JPH07298055A - Image forming device - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a copying apparatus capable of preventing show-through during copying of a two-sided original while suppressing deterioration of image quality as much as possible. [Structure] In the single-sided character mode, an image is formed with the correction pattern of (a). If there is a show-through image, it is included in the density range shaded in the figure. Therefore, in the case of the double-sided character mode, an appropriate one is selected from the correction patterns of (d) to form an image. At this time, an image having a density lower than a certain level (the range shown by the diagonal lines in the figure) is not formed. In the photographic mode, the image is formed with the correction pattern of (e) to form an image of high density to low density.

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 for forming an image on an original, and more particularly to an image forming apparatus which prevents show-through of a double-sided original.

[0002]

2. Description of the Related Art In recent years, most of general publications such as books and magazines are double-sided printing in which printing is performed on both front and back sides of paper. In addition, the number of copying machines or printers capable of recording on both the front and back sides of paper is increasing, and the number of documents recorded on both sides is increasing in order to reduce the amount of files in the office. Therefore, in the image forming apparatus such as a copying machine, the chances of making a copy of the double-sided printed matter or the double-sided recording document as a document are increasing.

However, when a double-sided printed matter having a relatively thin paper thickness is used as a document for copying, the image on the back side of the document may be transparent, and so-called show-through may occur to cause copying. Was causing a decline.

In order to prevent such a problem, when copying a two-sided original, the copy density is automatically lowered to perform copying as in JP-A-2-114278 and JP-A-2-156257. An image forming apparatus (copying apparatus) has been proposed that prevents the image from being captured.

[0005]

However, in such a conventional image forming apparatus, the copy density is lowered by changing the developing bias voltage during the copying operation, the exposure light amount to the original, etc. Prevents show-through. This method has a problem in that the density of the entire image to be copied is lowered, and the image density on the surface of the original document to be copied is lowered to deteriorate the image quality.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems in a conventional image forming apparatus, and to provide a copying apparatus capable of preventing show-through during copying of a double-sided original while suppressing deterioration of image quality as much as possible. .

[0007]

According to the present invention, there is provided a means for selecting a copy mode in an image forming apparatus for forming an image by performing a predetermined density correction on image information of a read original according to the present invention. A control means is provided for controlling the correction rate of the density correction according to the copy mode selected by the selection means, and when the double-sided original mode is selected by the selection means, the density level of the image in the same original is provided. The problem is solved by correcting the density reduction rate of the formed image so that it becomes different.

In order to solve the above problem, the present invention has a plurality of correction factors for the double-sided original mode,
It is proposed that the plurality of correction factors can be selected.

Further, in order to solve the above-mentioned problems, the present invention comprises a coordinate designating means for designating the coordinate of a document,
If the coordinates are designated by the coordinate designating means, the document is scanned before the document is read for image formation to detect the image density at the designated coordinate position, and the correction factor suitable for the detected density is set. We propose to select from multiple correction factors.

Further, in order to solve the above-mentioned problems, the present invention has a character mode and a photo mode, and is provided with a selecting means for selecting one of the character mode and the photo mode, and the character is selected by the selecting means. It is proposed to perform the density correction in the double-sided original mode only when the mode is selected.

[0011]

According to the copy mode selected by the copy mode selection means, the correction rate of the density correction during image formation is changed.
At that time, when the double-sided original mode is selected, the density reduction rate of the formed image is corrected so as to be different depending on the density level of the image in the same original. As a result, it is possible to form an image by reducing the image density of the unnecessary portion (show-through portion) without reducing the image density of the required portion.

Other functions will be apparent from the description of the embodiments below.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a copying apparatus which is an embodiment of the present invention. In this copying machine 1, an editor board 5 which also functions as a document pressure plate is mounted on the upper part of the apparatus main body 2. The editor board 5 is used to specify a position (coordinate input) when performing edit copy, etc., and is to specify a range by pushing the position of the document set at the reference position to be edited with the attached point pen 6. is there. An operation panel 4 is provided on the front surface of the upper cover 3 of the apparatus body 2. The operation panel 4 is provided with mode selection keys 7 and 8 as shown in FIG. The mode selection keys 7 and 8 are used to select a mode for copying a double-sided original on both sides of paper, a mode for copying a double-sided original on one side of two sheets of paper, a mode for copying a double-sided original on both sides of one sheet of paper, and the like. It is what you specify. Conventionally, these mode selection keys are mainly used for the automatic document feeder (ARD) with a reversing function.
F: Auto Reversible Document Feeder) and an automatic double-sided device for performing double-sided copying were used to specify the operation of each device, but in this embodiment, this mode selection key 7, Reference numeral 8 is used to determine the type of document. Therefore, even when the automatic double-sided device or the automatic document feeder with the reversing function and the automatic double-sided device are not mounted, the automatic double-sided device functions to specify the document. Of course, when they are mounted, the original mode designating function is also fulfilled.

Next, each part of the copying machine 1 will be described.
The main components of the copying machine body 2 are a document reading unit, an image forming unit,
Roughly divided into paper transport units. The image forming unit of the copying machine 1 is based on a conventionally well-known electrophotographic system, and the paper transporting unit is also the same as a conventionally well-known one, and therefore description thereof will be omitted.

FIG. 3 shows a schematic configuration of a document reading section of the copying machine 1. Below the contact glass 9 arranged on the upper surface of the copying machine body 2, a fluorescent lamp 10 for illuminating an original on the contact glass, first to third mirrors 11 to 13,
A first carriage 14 that movably supports the fluorescent lamp 10 and the first mirror 11, a second carriage 15 that movably supports the second and third mirrors 12 and 13, a scanner motor 16 that drives each carriage, and a condenser lens. 17 and CCD1
9 and the like are provided. Further, a reference white plate 18 for shading correction at the time of reading the original is installed on the lower surface side of the contact glass 9. In addition to the above, the document reading unit of the copying machine 1 includes an image reading plate 20, a VPU (Video Processi).
ng unit) plate 30, IPU (Image Processing Unit) plate 40, scanner motor control plate 50, and the like. CCD
Reference numeral 19 is a part of the image reading plate 20.

An original document (not shown) placed on the contact glass 9 is illuminated by a fluorescent lamp 10, and the reflected light from the original document is reflected by the first to third mirrors 11, 12, 13 and the condenser lens 17 is passed through. It passes through and enters the CCD 19. Image reading plate 2
At 0, the CCD 19 of 5000 pixels converts the incident light reflected from the document into an analog electric signal of 400 dpi (15.7 lines / mm).

FIG. 4 illustrates the function of the image reading plate 20. Since the signal output from the CCD 19 is weak, it needs to be amplified. At that time, the pixels of the CCD 19 are divided into an odd number and an even number, and each output (video signal)
Are amplified by the amplifier circuit 22. The amplified video signal is sent to the VPU board 30.

FIG. 5 illustrates the function of the VPU board 30. The video signal sent from the image reading board 20 is output to the IPU board 40 after being synthesized into a serial signal, amplified and A / D converted. That is, the analog video signal from the image reading plate 20 is combined with the serial signal by the switching element 31. A clock signal sent from the IPU board 40 is used as the combining timing at that time. The synthesized video signal is an amplifier circuit 3
It is variably amplified by 2. This variable amplification is IPU board 40
It is performed based on the AGC data sent from.
The AGC data is data for correcting the amount of light of the fluorescent lamp 10 by the amount of variation due to temperature and changes over time, based on the data when the reference white plate 18 is read during scanning of the document. The variably amplified video signal is converted into a digital signal by the A / D converter 33. The video signal is an 8-bit parallel signal in the present embodiment, which is the IPU board 4.
Output to 0.

FIG. 6 shows an outline of the structure and function of the IPU board 40. The IPU board 40 has six gate arrays GA1 to GA6 for image editing and the like.
The function of each gate array is as shown in the figure. Also,
The IPU board 40 includes a scanner motor control circuit 41 and a RAM.
42 and ROM 43 are also incorporated. An encoder 16e is connected to the scanner motor 16 and generates a pulse signal according to the rotation speed of the motor. The signal is sent to the scanner motor control circuit 41, and the control signal is output to the scanner motor control board 50 based on the signal.

FIG. 7 shows the procedure of the image editing function in the IPU board 40. As shown in this figure, VPU
After the shading correction is performed on the video signal sent from the plate 30, the main scanning scaling processing is performed by performing the processing according to the selected mode. Then, after performing gamma correction, which will be described later, to perform multi-valued signal processing or binarized signal processing, the edited video signal is output to the main control board 60.
(Shown in FIG. 8).

FIG. 8 shows the main flow of image information (video signal) in the copying machine of this embodiment. The reflected light from the document (not shown) on the contact glass 9 is CC
The video signal is inputted from D19 to the image reading board 20, and is sent to the VPU board 30 as a video signal which is photoelectrically converted and amplified. V
In the PU board 30, signal combination, variable amplification and A / D conversion are performed as described above, and the digitized video signal is output to the IPU board 40 as an 8-bit parallel signal. Then, the video signal, which has been subjected to image editing such as scaling and shading correction or gamma correction by the IPU board 40, is sent to the main control board 60 as a 4-bit parallel signal suitable for image writing. The main control board 60 controls the entire copying machine centering on a CPU (not shown). The video signal input to the main control board 60 is
The writing image data is sent to the PWM plate 70, and the laser diode 71 is driven based on the image data to form an electrostatic latent image on the photosensitive drum 75. In addition,
The laser light from the laser diode 71 is applied to the polygon mirror 73 via the cylinder lens 72. The laser light reflected by the polygon mirror 73 is irradiated onto the photoconductor drum 75 via the fθ lens 74, and the photoconductor drum 75
The surface of is exposed to create an electrostatic latent image. The formed electrostatic latent image is visualized by a known electrophotographic method.

FIG. 9 illustrates multi-valued control by the PWM board 70. PWM (Pulse Width Modulatio
n) The plate 70 has a function of generating a pulse width of laser irradiation suitable for image data. This PWM board 7
The multi-value control by 0 changes gradation of laser light per unit area and divides the potential of the portion of the photosensitive drum 75 on which the laser light is applied into 16 levels to obtain gradation. I am raising. That is, as shown in FIG. 9A, the value of the write image data is divided into 16 (4 bit data).
However, a gray color close to white (data value = 0) or a gray color close to black (data value = F) can be written.

The multi-valued image data (video signal) is sent from the main control board 60 to the PWM board 70, where the pulse width of laser irradiation for each data is determined according to the table shown in FIG. 9b. For example, gray close to white (data value = 1)
If so, the pulse width of laser irradiation is 4 ns (nanosecond:
(Nanosecond), the image density written is low. If it is black, it is as long as 54 ns, and the image density is high.
At the same time as multi-valued control, L from the main control board 60
Laser diode 71 by DB (LD bias) signal
It controls the value of the current that flows through.

Next, density correction during image formation, so-called γ
The correction will be described.

In the electrophotographic image forming process, the relationship between the original density and the formed image density (copy density) is not linear. For example, C of the document reading section
Due to the characteristics such as the sensitivity variation of each element of CD and the output of CCD itself is not perfectly linear, the document density and VPU
The output signal (image data) from the plate 30 is not linear. Therefore, it is necessary to perform density correction on the density of the read original to form an image, and the gradation of the read image data is corrected according to the gradation of the recording system. Normally, the γ correction is performed by including the gradation reproducibility and the like in the correction of the image forming density including the visual characteristics and preference of the person who views the formed image.

The correction process will be briefly described below.
The read image data is substituted into a predetermined correction function to obtain corrected image data. In general, correction data may be obtained using a preset relationship table in order to shorten the calculation time.

FIG. 10 is a graph showing the relationship between the document density and the image density, and shows a γ correction pattern.
(A) is a correction pattern in the single-sided character mode in this embodiment. The γ correction in the single-sided character mode is the same as that in the conventional image forming apparatus. In the character mode, it can be assumed that the image density in the document is high in the character portion and takes a uniformly low value in the portion other than the character if there is no image. If there is an image on the back side of the document, the density of the image on the front side (the show-through image) is relatively low and is included in the shaded area in the figure. The conventional method for preventing show-through is to reduce the entire image density (copy density) by changing the exposure light amount of the original document, the developing bias voltage, etc. so that the image in the shaded area is not formed. is there. (B) shows a case where the density of the entire copied image is reduced by the conventional method.
According to this, the show-through image having a density lower than a certain level is not copied, but the density is reduced to a necessary portion (the image of the original portion to be copied).

Therefore, in the present invention, in the case of the double-sided character mode, the density correction rate is changed to prevent show-through and maintain the image density of a necessary portion. That is, the correction function of the γ correction is changed to one suitable for the double-sided character mode, and only the image data with the density above a certain level is imaged, and the image with the density level below that is corrected so as not to be imaged. There is. The correction pattern at this time is as shown in (c). As can be seen from this graph, the image (show-through image) included in the density level shown by the dotted line in the figure is not formed, and the image density of the necessary portion is not lowered.

By the way, the degree of show-through differs depending on the paper thickness and paper type. Therefore, in this embodiment, a plurality of correction functions for γ correction in the double-sided character mode are prepared and an optimum correction function is selected from them so that show-through can be prevented in correspondence with a plurality of paper types. γ correction is performed.
(D) shows the correction pattern by the plurality of correction functions in one graph. As can be seen from this graph, P ₂ than the pattern of P _1, towards P ₃ than P ₂ is the concentration ranges not be imaged is wider. Therefore, when the sheet thickness is thin and the show-through is large, the pattern P ₃ is selected, and when the show-through is small, the pattern P ₁ is selected. The method of selecting the correction pattern will be described later. It should be noted that the number of correction patterns (the number of correction functions) is not limited to three, and can be set arbitrarily. Further, the correction function can be set so that the shape of the correction pattern is arbitrary.

In the photographic mode, since tone reproduction is more important than in the character mode, it is necessary to form an image even in a low density level range. So in the photo mode,
A correction pattern suitable for the photographic mode, that is, a correction pattern substantially linear from high density to low density as shown in (e) is used. In the case of a high-gradation original that is copied in the photo mode, paper that does not show through is often used, so there is no practical problem.

The actual operation of this embodiment will be briefly described below.

In the copying machine 1 shown in FIG. 1, the editor board 5 is mounted on the copying machine so that the rear side of the editor board 5 can be opened. Place the original on the contact glass (not shown) located below the editor board 5, and operate the operation panel 4
The start button (not shown) provided in the above is pressed. At this time, when a double-sided original is designated by the mode designation keys 7 and 8 shown in FIG. 2 and coordinate input is made from the editor board 5, a prescan is performed once before reading the original image. Then, the density data of the designated coordinate part is sampled. An optimum correction pattern is selected from FIG. 10D based on the sampling data, and image formation (copying) is performed by the image data subjected to γ correction by the optimum correction pattern. If only the double-sided original is designated but the coordinates are not designated, the prescan is not performed, the γ correction is performed by the initially set correction pattern, and the image data is formed. As the correction pattern to be initialized, the number of times each correction pattern is selected may be stored in the apparatus, and a frequently used correction pattern may be initialized when the mode is cleared. Then, when the double-sided original is not designated, that is, in the single-sided character mode or the photographic mode, FIG. 10A or FIG.
The correction pattern is selected and γ correction is performed to form an image. The operation in that case is similar to that of a general digital copying machine having a normal character mode and a photo mode.

The correction pattern selection process is shown in the flow chart of FIG. That is, it is determined whether or not the character mode is selected (step 1, hereinafter, step is abbreviated as S), and if the character mode is not selected, the correction pattern for the photo mode shown in FIG. 10E is selected. Yes (S8). When the character mode is selected, it is determined whether a double-sided original is designated (S2). Here, if the double-sided original is not designated, the correction pattern shown in FIG. 10A is selected (S7). Next, the editor board 5
It is determined whether or not there is a coordinate input from (S3). If the coordinates are not designated, the initially set pattern is selected from the correction patterns for the double-sided original shown in FIG. 10D (S6). If coordinates are designated, prescan is performed, density data is sampled (S4), and a correction pattern suitable for the density data is selected from the correction patterns shown in FIG. 10D (S5).

In the present embodiment, the γ-correction that is usually performed in a general digital copying machine can be used to effectively prevent the show-through of the double-sided original, and the correction of the image required at that time. Does not decrease.

[0036]

As described above, according to the image forming apparatus of the present invention, when the double-sided mode is designated, only image data having a density higher than a certain level is formed, and an image having a density level lower than that is formed. Is corrected so that it is not imaged, the show-through image is not imaged, and the image density of the necessary portion is not reduced.

According to the second aspect of the present invention, it is possible to more surely prevent the show-through by performing the density correction suitable for the paper type such as the paper thickness.

According to the third aspect of the present invention, the original image density of the portion designated by the coordinate designating means is detected, so that it is possible to prevent the show-through more reliably by performing the density correction suitable for the image density. Further, by directly designating the show-through portion, it is possible to further prevent the show-through.

According to the structure of claim 4, correction is performed so that an image having a density lower than a certain level is not formed only when a character mode is designated. Therefore, even in the case of an original having a high gradation such as a photograph, an appropriate image is obtained. Can be formed.

[Brief description of drawings]

FIG. 1 is a perspective view showing a copying machine according to an embodiment of the present invention.

FIG. 2 is a partial plan view showing a mode selection key provided in the copying machine.

FIG. 3 is a side view showing an outline of a document reading unit of the copying machine.

FIG. 4 is a block diagram for explaining a function of an image reading plate of a document reading unit.

FIG. 5 is a block diagram for explaining a function of a VPU plate of a document reading unit.

FIG. 6 is a block diagram showing a configuration and a functional outline of an IPU plate of a document reading unit.

FIG. 7 is a flowchart showing a procedure of an image editing function within the IPU board.

FIG. 8 is a block diagram showing a main flow of image information in this embodiment.

FIG. 9 is a diagram for explaining multi-valued control for controlling the pulse width of laser irradiation at the time of image writing in the present embodiment, and FIG. 9A is a graph showing write data divided into 16 stages. Yes, (b) is a table showing the pulse width of laser irradiation determined for each data.

10A and 10B are graphs showing a correction pattern showing the relationship between the document density and the image density, where FIG. 10A is a correction pattern in the single-sided character mode in the present embodiment, and FIG. The correction pattern when the density of the entire image is reduced, (c) the correction pattern in the double-sided character mode in this embodiment, (d) the correction pattern by a plurality of correction functions, and (e) the present embodiment. The correction patterns in the photo mode in the example are shown respectively.

FIG. 11 is a flowchart showing a correction pattern selection process in this embodiment.

[Explanation of symbols]

 1 Copying Machine 2 Copying Machine Main Body 3 Top Cover 4 Operation Panel 5 Editor Board 7, 8 Mode Selection Key 9 Contact Glass 10 Fluorescent Light 19 CCD 20 Image Reading Board 30 VPU Board 40 IPU Board 50 Scanner Motor Control Board 60 Main Control Board 70 PWM board

Claims (4)

[Claims] 1. An image forming apparatus for forming an image by performing predetermined density correction on image information of a read document, comprising means for selecting a copy mode, and the density according to the copy mode selected by the selecting means. Control means is provided for controlling to change the correction rate of the correction, and when the double-sided original mode is selected by the selecting means, the density reduction rate of the formed image is changed depending on the density level of the image in the same original. An image forming apparatus characterized by the above. 2. The image forming apparatus according to claim 1, wherein a plurality of correction factors for the double-sided original mode are provided, and the plurality of correction factors can be selected. 3. A coordinate designation means for designating a coordinate of an original, wherein when the coordinate is designated by the coordinate designating means, the original is scanned before the original is read for image formation, and the designated coordinate position is obtained. 3. The image forming apparatus according to claim 2, wherein the image density of the image is detected, and a correction rate suitable for the detected density is selected from the plurality of correction rates. 4. A double-sided original mode is provided only when a character mode and a photo mode are provided, and selection means for selecting one of the character mode and the photo mode is provided. The image forming apparatus according to claim 1, wherein density correction is performed.