JPH08293973A - Image forming device - Google Patents

Abstract

PURPOSE: To automatically properly control image density. CONSTITUTION: An image signal Va read by a CCD 3 is converted into digital image data 101 by an A/D converter 5 and sent to an image processing circuit 6. Besides, a switch 11 of an ABC circuit 7 is controlled corresponding to the image data 101 and a capacitor 8 is charged and discharged so that an output Vs can be provided. A switch 12 selects either the Vs or a fixed voltage Vrt corresponding to a control signal 102 and defines it as a reference voltage Vt of the A/D converter 5. When it is detected by a sensor 14 that originals in an automatic original sender 13 are successively sent to a reading position, the switch 12 selects the Vs and controls the image density corresponding to the image data. When reading just one original, the switch 12 selects the fixed voltage Vrt and density control is performed based on this result.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine which scans and reads an original image and makes a copy recording on a recording medium.

[0002]

2. Description of the Related Art Conventionally, as a device of this kind, a linear CCD for reading an image by photoelectric conversion, and a CC
There is known a digital copying machine having an A / D converter for converting a D output into a digital signal, a moving mirror stand as a reading position moving means, and a drive motor for the moving mirror stand. In such a digital copying machine, in order to improve the reproducibility of image information, automatic density adjusting means (hereinafter referred to as A
(E) is common. The AE generally scans an original with a CCD before recording an image, detects density information of the entire image, stores the density information, and determines a correction value for the density of the recording information based on the stored information. It is configured. Therefore, when recording an image, the same original is read once again.

Further, in a digital copying machine, an automatic document feeder (hereinafter referred to as SD) for continuously feeding a plurality of originals at a speed synchronized with a reading speed in order to continuously record the originals.
Some have F). When copying a single-leaf original with a copying machine having an SDF, the operator sequentially scans the original placed at the reading position by the CCD in the main scanning direction, and at the same time the original is moved in the sub-scanning direction by the reading position moving means. By moving at a speed, the image on the entire surface of the document is read. When copying a plurality of documents, the documents are stacked on the SDF and the documents are automatically fed one by one at a constant speed. At this time, since the reading position moving means is stopped at the position where the image can be read, it becomes possible to automatically scan the images of a plurality of originals.

However, when the SDF is used, the same image cannot be read twice, so it cannot be used together with the AE described above. Therefore, in the SDF-equipped copying machine, the output of the A / D converter is fed back to control the conversion reference voltage of the A / D converter, and a circuit for improving the density information (hereinafter, ABC circuit) is provided to adjust the density. I have to. This ABC circuit operates so as to change the reference voltage in the direction of decreasing the density when the output data has a high density, and to change the reference voltage in the direction of increasing the density when the output data has a low density. In addition, feedback is applied with a constant time constant so that the average value of a plurality of output data is reflected. By performing such control, there is an effect of improving the contrast between the information such as the recorded characters and the background color, especially when the background color of the document has an intermediate density.

In some digital copying machines, the image data of the original read by the CCD is temporarily stored in the image memory. In this case, even if the SDF is used, it is possible to perform the density correction on the stored data without using the ABC circuit.

[0006]

However, in the digital copying machine equipped with the above-described conventional ABC circuit, the reference voltage of the A / D converter fluctuates due to the ABC circuit when a single-leaf original is recorded. , AE function could not be used together. Further, when the original is small, the CCD reads the portion where the original does not exist, so that the reference voltage of the A / D converter cannot be properly controlled. Furthermore, by using the ABC circuit,
In some cases, the density of fine character information recorded at a high density is reduced, and so-called character skipping occurs.

[0007]

According to a first aspect of the present invention, reading means for optically reading a document and outputting an image signal, and the image signal is converted into digital image data according to a reference voltage for conversion. A / D converter for conversion, control means for controlling the reference voltage of the A / D converter according to the image data, and the reference voltage and fixed reference voltage obtained from the control means are selectively used for the A / D converter. And a selection means to be given to the / D converter.

According to a sixth aspect of the present invention, a reading means for optically reading a document and outputting an image signal, and a first A for converting the image signal into digital image data according to a conversion reference voltage. / D converter, control means for controlling the reference voltage of the first A / D converter according to the image data, the reference voltage obtained from the control means, and a reference held during control of the reference voltage. And a selecting means for selectively supplying the voltage to the first A / D converter.

[0009]

According to the first aspect of the present invention, the density of the image to be formed is appropriately adjusted by selecting whether to control the reference voltage of the A / D converter according to the image data or to fix it. Can be adjusted.

According to the sixth aspect of the invention, the reference voltage of the A / D converter is changed according to the image data, or whether the voltage held during the change is used is selected according to the use condition. , The density of the image can be adjusted appropriately.

[0011]

1 shows the structure of an image forming apparatus according to a first embodiment of the present invention. In FIG. 1, 1 is a fluorescent lamp for illuminating an original, 2 is a moving mirror, 3 is a CCD for reading the original,
Reference numeral 4 is a drive processing circuit for driving the CCD 3 and processing the CCD output signal, 5 is an A / D converter for converting the CCD output signal into a digital signal, and 6 is an image processing circuit for processing the digitally converted image data 101. is there. 7 is the output 101 (image signal 101) of the A / D converter 5
ABC that variably outputs the analog output voltage Vs according to
Circuit.

In the ABC circuit 7, 8 is a capacitor,
9 is a resistor for charging the capacitor 8 and 10 is a capacitor 8
And 11 is a switch (SW) for selectively connecting the resistors 9 and 10 to the capacitor 8. This SW1
1 is image data 1 converted by the A / D converter 5
The charging resistor 9 is selected when the value of 01 is maximum, and the discharging resistor 10 is selected when the value of 01 is lower than the maximum value. 12 is the output Vs of the ABC circuit 7 and the fixed voltage Vr.
SW for switching between t and t and inputting it as the reference voltage Vt to the A / D converter 5 is switched by the control signal 102 from the image processing circuit 6. Reference numeral 13 is an automatic document feeder (hereinafter referred to as SDF) which can be opened and closed, and 14 is an SDF.
A document detecting sensor provided at the document feeding port 13 and a document table 15 are provided.

FIG. 2 shows the output Vs of the A / D converter 5.
And the reference voltage Vt (Vs or V
It is a graph which shows a time-dependent change of rt). Va is an analog image signal obtained by sampling and holding the output signal of the CCD 3 at the time of scanning the original by the processing circuit 4, that is, A / D.
It is an input voltage of the converter 5.

Prior to a description of the entire operation, first, A
The operation of the BC circuit 7 will be described with reference to FIGS. SW
It is assumed that 11 is switched to the Vs side by the control signal 102, that is, to the side that enables the ABC circuit 7.
When the document is on the mounting table 15, the movable mirror table 2 and the fluorescent lamp 1 scan in the F direction to project the document image on the CCD 3. The CCD 3 is driven by the drive signal from the drive processing circuit 4, reads the projected image, and sequentially performs photoelectric conversion. The photoelectrically converted image signal is processed by the drive processing circuit 4 to become an analog image signal, that is, a voltage Va. As a result, according to the change in the density of the document, for example, as shown by Va in FIG.
The input to the / D converter 5 fluctuates. Here, the higher the voltage value of Va, the higher the brightness (low density), and the lower the voltage value of Va, the lower the brightness (high density). Further, the output 101 of the A / D converter 5 is closer to the maximum value as the voltage value is higher,
The lower the value, the closer to the minimum value.

In the area 201 of FIG. 2, since Vs> Va,
The output 101 (image data) of the A / D converter 5 is 10
1 <maximum value, and the SW 11 connects the discharge resistor 10 to the capacitor 8 to perform the discharge operation. Therefore, the voltage Vs
Decreases with a constant time constant due to the capacitor 8 and the resistor 10, whereby the output 101 of the A / D converter 5 approaches the maximum value and is improved from high concentration to low concentration. Next, since Va> Vs in the region 202, the output 101 = maximum value, and the SW 11 connects the charging resistor 9 to the capacitor 8 to perform the charging operation.

In the region 203, Va≈Vs stabilizes and SW
11 repeats charging and discharging every minute. Further, the output 101 becomes the maximum value. Since Vs> Va again in the region 204, the discharge resistor 10 is selected, and Vs is lowered until the output 101 becomes the maximum value and becomes stable. Thus, the function of the ABC circuit 7 is to improve the skipped characters in the image in real time.

Next, the overall operation of FIG. 1 will be described with reference to the flowchart of FIG. First, when a copy button (not shown) is pressed, the image processing circuit 6 determines whether or not there is a document in the paper feed port of the SDF 13 by the document detection sensor 14 (step S301). When there is a document, SW12 is closed to Vs by the control signal 102 and Vt = Vs.
To enable the ABC circuit 7 (step S30
2).

Next, the fluorescent lamp 1 and the movable mirror 2 are moved to the reading position by the scanning driving means (not shown) (step S303). After that, the document driving unit (not shown) feeds the document at a constant speed to the reading position and CCs the document image.
The data is sequentially read by D3 (step S304). Since the ABC circuit 7 operates as described above, the output 101 from the A / D converter 5 is image data whose density is corrected.

On the other hand, when a single-sheet original is placed on the table 15 by the operator at the reading position, the original detection sensor 14 does not detect the original in step S301, and the image processing circuit 6 receives the control signal 102. The SW12 switches the reference voltage Vt to the fixed voltage Vrt side. That is, the ABC circuit 7 is invalidated (step S305). Next, in order to measure the density of the original, the fluorescent lamp 1 and the moving mirror 2 are moved by the scanning driving means, and the whole or a part of the original is sequentially read by the CCD 3 (step S306).

The image processing circuit 6 calculates an optimum density correction value based on the read document density data (step S30).
7). Next, the document is scanned again to record the document (step S308). At this time, the image processing circuit 6
The output image data 101 of the D converter 5 is corrected using the density correction value calculated in step S307. Post-processing (external transfer, laser drive, etc.) is performed using the corrected image data (step S309).

As described above, according to the first embodiment, when the document detection sensor 14 provided in the SDF 13 detects a document, a plurality of documents are copied. At this time, the ABC circuit 7 is used. The density can be adjusted by. If the document detection sensor 14 does not detect a document, it is assumed that a single-leaf document is copied.
After the BC circuit 7 is cut off, the original can be read once to obtain the correction value, the original can be read again, and the read image data can be corrected with the above-mentioned correction value. That is, the above-mentioned AE function can be activated. Therefore, SD
The F function and the AE function can be used together.

FIG. 4 shows a second embodiment of the present invention, in which components equivalent to those in FIG. 1 are designated by the same reference numerals. In FIG. 4, 401 is a fixed disk as a storage means connected to the image processing circuit 6.

Next, the operation will be described. As in the first embodiment, when a start button (not shown) is pressed and the document detecting sensor 14 detects a document, the image processing circuit 6 has a free space in the fixed disk 401 for storing at least one document information. Check whether or not. If there is a vacant space, the SW12 selects the fixed voltage Vrt side, and then the document driving means (not shown) feeds the document to the reading position, and the CCD 3 sequentially reads the document. At this time, the image processing circuit 6 stores the image data 101 sequentially sent from the A / D converter 5 in the fixed disk 401 and calculates the density correction value from this image data.

When the storage of one document data is completed, the image processing circuit 6 reads the image data from the fixed disk 401, corrects this image data with the density correction value calculated above, and the corrected image data. Is used to perform post-processing such as external transfer. If the fixed disk 401 does not have sufficient free space, the SW 12 is switched to select the output voltage Vs of the ABC circuit 7, and the real-time density correction and post-processing by the corrected data are executed.

Although the fixed disk 401 is used as the image storage means here, it goes without saying that a memory such as a RAM may be used if the speed and capacity are sufficient.

As described above, according to the second embodiment, even when there is a document in the SDF 13, the correction value can be obtained without using the ABC circuit 7 as long as the fixed disk 401 has a free space. . Moreover, the correction value can be calculated and the image data can be corrected using the correction value by reading the original once, and the processing can be performed quickly.

FIG. 5 shows a third embodiment of the present invention, in which components equivalent to those in FIGS. 1 and 2 are designated by the same reference numerals. In FIG. 5, 501 is a second A / D converter to which the fixed voltage Vrt is input as the reference voltage Vt, and the same image signal Va as that of the first A / D converter 5 is input. 502 is a charging resistor 9 and a discharging resistor 1
SW for selecting either 0 or the empty terminal NC. Fifty
Reference numeral 3 is a control signal for controlling the SW 502. Fifty
Reference numeral 4 is a reference plate having a high reflectance such that the output 505 of the second A / D converter 501 is sufficiently high, and the document is fed between the reference plate 504 and the movable mirror base 2.

FIG. 6 shows the operation modes 601, 6 of the SW 502.
It is explanatory drawing which shows 02,603. Further, FIG. 7 is an explanatory diagram regarding the output 505 of the second A / D converter 501 at the time of feeding the document. The operation of this embodiment will be described below with reference to FIGS. As in the first embodiment, the original is SDF13.
Then, the image data is sent to the reading position by the CCD 3 and sequentially photoelectrically converted to read the image information. At this time, the SW 12 selects Vs and the ABC circuit 7 is operating. At this time, the width of the reference plate 504 is W1 in FIG. 7, and the width of the document 16 is W.
If it is 2, the reference plate 504 is read at the portions T1 and T2 on both sides of W2. Therefore, the A / D converter 5
Output 101 becomes high at both ends, and as a result, the reference voltage Vs = Vt also becomes high, and it cannot be said that only the density of the image portion (W2 portion) is correctly corrected.

Therefore, the output 505 of the second A / D converter 501 is also high at both ends, so if this output 505 is higher than the set value Dsh in FIG.
Regardless of the output, the SW 502 is controlled by the control signal 503 so as to select the empty terminal NC, charging / discharging is stopped, and Vs
Is held (operation mode 601 in FIG. 6). If the output 501 is lower than Dsh as in the image portion W2, the first
The output 10 of the second A / D converter 5 as in the embodiment
1 controls the SW 502 so that density correction is performed by switching charge / discharge (operation mode 602,
603). Note that here, the second A / D converter 50
The reference voltage Vt of 1 is fixed to Vrt, but the reference plate 5
A variable voltage may be input in order to adjust the difference between the output when 04 is read and the set value Dsh.

According to the third embodiment, even if the document size is small, the ABC circuit 7 can perform appropriate density adjustment.

FIG. 8 shows a fourth embodiment of the present invention, in which the same parts as those in FIGS. 1, 4 and 5 are designated by the same reference numerals. In FIG. 8, reference numeral 801 denotes an A / D converter in which two reference voltages Vt and Vb can be externally set. Reference numeral 802 denotes a differential amplifier for detecting fluctuations, to which the fixed voltage Vrt and the output voltage Vs of the ABC circuit 7 are input. Further, the output Ve is the above A /
It is input as the reference voltage Vb of the D converter 801. The SW 803 is controlled by the control signal 804 so that Ve and GND can be selected.

Next, the operation will be described. SW12 is V
When s is the reference voltage Vt, the SW 803 is controlled so that Ve becomes the reference voltage Vb. Therefore, A / D
The input voltage Va of the converter 801 is Ve ≦ Va ≦ Vs
Is converted into 8-bit image data of 0 to 255, for example. Further, as described in the first embodiment, Vs varies according to the document density. Ve is also Ve = α (Vrt-V
s), and fluctuates with the fluctuation of Vs. Here, α is the amplification factor of the differential amplifier 802. In addition, when disabling the ABC circuit 7, SW803
Is connected to GND.

As described above, according to the fourth embodiment,
Since the density correction is performed by changing both the upper and lower reference values Vt and Vb, the density of a fine character or the like can be kept constant by the high-density reference voltage Ve (= Vb). it can.

FIG. 9 shows a fifth embodiment, which is shown in FIG.
The same parts as those in FIGS. 4, 5 and 8 are designated by the same reference numerals. In FIG. 9, reference numeral 901 denotes A at the signal input terminal.
It is a second A / D converter to which the output Vs of the BC circuit 7 is input. An A / D converter 902 converts the output data 903 from the image processing circuit 6 into an analog voltage.
This analog voltage is input as the lower reference voltage Vb of the first A / D converter 801.

Next, the operation will be described. As in the fourth embodiment, when the output Vs fluctuates by enabling the ABC circuit 7 during image reading, the output data 904 of the A / D converter 901 also fluctuates. The image processing circuit 6 outputs the output data 903 to the A / D converter 902 according to this output.
Variable. Therefore, the lower reference voltage Vb of the first A / D converter 801 fluctuates, and this A / D converter 80
The lower value in the output 101 of 1, that is, the high density is corrected. Although the lower reference voltage Vb is changed and corrected here, the image processing circuit 6 has a correction data table corresponding to the output 904 of the A / D converter 901, and the output 904 is digitally corrected. You may do it.

According to the fifth embodiment, as in the fourth embodiment, the density of fine characters can be kept constant.

[0037]

As described above, according to the first aspect of the invention, the reference voltage of the A / D converter is formed by selecting whether to control or fix the reference voltage according to the image data according to the use condition. The density of the image to be displayed can be automatically adjusted appropriately.

According to the second aspect of the present invention, when copying is performed while automatically feeding a plurality of originals by using the original feeding means, the density is adjusted using the reference voltage obtained from the control means, and the originals are fed. When a single-leaf original is copied without using any means, the density can be adjusted by using a fixed reference voltage.

According to the third aspect of the invention, the AE operation can be performed only by reading the original once.

According to the inventions of claims 4 and 9, by providing two reference voltages, it is possible to adjust the density of fine characters and the like to a constant value. According to the inventions of claims 5 and 10, it is possible to appropriately control the density of fine characters and the like.

According to the invention of claim 6, the reference voltage of the A / D converter is changed according to the image data, or whether the voltage held during the change is used is selected according to the use condition. , The density of the image can be adjusted appropriately.

According to the seventh and eighth aspects of the present invention, it is possible to perform appropriate density adjustment even when the document size is small.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment.

FIG. 2 is a graph illustrating voltage behavior of an ABC circuit.

FIG. 3 is a flowchart showing the operation of the first embodiment.

FIG. 4 is a configuration diagram showing a second embodiment.

FIG. 5 is a configuration diagram showing a third embodiment.

FIG. 6 is an explanatory diagram of an operation mode of SW502.

FIG. 7 is an explanatory diagram of an A / D converter output in the third embodiment.

FIG. 8 is a configuration diagram showing a fourth embodiment.

FIG. 9 is a configuration diagram showing a fifth embodiment.

[Explanation of symbols]

 3 CCD 5 A / D converter 6 Image processing circuit 7 ABC circuit 11, 12 switch 13 SDF 14 Original detection sensor 401 Fixed disk 501 Second A / D converter 502 switch 801 A / D converter 802 Differential amplifier 803 switch 901 A / D converter 902 D / A converter

Front Page Continuation (72) Inventor Masahiro Kurahashi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Satoru Kanno 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Hiroaki Takeda 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Hidehiko Kinoshita 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (10)

[Claims] 1. A reading means for optically reading a document to output an image signal, an A / D converter for converting the image signal into digital image data according to a reference voltage for conversion, and the image data An image including control means for controlling the reference voltage of the A / D converter in response to the control signal, and selection means for selectively applying the reference voltage and the fixed reference voltage obtained from the control means to the A / D converter. Forming equipment. 2. A document feeding means for feeding one or more documents in sequence to a predetermined reading position, and a document detecting means for detecting the presence or absence of a document fed by the document feeding means, wherein the selection is made. The image forming apparatus according to claim 1, wherein the means performs a selection operation according to a detection result of the document detecting means. 3. A storage unit for storing the image data, a calculation unit for calculating a correction value from the image data obtained from the A / D converter, and image data read from the storage unit using the correction value. The image forming apparatus according to claim 1, further comprising a correcting unit that corrects the image. 4. The reference voltage of the A / D converter is first.
And a second reference voltage.
The image forming apparatus according to 2 or 3. 5. The image forming apparatus according to claim 4, wherein the control means controls the first and second reference voltages. 6. A reading means for optically reading a document and outputting an image signal, a first A / D converter for converting the image signal into digital image data according to a conversion reference voltage, and Control means for controlling the reference voltage of the first A / D converter according to image data, the reference voltage obtained from the control means, and the reference voltage held during control of the reference voltage are selectively selected. First A above
And an image forming apparatus provided with a selecting unit for giving to the D / D converter. 7. A reference plate having a high reflectance, which is arranged on the back surface of the original, and a reference plate detecting means for detecting that the reading means has read the reference plate, wherein the selecting means detects the reference plate. 7. The image forming apparatus according to claim 6, wherein the selecting operation is performed according to the detection result of the means. 8. The reference plate detection means is composed of a second A / D converter which receives the image signal, and the selection means has an output level of the second A / D converter exceeding a predetermined value. The image forming apparatus according to claim 7, wherein the held reference voltage is selected and applied to the first A / D converter. 9. The image forming apparatus according to claim 6, wherein the reference voltage of the first A / D converter has a first reference voltage and a second reference voltage. 10. The image forming apparatus according to claim 9, wherein the control means controls the first and second reference voltages.