JPH05284375A - Color image forming device - Google Patents

Abstract

PURPOSE:To simply and exactly correct a color slurring by uing the color slurring quantity detected from a monochromatic area in an original image. CONSTITUTION:An electric signal from an image pickup element is converted to a digital signal by an A/D converter 21, stored in a storage device 22, and thereafter, a color slurring correction processing is executed by using a CPU 25. As for the correction processing, first of all, by an edge part discriminating means, the case when a density difference of a notice picture element and a peripheral picture element is larger than reference density sR, sG and sB set to a ROM 23 is decided to be an edge of a monochromatic area. This output signal is inputted to a color slurring quantity detecting means, the color slurring quantity is measured, and the color slurring correction is executed, based thereon. In such a way, by executing the correction in accordance with the color slurring quantity detected from a picture element in the monochromatic area in an original image, a reproducing image can be obtained simply and exactly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus, and more particularly, to a color image forming apparatus for performing correction processing for color misregistration of an edge portion of an input image.

[0002]

2. Description of the Related Art An example of a color misregistration generation process in an image forming apparatus will be described with reference to FIGS. White light emitted from the fluorescent light 8 for the scanner light source is reflected by the color original. The reflected light is further reflected by the movable reflecting mirror 10, passes through the lens 11, the filters 12, 13, and 14, and is converted into an electric signal by the solid-state image sensor 15. Filter 1
Reference numerals 2, 13, and 14 are divided so as to transmit only the respective components of red, green, and blue, and the movable table 9 is moved by the driving of the light source moving device 16, and the filters are arranged for each line in the main scanning direction. 12, 13, and 14 are designed to change in the order of red, green, and blue.

An analog electric signal obtained from the solid-state image pickup device 15 is converted into a digital color signal by an analog / digital converter 21 pixel by pixel (target pixel) and stored in an image memory 22.

Here, when attention is paid to the edge portion of the character in the color original, in the ideal case, the positions of the pixels indicating the peak values of the R, G, and B color information signals should coincide with each other.

However, in reality, due to the misalignment of the position of the solid-state image pickup element for each color, an error signal for several pixels is output in the sub-scanning direction as the R, G, B color signals at the edge portion of the character. There was a problem.

When a reproduced image is formed on the basis of the color information signal in which such a color shift has occurred, naturally color shift also occurs in the reproduced image, and the color information signal in which the color shift has occurred is generated. When the color correction is performed, the color may be converted into a color having a large color difference from the color of the original, which causes a deterioration in image quality.

[0007]

However, it is a very difficult work to mechanically make adjustments so that the above-mentioned color shift does not occur, and there is a drawback that a great deal of labor is required. In addition, there is a drawback that the adjustment must be performed frequently.

The present invention has been made to solve the above-mentioned problems, and detects the color shift amount of pixels at the edge portion of the monochrome area in the original image and detects the original image according to the detected color shift amount. It is an object of the present invention to provide a reproduced image free from color misregistration by correcting the color misregistration.

[0009]

To achieve this object, in the color image forming apparatus of the present invention, as shown in FIG. 1, it is discriminated whether the target pixel in the original image is the edge portion of the monochrome area. Edge portion identifying means 102, and color shift amount detecting means 103 for detecting the color shift amount of the area identified by the edge portion identifying means 102 as a monochrome area.
And a color shift correction unit 104 that corrects the color shift of the original image according to the color shift amount detected by the color shift amount detection unit 103.

[0010]

The color image copying machine of the present invention having the above construction scans a color original and obtains color separation data from each pixel. Using the color separation data obtained in this way, the edge portion identification means identifies whether or not the pixel of interest in the original image is the edge portion of the monochrome area. The color shift amount of the area identified as the edge portion of the monochrome area is detected by using the color shift amount detecting means. The color shift correction unit corrects the color shift of the original image according to the color shift amount detected by the color shift amount detection unit. Next, using the matrix (A) of row i and column j, matrix conversion is performed on the color information signal whose color misregistration has been corrected. A reproduced color image is formed based on the printer control signal generated thereby.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In the description, the same parts as the conventional ones will be denoted by the same reference numerals.

FIG. 2 is a sectional view showing the arrangement of a color image copying machine equipped with a color shift correction circuit embodying an embodiment of the present invention. The color image copying machine of the present embodiment comprises a color document reading section 2, a color correction processing section 4, and a color image recording section 5.

The color original reading section 2 is installed above the color image copying machine 1. On the upper part of the color document reading section 2, there is provided a document cover 7 that can cover a transparent document table 6 on which a color document is placed and that holds the color document. A fluorescent lamp 8 for a scanner light source is provided below the transparent original table 6 so as to extend in the main scanning direction, and the fluorescent lamp 8 for a scanner light source emits light toward the transparent original table 6. It is configured.

The moving reflecting mirror 10 is installed on a moving table 9 that moves the fluorescent light 8 for the scanner light source, and is configured to reflect the light emitted from the fluorescent light 8 for the scanner light source and reflected by the color original. There is. The lens 11 is a moving reflecting mirror 1.
It is installed on the moving table 9 so as to concentrate the light reflected at 0. A red filter 12, a green filter 13, and a blue filter 14 for decomposing the light concentrated by the lens 11 into red, green, and blue components take in the decomposed light and convert the decomposed light into electricity. It is arranged in front of a solid-state image pickup device (CCD) 15 for converting into a signal, and the filters 12, 13, 14 and the solid-state image pickup device 15 are all installed on a moving table 9.

The light source moving device 16 includes a fluorescent lamp 8 for a scanner light source, a moving reflecting mirror 10, a lens 11, a filter 12, and 1.
The moving table 9 is configured to move in the left-right direction (sub-scanning direction) in FIG. At the end of the color document reading unit 2, the document feeder 1
9, the color original on the original feeding table 17 can be sent from the color original feeding section 18 to the transparent original table 6. In addition, on the opposite side of the document feeder 17,
A document discharge tray 20 for discharging color documents after copying is installed. A color correction image display monitor 48 and a color correction button 4 are provided on the upper side surface of the color original reading unit 2.
9. An operation panel 3 including a copy start button 50 and the like, and a light pen 51 (not shown) for selecting a color region on the monitor 48 are installed.

The color image processing unit 4 performs a required color calculation process on the input data. As shown in FIG. 3, the color original information signal corresponding to the color information signal obtained from the solid-state image pickup device 15 is converted into an analog signal. An analog / digital converter (A / D converter) 21 for converting an electric signal into a digital electric signal, a manuscript storage device (image memory) 22 for storing a part of color manuscript information by a digital electric signal, and a color manuscript reading Various images are recorded using a ROM 23 that stores color correction coefficients and the like that are obtained in advance so that sufficient color reproduction can be performed in consideration of the characteristics of the unit 2 and the color image recording unit 4, and a RAM 24 that stores each calculation result. CPU for processing
25 and a laser control unit 27 for driving the laser drive unit 31 of the color image recording unit 4 based on the color-corrected signal.
It is composed of and.

The color image recording section 5 is arranged below the color image copying machine 1. In the color image recording unit 5, a laser modulation unit 33 that emits laser light to the polygon mirror 32 based on a laser drive signal from the laser control unit 27 is configured. The photosensitive drum 34 is configured to be exposed to the laser light reflected by the polygon mirror 32. The charger 35 is arranged around the photosensitive drum 34 so as to uniformly charge the photosensitive drum 34 negatively. Cyan, magenta, and yellow toners are adhered to the electrostatic latent image on the photoconductor drum 34 created by irradiating the photoconductor drum 34 charged by the charger 35 with laser light. The developing device 36, the magenta developing device 37, and the yellow developing device 38 are configured.

A cyan / toner co-feeder 39, a magenta / toner feeder 40, and a yellow / toner feeder 41, which supply toner to the developing devices 36, 37 and 38, are installed below the color image recording section 5. Has been done. Further, around the photosensitive drum 34, the photosensitive drum 34 to which toner is attached is attached.
A cleaner 42 for removing the toner is installed. A transfer drum 44 that transfers the toner on the photosensitive drum 34 to the recording sheet supplied from the supply case 43 and a fixing unit 45 that thermally fixes the transferred recording sheet are installed at the tip of the photosensitive drum. There is. Above the supply case 43, a paper feeding unit 47 that feeds the recording paper so that the paper after fixing is discharged to the output tray 46 is configured.

Next, the operation of the digital color copying machine 1 of this embodiment will be described with reference to FIGS.

Copying of a color original is started by pressing a copy start button. ..

Then, the color document on the document feed table 17 is sent to the transparent document table 6 by the document feeding device 19 (the document cover 7 may be directly opened and placed on the transparent document table 6), and the light source moving device 16 sub-displays it. The moving reflecting mirror 10 moves the white light emitted from the fluorescent lamp 8 for the scanner light source while moving in the scanning direction.
Is reflected by the solid-state image sensor 15 and is converted into an electric signal by the solid-state image sensor 15. The filters 12, 13 and 14 are divided into those which transmit only the respective components of red, green and blue, and the movable table 9 is moved by the drive of the light source moving device 16, and every line of the main scanning direction. The filters 12, 13 and 14 are designed to change in the order of red, green and blue.

The analog electric signal obtained from the solid-state image pickup device 15 is converted into a digital color signal by the analog-digital converter 21 pixel by pixel (pixel of interest) and stored in the document storage device 22. The CPU 25 performs color misregistration correction processing on the stored digital signal of color information.

Color misregistration correction processing in this embodiment will be described below with reference to FIGS.

First, the edge portion identifying means is used to identify whether or not the input color information digital signal is an edge portion of a monochrome area. This identification method will be described below with reference to FIGS. 4 and 5.

The input signals R ₁ , G ₁ and B ₁ are input to the edge portion identifying means. The edge portion identifying means of this embodiment uses the pixel of interest and the four pixels around it in order to identify whether or not the pixel of interest is the edge portion of the monochrome area. The density of the R color information signal of the pixel of interest z is Rz, and the densities of the R color information signals of the surrounding pixels a, b, c, d are Ra, Rb, Rc, and Rd, respectively (in the flowchart of FIG. 4, R , G, and B concentrations are expressed as “D”). At this time, the absolute values ΔRa, ΔRb, Δ of the density differences between the target pixel z and the surrounding pixels a, b, c, d.
Rc and ΔRd are determined as follows: ΔRa = | Ra-Rz | ΔRb = | Rb-Rz | ΔRc = | Rc-Rz | ΔRd = | Rd-Rz |. Next, the density difference ΔRa, ΔR
The maximum density difference ΔRmax is obtained from b, ΔRc, and ΔRd. ΔRmax and preset density reference value s
Compare with R. The G color information signal and the B color information signal are similarly compared. When the maximum density difference is larger than the density reference value for all color information signals, that is, ΔRmax
If> sR and ΔGmax> sG and ΔBmax> sB, it is determined that the pixel is at the edge portion of the monochrome area.
In the pixel determined to be the edge part of the monochrome area, the output signal of the edge part identification means is "1", and in other cases, the output signal of the edge part identification means is "0".

The output signal from the edge identifying means is input to the color shift amount detecting means.

When the output signal of the edge identifying means is "1", the color shift amount detecting means obtains the color shift amount of the target pixel. The procedure for detecting the color shift amount will be described below with reference to FIGS. 6 and 7.

The place where the output signal of the edge identifying means changes from "0" to "1" is considered to be the edge of the character. Therefore, the color misregistration amount detection circuit detects the color misregistration amount by using the color information signals of the p pixels before and after the pixel where the output signal of the edge identifying unit changes from "0" to "1". To do. p is a predetermined constant.

P pixels before and after the pixel of interest z, that is, (2p + 1)
The number of pixels is z _-p , z- _(p-1) , ..., Z ₀ = z, ...
, Z _(p-1) and z _p . z _j (j = -p, ...,
In p), the one in which the R color information signal has the maximum value is z _r ,
_{Let g g} be the maximum value of the G color information signal and z _b be the maximum value of the B color information signal. The color shift amount of G is δ
If the amount of color misregistration between G and B is δB, then δG = r−g δB = r−b. Here, r represents the relative position of the pixel z _r for which the R color information signal has the maximum value from the target pixel z ₀ . Similarly, g is z _{0 of the} pixel z _g for which the G color information signal has the maximum value.
Shows the relative position, and b shows the relative position from z _{0 of the} pixel z _b where the B color information signal has the maximum value.

The color shift amount detecting means outputs the color shift amount δG of the G color information signal based on the R color information signal and the color shift amount δB of the B color information signal based on the R color information signal. ..

When actually detecting the color shift amount of the image,
For example, measure the amount of color shift for 10 edge parts,
The average value is set as the color shift amount of the entire image.

The color shift amount output by the color shift amount detecting means is input to the color shift correction circuit.

The color misregistration correction circuit corrects the color misregistration for the color information signal of the original image based on the input color misregistration amount.

First, the G color information signal will be described.

When δG = 0, the G color information signal has no color misregistration and is not corrected.

When δG ≠ 0, G is larger than that of the R color information signal.
The color information signal is shifted by δG in the main scanning direction. Therefore, _{G r} is set so that z _r and z _g are color information signals of the same pixel.
The color information signal is shifted by δG over the entire image. At this time, at both ends of the image, G for the R color information signal
An excess or deficiency of color information signals occurs. The excess G color information signal is discarded on the side where the G color information signal is excess. On the side where the G color information signal is insufficient, the G color information signal at the end is
Add the number of missing pixels.

For the B color information signal, the same color shift correction processing as for the G color information signal is performed.

According to the above procedure, the color separation signal of the original image which has been subjected to the color misregistration correction processing can be obtained.

Next, color correction processing is performed by masking as in Expression 1 to determine the cyan, magenta, and yellow printer control signals.

[0040]

[Equation 1]

However, C, M, and Y are cyan, magenta, and yellow printer control signals, and aij is a color correction coefficient.

The printer control signal for each component obtained by the above color correction is sent to the laser control unit 27, and the laser drive unit 31 drives the laser 33 according to this data, and the laser light is emitted from the laser 33. The light is reflected by the polygon mirror 32 and is exposed on the photosensitive drum 34 uniformly charged by the charger 35, so that a latent image is formed on the photosensitive drum 34. Depending on the latent image, it is developed (toned) by either the cyan developer 36 or the magenta developer 37 or the yellow developer 38, depending on the corresponding color separation of the data. The recording sheet fed from the paper feed case 43 is wound around the transfer drum 44, is transferred from the _{photosensitive} optical drum 34 developed on a recording paper. Further, the photosensitive drum 34 uses a cleaner 42 to remove toner. The transferred recording paper is fed to the paper feeding section 4
In the middle of 7, the image is thermally fixed by the fixing unit 45 and output to the output image tray 46.

The present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the invention. For example, in the present embodiment, the monochrome area is determined by using the maximum value of the density difference of each color information signal between the pixel of interest and the four pixels around it.
Differences of input color signals of target pixel | R ₁ −G ₁ |, | G ₁ −
It is also possible to discriminate the monochrome area using B ₁ |.
In addition, the minimum value min (R ₁ , G ₁ , B of the input color signals is
_It may be judged in ₁ ) whether it is a monochrome area.

Further, in the present embodiment, the correction is made so that the positions where the maximum densities are obtained coincide with each other in the vicinity of the edge portion, but the positions where the maximum density change occurs may be coincident with each other.

Yes.

As is apparent from the above description, according to the color image forming apparatus of the present invention, the color shift amount of the pixel in the monochrome area in the original image is detected, and the detected color shift amount is calculated. Therefore, by correcting the color shift of the original image, it is possible to provide a reproduced image without color shift.

[Brief description of drawings]

FIG. 1 is a claim correspondence diagram showing the configuration of the present embodiment.

FIG. 2 is a configuration diagram showing the configuration of the entire apparatus of this embodiment.

FIG. 3 is a block diagram illustrating a masking processing circuit of this embodiment.

FIG. 4 is a flowchart showing a procedure for obtaining a maximum density difference between a pixel of interest and an adjacent pixel in identifying a monochrome area in the present embodiment.

FIG. 5 is a flowchart showing a procedure for identifying a monochrome area in this embodiment.

FIG. 6 is a flow chart showing a procedure for obtaining the position of the pixel having the maximum color information signal for the pixels in the vicinity of the pixel of interest in the detection of the color shift amount in the present embodiment.

FIG. 7 is a flowchart showing a procedure for detecting a color misregistration amount in this embodiment.

FIG. 8 is a configuration diagram showing a configuration of an entire conventional device.

FIG. 9 is a block diagram illustrating a conventional masking processing circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Digital color copying machine 2 Color original reading section 4 Color image processing section 5 Color image recording section 15 Solid-state image sensor 23 ROM 24 RAM 25 CPU

Claims (1)

[Claims] 1. A color gradation image forming apparatus comprising recording means for recording a color gradation image by superimposing j color primary colors in accordance with i color primary image color separation data input by an image input means, An edge part identification means for identifying whether or not the pixel of interest in the original image is an edge part of a monochrome area, and a color shift amount of the area identified by the edge part identification means as an edge part of the monochrome area is detected. A color image forming apparatus comprising: a color shift amount detecting unit; and a color shift correcting unit that corrects a color shift of an original image according to a color shift amount detected by the color shift amount detecting unit.