JPH1093829A - Digital color image forming device with automatic color selection function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain automatic color selection with high accuracy by avoiding a chromatic color picture element from being a chromatic color when achromatic picture elements surrounding a chromatic picture element have a density change. SOLUTION: An image sensor 410 of an image scanner 400 reads R, G, B color components of an original image and provides an output of the result as 8-bit color image information. An image visualized by M, C, Y and BK toner on a photoreceptor drum 1 in a laser printer 100 is transferred onto transfer paper. An image processing unit applies various processing to an output image signal from the image scanner 400 and gives the result to the laser printer 100. When a maximum value of differences between R, G, B data for each picture element is extracted and larger than a prescribed value, the picture element is discriminated to be a chromatic color. Then a chromatic color picture element surrounded by achromatic colors is detected by pattern matching in the unit of 5. 5 picture element block. When there exists any density change in the surrounding achromatic color area, the noted picture element is not selected for a chromatic color discrimination object.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image forming operation,
The present invention relates to a digital color image forming apparatus capable of automatically switching between monochrome and color.

[0002]

2. Description of the Related Art Such a technique is disclosed in Japanese Patent Application Laid-Open Nos. 3-54972 and 4-33787. Both publications relate to a color copying machine having an automatic color selection function, but there is a disclosure of a method for determining whether the image is chromatic or achromatic. According to the determination method disclosed in Japanese Patent Application Laid-Open No. 3-54972, a chromatic determination may be made even though the periphery of an edge is achromatic, so that color identification means and edge detection means are used. It does not count as pixels. Japanese Patent Application Laid-Open No. 4-33787 discloses a color identification method.
The RGB input signal is converted into L, a, b signals, and a chromatic / achromatic determination is made in the a, b space. Furthermore,
The boundary of chromatic / achromatic judgment in a and b is changed by the value of L, and the blocks judged as color pixels are counted on the entire document surface, and the chromatic judgment is not performed until the number reaches a predetermined value or more.
Processing for improving the accuracy of chromatic / achromatic judgment is employed.

Here, the electric system of the digital color image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 3-54972 is shown in FIG.
The output of the UCR generation circuit 73 is sent to the color identification circuit 80 on the one hand. The color identification circuit 80 is a circuit for identifying whether a chromatic color is included in a document image. Since the UCR black generation circuit 73 extracts black, that is, an achromatic color density component from the input image information as a BK signal, the Y, M, and C signals output from the UCR black generation circuit 73 are components of only chromatic colors. Is a color signal. Therefore UC
Whether or not the original image is a color image can be identified by the presence or absence of the components of the Y, M, and C color signals output from the R black generation circuit 73. By the way, the actual color of the original image
It is unavoidable that a slight error occurs between the color detected by the image scanner 400 and the chromatic stain in the original image. is there.

Therefore, in this example, a UCR black generation circuit 73 is used.
Ignores the relatively small chromatic components output by
The chromatic color identification signal SG1 = H is output only when the chromatic image area is larger than a predetermined range. That is, only the most significant bit (MSB) signal of the Y, M, and C color signals output from the UCR black generation circuit 73 is input to the color identification circuit 80. In other words, the setting is made such that when any one of the chromatic color signals Y, M, and C has a value of 128, that is, 50% or more, that color signal is regarded as a valid signal. In addition, for colors registered as special colors,
A chromatic color identification signal SG1 = L is output, and Y, M, C
Is corrected in consideration of the upper and lower 10% errors in the validity determination of each color signal. Effective signal SG1 = H after such correction
Is detected by the color identification circuit 80, the size of the pixel area of the color signal is counted by the counter 84.

The counting by the counter 84 is performed for each document to be read. That is, the counter 84 is cleared by the clear signal CLR when reading scanning of the document is started, and counting is permitted. The size signal SIZE is a signal determined according to the detected document size. The size signal SIZE is at a high level H during a period in which the image scanner 400 scans the range where the document actually exists. Becomes low level during the scanning of. Also, the clock pulse appears at the pixel timing of each clock signal CLK. At the start of reading of the document, the counter 84 is cleared by the clear signal CLR, so that the output of the inverter 85 is H, and while reading the area where the document exists, the output of the AND gate 82 is A high-level clock pulse CLK appears at each read. In this state, the counter 84 calculates the number of clock pulses CLK, that is, the number of pixels while a chromatic signal having a density of 50% or more is being input.

The output terminal of the color identification circuit 80 is connected via an inverter 85 to the bit 8 input terminal of a binary counter 84. Therefore, the count value of the counter 84 becomes 51
When the number reaches 2, the chromatic color identification signal SG1 output from the color identification circuit 80 switches from L to H, so that no more clock pulse CLK is applied to the counter 84, and the level of the chromatic color identification signal SG1 becomes , Is kept at H until the next clear signal CLR is applied from the system controller 50. The SG1 signal thus held is 1
When the scanning (or pre-scanning) is completed, it is sent to the system controller 50 to determine whether the original is chromatic or achromatic. This is the flow of the automatic color selection function called ACS.

[0007]

When a black-and-white document is read, color pixels are often detected around a character or a line drawing, and the pixel is often determined to be a chromatic image. The chromatic color identification by the color identification circuit 80 shown in FIG. However, conversely, when there is a character that is chromatic and thin but has high saturation, it should be judged chromatic. However, this has a drawback that it is determined to be chromatic around the edge and is excluded from the chromatic count. Although the technique disclosed in Japanese Patent Application Laid-Open No. 4-33787 can save chromaticity to some extent, it does not pay attention to edges, and therefore, for a document mainly composed of a black-and-white image, the chromatic / achromatic determination accuracy around the edges is reduced. Is low.

An object of the present invention is to reduce erroneous chromatic determination of an original mainly composed of black and white to eliminate these drawbacks and to properly determine chromaticity of thin chromatic characters.

[0009]

[Means for Solving the Problems]

(1) Image reading means for optically scanning a document image to convert it into image data, color identification means for decomposing the read image data into color components to identify whether the document image is a single color, and its color A digital color image forming apparatus having control means for automatically switching an image forming operation between a single color and a color based on the identification result of the identification means; When there is a change in achromatic color density around a chromatic color pixel surrounded by, a means for removing the chromatic color pixel from the chromatic determination candidates is provided.

According to this, when a change in achromatic color density exists around a chromatic color pixel surrounded by achromatic colors, the chromatic color pixel is excluded from the chromatic determination candidates, so that black and white is mainly used. Erroneous chromatic judgment of original documents to be processed, and when there is no change in achromatic color density, the chromatic pixel is included in the chromatic judgment candidate. Can be.

(2) Image reading means for optically scanning an original image to convert it into image data, and color identification means for decomposing the read image data into color components to identify whether the original image is a single color or not. A digital color image forming apparatus having control means for automatically switching an image forming operation between a single color and a color based on the identification result of the color identification means; Means for detecting a chromatic color edge, and when there is a change in achromatic color density around a chromatic color pixel surrounded by achromatic color, means for removing the chromatic color pixel from chromatic determination candidates When,
When there is no change in the achromatic color density, the chromatic color pixel has a means for expanding the chromatic determination candidate of the chromatic color pixel by an edge of the chromatic color.

According to this, when there is a change in achromatic color density around a chromatic pixel surrounded by achromatic colors, the chromatic pixel is excluded from the chromatic determination candidates, so that black and white is mainly used. In the case where the chromatic error determination of the original to be performed is prevented and the change in the achromatic color density does not exist, the chromatic pixel is included in the chromatic determination candidate, and the chromatic determination candidate for the edge of the chromatic color is expanded. Therefore, it is possible to prevent erroneous achromatic determination of a thin chromatic image, particularly a thin chromatic image surrounded by black having a high density.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

[0014]

【Example】

-First Embodiment- Next, a first embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a configuration diagram showing a mechanism configuration of a digital color copying machine according to a first embodiment of the present invention. In the figure, 100 is a laser printer, 200 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 disposed below a contact glass 401 is mounted in a horizontal direction (sub-scanning direction) in FIG. An image reading unit that reads an image. The light emitted from the illumination lamp 402 is
The light is reflected on the surface of the document placed on the contact glass 401 according to the density of the document 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 4
Numeral 10 splits the incident light into three colors of R, G and B according to the wavelength. Each of the three split lights enters a different one-dimensional charge-coupled device (CCD) image sensor 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-scanning of the moving body.

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. 21
Reference numeral 3 denotes a separation roller for avoiding double feeding. The original fed out to a predetermined position is driven by a pull-out roller 217 and a conveyor belt 216 to drive the image scanner 4.
When the document is further conveyed over the contact glass 401 and advances to a predetermined reading position, that is, when the leading edge of the document reaches the left end position of the contact glass 401, it stops. When reading of the document is completed, the transport belt 216 is driven again, the document on the contact glass 401 is discharged, and the next document 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 a leading edge and size of the document are detected between the separation roller 213 and the pull-out roller 217. And a document leading edge sensor 214.

The document leading edge sensor 214 is composed of a plurality of sensors arranged at different positions in the main scanning direction (perpendicular to the paper surface), and depending on the combination of the detection states of these sensors, the sensor in the main scanning direction is determined. The original size, that is, the original width can be detected. Also, a pulse generator for outputting a pulse corresponding to the rotation amount is provided in a paper feed motor (not shown), and the control device of the ADF 200 measures the time until the document passes the document leading edge sensor 214 so that The document size in the scanning direction, that is, the length of the document is detected. Note that the call roller 212 and the separation roller 213 are driven by a paper feed motor, and the pull-out roller 217 and the transport belt 216 are driven by a transport motor. Registration sensor 21 composed of an optical sensor
5 is disposed downstream of the pull-out roller 217.

The external sensor 500 is the image scanner 40
This is a handy type scanner composed of a CCD that can simultaneously detect the R, G, and B color components of the original image as in the case of 0.

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 charging 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), and the laser light emitted from the writing unit 3 is irradiated on the surface of the photosensitive drum 1 via the rotating polyhedron 3b, the lens 3c, the mirror 3d, and the lens 3e. The rotating polygon mirror 3b is driven to rotate at a constant high speed by the polygon motor 3a.

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, at each scanning position on the surface of the photosensitive drum 1,
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 emitted. 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 embodiment, the developing unit 4 is provided with four sets of developing units 4M, 4C, 4Y and 4BK, and each developing unit has M (magenta) and C of different colors.
(Cyan), Y (yellow) and BK (black) toners. Since the laser printer 100 is configured so that any one of the four developing units is selectively energized, the electrostatic latent image is M, C, Y, or Bk.
The image is visualized with any one of the toner colors.

On the other hand, the transfer paper stored in the paper feed cut 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 attracted to the surface. Moves with the rotation of the transfer drum 2. Then, at a position close to the surface of the photosensitive drum 1, the toner image formed on the photosensitive drum 1 by charging by the transfer charger 7 is transferred to the surface of the transfer paper.

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
The image is fixed and discharged to the discharge tray 10. In the case of the full-color mode, it is necessary to form images of four colors of BK, M, C, and Y on a single transfer sheet. In this case, first, a BK color toner image is formed on the photosensitive drum 1 and transferred to a transfer sheet, and then the next M color image is formed on the photosensitive drum 1 without separating the transfer sheet from the transfer drum 2. A toner image is formed, and the toner image is transferred to a transfer sheet 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. In other words, by repeating the process of forming and transferring the toner image,
One color image is formed on the transfer paper. 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 the fixing device 9
After receiving the toner image fixing process, the toner image is discharged to the paper discharge tray 10.

FIG. 2 is a circuit block diagram showing a schematic configuration of the electrical unit of the digital copying machine shown in FIG. 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. In the present embodiment, the main scanning synchronization signal based on the scanning timing is the laser printer 1
The rotation is synchronized with the scanning start timing of the laser beam by the rotation of the rotating polygon mirror 3b at 00. The R, G, and B image signals read by the image scanner 400 are A / D converted and output as 8-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 includes circuits for gamma correction 71, complementary color generation 72, under color removal (U-CR) black generation 73, selector 74, and gradation processing 75. The gamma correction 71 converts the reflectance linear R, G, and B data read by the image scanner 400 into linear density R, G, and B data. The complementary color generation circuit 72 converts the image information of each color of R, G, and B into image information of each color of Y, M, and C, which are the complementary colors. UCR
The black generation circuit 73 extracts a black component included in the color of the image signal obtained by synthesizing all of the input image information of the Y, M, and C colors, outputs it as a BK signal, and outputs the image signals of the remaining colors. From the black component. The selector 74 inputs Y,
Any one of the M, C, and BK color signals is selected and output to the gradation processing circuit 75. Gradation processing circuit 75
Is a circuit for binarizing or multi-leveling the input 8-bit density information. The circuit performs dither processing on an obtained image signal to enable output of a halftone image.
A binarized or multi-valued image signal is output to the laser printer 100.

When the color registration mode is set by the system controller 50, the special color data input from the external sensor 500 is stored in the image scanner 40.
As with the normal image data read at 0, the gamma correction, the complementary color generation, and the UCR black generation are performed, and then sent to the color identification circuit 90 and registered. The special color data is not determined by the color identification circuit 90 as a chromatic color.

FIG. 2 differs from the conventional example shown in FIG. 11 in the color identification circuit 90 and its input. In the conventional example (FIG. 11), it was sufficient to determine the edge based on the BK output of the UCR black generation circuit 73. However, in the present embodiment, it is necessary to determine not only black but also achromatic color by the UCR circuit.
Scanner gamma correction 7 before UCR black generation circuit 73
The data R, G, and B output by the data 1 are supplied to a color identification circuit 90. The operation itself after detecting the color identification signal SG1 is as follows.
There is no difference from the conventional example (FIG. 11).

FIG. 3 shows the configuration of the color identification circuit 90. The R, G, and B data output from the scanner gamma correction 71 are input to two determination blocks, a chromatic determination block 91 and a density determination block 92.

In the chromatic determination block 91, it is determined whether the color is chromatic or achromatic. First, R, G, and B data of one pixel
The maximum value of the difference value between the parties is extracted. If this is greater than a predetermined value, the pixel is determined to be chromatic. This is the case when the chromatic / achromatic determination is performed in units of one pixel, but may be performed in units of blocks. In this case, for example, the condition of the high-saturation pixel is divided into the high-saturation pixel and the low-saturation pixel, and the condition of the high-saturation pixel is the same as the condition of one pixel unit, and the maximum value of the difference value between the R, G, and B data is In the case of being larger than the predetermined value, the condition of the low-saturation color pixel is that the maximum value of the difference value between the two of the R, G, B data is larger than the predetermined value and the R, G, B data When the minimum value of the data is smaller than a predetermined value, the maximum value of the difference value between the two of the R, G, and B data at the low chroma pixel in this case is larger than that at the high chroma pixel. The conditions are such that they are chromatic even if they are small. The chromatic / achromatic determination of the block is, for example, when determining in a 4 × 4 block, two or more high-saturation pixels out of 16 pixels or 16/16 low-saturation pixels are used.
If a pixel exists, the block is determined to be chromatic.

In the density determination block 92, the density of the document is detected. There are several possible methods. The G data has characteristics similar to those of the luminance signal, so the G data is used as it is, and if the luminance is to be faithfully reproduced (R, G,
B) = a method using data of (3,6,1), a method of converting RGB into L, a, b signals, and using an L signal. Whatever data is used, it is binarized with a predetermined value and output to the next block.

The block determination 93 is a block for searching for a chromatic pixel surrounded by achromatic colors and a change point of density in block units. The chromatic pixels surrounded by achromatic colors are regarded as vertical, horizontal, and slanted lines, and pattern matching is performed using a 5 × 5 or 7 × 7 matrix. When a chromatic pixel under the above conditions exists in a matrix, a change in density in the matrix is observed. If there is a change in the density in an area determined to be an achromatic pixel by pattern matching, the target pixel is not set as a chromatic determination candidate, and the density of the area is determined to be achromatic in the pattern matching. If there is no change, the target pixel is output as a chromatic determination candidate.

As an example, FIGS. 4A to 4H show 5 × 5 vertical, horizontal, and oblique patterns. In the hatched portions of these patterns, at least five or more chromatic pixels exist, all white blank portions must have five or more achromatic pixels, and all white blank portions must be achromatic pixels. Becomes Since the chromatic judgment candidates are output over the entire surface of the document by the block judgment 93, the counting judgment 94 is a block for counting how many chromatic judgment candidates are present or how many are continuous. It is finally determined whether the original is chromatic or achromatic based on whether there is a chromatic determination candidate equal to or more than a predetermined value or whether chromatic determination candidates are equal to or more than a predetermined value.

For example, when it is desired to determine that a document having a length and width of 1 mm or more consecutively is chromatic, if the count is at most 1 mm (corresponding to 16 counts in 16 mm lines), the document is determined to be a chromatic original. Will do.

FIG. 5 shows an example of the flow of processing in the color identification circuit 90 shown in FIG. This is an example in which a chromatic color with high saturation and black with high density exist on a white background as a document. The output of the chromatic determination 91 is a "chromatic / achromatic" signal in FIG. 5, the output of the density determination 92 is a "density (dotted line indicates achromatic density)" signal in FIG. The output of 93 is shown as a "chromatic count" signal in FIG. As can be seen from FIG. 5, the chromatic judgment (Er) appearing at the edge portion of “achromatic color: black” is ignored and does not appear in the chromatic count, and the chromatic judgment is valid for the chromatic color as it is. I have.

Next, the synchronization signal input to the color identification circuit 90 in FIG. 2 will be described. The synchronization signals include three signals CLK, CLR, and SIZE from the synchronization control circuit 60. The respective timing charts are shown in FIGS. The CLR signal is one frame (F
(GATE) start signal, the signal goes low (low level L) once at the beginning of one scan, and then remains high (high level H) until the next scan start. This is shown in FIG.
Is a reset signal of the count judgment 94 in the above. That is, 1
One chromatic / achromatic determination is determined for each scan.

The SIZE signal indicates an area in which chromatic / achromatic determination is performed. In FIG. 6, an AND signal of an effective width LGATE signal in the main scanning direction and an effective width FGATE signal in the sub-scanning direction is used. . The CLK signal is a clock signal in the main scanning direction and indicates a pixel clock.

As described above, the first embodiment of the present invention
According to (FIG. 3), when a change in achromatic color density exists around a chromatic pixel surrounded by achromatic colors, the chromatic pixel is excluded from the chromatic determination candidates (FIG. 5). Prevent chromatic misjudgment in black-and-white documents and, if there is no change in achromatic color density, the chromatic pixel is included in the chromatic judgment candidate. Can be
Since automatic color selection can be performed with high accuracy, copy failures can be reduced and waste can be eliminated.

Second Embodiment A second embodiment is also the same as the digital color copying machine shown in FIG. 1 and has the same electrical system configuration as that shown in FIG. , The first embodiment (FIG. 3). FIG. 7 shows the configuration of the color identification circuit 90 of the second embodiment. The R, G, and B data output from the scanner gamma correction 71 are input to two determination blocks, a chromatic determination block 91 and a density determination block 92. Both the chromatic determination block 91 and the density determination block 92 perform the same processing as that of the first embodiment, and thus the details are omitted here.

To the block judgment 93, in addition to the output of the chromatic judgment 91 and the output of the density judgment 92, the output of the edge judgment 95 is input. This is a feature of the second embodiment. The edge judgment 95 is a block for extracting a chromatic color edge. The output result of the chromatic determination 91 is, for example, 3 × 3
, And detects both the plus edge and the minus edge. FIGS. 8A and 8B show two examples of the Laplacian filter.

In the block judgment 93, a chromatic pixel surrounded by an achromatic color, a change point of density, and an edge of the chromatic pixel are searched for in blocks, and a chromatic judgment candidate is corrected. The method of finding a chromatic pixel surrounded by achromatic colors is the same as that of the first embodiment (FIG. 3), and thus the details are omitted here. In the block determination 93, when a chromatic pixel surrounded by an achromatic color exists in a matrix, a change in density in the matrix is checked. If there is a change in the density in the achromatic pixel area in the matrix, the target pixel is not set as a chromatic determination candidate. This is the same as the first embodiment (FIG. 3).

If there is no change in the density in the achromatic color pixel area in the matrix, the result of the chromatic judgment and the result of the chromatic edge judgment are added up and output as a chromatic judgment candidate of the pixel of interest.

The processing of the next count judgment 94 is the same as that of the first embodiment (FIG. 3), and thus the details are omitted.

FIG. 9 shows an example of the processing flow of the color identification circuit 90 shown in FIG. This is an example of a case where a chromatic color with high saturation and a black with high density exist on a white background. The output of the chromatic determination 91 is a “chromatic / achromatic” signal in FIG. 9, and the output of the density determination 92 is a “density (dotted line indicates the density in achromatic color)” signal in FIG. The output of the edge judgment 95 is shown as a "chromatic edge" signal in FIG. 9, and the output of the block judgment 93 is shown as a "chromatic count" signal in FIG. As can be seen from FIG. 9, the chromaticity judgment (Er
i) is ignored, and the chromatic color is added by the chromatic edge (Ero) to be a chromatic determination candidate. The reason why the processing of the second embodiment is effective is that “achromatic color: black” around the chromatic pixel.
Is present.

FIG. 10 shows an example. This is an example of a case where a highly saturated chromatic color and white exist on a black background as a document. The output of the chromaticity determination 91 is “chromatic /
As an “achromatic” signal, the output of the density determination 92 is a “density (dotted line indicates achromatic color density)” signal in FIG.
The output of the edge judgment 95 is shown as a "chromatic edge" signal in FIG. 10, and the output of the block judgment 93 is shown as a "chromatic count" signal in FIG. When a chromatic color with high saturation exists on a black background, the chromatic judgment tends to be thinner than the actual one due to the influence of surrounding black (Ern). If this is counted as it is, there is a possibility that the thin line of the chromatic color pixel will fall without being counted chromatically. This is expanded and corrected (H level of “chromatic count” in FIG. 10). This is a feature of the second embodiment.

As described above, according to the second embodiment of the present invention (FIG. 7), when there is a change in achromatic color density around a chromatic pixel surrounded by achromatic colors, the chromatic color changes. Since the pixel is excluded from the chromatic determination candidate (FIG. 9), erroneous chromatic determination of a black-and-white document is prevented, and when there is no change in achromatic color density, the chromatic pixel is included in the chromatic determination candidate. In addition, since the chromatic judgment candidates for the chromatic edge are expanded (FIG. 10), it is possible to prevent achromatic erroneous judgment of a thin chromatic image, particularly a thin chromatic image surrounded by black with high density. Since automatic color selection can be performed with high accuracy, copy failures can be reduced and waste can be eliminated.

[Brief description of the drawings]

FIG. 1 is a side view showing a schematic configuration of a mechanical part of a digital color copying machine according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of an electrical unit of the digital color copying machine shown in FIG.

FIG. 3 is a block diagram showing a configuration of a color identification circuit 90 shown in FIG.

FIGS. 4A to 4H are plan views showing a 5 × 5 pixel pattern used in the block determination 93 shown in FIG. 3 for detecting chromatic pixels surrounded by achromatic pixels. is there.

5 is a time chart showing a change in output level of each block in the color identification circuit 90 shown in FIG. 3, and the horizontal axis is a position in the main scanning direction.

6A and 6B are time charts showing timings of generation of a synchronization signal, CLK, CLR, and SIZE signals input to a color identification circuit 90 shown in FIG. 3, and FIG. 6A shows a relationship between a document and a scanning synchronization signal. , (B) shows a signal generated in synchronization with the sub-scanning, and (c) shows a signal generated in synchronization with the main scanning.

FIG. 7 is a block diagram showing a configuration of a color identification circuit 90 used in a second embodiment of the present invention.

FIGS. 8A and 8B are plan views showing a Laplacian filter of a 3 × 3 pixel matrix used by the edge judgment 95 shown in FIG. 7;

9 is a time chart showing an example of a change in the output level of each block in the color identification circuit 90 shown in FIG. 7,
The horizontal axis is the position in the main scanning direction.

FIG. 10 is a time chart showing another example of a change in the output level of each block in the color identification circuit 90 shown in FIG. 7;
And the horizontal axis is the position in the main scanning direction.

FIG. 11 is a block diagram showing a schematic configuration of an electrical unit of a conventional digital color copying machine.

[Explanation of symbols]

1: Photoconductor drum 2: Transfer drum 3: Writing unit 4: Developing unit 9: Fixing unit 10: Discharge tray 11: Paper cassette 100: Laser printer 200: Automatic document feeder 300: Operation board 400: Image scanner 500 : External sensor

Claims (2)

[Claims] An image reading unit that optically scans an original image to convert the image data into image data; a color identification unit that separates the read image data into color components to identify whether the original image is a single color; A digital color image forming apparatus including a control unit for automatically switching an image forming operation between a single color and a color based on the identification result of the color identification unit; A digital color image forming apparatus comprising: means for removing a chromatic color pixel from chromatic determination candidates when a change in achromatic color density exists around a chromatic color pixel surrounded by achromatic colors. 2. An image reading means for optically scanning a document image to convert it into image data, a color identification means for decomposing the read image data into color components and identifying whether or not the document image is a single color; A digital color image forming apparatus including a control unit for automatically switching an image forming operation between a single color and a color based on the identification result of the color identification unit; A means for detecting a chromatic color edge, and when there is a change in achromatic color density around a chromatic color pixel surrounded by achromatic color, the chromatic color pixel is excluded from the chromatic determination candidates and A digital color image forming apparatus comprising means for expanding a chromatic judgment candidate of a chromatic color pixel by an edge of a chromatic color when there is no change in chromatic color density.