JPH07212597A - Digital agc circuit for processing picture - Google Patents

Abstract

PURPOSE:To provide an inexpensive digital AGC circuit with high precision. CONSTITUTION:Before actual original picture reading, an AGC processing part 32 obtains white reference data corresponding to the pure white original picture and it is set in a register 32a. Data corresponding to white reference data set in the register 32a is generated and the generated data is set in the register 32b. Generated data is given to a D/A converting part 34, converted into analog data and, then, given to an A/D converting part 32 as a low reference voltage VrefL. In result, The max. amplitude range of analog picture data becomes almost equal to an input voltage range. Thus, an AGC processing is digitally realized so that circuit configuration is facilitated than heretofore and also fine adjustment is easily executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital AGC circuit for digitally adjusting a dynamic range of an input signal used in an image processing apparatus such as a facsimile machine or a digital copying machine.

[0002]

2. Description of the Related Art Conventionally, in an image processing apparatus such as a facsimile machine or a copying machine which optically reads and processes an image, in order to adjust the dynamic range of the read image signal, AGC (Automati
c Gain Control) processing is applied.

FIG. 6 shows an AGC for realizing AGC processing.
It is a block diagram for explaining an example of an electrical configuration of a circuit. The AGC circuit 100 includes an input interface section 102, an analog / digital conversion section (hereinafter referred to as “A / D
A conversion unit) 103 and an AGC processing unit 104. Image data output from the scanner 101 for reading an image, such as a CCD image sensor or a CIS image sensor, is given to the input interface unit 102. The input interface unit 102 performs AGC processing on the supplied image data. As a result, the dynamic range of given image data is adjusted.

After that, the image data whose dynamic range has been adjusted is given to the A / D conversion unit 103, converted into digital image data by this A / D conversion unit 103, and then the AGC processing in the input interface unit 102 is controlled. Is supplied to the AGC processing unit 104. The AGC processing in the input interface unit 102 is performed based on the gain control signal output from the AGC processing unit 104. More specifically, the input interface unit 102 includes two-stage amplification units 102a and 102b for amplifying the image data output from the scanner 101.
And a gain adjusting element 102c such as a variable resistance element for adjusting the gain of the amplification section 102a in the preceding stage, and the gain control signal is given to the gain adjusting element 102c.

When the gain control element 102c is supplied with a gain control signal, the gain control element 102c adjusts the gain of the amplification section 102a in the preceding stage according to the gain control signal.
As a result, the dynamic range of the image data output from the amplification unit 102a is adjusted. In this way, the AGC process is achieved.

[0006]

However, the above-mentioned AGC
In the circuit 100, analog elements such as the gain adjusting element 102c are indispensable, and there is a problem that the circuit configuration becomes complicated. Further, in the AGC circuit 100, since the image data read by the scanner 101 is weak, it is very difficult to finely adjust the dynamic range. Therefore, there is a problem that the density gradation is deteriorated in the subsequent image processing. On the other hand, if fine adjustment is to be realized, an expensive element is required, which causes a problem of cost increase.

Therefore, an object of the present invention is to solve the above-mentioned technical problems and to have a simple circuit configuration and high accuracy.
An object of the present invention is to provide an inexpensive digital AGC circuit that can perform processing.

[0008]

In order to achieve the above object, a digital AGC circuit according to claim 1 has an input voltage range set in advance, and optically reads an image to output analog image data. A digital AGC circuit for image processing including analog / digital conversion means for converting analog image data output from the means into digital image data, wherein the maximum amplitude range of the analog image data output from the optical reading means. And range input means for changing the effective input voltage range of the analog / digital conversion means so as to correspond to the maximum amplitude range obtained by the range calculation means. To do.

Further, in the digital AGC circuit according to the present invention, the range calculating means obtains the minimum value or the maximum value of the digital image data output from the analog / digital converting means, and the input voltage range. The changing means changes the minimum value or the maximum value of the effective input voltage range of the analog / digital converting means so as to correspond to the minimum value or the maximum value obtained by the range calculating means. To do.

[0010]

In the above structure, the analog image data outputted from the optical reading means is made to correspond to the maximum amplitude range,
The effective input voltage range of the analog / digital conversion means can be changed. For example, the minimum value or the maximum value of the effective input voltage range of the analog / digital conversion means is changed so as to correspond to the minimum value or the maximum value of the digital image data (claim 2). Therefore, it is possible to adjust so that the dynamic range of the analog image data is maximized.

As described above, since only the effective input voltage range of the analog / digital conversion means is changed in order to realize the AGC processing, the analog element such as the variable resistance element and its peripheral circuit are unnecessary. Further, since it is only necessary to change the minimum value or the maximum value of the effective input voltage range of the analog / digital converting means, the fine adjustment of the analog image data can be easily performed.

[0012]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a block diagram showing an electrical configuration of an image reading mechanism of a facsimile apparatus in which an embodiment of the present invention is incorporated. First, with reference to FIG. 1, an image reading process in this facsimile apparatus will be briefly described.

The original set on the facsimile is
It is read by the scanner 1. The scanner 1 includes an image sensor such as a CCD image sensor and a CIS image sensor for reading an image. The image sensor may be an area image sensor that reads two-dimensional data,
It may be a linear image sensor that reads line data. Usually, a line image sensor is used in order to make the device inexpensive.

Image data of a document read by the scanner 1 is given to an input interface section 2, and the input interface section 2 performs sample hold processing of signals and the like. The input interface unit 2 is composed of an analog circuit in this embodiment, and the above processing is performed in an analog manner. The image data processed by the input interface unit 2 is then supplied to the digital AGC circuit 3 to perform gain control (AGC processing) for keeping the level of the signal (image data) within a desired range, and The data is converted from an analog signal to a digital signal.

Next, the gain-controlled image data is applied to the shading correction circuit 4, where shading distortion is reduced or eliminated. The shading distortion is uneven density between pixels due to uneven lighting of a reading light source when reading a document with the scanner 1. The image data from which the shading distortion has been reduced or removed is then supplied to the area separation circuit 5. In the area separating circuit 5, whether the input image data is image data obtained by reading characters (character data), image data obtained by reading a photograph (photograph data), or printed photographs such as newspapers and magazines. It is discriminated whether or not it is the image data (halftone dot data) of the halftone dot obtained by reading the photographic image.

If the input image data includes character data, photographic data and halftone dot data, the areas of the respective data are separated. The reason why the region separation is performed according to the type of data is to perform an appropriate process suitable for the type of data in the subsequent process. On the output side of the area separation circuit 5, in order to perform different processing depending on the type of the area-separated data, the differential filter 6, the integration filter 7 and the pass-through circuit (pass through the signal without any processing). (Only circuit) 8 is connected. The character data separated into regions is given to the differential filter 6, and the contour is sharpened by the differential filter 6. The halftone dot data is given to the integration filter 7, and the data is smoothed. The data other than the character data and the halftone dot data, that is, the photographic data is given to the pass-through circuit 8 and sent as it is to the next circuit.

In this way, the image data is subjected to a predetermined process depending on the type, or a process of not performing the process. Then, these data are given to the zoom smoothing circuit 9. When enlarging or reducing an image, the zoom / smoothing circuit 9 performs the enlarging or reducing process and the process of correcting the image distortion associated therewith. If the image is not enlarged or reduced, the zoom / smoothing circuit 9 does not process the image data.

The image data that has been processed up to the zoom / smoothing circuit 9 is then processed by one of the following circuits according to the type. That is, when the image data is photographic data or halftone dot data and halftone output processing is performed, the γ correction circuit 1
It is given to 0, and the sensitivity characteristic of the data is corrected so as to match with human eyes. Further, it is given to the error diffusion circuit 11 and subjected to processing for good halftone expression.

On the other hand, when the image data is character data and is data to be binarized, the binarization circuit 1
Given to 2. The binarization circuit 12 adjusts the slice level for binarization to separate the background from the characters and line drawings. At this time, automatic density adjustment processing is also performed so that the density becomes appropriate. Then, the output of the binarization circuit 12 is given to the isolated point removal circuit 13 to remove the isolated black points, white points, etc. that appear due to noise or the like.

The data that has undergone the above processing is DMA (Dire
ct Memory Access) circuit 14 to output to a transmission circuit (not shown) or to a printing circuit.
This embodiment relates to the digital AGC circuit 3 of the image reading processing circuits described above. FIG. 2 is a diagram for explaining the configuration of the digital AGC circuit 3 according to this embodiment.

In the facsimile apparatus employing the digital AGC circuit 3 according to this embodiment, the scanner 1 is
The maximum output is obtained when a pure black original image is read, and the minimum output is obtained when a pure white original image is read. As described above with reference to FIG. 1, the scanner 1 outputs the input interface unit. Given to 2. The input interface unit 2 performs amplification processing and clamp processing in addition to the sample hold processing. The clamp processing is performed by the scanner 1 when a black original image is read.
The image data (hereinafter, referred to as "black level data") output from is always set to a constant value. In the present embodiment, the clamp processing is performed so that the black level data is always at the upper limit value of the input voltage range of the A / D conversion unit described later. The image data that has been subjected to these processes is given to the digital AGC circuit 3 as described in FIG.

The digital AGC circuit 3 includes analog / analog
Digital converter (hereinafter referred to as "A / D converter") 3
1, AGC processing unit 32, CPU 33 and digital /
An analog converter (hereinafter referred to as “D / A converter”) 34 is provided. In this embodiment, the AGC processing section 32 functions as a range calculation means. In addition, the AGC processing unit 3
2. The CPU 33 and the D / A converter 34 function as an input voltage range changing unit.

The A / D converter 31 has a resolution of n bits (for example, n = 8), and converts given image data into 2 ⁿ (for example, 256 when n = 8) digital image data. And output it. The high reference voltage V _ref H, which is the upper limit value of the input voltage range FSR of the A / D converter 31, is preset.
For example, it is fixed at 5 (V). The low reference voltage V _ref L, which is the lower limit value of the input voltage range, is set by the AGC process described later.

The digital image data output from the A / D converter 31 is an AG for performing the AGC processing described later.
It is given to the C processing unit 32. The AGC processing unit 32 has registers 32a and 32b used for AGC processing in advance. A CPU 33 for controlling the operation of the AGC processing unit 32 is connected to the AGC processing unit 32. Further, the AGC processing section 32 is connected to the A / D conversion section 31 via an analog / digital conversion section (hereinafter referred to as “D / A conversion section”) 34.

FIG. 3 is a flow chart for explaining the AGC processing in the digital AGC circuit 3. Next, the AGC process in the digital AGC circuit 3 shown in FIG. 1 will be described with reference to FIG. This AGC processing is performed before the actual reading of the original image, and is performed to adjust the dynamic range of the image data output from the scanner 1.

At step S1, AGC processing should be performed.
Registers provided in the section and AGC processing unit 32
The initial value of the data AGCDA that should be set to 32b is set.
Be done. That is, the section in which AGC processing is performed is
White reference required to create white reference data in step S2
It is set to the length in the main scanning direction for one line of plate reading.
It The initial value of the register 32b is the low value of the A / D converter 31.
-Reference voltage V _refWhen L becomes 0 (V),
For example, 00h (note that h is a hexadecimal number
No.) is set.

Data AGC set in the register 32b
DA is provided to the D / A conversion unit 34. In the D / A conversion unit 34, when the data AGCDA is supplied, the data AGCDA is converted into analog data, and the converted analog data is supplied to the A / D conversion unit 31 as the low reference voltage V _ref L. In step S2, the AGC processing unit 32 causes the white reference data AGCA.
V is created, and the created white reference data AGCAV
Are set in the register 32a. White reference data AGCA
V is digital image data corresponding to a pure white original image, and is created as follows, for example.

That is, while the light source for illuminating the original document is turned on, the white reference plate on which the white reference image corresponding to the whitest image of the original image is formed on the scanner 1 is 1 line over m lines (for example, m = 8). Have each read. At this time, the main scanning of the scanner 1 for one line is performed over the length of the AGC processing section set in step S1. Then, the minimum value of the digital image data for one line is obtained for each line, and the average value of the minimum values obtained for each line is obtained. The average value of the minimum values corresponds to the white reference data AGCAV. That is, the white reference data AGCAV corresponds to the lower limit value of the maximum amplitude range of the image data given to the A / D converter 31.

In step S3, the data AGCDA set in the register 32b is updated by the CPU 33. That is, the initial value (00h) is set in the register 32b in step S1, and this initial value is rewritten to the data AGCDA corresponding to the white reference data AGCAV. More specifically, the AGC processing unit 3
When the white reference data AGCAV is set in the register 32a in 2, the CPU 33 monitors the white reference data AGCAV set in the register 32a.
Then, the CPU 33, based on the correspondence relationship described later,
Data AGCDA corresponding to the monitored white reference data AGCAV is obtained, and the initial value set in the register 32b is rewritten to this data AGCDA.

The CPU 33 stores in advance a corresponding relational expression between the white reference data AGCAV and the data AGCDA according to the graph shown in FIG. That is, AGCDA = 0 (where 0 ≦ AG
CAV <α) AGCDA = AGCAV−α (however, AGCA
V ≧ α) is stored.

Here, -α is the white reference data AGCAV.
Is the averaged data, and the minimum value of the image data output when the original image is actually read may be slightly lower than the white reference data AGCAV. It is inserted to set it slightly lower. In step S4, the D / A conversion unit 34
At the low reference voltage V of the A / D converter 31
_ref L is set. In the D / A converter 34, when the updated data AGCDA set in the register 32b is given from the AGC processor 32, the given data A
GCDA is converted to analog data. Then, this analog data is given to the A / D conversion unit 31 as the low reference voltage V _ref L.

As described above, the low reference voltage V of the A / D converter 31 is read before the actual document image is read.
_ref L is set to a voltage corresponding to the white reference data AGCAV. Therefore, considering that the black level data is always clamped to the high reference voltage V _ref H in the input interface unit 2, the maximum amplitude range of the image data supplied to the A / D conversion unit 31 and the A / D conversion unit 31 are considered. Is almost the same as the input voltage range FSR.

This will be described more specifically with reference to FIG. FIG. 5A shows the A / D when the original image is actually read when the above AGC processing is not performed.
6 is a diagram showing a voltage waveform of image data given to a conversion unit 31. FIG. FIG. 5B is a diagram showing a voltage waveform of the image data given to the A / D converter 31 when the original image is actually read in the case of performing the AGC processing described above. In both figures, the vertical axis corresponds to the input voltage range FSR of the A / D converter 31.

As is clear from a comparison between these two figures, it is found that the maximum amplitude range of the image data and the input voltage range FSR of the A / D converter 31 become substantially the same by performing the AGC process. . That is, the dynamic range of the image data is almost maximum. In addition, as shown in steps S5 to S7, the above step S2 is performed again.
By repeating the same processing as S4, AGC processing can be performed with higher accuracy. That is, the processing of steps S5 to S7 is
You can do it as needed.

As described above, according to this embodiment, the low reference voltage V _ref L of the A / D converter 31 is set to a voltage corresponding to the white reference data AGCAV in order to realize the AGC process. Is. Therefore, the analog element and its peripheral elements are unnecessary. Therefore, the circuit configuration can be simplified as compared with the related art. Further, since the circuit configuration can be simplified, it is possible to reduce the influence of variations in each element that constitutes the digital AGC circuit.
A stable AGC process can be performed.

Further, since the AGC processing is performed digitally by using the AGC processing section 32 and the CPU 33, fine adjustment can be easily performed. For example, if the output of the A / D converter 31 is 8 bits, it can be adjusted with a resolution of 2 ⁸ (= 256). Therefore, there is no need for a component dedicated to fine adjustment. Therefore, an inexpensive AGC circuit can be provided.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. For example, in the above-described embodiment, the facsimile apparatus is described as an example, but the present invention can be applied to, for example, a copying machine or other image processing apparatus. Further, in the above embodiment, the scanner 1 has been described as having the maximum output when a black original image is read and the minimum output when a white original image is read. The minimum output may be obtained when the image is read, and the maximum output may be obtained when the white original image is read. In this case, in the AGC process, the high reference voltage V _ref H of the A / D converter 31 is set to the white reference data A.
It may be changed so as to correspond to GCAV.

In addition, various design changes can be made without changing the gist of the present invention.

[0039]

As described above, according to the present invention, in order to realize the AGC processing, the effective input voltage range of the analog / digital converting means is changed so as to correspond to the maximum amplitude range of the analog image data. Therefore, analog elements and their peripheral circuits are unnecessary. Therefore, the circuit configuration can be simplified as compared with the related art.

Further, since the influence of variations in the characteristics of each circuit element can be reduced, stable AGC processing can be realized. Furthermore, since the AGC processing is realized digitally, fine adjustment can be easily performed. Therefore, the AGC circuit can be provided at low cost.

[Brief description of drawings]

FIG. 1 is a block diagram showing an electrical configuration of an image reading mechanism of a facsimile apparatus in which an embodiment of the present invention is incorporated.

FIG. 2 is a diagram for explaining a configuration of a digital AGC circuit which constitutes a part of the facsimile device.

FIG. 3 is a flowchart for explaining AGC processing in the digital AGC circuit.

FIG. 4 is a graph showing a correspondence relationship between white reference data AGCAV and data AGCDA.

FIG. 5 is a diagram for explaining a difference in maximum amplitude range of image data.

FIG. 6 is a block diagram for explaining an example of an electrical configuration of a conventional AGC circuit.

[Explanation of symbols]

1 Scanner 2 Input Interface 3 Digital AGC Circuit 31 A / D Converter 32 AGC Processor 32a, 32b Register 33 CPU 34 D / A Converter AGCAV White Reference Data FSR Input Voltage Range _Vref L Low Reference Voltage _Vref H High Reference voltage

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Claims (2)

[Claims] 1. An analog / digital conversion means for converting analog image data output from an optical reading means for optically reading an image and outputting analog image data into a digital image data with an input voltage range set in advance. A digital AGC circuit for image processing including, corresponding to a range calculating means for obtaining a maximum amplitude range of analog image data output from the optical reading means, and a maximum amplitude range obtained by the range calculating means. As described above, the digital AGC circuit including the input voltage range changing means for changing the effective input voltage range of the analog / digital converting means. 2. The range calculating means obtains a minimum value or a maximum value of the digital image data output from the analog / digital converting means, and the input voltage range changing means obtains by the range calculating means. 2. The digital AGC circuit according to claim 1, wherein the minimum or maximum value of the effective input voltage range of the analog / digital conversion means is changed so as to correspond to the minimum or maximum value.