltage Vref L as shown on the right side of the figure, and has, for example, 16 levels according to the voltage value. Quantize into.

When an instruction for intermediate processing is issued to read a photograph or the like, the dither circuit can thin the white portion of the original paper sheet by a slight stain, although 16 steps of quantization are possible. The voltage value lower than the line W, which is the voltage value serving as the reference value of white described above, is set to be processed as white so as not to be processed as gray. For example, the level 14 obtained by quantizing the voltage value P1 lower than the line W is processed as white. Similarly, the dither circuit sets a voltage value higher than that of the black line B, which is a reference voltage value of black, for example, a voltage value P2 so as not to process black such as characters printed on the document sheet as dark gray. Quantized level 3 is treated as black. Then, the shaded portion G is processed from light gray to dark gray based on the quantized level.

[0005]

That is, in the conventional image reading apparatus, only a part of the quantization level is used when quantizing the halftone. That is, as shown in FIG. 9, the analog / digital converter can quantize 16 levels, while the halftone voltage value is substantially between 10 levels from level 4 to level 13. Only quantized. For this reason, the resolution of the halftone is lowered, and a smooth halftone image cannot be obtained when reading a photograph or the like.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an image reading apparatus capable of reading halftone with high resolution.

[0007]

To achieve the above object, the image reading apparatus of the present invention is, in the first aspect, a white level side reference voltage applied with an image signal obtained by reading an original. And the reference voltage on the black level side, and an analog / digital converter for quantizing, a halftone instructing means for instructing a halftone, and the analog / digital converter for reference voltage on the white level side and black level side. And a halftone processing unit that stochastically determines white and black of the image signal for halftone reproduction based on the output from the analog / digital converter. In response to the halftone instruction by the halftone instructing means, the voltage applying means narrows the potential difference between the white level side reference voltage and the black level side reference voltage. It is characterized in.

In order to achieve the above object, the image reading apparatus of the present invention is, in a second aspect, an amplifying means for amplifying an image signal obtained by reading an original, and adjusting a bias and an amplification factor. A possible amplification means, an analog / digital converter for quantizing the image signal between the applied white level side reference voltage and the black level side reference voltage, and a halftone instructing means for instructing an intermediate tone. A halftone processing unit that stochastically determines white and black of the image signal for halftone reproduction based on the output from the analog / digital converter, Accordingly, the amplifying means lowers the bias of the image signal and increases the amplification factor.

[0009]

In the image reading apparatus constructed as described above, in the first mode, the white level applied to the analog / digital converter by the voltage applying means in response to the halftone instruction by the halftone instructing means. The potential difference between the side reference voltage and the black level side reference voltage is narrowed. As a result, the analog / digital converter quantizes the image signal between the narrowed reference voltage on the white level side and the reference voltage on the black level side, so that the halftone can be quantized with high resolution.

In the image reading apparatus configured as described above, in the second aspect, the amplifying means lowers the bias of the image signal and increases the amplification rate in response to the halftone instruction by the halftone instructing means. Then, the potential difference in the halftone is enlarged. This allows the analog / digital converter to
Since the image signal expanded between the reference voltage on the white level side and the reference voltage on the black level side is quantized, the halftone can be quantized with high resolution.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the electrical configuration of an image reading apparatus according to the first embodiment of the present invention. The control device 10 of the image reading device controls the CCD 12, the amplifier 14, and the image signal correction circuit 20. CCD12 is A4
The control device 10 is composed of a one-dimensional CCD having 1728 reading pixels corresponding to one line of a document of a size.
The original is read by photoelectrically converting it in pixel units in the main scanning direction. The CCD 12 generates a high value voltage corresponding to the brightness of the original. That is, a high voltage is generated when white is read on the original, a low voltage is generated when black is read, and a voltage corresponding to the brightness of the gray is generated when an intermediate gray is read. Occur. The amplifier 14 amplifies the potential generated in the CCD 12 and applies it to the analog / digital converter 16.

On the other hand, the analog / digital converter 16
, A potential obtained by dividing the power supply voltage Vcc by the resistors R1, R2, R3, R4 is applied as a white reference voltage RefH and a black reference voltage RefL by the switch circuit 24. The analog / digital converter 16 quantizes the potential of the image signal applied from the amplifier 14 into 64 levels between the white reference voltage RefH and the black reference voltage RefL, and quantizes it through a 4-bit bus line 17. It is sent to the image signal correction circuit 20. The image signal correction circuit 20
The quantized image signal is corrected based on the correction value held in the RAM 18 and output to the dither circuit 22 side.

The dither circuit 22 determines white or black of the image signal according to the level of the image signal. Ie the highest level 6
4 is determined as white for the picture signal, conversely black is determined for the lowest level 1 picture signal, and level 2 is determined.
For .about.63 (halftone), white and black in the image are stochastically determined for halftone reproduction according to the level. At this time, the ratio of white and black in the 5 mm square matrix of 4 pixels × 4 pixels shown in FIG. 4 is determined. That is, when a gray color close to white is read and the level of the image signal is high, the first line L1 is entirely white and only the third pixel of the second line L2 is black as in the matrix M1, and the third, By making the fourth lines L3 and L4 white, the ratio of determining the image signal as white is increased and the matrix M1 is expressed as light gray. On the other hand, when a gray color close to black is read out and the level of the image signal is low, the matrix M2 is increased by increasing the ratio of judging the image signal as black as in the matrix M2.
1 is represented as dark gray.

On the other hand, the binary image circuit 21 sets a threshold value for one line to determine white or black when transmitting character information or the like printed on a normal document or the like. The binary / halftone switching circuit 26 is selected on the binary side when the operator sends character information printed on a normal document or the like, and on the other hand, on the halftone side when sending a photograph or the like. When the above-mentioned halftone side is selected, the halftone signal is output to the switch circuits 24 and 23. When the halftone signal is input, the switch circuit 24 receives the first contact 24a and the second contact 24 of the switch circuit 24.
Switch b to b. As a result, the relatively low potential obtained by dividing the power supply voltage Vcc by the resistors R1 and R2 is applied to the analog / digital converter 16 as the white reference voltage R.
It is applied as efH. Further, the power supply voltage Vcc is a resistor R
The relatively high potential divided by 4 is applied to the analog / digital converter 16 as the black reference voltage RefL. At the same time, the switch circuit 23 operates as the dither circuit 2
Switch from 2 to output the image signal to the outside. When the binary side is selected, that is, when the halftone signal is not output, the switch circuit 24 keeps the first contact point 24a and the second contact point 24b on the a side. As a result, the power supply voltage V
A relatively high potential obtained by dividing cc by the resistor R1 is applied to the analog / digital converter 16 as a white reference voltage Ref.
H is applied, and the ground potential is applied to the analog / digital converter 16 as a black reference voltage RefL. At the same time, the switch circuit 23 changes the binary image circuit 21.
To output the image signal to the outside.

On the other hand, when the halftone signal from the binary / halftone switching circuit 26 is added, the dither circuit 22 performs binary processing by setting level 1 to black and level 64 to white, as will be described later. Dithering is performed on the halftones corresponding to the other 62 levels.

Prior to the description of the operation of this embodiment, the correction of the image signal by the image signal correction circuit 20 will be described. Figure 2
Shows the state of quantization by the analog / digital converter 16 of the present embodiment. A line W on the left side of the drawing shows a white reference potential which is a potential of an image signal for one scan for reading white for calibration provided in the facsimile apparatus. The value of the white reference potential fluctuates (fluctuates) as shown in the figure due to variations in reading by the CCD 12 and an optical system (not shown). Therefore, if dithering is performed without calibrating this fluctuation, even if gray of uniform density is read, shading occurs in gray. Therefore, in the image reading apparatus according to the present embodiment, the built-in calibration white is periodically read to obtain the image signal for one scan, and the correction value is set so that the image signal becomes a constant value. RA of the signal correction circuit 20
Hold on to M18. Then, the image signal correction circuit 20
As described above, the image signal quantized by the analog / digital converter 16 is corrected based on the correction value held in the RAM 18. Black reference potential (line B)
Is determined based on this white reference potential (line W). Also, the shaded portion G in the figure indicates the voltage value when the gray level, that is, gray is read.

Next, the operation of the image reading apparatus of this embodiment will be described. Here, first, the binary / halftone switching circuit 2 is used in order for the operator to transmit the character information and the like printed on the document.
The operation when the binary side of 6 is selected will be described with reference to FIG. When the binary side of the binary / halftone switching circuit 26 is selected, the first contact 24a and the second contact 24b of the switch circuit 24 are connected to the side a. As a result, a relatively high potential obtained by dividing the power supply voltage Vcc by the resistor R1 is applied as a white reference voltage RefH to the analog / digital converter 16, and a ground potential is supplied to the analog / digital converter 16 as a black reference voltage. It is applied as RefL. Here, as shown in FIG. 2, a white reference voltage RefH higher than the white reference potential W and a black reference voltage RefL lower than the black reference potential B are applied to the analog / digital converter 16. ing. The analog / digital converter 16
Is 6 between the white reference voltage RefH and the black reference voltage RefL as shown in the right side of FIG.
4 levels are quantized and output to the dither circuit 22 side (note that 64 levels are represented as 16 levels in FIG. 2 for convenience).

On the other hand, the binary image circuit 21 determines white or black with one threshold level. The threshold value is set to an intermediate value between them by detecting the potentials of the whitest portion and the black portion of the original document (that is, determining the whiteness / blackness of the original document) as is well known. As described above, the white reference potential RefH is increased and the black reference potential RefL is read in order to read the white and black portions of the document.
Is lowered. Thereby, the binary image circuit 21
Can eliminate halftone and perform black and white processing.

The operation when the operator selects the halftone of the binary / halftone switching circuit 26 for transmitting a photograph will be described with reference to FIG. When the binary / halftone switching circuit 26 is switched to the halftone, a halftone signal is sent from the binary / halftone switching circuit 26. In response to this, the switch circuit 24 causes the first contact 24a and the second contact 2
4b is switched to the b side. As a result, a relatively low potential obtained by dividing the power supply voltage Vcc by the resistors R1 and R2,
The white reference voltage RefH is applied to the analog / digital converter 16, and the relatively high potential obtained by dividing the power supply voltage Vcc by the resistor R4 is the black reference voltage RefL.
Is applied as. As shown in FIG. 3, a white reference voltage RefH having a voltage lower than the white reference potential W,
Black reference voltage RefL higher than the black reference potential B
Are applied to the analog / digital converter 16, and the analog / digital converter 1 is provided between the white reference voltage RefH and the black reference voltage RefL.
Reference numeral 6 quantizes each image signal voltage value to a level of 64 as shown on the right side in the figure and outputs it to the dither circuit 22 side. That is, the halftone potential is quantized with increased resolution. The voltage value P3 ′ higher than the white reference voltage RefH is quantized as the highest level level 64, and the voltage value lower than the black reference voltage RefL, for example, the voltage value P4 ′ is the lowest level level 1. Is quantized as.

On the other hand, when the binary / halftone switching circuit 26 is switched to the halftone as described above, the dither circuit 22 is operated.
Is slightly lower than the white reference voltage RefH, and in the black-and-white processing, the halftone potential P3 judged to be white.
Are treated as light gray in the midtones. Further, the halftone potential P4, which is slightly higher than the black reference voltage RefL and is judged to be black in the black-and-white processing, is processed as dark gray. Therefore, even when characters and the like are drawn in the dark gray portion, it is possible to identify them and perform dither processing.

In this halftone processing, dither processing is performed on 62 levels which are all quantization levels of the analog / digital converter except level 1 which is black and level 64 which is white. . That is, since the ratio of white and black in the 5 mm square matrix of 4 pixels × 4 pixels is determined according to the level of 62, a smooth halftone image can be obtained when reading a photograph or the like.

A second embodiment of the present invention will be described with reference to FIG. In the second embodiment, the same members as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted. In the second embodiment, the white reference voltage RefH of the analog / digital converter 16 is set.
Is supplied with the potential from the digital / analog converter 28, and the black reference voltage Ref
The potential from the digital / analog converter 30 is applied to L. The digital / analog converters 28, 30 are provided with a digital command value from the binary / halftone switching circuit 26, and a potential corresponding to the command value is applied to the analog / digital converter 46. ing.

In the first embodiment described above, the analog / digital converter 16 quantizes the halftone into 4 bits, that is, 64 steps, but in the second embodiment, the analog / digital converter 46 has 3 bits. That is, the halftone is quantized into 32 steps.

Next, the operation of the image reading apparatus of the second embodiment will be described with reference to FIG. First, the operation when the operator selects the binary side by the binary / halftone switching circuit 26 in order to transmit the character information printed on the document will be described. In the state where the binary side of the binary / halftone switching circuit 26 is selected, as shown in FIG. 6, a relatively high potential from the digital / analog converter 28 becomes white to the analog / digital converter 16. It is applied as a reference voltage RefH, and a relatively low potential is applied from the digital / analog converter 30 as a black reference voltage RefL. The analog / digital converter 46 quantizes each image signal voltage value between the white reference voltage RefH and the black reference voltage RefL into 32 levels and outputs the quantized image signal voltage value to the binary image circuit 21 side. Performs black and white processing as in the above embodiment.

The operation in the case where the operator selects the halftone by the binary / halftone switching circuit 26 for transmitting the photograph will be described. Operators who send photographs etc. are binary /
The halftone of the halftone switching circuit 26 is selected. As a result, from the binary / halftone switching circuit 26, the command value for lowering the potential of the white reference voltage RefH to the digital / analog converter 28 and the potential of the black reference voltage RefL to the digital / analog converter 30 are raised. And the command value for According to these command values, the digital / analog converter 28 lowers the potential of the white reference voltage RefH, and the digital / analog converter 30 raises the potential of the black reference voltage RefL. When selecting the halftone, the operator can adjust the potential of the white reference voltage RefH in the binary / halftone switching circuit 26. For example, the white portion of a photograph is not treated as a light gray color, so that the potential can be set to be lowered. In response to this, a command value for lowering the potential is sent from the binary / halftone switching circuit 26 to the digital / analog converter 28 side. Similarly, the operator can set, for example, to increase the black reference voltage RefL so that the black portion of the photograph is not treated as dark gray.

The analog / digital converter 16 to which the white reference voltage RefH having a relatively low voltage and the black reference potential B having a relatively high voltage are applied to the analog / digital converter 16 thus narrowed down.
With L, the voltage value of each image signal is quantized into 32 levels and output to the dither circuit 22 side. That is, the halftone potential is quantized with increased resolution. It should be noted that a voltage value higher than the white reference voltage RefH is quantized as the highest level level 32, and the black reference voltage R
Voltage values lower than efL are quantized as the lowest level, level 1.

On the other hand, when the binary / halftone switching circuit 26 is switched to the halftone as described above, the dither circuit 22 is operated.
Is slightly lower than the white reference voltage RefH, and the halftone potential which is judged to be white in the above-described binary value is processed as light gray. Also, the black reference voltage RefL
It is slightly higher than that, and the halftone potential which is judged to be black at the time of the binary value is treated as dark gray. This allows
Even when characters and the like are drawn in the dark gray portion, it is possible to identify them and perform dither processing.

In this halftone processing, dithering is performed on all 30 quantization levels of the analog / digital converter except for level 1 which is black and level 32 which is white. . That is, since the ratio of white and black is determined within a 5 mm square matrix consisting of 4 pixels × 4 pixels according to each level of 30, it is possible to obtain a smooth halftone image when reading a photograph or the like.

As described above, in the second embodiment, the operator can arbitrarily set the adjustment of the halftone reading. Also,
In the second embodiment, the analog / digital converter 46 is used.
Using a bit number lower than that of the prior art,
It is possible to achieve a halftone resolution comparable to the conventional one. That is, since it is possible to obtain a resolution similar to that of an analog / digital converter that has conventionally used 4 bits with 3 bits, it is possible to configure the analog / digital converter at low cost.

Next, a third embodiment of the present invention will be described with reference to FIGS. In this third embodiment,
The same reference numerals are used for the same members as those in the first and second embodiments, and the description thereof will be omitted. In the third embodiment, as the white reference voltage RefH applied to the analog / digital converter 16, a constant potential obtained by dividing the power supply voltage Vcc by the resistor R5 is applied, and as the black reference voltage RefL. Is configured so that the earth potential is always applied. On the other hand, the enlarging circuit 34 to which the potential obtained by reading the original document by the CCD 12 is applied
By applying the halftone signal from the halftone switching circuit 26, the bias potential and the amplification factor are changed to change the CCD 12
Amplify the potential from the analog / digital converter 16
Output to the side. The image signal quantized by the analog / digital converter 16 is corrected by the image signal correction circuit 20 to obtain 2
It is input to the value image circuit 21 or the error diffusion circuit 36.
The error diffusion circuit 36 corrects the value of the image signal by a known error diffusion process, and the corrected value is added to the binarization circuit 38 to obtain binary data of white and black. The processing in the error diffusion circuit 36 and the binarization circuit 38 is for obtaining the same value as the processing in the dither circuit 22 of the first embodiment described above, and therefore its explanation is omitted.

Next, the operation of the image reading apparatus of the third embodiment will be described with reference to FIG. Since the operation when the binary side is set in the binary / halftone switching circuit 26 is the same as that of the first embodiment described above, the halftone is set in the binary / halftone switching circuit 26 here. Only the processing in the case of being described will be described. The operator who sends the photo etc. is binary /
By selecting a halftone in the halftone switching circuit 26, the halftone signal from the binary / halftone switching circuit 26 is added to the expansion circuit 34. As a result, the expansion circuit 34
The potential from D12 is amplified by increasing the amplification factor, and the bias potential is lowered and amplified so that the amplified potential enters the black and white reference potentials W and B, and the amplified potential is output to the analog / digital converter 16 side. FIG. 8 shows a halftone G of a picture signal amplified with an increased amplification factor. As described above, the analog / digital converter 16 is applied with the white reference voltage RefH and the black reference voltage RefL, which have the same values as when the binary side is selected, and the voltage value of each image signal between them is applied. Are quantized to 64 levels and output to the image signal correction circuit 20 side. That is, since the halftone with the increased potential difference is quantized, the quantization can be performed with high resolution as in the first embodiment.

In the first and second embodiments described above, the image signal is quantized between the narrowed reference voltage on the white level side and the reference voltage on the black level side. Therefore, the halftone is quantized with high resolution. This makes it possible to obtain a smooth halftone image when reading a photograph or the like. Similarly, in the third embodiment, the enlargement circuit 34 lowers the bias of the image signal and increases the amplification factor to enlarge the potential difference in the halftone. As a result, the analog / digital converter 16 becomes
Since the image signal with the increased potential difference is quantized, the halftone can be quantized with high resolution. In addition, in the second embodiment, since it is possible to obtain, with 3 bits, the same resolution as that achieved by the conventional 4-bit analog / digital converter, it is possible to inexpensively construct the analog / digital converter. There is.

[0033]

As described above, in the image reading apparatus of the present invention, since halftone can be quantized with high resolution, a smooth halftone image can be obtained when reading a photograph or the like.
Further, if the resolution is suppressed to the same level as in the conventional case, the analog / digital converter can be constructed at low cost.

[Brief description of drawings]

FIG. 1 is a block diagram showing an electrical configuration of an image reading apparatus according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a mode of quantization of an image signal according to the first embodiment.

FIG. 3 is an explanatory diagram showing an aspect of quantization of an image signal according to the first embodiment.

FIG. 4 is an explanatory diagram showing a mode of dither processing.

FIG. 5 is a block diagram showing an electrical configuration of an image reading apparatus according to a second embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a mode of quantization of an image signal according to the second embodiment.

FIG. 7 is a block diagram showing an electrical configuration of an image reading device according to a third embodiment of the invention.

FIG. 8 is an explanatory diagram showing a mode of quantization of an image signal according to the third embodiment.

FIG. 9 is an explanatory diagram showing a mode of quantization of an image signal in the conventional technique.

[Explanation of symbols]

 10 Control Device 12 CCD 14 Amplifier 16 Analog / Digital Converter 20 Image Signal Correction Circuit 22 Dither Circuit 28 Digital / Analog Converter 34 Enlarged Circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H04N 1/40 G06F 15/68 320 A H04N 1/40 103 B

Claims (5)

[Claims] 1. An analog / digital converter for quantizing an image signal obtained by scanning an original between an applied white level side reference voltage and a black level side reference voltage, and instructing a halftone. Halftone instructing means, voltage applying means for applying the white level side reference voltage and the black level side reference voltage to the analog / digital converter, and halftone reproduction based on the output from the analog / digital converter. For halftone processing means for probabilistically determining white and black of the image signal, and in accordance with the halftone instruction by the halftone instructing means, the voltage applying means causes the reference voltage on the white level side to be set. And an image reading device characterized by narrowing a potential difference between the reference voltage on the black level side. 2. The image reading apparatus according to claim 1, wherein the voltage applying unit lowers the white level side reference voltage and raises the black level side reference voltage. 3. The image reading device according to claim 2, wherein the voltage applying unit lowers the white level side reference voltage below a white reference potential and raises the black level side reference voltage above a black reference potential. apparatus. 4. The image reading apparatus according to claim 2, wherein the voltage applying unit gradually narrows a potential difference between the white level side reference voltage and the black level side reference voltage. 5. An amplifying means for amplifying an image signal obtained by reading a document, the amplifying means having an adjustable bias and an amplification factor, and a white level side reference voltage applied with the image signal. An analog / digital converter that quantizes between the reference voltage on the black level side, a halftone indicating means that indicates a halftone, and a stochastic for reproducing a halftone based on the output from the analog / digital converter. A halftone processing means for determining white and black of the image signal, and the amplifying means lowers the bias of the image signal and increases the amplification factor in response to the halftone instruction by the halftone instructing means. An image reading device characterized by.