JP3445684B2 - Image reading device - Google Patents

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 such as a character or a figure and converting it into digital data, and more specifically, an upper reference voltage adjusting method for an A / D converting means when reading a halftone original. It is about.

[0002]

2. Description of the Related Art Conventionally, as an image reading apparatus used in a facsimile apparatus, image reading means for reading an image and outputting an analog signal of a voltage corresponding to the density of the image,
A / D converting means for converting an analog signal from the image reading means into a digital signal, and an upper reference voltage adjusting means for adjusting an upper reference voltage of the A / D converting means based on an output from the A / D converting means. , An image reading device including a light amount adjusting unit that adjusts the light amount of the light source of the image reading unit based on the output from the A / D conversion unit.

In such a conventional image reading apparatus, in order to improve gradation when adjusting the upper reference voltage when reading the halftone original, the upper side corresponding to the level of the output of the image reading means when reading the original is read. The reference voltage was reduced at a predetermined rate and used as the upper reference voltage. Specifically, the signal from the image reading means is divided by the voltage dividing circuit and input to the A / D conversion means,
In that state, the input signal is digitized by the A / D converting means, and the upper reference voltage of the A / D converting means is adjusted by the upper reference voltage adjusting means.

[0004]

However, in the conventional image reading apparatus, the voltage dividing circuit is required for adjusting the upper side reference voltage at the time of reading the halftone original, which hinders the reduction of the manufacturing cost. .

The present invention has been proposed in view of the above points, and an image reading apparatus that does not require a voltage dividing circuit for adjusting the upper reference voltage at the time of reading a halftone original and can reduce the manufacturing cost is provided. It is intended to be provided.

[0006]

In order to achieve the above object, the image reading apparatus of the invention described in claim 1 reads an image of a document and outputs an analog signal of a voltage corresponding to the density of the image. Means and a light quantity control for illuminating the original.
A light source capable integer, an image having an A / D converting means for converting the analog signal from the image reading means into a digital signal
In the reading device, the image reading means provides a predetermined reflectance.
Read the reference member, and change the A / D value at that time.
The light amount of the light source based on the output from the conversion means,
Proper light intensity for the original document with the specified reflectance
The light amount adjusting means for adjusting and the light amount adjusting means
Light amount reducing means for reducing the appropriate light amount at a predetermined ratio
And the light amount reduced by the light amount reducing means
The reference member illuminated by the light source
Read from the A / D conversion means at that time
Based on the output, the A /
Upper reference for defining the upper input limit of D conversion means
Upper reference voltage adjusting means for adjusting the reference voltage
It is equipped with .

An image reading apparatus according to a second aspect of the present invention is the image reading apparatus according to the first aspect , wherein the upper reference voltage adjusting means is provided above the A / D converting means for each halftone original. The reference voltage is adjusted.

[0008]

According to the image reading apparatus of the present invention having the above-mentioned structure, the light amount reducing means is used for adjusting the upper reference voltage for reading a halftone original.
An appropriate amount of light is reduced at a predetermined ratio with respect to an original document having a predetermined reflectance .

That is, if the light quantity of the light source is reduced by a predetermined ratio, the voltage of the signal from the image reading means is reduced by a predetermined ratio accordingly. Therefore, the same result is obtained as when the output of the image reading means is divided by the voltage dividing circuit and supplied to the A / D converting means, and if the upper reference voltage of the A / D converting means is adjusted in this state, halftone is obtained. An upper reference voltage suitable for reading a document is obtained.

Thus, without providing a voltage dividing circuit,
Since the upper reference voltage can be adjusted to a voltage suitable for reading a halftone original by simply adjusting the light amount of the light source by the existing light amount adjusting means, the manufacturing cost can be reduced.

Further, in the image reading apparatus of the invention described in claim 2, in addition to the operation of the image reading apparatus of claim 1, the upper reference voltage adjusting means is an A / D converting means for each halftone original. Adjust the upper reference voltage of.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be specifically described below with reference to the drawings.

FIG. 1 is a circuit block diagram of a facsimile apparatus equipped with an image reading apparatus according to the present invention. This facsimile apparatus includes a facsimile section 1. The facsimile unit 1 is composed of an LCD, is arranged on an operation panel (not shown) and displays 11 for various displays such as time display, and RAM 12 for storing various data.
A CPU 13 that controls the entire facsimile unit 1; a ROM 14 that stores various programs; an NCU 15 that is connected to a telephone line to control the network; EEPRO for storing a keyboard 16 for outputting, a telephone directory consisting of speed dial numbers, destination names, etc., and certain flags
M17, a gate array 18, a modem 19 that modulates a transmission signal and a demodulation of a reception signal, a DMAC 20 that directly transfers data such as the RAM 12, and a read image signal from an image sensor 21 that reads a document. An image processing IC 23 and the like are provided, and the gate array 18
A main motor 22 that feeds an original and recording paper at a predetermined pitch and a thermal recording head 24 that thermally transfers an ink ribbon onto the recording paper are connected to.

FIG. 2 is a circuit block diagram of an image reading apparatus according to the present invention. This image reading apparatus includes an image sensor 21, an A / D converter 51, and an image processing circuit 5.
2, D / A converters 53 and 54, and LED array 5
5 and. The output end of the image sensor 21 is A /
It is connected to the input end of the D converter 51, and the output end of the A / D converter 51 is connected to the input end of the image processing circuit 52. The control signal output terminal of the image processing circuit 52 is D
It is connected to the input terminals of the / A converters 53 and 54.
The output end of the D / A converter 53 is connected to the input end of the LED array 55, and the output end of the D / A converter 54 is connected to the upper reference voltage input end of the A / D converter 51. The lower reference voltage input terminal of the A / D converter 51 is grounded.

The image sensor 21 constitutes image reading means for reading an image and outputting an analog signal having a voltage corresponding to the density of the image. The A / D converter 51 constitutes A / D conversion means for converting an analog signal from the image sensor 21 into a digital signal. The image processing circuit 52 and the D / A converter 54 constitute an upper reference voltage adjusting means for adjusting the upper reference voltage of the A / D converter 51 based on the output from the A / D converter 51. Image processing circuit 52 and D / A
The converter 53 constitutes a light amount adjusting means for adjusting the light amount of the LED array 55, which is the light source of the image sensor 21, based on the output from the A / D converter 51.
The image processing circuit 52 constitutes a light amount reducing unit that controls the D / A converter 53 to reduce the light amount of the LED array 55 at a predetermined ratio. The A / D converter 51, the image processing circuit 52, and the D / A converter 54 are included in the image processing IC 23, and the D / A converter 53.
Are included in the gate array 18.

Next, the procedure of the upper reference voltage adjustment processing at the time of reading the halftone original will be described with reference to the flowchart shown in FIG. This upper reference voltage adjustment processing is performed for each halftone original.

In adjusting the upper reference voltage of the A / D converter 51 for reading a halftone original, the image processing circuit 52 first causes the D / A converter 53 to operate.
Then, predetermined initial value data is output. This initial value data is, for example, hexadecimal 0F. As a result, the D / A converter 53 supplies a predetermined voltage to the LED array 55 and the LED array 55 emits a predetermined amount of light (S
1). Next, the image processing circuit 52 causes the D / A converter 5
The predetermined initial value data is output to 4. This initial value data is, for example, hexadecimal 3F. By this, D / A
The converter 54 supplies a predetermined voltage to the upper reference voltage input terminal of the A / D converter 51 (S2).
Next, the image sensor 21 reads a reference member having a predetermined reflectance (S3). As a result, the image sensor 21
An analog signal corresponding to the reflected light amount of the reference member is output from the A / D converter 51. The analog signal is converted into a digital signal by the A / D converter 51 and supplied to the image processing circuit 52. As a result, the image processing circuit 52 causes the LED array 5
It is determined whether or not the light source light amount by 5 is appropriate (S4).

If the light amount of the light source is not appropriate (S4: N
O), the image processing circuit 52 reduces the data output to the D / A converter 53 by one step to reduce the light amount of the LED array 55 (S5), and returns to S3 to read the reference member again. If the amount of light from the light source becomes appropriate (S4: YES),
The image processing circuit 52 reduces the data output to the D / A converter 53 at a predetermined ratio (S6). That is,
The data corresponding to the amount of light determined to be appropriate in S4 is multiplied by the coefficient a. The coefficient a is a value larger than 0 and smaller than 1, and as a result, the set light amount set in S6 is S4.
The amount of light is smaller than the appropriate amount of light determined to be appropriate, and the difference between the appropriate amount of light and the set amount of light has a value proportional to the appropriate amount of light. Next, the image processing circuit 52 outputs the light amount data to the D / A converter 53 so that the light amount from the LED array 55 becomes the set light amount calculated in S6. The light amount data is converted into an analog signal by the D / A converter 53 and supplied to the LED array 55. This allows the LED
The array 55 emits light with a set light amount smaller than the appropriate light amount. Next, the image sensor 21 reads the reference member (S
7). As a result, the image sensor 21 outputs an analog signal corresponding to the amount of reflected light from the reference member, and this analog signal is converted into a digital signal by the A / D converter 51 and supplied to the image processing circuit 52. As a result, the image processing circuit 52 determines the upper reference voltage of the A / D converter 51 based on the digital signal from the A / D converter 51 (S8), and this routine ends.

Since the procedure of the determination process of the upper reference voltage in S8 is well known, the details will be omitted, but since the light quantity from the LED array 55 is a set light quantity smaller than the appropriate light quantity, A / The upper reference voltage of the D converter 51 is also determined to be low. That is, when the light amount from the LED array 55 is set to an appropriate light amount, as shown by the solid line A in FIG.
The input from the A / D converter 51 is large, and the upper reference voltage of the A / D converter 51 is also determined to be RefH1 as shown by the chain line B.
Since the light amount from the D array 55 is a set light amount smaller than the appropriate light amount, the output from the image sensor 21, that is, the input to the A / D converter 51 is small as indicated by the alternate long and short dash line C, and the upper reference voltage of the A / D converter 51 is small. Is also set as low as RefH2 as indicated by the solid line D. Since the set light amount is obtained by reducing the appropriate light amount at a constant rate, the output of the image sensor 21, that is, the signal indicated by the alternate long and short dash line C, which is the input of the A / D converter 51, is the signal indicated by the solid line A, reduced at a constant rate. A, shown by the solid line D
Upper reference voltage RefH2 of D converter 51
Also indicates the upper reference voltage RefH1 indicated by the one-dot chain line B.
Will be reduced by a fixed ratio.

Then, when the upper reference voltage adjustment processing at the time of reading the halftone original is finished and the halftone original is actually read, the image processing circuit 52 causes the D / A converter 53 to set the appropriate light amount calculated in S4. The corresponding light amount data is output, and the upper reference voltage data corresponding to the upper reference voltage determined in S8 is output to the D / A converter 54. Therefore, while the output of the image sensor 21, that is, the input of the A / D converter 51 has a waveform shown by the solid line A in FIG. 4, the upper reference voltage of the A / D converter 51 becomes RefH2 as shown by the solid line D. . That is, since the upper reference voltage is set low for the image signal and the gradation is improved,
A halftone original can be read well.

As described above, the image processing circuit 52 is used when adjusting the upper reference voltage for reading a halftone original.
As a result, the light amount of the LED array 55 is reduced at a predetermined ratio, and accordingly, the voltage of the signal from the image sensor 21 is reduced and the input and output of the A / D converter 51 are also reduced. Therefore, the same result as that when the output of the image sensor 21 is divided by the voltage dividing circuit and supplied to the A / D converter 51 is obtained, and if the upper reference voltage of the A / D converter 51 is adjusted in this state, halftone is obtained. An upper reference voltage RefH2 suitable for reading a document is obtained. That is, the upper side reference voltage of the A / D converter 51 is adjusted to a voltage RefH2 suitable for reading a halftone original by simply adjusting the light amount of the LED array 55 by the existing image processing circuit 52 without providing a voltage dividing circuit.
Therefore, the manufacturing cost can be reduced.

[0022]

As described above, according to the image reading apparatus of the first aspect of the present invention, the light quantity of the light source is adjusted by the existing light quantity adjusting means and light quantity reducing means without providing the voltage dividing circuit. Since the upper reference voltage can be adjusted to a voltage suitable for reading a halftone original, the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit block diagram of a facsimile apparatus including an image reading apparatus according to the present invention.

FIG. 2 is a circuit block diagram of an image reading apparatus according to the present invention.

FIG. 3 is a flowchart illustrating a procedure of an upper side reference voltage adjustment process when an image reading apparatus according to the present invention reads a halftone original.

FIG. 4 is an explanatory diagram of a relationship between an image signal and an upper reference voltage in the image reading device according to the present invention.

[Explanation of symbols]

13 CPU 21 image sensor 51 A / D converter 52 image processing circuit 53 D / A converter 54 D / A converter 55 LED array

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Claims (2)

(57) [Claims] 1. An image reading unit for reading an image of a document and outputting an analog signal having a voltage corresponding to the density of the image, a light source capable of adjusting a light amount for illuminating the document, and an analog signal from the image reading unit. In an image reading apparatus provided with A / D conversion means for converting into a digital signal, the image reading means reads a reference member having a predetermined reflectance.
The output from the A / D conversion means at that time.
Based on the light amount of the light source, the predetermined reflectance
Adjust the light intensity to the appropriate intensity for the original
And the appropriate light amount adjusted by the light amount adjusting means at a predetermined ratio.
And a light quantity reducing means for reducing the light quantity by the light quantity reducing means set by the light quantity reducing means.
The reference member illuminated by a source by the image reading means.
Read and output from the A / D conversion means at that time
The A / D conversion when scanning halftone originals based on
Upper reference for defining the upper input range of the conversion means
Image reading device comprising an upper reference voltage adjusting means for adjusting the scan voltage, further comprising a. 2. The upper reference voltage adjusting means,
2. The configuration in which the upper reference voltage of the A / D conversion means is adjusted for each halftone original.
The image reading apparatus described in 1.