JPH10145599A - Copying machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printer by which overlapped parts of images on front and rear sides of an original are printed out while reproducing a color and a density close to those of the substantial original. SOLUTION: Multiplier circuits 904-906 multiply a light transmittance ave of an original detected separately with density data (bR, bG, bB) of a 2nd side image. Thus, density data (bR', bG', bB') of an image of a 2nd side read from the 1st side are obtained. Then subtractor circuits 907-909 subtract the density data (bR', bG', bB') from the density data (bR, bG, bB) of the image of the 1st side in the same address. Thus, the adverse effect onto the 1st side image by the 2nd side image is excluded to figure out density data density data (bRo, bGo, bBo) close to the color density of the image of the substantial original thereby figuring out the original color and contrast.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying apparatus, and more particularly to a copying apparatus designed to prevent show-through copying.

[0002]

2. Description of the Related Art In a copying apparatus, when reading a double-sided document, a high-density portion in an image of a second page, which is a back side, is read together with a read image of a first page. "May be caused. This tendency is particularly large when the document is thin.

In order to avoid this phenomenon, Japanese Patent Application Laid-Open No. 7-8
Japanese Patent Application Laid-Open No. 7295 discloses a technique for performing the following processing on each pixel data read from a document stored in a memory to avoid show-through copying and improve print quality. Specifically, if the image is a single color (for example,
In the case of (monochrome), if the density of the front-side pixel is equal to or lower than a predetermined value and the density of the rear-side pixel is equal to or higher than the predetermined value, it is determined that the front-side pixel is a show-through of the rear-side pixel. , Delete the pixel data on the surface.

In the case where the image is in color, if the color density of each pixel on the front surface is equal to or less than a predetermined value and the color patterns on the front and back surfaces are the same, the pixels on the front surface show off the pixels on the back surface. Is determined, and the pixel data on the surface is deleted. In this way, the processed show-through image can be deleted, and the copy quality can be improved.

[0005]

However, according to the above-mentioned conventional technique, when the front side is a white background and the back side image is show-through, it is possible to delete the show-through back side image. When the front and back images are located at overlapping positions, the front image is inevitably affected by the overlapped back image, which impairs the original color and density of the front image.

For example, even if the original front side image is light blue and the back side image is dark red, the image portion on the front side where the back side image overlaps is affected by the dark red on the back side, and is purple. It is actually printed on paper in color. SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a copying apparatus capable of reproducing and printing colors and densities close to the original of the original in the overlapping portions of the images on the front and back surfaces of the original. It is intended to be.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention relates to a copying apparatus capable of reading a first side and a second side of an original. A density detecting means for detecting density data of an image on the second face read from the first face in an overlapping portion of the images, and a density correction for correcting the read image data on the first face with the density data detected by the density detecting means. Means for providing a copying apparatus.

Further, the density detecting means detects a density of the same color component of the first surface image and the second color image at the same position on the document, and a density detector for detecting the first surface image and the second surface image. When the densities are equal to or higher than the predetermined densities, a determination unit is provided for determining that the images overlap at the position on the document. Further, the density detecting means, when the determination unit obtains a determination result that an overlap has occurred, multiplies the density data of the second-side read image by the light transmittance of the document and obtains a multiplied value. First
The density correction unit detects the density data of the image of the second surface read from the surface direction, and the density correction unit performs an arithmetic process on the density data of the image of the first surface read using the multiplication value, thereby reading the first surface. It is characterized in that image density correction is performed.

[0009]

FIG. 1 shows a copying apparatus 1 according to the present invention.
It is a figure which shows schematic structure of. The copying apparatus 1 includes a document reading unit 100 and an image forming unit 200. The document reading unit 100 includes a document feed tray 2 serving as a mounting table for a two-sided document D, a document feed roller 3 and a document separating roller 4,
Illumination light source 5 and first surface reading CCD 6 for irradiating the first surface of double-sided document D, and illumination light source 7 and second surface reading CCD 8 for irradiating the second surface of double-sided document D
And a document discharge roller pair 9, a document discharge tray 10 for carrying out the double-sided document D after reading, and a sensor 31 for detecting the end of the document.

The image forming unit 200 includes, as an image forming system, a control unit 14 that inputs image data of the double-sided document D read by the document reading unit 100 via the image data bus 12 and drives the exposure unit 13. And a charger 16 disposed around the photosensitive drum 15, a developing device 17, a transfer separation charger 18, and a cleaner 19. Further, as a paper supply system, a paper supply unit 20 on which copy paper is arranged, a paper supply roller 21, a paper supply conveyance path 22, a timing roller pair 23, a fixing roller pair 24, a discharge roller pair 25,
And a discharge tray 26. Furthermore, the re-feed tray 2
7, a paper re-feed roller 28, a switching claw 29, and a paper feed path 30 for paper re-feed, so that the read image can be copied on both sides of the copy paper.

In the copying apparatus 1, images on the first and second sides of the double-sided document D are simultaneously read by the document reading unit 100, and the control unit 14 performs a bleed-through erasure process and a front and back surface of the document, which will be described later. After subjecting the read data to a color correction process or the like that eliminates the influence of the image data of the opposing document surface on the overlapping portion of the image, the exposure device 13 is driven to irradiate the surface of the photosensitive drum 15 with a laser beam. An electrostatic latent image is formed, and the read original image is transferred onto a copy sheet by a well-known electrostatic copying process.

In the above configuration, for example, when two double-sided originals are to be copied on both front and back sides of two copy sheets, the first original (upper surface) is placed on the original feed tray 2 in order from the bottom. Is placed on P4 and the lower surface is P3), and the second document (the upper surface is P2 and the lower surface is P1) is placed. Then, the original feed roller 3 and the original separating roller 4 cause
The document is fed out from the first document, and P4 is read by the CCD for reading the first surface, and P3 is read by the CCD for reading the second surface.
Read. Each of the image data P4 and P3 is input to the control unit 14 via the image data bus 12, and is sequentially subjected to the show-through elimination process and the color correction process for the image of the overlapping portion (these processes are performed). Will be described later).

After each of the above processes, the exposure device 13 is driven according to the image data of P4, and the surface of the photosensitive drum 15 charged to a predetermined potential by the charger 16 is irradiated with a laser beam. As a result, an electrostatic latent image corresponding to the image data of P4 is formed on the surface of the photosensitive drum 15,
The developing unit 19 visualizes the toner image to form a toner image. Then, the toner image is transferred from the paper supply unit 20 to one surface of the copy paper fed to the paper feed path 22 by the paper feed roller 21 by the transfer separation charger 18, and the fixing process is performed by the fixing roller pair 24. Is done. The copy paper after fixing is guided to the refeeding conveyance path 30 by the switching claw 29 and is once carried onto the refeeding tray 27. At this time, the copy paper is stored on the re-feed tray 27 in this state, with the upper surface serving as an image forming surface for P4.

Next, from the sheet re-feed tray 27 to the sheet feed path 2
Similarly, a toner image for P3 is formed on the remaining surface of the sheet re-fed to the second sheet, and the fixing roller pair 24
Is discharged onto a discharge tray 26 by a discharge roller pair 25. In this case, copy paper is stacked on the discharge tray 26 with the image of P3 facing up.

When the copying of the first document is completed, the second document is fed out, the image is read and the copying process is performed in the same manner as the first document, and the copy paper is placed with the P1 image on the upper surface. The paper is discharged onto the copy paper of the previous time in the discharge tray 26. FIG. 2 shows a data processing configuration for outputting image data obtained by the first surface reading CCD 6 and the second surface reading CCD 8 shown in FIG. 1 to a print head (corresponding to the exposure unit 13). It is a block diagram shown. As shown in the figure, output signals from the first surface reading CCD 6 and the second surface reading CCD 8 have been subjected to preprocessing such as pseudo-correction and A / D conversion by preprocessing circuits 201 and 202, respectively. Thereafter, each pixel is color-separated into color components of a total of 24 bits consisting of 256-bit gradation data of 8 bits each of R (red), G (green) and B (blue), and the corresponding image memory 203 and Image memory 20
4 is stored. Here, the image memory 203 stores the original page image data of the odd-numbered pages, and the image memory 204 stores the original page image data of the even-numbered pages. In the subsequent color determination circuit 205, the image memory 203
And the image data from the image memory 204 are input for each scanning line, and a show-through image erasing process and a color correction process are performed.

The output switching circuit 206 temporarily stores the image data of the first surface and the second surface in each of the image memories 203 and 204 that have been subjected to various processes through the color discriminating circuit 205. A selection is made whether to output data. In the print head, laser light of 256 gradations is modulated for each color according to the image output, and is irradiated on the surface of the photosensitive drum 15. Note that the timing generation circuit 2
At 07, a timing generation signal for operating each of the above function blocks is generated.

FIG. 3 is a block diagram of the color determining circuit 205. The color discriminating circuit 205 is a circuit for performing processing for avoiding show-through of the image on the opposite surface in a portion where the image on the first surface and the image on the second surface do not overlap.
1, a color correction circuit 302 for correcting color and density in a portion where the image on the first surface and the image on the second surface overlap, a CPU and an image memory 2 (not shown) for issuing a processing command to each circuit.
03 and a buffer memory (not shown) for storing image data for each scanning line from the image memory 204.
And R for storing various programs (not shown)
OM and the light transmittance ave. RAM for storing
(Also not shown).

FIG. 4 is a diagram showing a pixel data storage structure in the image memories 203 and 204. A two-dimensional address (x, y) is assigned to each read pixel. The horizontal address y of this image memory is
The column address of the pixel read in the main scanning direction is shown, and the address x in the vertical direction is in the sub-scanning direction, that is,
The row address in the document feed direction is shown. Here, when the dot density is 400 dpi, in the case of an A3-size original, the number of pixel data stored in each image memory is up to 4800 pixels in the main scanning direction and up to 6400 pixels in the sub-scanning direction. It is necessary to store pixel data. .. P43, P53... In the figure indicate pixel data stored therein (subscripts indicate row addresses and column addresses in order). FIG. 5 is stored in the image memories 203 and 204 described above. FIG. 9 is a schematic diagram showing a data configuration of one pixel (P11, P21,... P43, P53,...). Each of the color component data R, G and B is configured as data of 8 bits and 256 gradations. As shown in the figure, the R data is "D23, D
22, D21, D20, D19, D18, D17, D1
6 ", and the G data is" D15,
D14, D13, D12, D11, D10, D09, D
08 ”, and the B data is“ D0 ”.
7, D06, D05, D04, D03, D02, D0
1, D00 ". Thus, the color component data for one pixel has a 24-bit data configuration.

FIG. 6 is a schematic diagram showing the relationship between memory images on the image memories 203 and 204 and addresses. (A) shows the relationship between the memory image "1" and its address for the first side (front side) of the document on the image memory 20403, and (b)
5 shows the relationship between the memory image “2” on the second surface (back surface) of the same document on the image memory 204 and its address. Each image memory 203 and 2
As for 04, as described above, 1 to 4800 is assigned as a column address, and 1 to 6400 is assigned as a row address. Further, regarding the storage addresses of the read image data of the first surface and the read image data of the second surface in each of the image memories 203 and 204, the arrangement directions of the column addresses are reversed left and right.

In (a), a part of the image memory image "2" on the second surface, which is the back surface, becomes image data at the same address as the image memory image "1" on the first surface and overlapping. I have. At an address that does not overlap in FIG. 9A, the image memory image “2” on the second surface is shown off on the first surface. That is, a character displayed by adding a spot obtained by rotating the number “2” by 180 degrees partially overlaps with “1”, and in a non-overlapping portion, shows off in the vicinity of “1”. .

In (b), a part of the image memory image "1" on the first surface which is the front surface is different from the image memory image "2" on the second surface which overlaps with the image data at the same address. Has become. At the addresses that do not overlap in FIG. 9B, the image memory image “1” on the first surface is shown off on the second surface. In other words, the character displayed by adding the spots obtained by rotating the number “1” by 180 degrees partially overlaps with “2”, and in the non-overlapping part, shows off in the vicinity of “2”. .

The processing for eliminating the influence of the image on the opposite surface of the same document is performed by the color discriminating circuit 205 described above. FIG. 7 is a flowchart showing a process for removing the influence of the image on the facing surface.
This will be described with reference to FIG. First, the original is driven (S
1) The images of the first and second surfaces are read (S2, S
3) Store the read image data in each memory. At this stage, the stored image data is data that is affected by the images of the opposing surfaces and that image data is added. When the end of the original is detected by the sensor 31 while the original is being conveyed (S4), the original is stopped (S5), and the read image data is used for each of the R, G, and B color components on both the first and second surfaces. Is detected, that is, an area in which the density data indicates “00000000”, that is, an area in which the first surface and the second surface are white backgrounds (S6). Then, the document is fed backward (S7), and stopped when the detected area reaches the position of the CCD 8 (S7).
8). Thereafter, the exposure lamp 7 is turned on, the transmitted light in the white background area is received by the CCD 8, the light amount is monitored, and the light transmittance ave. Is detected (S9 to S
10). The detected light transmittance ave. Is a color discrimination circuit 2
05 is temporarily stored in the RAM.

Next, the driving of the original is started again and the original is discharged (S11, S12). The light transmittance ave. And color discriminating processes such as a process of determining the original color of the original and a process of erasing a show-through image in a portion where images do not overlap (S13). Is performed (S14). The color determination processing in step S13 is performed by the color determination circuit 205 as described below.

First, the process of erasing a show-through image in the erasing circuit 301 will be described with reference to FIG. 8 which is a circuit diagram showing the configuration of the erasing circuit 301. . The density data (gradation data) for each of the color component data R, G, and B of the specific pixel a (x, y) on the first surface is read from the image memory 203, and is compared with the comparison circuits 801 to 80, respectively.
At 3, it is compared with a predetermined threshold. When the respective color density values are equal to or less than a predetermined value, the comparison circuits 801 to
From 803, “0” is output. Further, when the density of each of the R, G, and B color components is equal to or less than a predetermined value (that is, when the pixel is a bright pixel), the output of the OR circuit 810 becomes “0”.

On the other hand, the image memory 203 and the image memory 2
Specific pixels a (x, y) and b read from
(X, y) ｛This pixel is located at a position facing the specific pixel a (x, y). ), The calculation circuit 800 calculates the ratio of the color density for each of the R, G, and B color components.
Here, the density aR (expressed as 8-bit gradation data) for the color component data R read from the image memory 203 and the density bR for the color component data R read from the image memory 204. (Expressed as 8-bit gradation data), aR ÷ b
R = r is calculated. Similarly, for the densities aG, bG, aB, and bB of the other color component data, aG ÷ bG
= G and aB ÷ bB = b are calculated. Then, the calculated values of the density ratios r, g, and b of the respective colors are input to the comparison circuit 809, and are compared to determine whether they match. Therefore, when all the input values r, g, and b match, that is, r =
When g = b, the comparison circuit 809 outputs “0”. The output of the comparison circuit 809 and the output of the OR circuit 804 are input to the OR circuit 810. Furthermore, OR
The output of the circuit 810 and the color density data of each of the R, G, and B color components for the specific pixel a (x, y) read from the image memory 203 are output from the AND circuits 812 to 812, respectively.
14 is input.

The comparison circuits 805 to 807, the calculation circuit 800, the OR circuit 808, the OR circuit 811 and the AND circuits 815 to 817 are also applied to specific pixels in the image on the second surface.
The processing is performed in the same manner as the first surface. As a result,
The output of the OR circuit 810 (OR circuit 811) is “0” because the output of the OR circuit 804 (OR circuit 808) is “0”. That is, the specific pixel a (x, y) (b (x ,
This is a case where the color density value of each of the color components R, G, and B for y)) is a predetermined value or less and is a bright pixel. {And the output of the comparison circuit 809 is “0”}. That is, the density ratio of each color component of the specific pixel a (x, y) and the corresponding pixel b (x, y) is the same. ｝ Case. Then, in this state, the specific pixel a (x, y) on the first surface of the original document
(B (x, y)) is determined to be show-through,
“0” is output from the OR circuit 810 (OR circuit 711). Therefore, the AND circuits 812 to 814 (AND circuits 815 to 817) are connected to the OR circuit 810 (OR circuit 81).
When the output “0” from 1) is input, “0” is output from the AND circuits 812 to 814 (AND circuits 815 to 817), and the specific pixel a (x, y)
The pixel data for (b (x, y)) is discarded.

Next, with regard to the color correction processing in the overlapping portion between the image of the first surface and the image of the second surface, the color correction circuit 302
This will be described with reference to FIG. The output of the OR circuit 804 and the OR circuit 808 of the erasing circuit 301 is "1", that is, the following processing is performed for pixels having a density equal to or higher than a predetermined value. Output to the switching circuit.

First, in the multiplication circuits 904 to 906, the density data (bR, bG, bB) of the second surface image is converted into the light transmittance ave. Is multiplied. Thus, density data (bR ′, bG ′, bB ′) of the image on the second surface read from the first surface side is obtained. Then, the subtraction circuits 907 to 909 for each color component use the density data (aR, a) of the image of the first surface at the same address.
G, aB) from the density data (bR ′, bG ′, b
B ′) is subjected to a subtraction process. As a result, density data (aRo, aGo, aBo) close to the color density of the original image of the original can be calculated by excluding the adverse effect of the first surface image due to the second surface image, and the original color and density can be calculated. It becomes possible.

Similarly, the color densities (bRo, bGo, bBo) of the image on the second surface which are close to the originals of the original are also multiplied by the multiplication circuits 901 to 903 in the same manner as described above. The density data (aR ', aG', aB ') is calculated, and this value is subtracted from the density data (bR, bG, bB) of the image on the second surface at the same address for each color component in the subtraction circuits 910 to 912. It is calculated by subtraction processing.

By the above-described color discrimination processing, the quality of image data can be improved before printing on copy paper. [Other Matters] Needless to say, the present invention is not limited to the above-described embodiment, and the following contents are also included in the present invention.

(1) In the copying apparatus 1, both sides of the original are read by the two CCDs 6 and 8. However, a mechanism for inverting the original is provided in the original
D may be read. (2) The case where the color components are R, G, and B has been described. Available.

(3) Light transmittance ave. Was detected by the CCD 8 at the time of reading the original.
It is also possible to store this value in advance in accordance with the type of the document, and to perform processing using the corresponding value according to the user's selection.

[0033]

As described above, according to the copying apparatus of the present invention, the density detecting means for detecting the density data of the image on the second surface read from the first surface in the overlapping portion of the images on both sides of the document. And a density correction means for correcting the first-side read image data with the density data detected by the density detection means, so that an image overlapped on both sides can be printed in a state close to the original color and density of the original. It is possible to do.

Further, the density detecting means detects a density of the same color component of the first surface image and the second color image at the same position on the document, and a density detector of the first surface image and the second surface image. When the densities are equal to or higher than the predetermined densities, a determination unit is provided for determining that the image overlaps at a position on the original, so that the first surface can be easily determined based on the density data of the read image. It is possible to determine whether the image on the second surface and the image on the second surface overlap.

Further, the density detecting means simply multiplies the density data of the second-side read image by the light transmittance of the document when the judgment section obtains the judgment result that the overlap has occurred. In addition, it is possible to easily detect the density data of the second surface image read from the first surface direction. Further, it is possible to easily calculate the correction value of the density data of the first-side read image simply by performing the arithmetic processing using the multiplication value obtained by the multiplication processing.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an entire configuration of a copying apparatus according to an embodiment.

FIG. 2 is a block diagram showing a data processing configuration for outputting image data obtained by a first surface reading CCD 6 and a second surface reading CCD 8 shown in FIG. 1 to a print head.

FIG. 3 is a block diagram illustrating a configuration of a color determination circuit illustrated in FIG. 2;

FIG. 4 is a diagram showing a data storage structure of an image memory.

FIG. 5 is a diagram illustrating a data configuration of one pixel of image data.

FIG. 6 is a diagram illustrating a memory image on an image memory 203 and an image memory 204.

FIG. 7 is a flowchart illustrating an operation process of the copying apparatus.

FIG. 8 is a circuit diagram showing a configuration of an erasing circuit.

FIG. 9 is a circuit diagram illustrating a configuration of a color correction circuit.

[Explanation of symbols]

 Reference Signs List 1 copying apparatus 6, 8 CCD 5, 7 light source 203, 204 image memory 205 color discriminating circuit 301 erasing circuit 302 color correcting circuit 800 calculating circuit 801-803, 805-807, 809 comparing circuit 804, 808, 810, 811 OR circuit 812 817 AND circuit 901-906 Multiplication circuit 907-912 Subtraction circuit

Claims (3)

[Claims] 1. A copying apparatus capable of reading a first side and a second side of a document, wherein: at a portion where the first side image and the second side image of the document overlap,
Density detecting means for detecting density data of a second surface image read from the first surface direction; and density correcting means for correcting the first surface read image data with the density data detected by the density detecting means. A copying apparatus characterized by the above-mentioned. 2. A density detecting section for detecting the density of the same color component of a first-side image and a second-side image located at the same position on a document; 2. The copying apparatus according to claim 1, further comprising: a determination unit configured to determine that an image overlaps at a position on the document when the density is equal to or higher than a predetermined density. 3. The density detector is obtained by multiplying the density data of the second-side read image by the light transmittance of the document when the determination unit obtains a determination result indicating that an overlap has occurred. The multiplication value is detected as density data of an image of the second surface read from the first surface direction, and the density correction unit performs an arithmetic process on the density data of the first surface read image using the multiplication value. 3. The copying apparatus according to claim 2, wherein the density correction of the first-side read image is performed.