JPH10210314A - Digital image-processing unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent production of dust due to too much toner around an edge. SOLUTION: Data stored in a memory, equivalent to two lines feed for each development color, are given to a Laplacian filter 501. An edge obtained thereby is smoothed (502) by three pixels in the main scanning direction, and the resulting data are shifted by division according to a shift table 503, in which normally a small table value is selected for a high edge and a large table value is selected for a small edge. The result is outputted, while being added to the 8-bit image data. Whether the image data of the color component is monochromatic or full color data is selected. When the image-forming operation is monochromatic and at least two development colors or over overlapped, the density curve is set lower overall in comparison with the density curve in monochromatic development. Then image deterioration due to too much dust around the edge is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital image processing apparatus, and more particularly, to a digital image processing apparatus adapted to a one-drum system for developing digital color images one by one.

[0002]

2. Description of the Related Art Conventionally, most digital image processing apparatuses have two types of color modes of a copying machine: a black and white mode and a full color mode. The ability to adjust each color (or density) is important to get a more faithful copy. Color correction coefficients, UCRs, and printer gammas occupy a major position in the full-color mode color adjustment functions. In particular, printer gammas have a look-up table that can be used to accurately adjust the colors of output images. ing.

In general, the printer gamma occupies a large position as a density adjustment function in the black-and-white mode, and is prepared separately from the printer gamma in the full-color mode.
It is designed so that the density of the output image can be adjusted with high accuracy.

As a conventional example 1 similar in technical field to the present invention, there is "Image processing method in color image forming apparatus" in Japanese Patent Laid-Open No. 1-252069. In this conventional example, U
It is related to CR and judges the edge part on the document,
It is characterized in that the UCR rate is increased in an edge portion and the UCR rate is decreased in a non-edge portion.

As a second conventional example, Japanese Patent Application Laid-Open No. 2-128869
There is a "color correction processing method having a color conversion function" in Japanese Patent Application Laid-Open No. H10-260, 1988. This conventional example relates to a color correction coefficient, and is characterized in that the color correction coefficient is switched based on the amounts of chromatic components and achromatic components of input data.

A third conventional example is disclosed in Japanese Patent Laid-Open No. 4-260274.
There is a “color separation device” in Japanese Patent Publication No. This conventional example relates to a color correction coefficient, and is characterized in that, when the type of a color film is changed in a film output mode, the color correction coefficient is switched according to the characteristic.

Further, as a conventional example 4, Japanese Patent Laid-Open No. 4-329
No. 068 discloses an “image reading device”. In this conventional example,
This is related to edge emphasis, and is characterized in that the degree of edge emphasis is switched according to the document type.

[0008]

However, in the above-mentioned prior art, the processing is switched to an appropriate processing based on the type of the original and the density of the original, but the processing is switched up to a combination of a color mode and a developing color. Nothing to do. For example, a single color mode which is a color mode other than the above is often not mentioned much.

In consideration of this point, when considering image processing in the single color mode, the density of a single color, particularly the density of a secondary color (RGB), overlaps the density of the primary color (CMY) by two colors. As a result, there is a problem that toner is excessively applied and dust occurs near the edge. In particular, this phenomenon is remarkable in the vicinity of a strong edge such as a character portion. By further developing this, not only in the single color mode but also in the full color mode, black (chromatic color with low saturation) including secondary colors (RGB) and CMY components may cause dust near the edge due to excessive toner. Will happen.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a digital image processing apparatus in which dust is prevented from being generated due to excessive toner running near an edge.

[0011]

In order to achieve the above object, a digital image processing apparatus according to the present invention comprises: an image reading means for optically scanning a document image to convert the image data into image data; A color component separating means for separating,
An image forming unit that outputs image data of a color component decomposed by the color component decomposing unit; a selecting unit that selects whether the image data of the color component is a single color or a full color; When at least two or more colors are superimposed, a density adjustment function means for lowering the density curve as a whole as compared with the density curve in one-color development is provided.

Further, it is preferable that the above-mentioned density adjusting function means weaken the degree of edge emphasis as a whole.

The digital image processing apparatus further comprises a character / pattern determining means for determining whether the original image is a character or a picture, and a chromatic / non-color determining means for determining whether the original image is chromatic or achromatic. It is preferable to have coloring determination means, and to weaken the degree of edge enhancement based on the determination results of these determination means.

Further, the chromatic / achromatic color judging means includes:
The chromatic color is a primary color (CMY) or a secondary color (R
GB), and when it is determined that the character is a secondary color and a character of a secondary color, it is compared with a case where the character is a primary color and a character of a primary color. , The edge emphasis degree may be weakened.

The density adjustment for weakening the edge emphasis degree is performed by switching a color correction coefficient between an area determined to be a character of a secondary color and an area determined to be a character of a primary color. The color correction coefficient for text may be density adjustment for narrowing the color reproduction range on the high saturation side of the secondary color.

Further, the density adjustment for weakening the edge emphasis level is performed when the original image is determined to be an achromatic color and a black character, and the edge emphasis level in the development color Bk version and the edge enhancement level in the development color CMY version are determined. Compared with the degree of edge enhancement, C
It is preferable to perform density adjustment for weakening the degree of edge enhancement in the MY plane.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a digital image processing apparatus according to the present invention will be described in detail with reference to the accompanying drawings. 1 to 16 show an embodiment of a digital image processing apparatus according to the present invention. FIG. 1 is an overall configuration diagram when an embodiment of the digital image processing apparatus of the present invention is applied to a digital color copying machine.

In FIG. 1, reference numeral 100 denotes a laser printer, 2
00 is an automatic document feeder, 300 is an operation board, 400
Is an image scanner, and 500 is an external sensor.

An image scanner 400 mechanically moves a moving body on which an illumination lamp 402 mounted below a contact glass 401 is mounted at a constant speed in the horizontal direction (sub-scanning direction) in the figure to convert a document image. This is an image reading unit to read.

Light emitted from the illumination lamp 402 is reflected on the surface of the original placed on the contact glass 401 in accordance with the density of the original image. This reflected light, that is, the light image of the document, passes through a number of mirrors and lenses and enters the dichroic prism 410. Dichroic prism 410
Separates the incident light into three colors of R, G and B according to the wavelength.
The three split lights are incident on different one-dimensional charge-coupled device (CCD) image sensors 410. Thus, the three one-dimensional image sensors 410 provided in the image scanner 400 can simultaneously read the R, G, and B color components of one line in the main scanning direction on the document image. The two-dimensional image of the document is sequentially read by the sub-scan of the moving body.

The external sensor 500 is an image scanner 4
As in the case of 00, it is built in a hand-held scanner composed of a CCD that can simultaneously detect the R, G, and B color components of the original image.

The ADF 200 is an image scanner 400
, And a large number of originals can be held on the original platen 210 in a stacked state. When performing the document feeding operation, the rotating call roller 212 comes into contact with the uppermost document upper surface, and the contacted document is fed out.

Reference numeral 213 denotes a separation roller for avoiding double feeding. The document fed out to the predetermined position is further conveyed on the contact glass 401 of the image scanner 400 by driving the pull-out roller 217 and the conveyance belt 216, and when the document advances to the predetermined reading position, that is,
The operation stops when the leading edge of the document reaches the left end position of the contact glass 401. When the reading of the document is completed, the conveyor belt 216 is driven again to contact the contact glass 40.
The original on top 1 is discharged, and the next original is sent to the reading position. An optical sensor for detecting whether a document is loaded or not, a document presence / absence sensor 211 is provided in front of the call roller 212, and the leading edge and size of the document are provided between the separation roller 213 and the pull-out roller 217. And a document leading edge sensor 214 for detecting an image.

The original leading edge sensor 214 is composed of a plurality of sensors arranged at different positions in the main scanning direction (a direction perpendicular to the paper surface). Manuscript size, ie
The document width can be detected. Further, a pulse generator for outputting a pulse corresponding to the rotation amount is provided in a paper feed motor (not shown). The control device of the ADF 200 measures the time until the document passes the document leading edge sensor 214, thereby The original size in the scanning direction, that is, the original length is detected.

The call roller 212 and the separation roller 2
Reference numeral 13 denotes a pull-out roller 2 driven by a feed motor.
17 and the conveyor belt 216 are driven by a conveyor motor. Also, a registration sensor 215 composed of an optical sensor
Is disposed downstream of the pull-out roller 217.

Next, the schematic structure and operation of the laser printer 100 will be described. Image reproduction is performed on the photosensitive drum 1. Around the photosensitive drum 1, a series of electrophotographic process units, that is, a charger 5, a writing unit 3, a developing unit 4, a transfer drum 2, a cleaning unit 6, and the like are provided. The writing unit 3 includes a laser diode (not shown).
The laser light emitted by the polygon mirror 3b, the lens 3c,
The light is irradiated on the surface of the photosensitive drum 1 via the mirror 3d and the lens 3e. The rotating polygon mirror 3b is a polygon motor 3a
, And is driven to rotate at a constant speed at a high speed.

The image control device controls the light emission timing of a laser diode driven by a binary signal (recording / non-recording) in pixel units corresponding to the density of an image to be recorded, by rotating the laser diode sequentially scanning each pixel position. The drive signal of the laser diode is controlled so as to synchronize with the rotation / deflection operation of the polygon mirror 3b. That is, the on / off control of the laser diode is performed so that a laser beam corresponding to the density (recording / non-recording) of the pixel is irradiated at each scanning position of the image on the surface of the photosensitive drum 1.

The surface of the photosensitive drum 1 is uniformly charged to a high potential in advance by corona discharge by the charging charger 5. When this surface is irradiated with the laser light emitted from the writing unit 3, the charging potential changes according to the intensity of the light. That is, a potential distribution is formed on the photosensitive drum 1 in accordance with the presence or absence of the laser light emitted from the laser diode included in the writing unit 3.
Thus, a potential distribution corresponding to the density of the original image, that is, an electrostatic latent image is formed on the photosensitive drum 1. This electrostatic latent image is visualized by a developing unit 4 disposed downstream of the writing unit 3.

In this configuration example, the developing unit 4 is provided with four sets of developing units 4M, 4C, 4Y and 4Bk, each of which has a different color M (magenta) and C (cyan). , Y (yellow) and Bk (black) toners. Laser printer 10
0 is such that any one of the four developing units is selectively energized, so that the electrostatic latent images are M, C,
A visible image is formed with any one of the Y or Bk toners. On the other hand, the transfer paper stored in the paper feed cassette 11 is fed out by the paper feed roller 12, sent to the surface of the transfer drum 2 at a timing by the registration roller 13, and
It moves with the rotation of the transfer drum 2 while being attracted to the surface. Then, at a position close to the surface of the photosensitive drum 1, the toner image formed on the photosensitive drum 1 is transferred to the surface of the transfer paper by charging by the transfer charger 7.

In the case of the single-color copy mode, the transfer of the toner image is completed, and the transfer paper separated from the transfer drum 2 is fixed and discharged to the paper discharge tray 10. It is necessary to form images of four colors of Bk, M, C and Y on a single sheet of transfer paper. in this case,
First, a Bk color toner image is formed on the photosensitive drum 1 and transferred to a transfer sheet. Then, the next M color toner image is formed on the photosensitive drum 1 without separating the transfer sheet from the transfer drum 2. The toner image is formed, and the toner image is transferred to the transfer paper again. Further, for the C color and the Y color, a toner image is formed on the photosensitive drum 1 and transferred to a transfer sheet. That is, one color image is formed on the transfer paper by repeating the process of forming and transferring the toner image.

When the transfer of all the toner images is completed, the transfer paper is separated from the transfer drum 2 by charging by the separation charger 8, and after being subjected to the fixing process of the toner image by the fixing device 9, is discharged to the paper discharge tray 10. .

FIG. 2 is a circuit block diagram showing a configuration example of the image processing unit of the digital copying machine. The operation control of the entire copying machine is controlled by a system controller 50 composed of a microcomputer.

The synchronization control circuit 60 generates a clock pulse as a reference for control timing, and inputs and outputs various synchronization signals for synchronizing signals between the control units.
The main scanning synchronization signal based on the scanning timing in this configuration example is synchronized with the scanning start timing of the laser beam by the rotation of the rotary polygon mirror 3b of the laser printer 100.

The R, G, and B color image signals read by the image scanner 400 are A / D converted, and are converted into 8 signals.
It is output as bit color image information. This image information is output to the laser printer 100 after undergoing various processes in the image processing unit. The image processing unit
Scanner gamma correction 71, RGB smoothing filter 72, color correction 73, under color removal (UCR) / UCA 74, selector 75, edge enhancement filter 76, printer gamma 77 as a density curve, gradation processing 78, image area separation 79, and A
Each circuit of CS80 is provided.

The scanner gamma correction 71 converts the linear RGB data of the reflectance read by the image scanner 400 into the linear RGB data of the density. The RGB smoothing filter 72 performs a smoothing process for suppressing moire caused by a halftone dot document.

The color correction circuit 73 converts the image information of each color of R, G, and B into image information of each of the complementary colors Y, M, and C. The UCR / UCA circuit 74 extracts a black component included in the color of the image signal obtained by synthesizing all the input image information of the Y, M, and C colors, outputs the extracted black component as a Bk signal, and outputs the remaining color image. The black component is removed from the signal, and the YMC component is added.

The selector 75 is connected to the system controller 5
In response to the instruction of 0, any one of the input Y, M, C, and Bk color signals is selected and output to the next block.

The edge emphasis filter circuit 76 emphasizes edge information of a character portion or a picture portion. Also,
In the printer gamma 77, a curve is set according to the printer characteristics so that the density becomes linear including gradation processing.

The gradation processing circuit 78 is a circuit for binarizing or converting the inputted 8-bit density information into binary or multi-valued information.
Generally, dither processing is often performed, and an image signal subjected to dither processing is output to the laser printer 100.

The output of the scanner gamma 71 is sent to an image area separation circuit 79 and an ACS circuit 80. The image area separation circuit 79 has a circuit for determining whether the input image is a character part or a picture part, and a circuit for determining whether the image is chromatic or achromatic. The data is sent to each processing block in units of one pixel. In each processing block, processing is switched according to the result of the image area separation circuit 79.

The ACS circuit 80 determines whether the original set on the scanner 200 is a black-and-white original or a color original, and sends the result to the system controller 50 at the end of the Bk scan. For color manuscripts, the remaining 3
The scanning is performed, and if the document is a black-and-white document, the operation is terminated by Bk scanning.

FIG. 3 is a detailed diagram of the image processing section shown in FIG. 2 to which the present embodiment is applied. The parameters of the image processing blocks 71 to 80 are all set by the CPU of the system controller 50. FIG. 3 shows only the edge enhancement filter 76 and the printer gamma 77 therein.

The first embodiment will be described with reference to FIGS. When the single color is set by the operation unit 300, the CPU 304 of the operation unit 300 sends a CP for image processing.
A single color is transmitted to U301 by serial communication. In the image processing CPU 301, the printer gamma to be set by looking at the single color is set to the printer gamma 77.
Set to However, conventionally, since a printer gamma table for a single color is prepared regardless of the development color, it has only to be set when the start key is pressed.

Normally, the printer gamma table is
There are five to nine types of tables for density adjustment using a density key as shown in FIG. When the density adjustment is not performed, a center curve, a third table in FIG. 4, is set. In the first embodiment, a single color C,
When M, Y, and Bk are selected, the same third table as usual is set. However, if R, G, B, or a registered color is selected, the image processing CPU 30 sets the second or first table having a lower density than the normal gamma.
1 is programmed in the ROM 303. Thus, the gamma table is switched.

The second embodiment is also applied to the image processing section shown in FIG. FIG. 5 shows a configuration example of the edge enhancement filter 76.
I will explain using. An edge enhancement filter generally employs a fixed coefficient method. For example, edge enhancement is performed by calculating the following (1).

[0046]

The first embodiment shows adaptive edge emphasis in which the degree of emphasis is changed according to the degree of edge. 8-bit image data is sent from the selector 75 for each developed color. The data is stored in the memory for two lines and input to the Laplacian filter 501. The edge degree thus obtained is subjected to smoothing (502) for three pixels in the main scanning direction, and thereafter, shift division is performed.

The shift division is performed according to the shift table 503. Usually, a small value is set when the edge degree is large, and a large value is set when the edge degree is small.
Then, the result of the shift division is added to the 8-bit image data and output.

Next, a second embodiment will be described. The color mode is selected from the operation unit, and the content is selected by the CPU 3 for image processing.
Until it is transmitted to 01, it is the same as in the first embodiment, and a description thereof will be omitted. Single color C, M,
When Y and Bk are selected, the same shift table 503 as usual is set. However, when R, G, B, and registered colors are selected, the overall shift amount is larger than that of the normal shift table. The edge enhancement degree is programmed in the ROM 303 of the image processing CPU 301 so that the weak shift table 2 is set.

The same can be realized by preparing and switching two or more types of edge enhancement filters by the fixed coefficient method. For example, the following edge enhancement filter (2) is prepared.

[0051]

The single color C, M,
When Y and Bk are selected, the filter (1) is selected, and when R, G, B, and the registered color are selected, the filter (2) is selected so that the filter (2) is selected.
What is necessary is just to program in OM303.

In the third embodiment, means for switching each processing by the image area separation 79 is added. FIG. 6 shows a basic configuration example of the image area separation 79.
The RGB output of the scanner gamma 71 is used for the chromatic determination 603,
Only the G signal among them is the edge determination 601 and the halftone determination 60
2, respectively.

One bit of a chromatic / achromatic signal is output from the output of the chromatic determination 603, and the edge determination 601 and the halftone determination 60
2 outputs a 1-bit character / photo signal. Characters are areas that are edges and are not halftone dots, and photographs are areas that are not characters. From the two-bit output, the final judgment 604 divides the image into three types of areas: color characters, black characters, and patterns. Colored letters are chromatic and letters. Black letters are achromatic and letters. The picture indicates an area that is neither of these two.

An example of the configuration of each of the edge determination 601, the halftone determination 602, and the chromatic determination 603 will be described. FIG. 8 shows a configuration example of the edge determination 601. First, binarization (801) of the input G data is performed. This is to detect edges by pattern matching. In this configuration example, binarization is used, but there is also a method of binarization in order to weaken data gray as a target of pattern matching. Either binarization or ternarization may be performed. After that, the binarized result is stored in the line memory of the pattern matching size minus one minute, and the pattern matching (edge detection 8
02).

FIG. 9 shows an example of a pattern in a 4 × 4 size.
(A) and FIG. 9 (b). A solid circle indicates 1 (high density) after binarization, an open circle indicates 0 (low density) after binarization, and a cross indicates don't care. "1" is output when the pattern matches, and "0" is output otherwise. After edge detection 802, in order to count edge candidates in a specific area, data is stored in a line memory of area size of −1 in the sub-scanning direction, and counting is performed by edge count 803.

If the count number is equal to or greater than a certain value, the pixel of interest in that area is determined to be an edge. FIG.
(C) shows an example of a 4 × 4 area. If the threshold is "10", it is determined to be an edge portion, and if the threshold is "14", it is determined to be a non-edge portion.

Normally, this produces an edge judgment output, but a block judgment 804 may be further provided in order to remove isolated points and the like. In this case, looking at the determination results around the target pixel for which the edge determination has been made, the edge determination is validated as it is when there are many edge determinations, and the edge determination is invalidated when there are few edge determinations. The above is the edge determination algorithm.

FIG. 10 shows an example of the configuration of the halftone dot determination 602.
First, the input G data is binarized (1001).
This is to detect halftone dots by pattern matching. In this configuration example, the data is binarized. However, in order to weaken the gray of the data as an object of pattern matching,
There is also a three-value method. Either binarization or ternarization may be performed. After that, the binarized result is stored in the line memory of the pattern matching size minus one minute, and pattern matching (dot detection 1002) is performed.

FIG. 1 shows an example of a pattern in a 4 × 4 size.
1 (a) and FIG. 11 (b). A black circle indicates “1” (high density) after binarization, an open circle indicates “0” (low density) after binarization, and a cross indicates don't care. "1" is output when the pattern matches, and "0" is output otherwise. After halftone dot detection 1002, in order to count halftone dot candidates in a specific area, data is stored in a line memory of sub-scanning direction area size minus one, and counting is performed by halftone dot count 1003.

If the count number is equal to or more than a certain value, it is determined that the pixel of interest in that area is a halftone dot. FIG.
(C) shows an example of a 4 × 4 area. If the threshold is "10", it is determined to be a halftone portion, and if the threshold is "14", it is determined to be a non-dot portion. Normally, this produces a halftone dot determination output, but an expansion process 1004 may be further provided in order to prevent missing dot detection. This means that the area around the target pixel for which the halftone dot determination has been performed is also changed to the halftone dot determination. The above is the halftone determination algorithm.

FIG. 12 shows a configuration example of the chromaticity determination 603.
First, the input RGB data is smoothed (smoothing 1201). This is to eliminate unevenness of density of halftone dot data or the like and output a uniform determination result. Then R
The minimum and maximum values of GB are obtained, and the minimum value (= minRG
B) and the difference value (= △ = (maxRGB−minRG)
B)) is detected (difference detection 1202). Then, the level is divided into several stages by the minimum value, and for example, (minR
GB <TH11) &(△> TH12) or (TH
11 ≦ minRGB <TH21) &(△> TH22),
Alternatively, (TH21 ≦ minRGB <TH31) & (△
> TH33), it is determined to be a chromatic portion, and otherwise, it is determined to be an achromatic portion by the chromatic determination 1203.

Normally, a chromaticity determination output is obtained, but a block determination 1204 may be further provided in order to remove isolated points and the like. This is because the chromatic judgment is made valid as it is when there are many chromatic judgments, and the chromatic judgment is invalidated when there are few chromatic judgments by looking at the judgment result around the pixel of interest where the chromatic judgment is made. It changes to color judgment.
The above is the chromatic determination algorithm.

The adaptive edge enhancement which is an example of the configuration of the edge enhancement filter 76 shown in FIG. 5 has been described above. In the above description, the shift table 503 is switched according to the color mode input from the operation unit 300. However, in the fourth embodiment, switching is performed in units of one pixel based on the output of the image area separation 79 described above. The circuit has two types of shift tables 503. One is a table for normal processing and the other is a table for black characters. The table for normal processing is always selected when the developing color is Bk, and the black characters are used when the developing color is CMY. Is determined, the RO for the image processing CPU 301 is selected such that the table for black characters is selected, and otherwise the table for normal is selected.
M303 is programmed.

FIG. 7 shows the overall configuration of the new image area separation 79. In the fifth embodiment, color judgment is added in addition to the image area separation of the basic function shown in FIG. In FIG. 7, an edge determination 601, a halftone determination 602, a chromatic determination 60
3 is the same as the conventional one, and the description is omitted. First, the newly added color judgment 701 will be described. FIG. 13 shows a configuration example of the color determination 701. First, the input RGB data is smoothed (smoothing 1301). This is to eliminate unevenness of density of halftone dot data or the like and output a uniform determination result. After that, the RGB is ranked in three stages: large, medium, and small.

The largest data now is L = maxRGB,
The smallest data is output as S = minRGB, and the middle data is output as M = middleRGB (small / small detection 13
02). In the color determination 1303, detection of RGB as a secondary color is performed. As shown in FIG. 14 as a point for separating a chromatic secondary color and a primary color, the level of only one of RGB is low, while the primary color is RGB.
The determination is made using the fact that the levels of up to two colors are low. That is, when the following conditions are satisfied, it is determined that the color is a secondary color.

(S <TH1) &(L> TH2) & ((L
-M) <TH3)

In practice, the relational expression may vary depending on the density even in RGB, so that, for example, S may be divided into several stages and the determination may be made by applying a condition to each stage.

(S <TH11) &(L> TH12) & ((LM) <TH13) (TH11 ≦ S <TH21) &(L> TH22) & ((LM) <TH23) (TH21 ≦ S <TH31) &(L> TH32) & ((LM) <TH33) Also, since conditions may be different depending on RGB colors,
Actually, TH is given separately for R, G, and B. If at least one of them is satisfied, O.T. K. And

Normally, a color determination output is obtained. However, a block determination 1304 may be further provided in order to remove isolated points and the like. This is based on the result of determination around the target pixel for which the secondary color determination has been made, and if there are many secondary color determinations, the second
The secondary color determination is valid, and if the secondary color determination is small, the secondary color determination is invalidated and the primary color determination is performed. The above is the algorithm for color determination. By adding the color judgment 701, the output of the final judgment 702 is divided into four types of areas: secondary color characters, primary color characters, black characters, and pictures. The secondary color characters are chromatic, secondary colors, and characters. The primary color characters are chromatic, primary colors, and characters. Black letters are achromatic and letters. The picture indicates an area that is not one of these three areas.

A configuration example of the fifth embodiment will be described. As the circuit configuration, the adaptive edge enhancement circuit shown in FIG. 5 is used. The description of the edge enhancement circuit is omitted here. There are two types of shift tables. Table 1 sets the shift amount in a normal character portion, Table 2 sets the shift amount for secondary color characters in the image processing CPU 301, and sets the secondary image character Looking at ON / OFF of the color character output, the ROM 303 of the image processing CPU 301 is programmed so that the table 1 is selected when the output is OFF and the table 2 is selected when the output is ON. It is often realized by hardware as a selector for switching between tables 1 and 2. For example, FIG.
An example is the selector 1602 of No. 6.

A description will be given of a modification of the fifth embodiment. The color correction coefficient is switched according to the secondary color character signal output from the new image area separation 79. FIG. 15A shows a reproduction range with a normal color correction coefficient. The color correction method includes a masking method, a Neugebauer method (area ratio), and a black box method. In this embodiment, the masking method is used. The masking method is a method for obtaining the density of all colors from the solid density of the primary color and the secondary color. In practice, it is difficult to cover all highlights, intermediate densities, and shadows from solid density, so in this example, solid density (FIG. 15A)
, G2) represents the range from the intermediate density to the shadow, and represents the intermediate density (Y1, R1,.
.., G1) indicate from highlight to intermediate density.

FIG. 15B shows the color reproduction range based on the color correction coefficient.
Shown in If the solid density of the secondary color is expressed as it is, dust will occur due to excessive toner riding. Therefore, the coefficient is used as a coefficient for suppressing the high chroma portion of the secondary color (R2, G in FIG. 15B).
2, B2). An embodiment of the circuit is shown in FIG. The image processing CPU 301 sets the normal color correction coefficient to the color correction coefficient 1 (1603) and the color correction coefficient for the secondary color character to the color correction coefficient 2 (1604). The selector 1602 is switched by the secondary color character output of the new image area separation 79, and the operation is performed using the respective color correction coefficients.
Going at 1. The above operation is programmed in the ROM 303 of the CPU 301 for image processing.

[0074]

As is apparent from the above description, the digital image processing apparatus of the present invention separates image data obtained by scanning an original image into color components, and outputs the separated color component image data. The image data of the color component is selected from a single color or a full color. When the image forming operation is a single color and at least two or more developed colors are overlapped, the density curve is compared with the density curve in one-color development. Lower. Therefore, it is possible to prevent image deterioration due to toner dust without inferiority of edges. Further, since the circuit configuration can be used as it is, there is no need to increase the cost, and it is practical as a product.

According to the second aspect, when the monochrome mode is selected as the image forming operation and two or more developed colors are output in an overlapping manner, the degree of edge emphasis is lowered as a whole, so that the solid density of the picture portion is reduced. Can be prevented from deteriorating due to toner dust. Further, since the circuit configuration can be used as it is, there is no need to increase the cost, and it is practical as a product.

In the third aspect, the full-color mode is selected as the image forming operation, and the original image is formed in the secondary color (RG
B) In the case of a character, by weakening the degree of edge enhancement as compared with a primary color (CMYBk) character, it is possible to prevent image quality deterioration due to toner dust in a character portion of two-color superposition.

In the fourth aspect, the full-color mode is selected as the image forming operation, and the original image is formed in the secondary color (RG
B) In the case of a character, a color correction coefficient different from the primary color (CMYBk) character is set. The color correction coefficient of the secondary color character is 2
By narrowing the color reproduction range on the high chroma side of the next color, it is possible to prevent image quality deterioration due to toner dust in a two-color superimposed character portion.

In the fifth aspect, when the full-color mode is selected as the image forming operation and the original image is an achromatic character, the edge enhancement degree in the Bk plane and the edge enhancement degree in the CMY plane are changed. Therefore, it is possible to avoid excessive color component enhancement and prevent image quality degradation due to toner dust due to color superposition.

According to the sixth aspect, by making the edge enhancement degree in the CMY plane weaker than the edge enhancement degree in the Bk plane, it is possible to further avoid excessive color component enhancement and prevent image quality deterioration due to toner dust due to color superposition. it can.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram when an embodiment of a digital image processing apparatus of the present invention is applied to a digital color copying machine.

FIG. 2 is a block diagram illustrating a schematic configuration of an electrical unit (image processing unit) of the digital color copying machine.

FIG. 3 is a block diagram illustrating a schematic configuration of an electrical unit in FIG. 2;

FIG. 4 is a diagram illustrating a printer gamma curve.

FIG. 5 is a diagram illustrating an example of the configuration of an edge enhancement filter, and illustrating an adaptive edge enhancement circuit.

FIG. 6 is a block diagram illustrating a basic configuration example of an image area separation circuit.

FIG. 7 is a block diagram illustrating a configuration example of an image area separation circuit including secondary color determination.

FIG. 8 is a block diagram of an edge determination circuit in image area separation.

FIG. 9 is an example of an edge determination, edge detection, and edge count pattern.

FIG. 10 is a block diagram of a halftone dot determination circuit in image area separation.

FIG. 11 is an example of a dot detection pattern, a dot detection pattern, and a dot count pattern.

FIG. 12 is a block diagram of a chromaticity determination circuit in image area separation.

FIG. 13 is a block diagram of a color determination circuit in the image area separation.

FIG. 14 is a diagram illustrating RGB density distributions of a secondary color and a primary color.

FIG. 15 is a diagram illustrating a color reproduction range.

FIG. 16 is a block diagram illustrating a configuration of an electrical unit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor drum 2 transfer drum 3 writing unit 4 developing unit 9 fixing device 10 paper output tray 11 paper feed cassette 50 system controller 60 synchronization control circuit 71 scanner gamma 72 smoothing filter 73 color correction 74 UCR / UCA 75 selector 76 edge enhancement filter 77 printer gamma 78 gradation processing 79 image area separation 80 ACS 100 laser printer 200 automatic document feeder 300 operation unit 400 image scanner 500 external sensor

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI H04N 1/46 H04N 1/46 Z

Claims (6)

[Claims] An image reading unit that optically scans an original image to convert the image data into image data; a color component separating unit that separates the image data into color components; and a color component separated by the color component separating unit. Image forming means for outputting the image data of the color component; selecting means for selecting whether the image data of the color component is a single color or full color;
A digital image processing apparatus, comprising: a density adjustment function unit for lowering a density curve as a whole as compared with a density curve in one-color development when superimposing more than one color. 2. The apparatus according to claim 1, wherein the density adjustment function unit further weakens the degree of edge emphasis as a whole.
The digital image processing apparatus according to claim 1. 3. The digital image processing apparatus further comprises a character / pattern determining means for determining whether the original image is a character or a picture, and determining whether the original image is chromatic or achromatic. 3. The digital image processing apparatus according to claim 2, further comprising chromatic / achromatic color determining means, wherein the edge emphasis degree is reduced based on a result of the determination by the determining means. 4. The chromatic / achromatic color judging means, wherein the chromatic color is a primary color (CMY) or a secondary color (RGB) of a developed color.
It is determined whether the character is a secondary color, and if it is determined that the character is a secondary color, it is a primary color, and compared with the case where the character is determined to be a primary color, 4. The digital image processing apparatus according to claim 3, wherein the degree of edge enhancement is reduced. 5. The density adjustment for weakening the edge emphasis degree is performed by switching a color correction coefficient between an area determined to be a character of the secondary color and an area determined to be a character of the primary color.
5. The digital image processing apparatus according to claim 4, wherein the color correction coefficient for the next color character is density adjustment for narrowing the color reproduction range of the secondary color on the high saturation side. 6. The density adjustment for weakening the edge emphasis degree is performed when the original image is determined to be an achromatic color and is determined to be a black character. In comparison with the degree of edge enhancement in
5. The digital image processing apparatus according to claim 4, wherein the density adjustment is performed to weaken the degree of edge enhancement in the MY plane.