JP2004297609A - Two-color image forming method and color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a two-color image forming method and a color image forming apparatus for selecting 2-color processing in automatic color selection (ACS). <P>SOLUTION: Basic setting procedures for the two-color processing includes: a step S2 of applying automatic color select processing to an original so as to discriminate the original is a full color original or a monochromatic original; a step S3 of discriminating whether or not a character region in two colors or more is present on the original when the original is discriminated to be the monochromatic original; a step S4 of making a user select monochromatic processing or two-color processing when the character region in two colors or more is present on the original; and steps S9 to S11 of applying the monochromatic processing or the two-color processing to the original depending on the selection result to form an image. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a two-color image forming method and a color image forming apparatus for forming an image by performing two-color processing on a document.
[0002]
[Prior art]
A color copier has a determination unit (auto color select (ACS)) for automatically determining whether a document is color or monochrome. If the determination is monochrome, a monochrome copy is performed. In such a case, a monochrome copy is performed, and a color copy is performed when it is determined that the document is a color document and the document is determined to be a photo document.
[0003]
On the other hand, a color image forming apparatus capable of setting a two-color processing function has been developed because two-color copying with less toner consumption than three-color or four-color full-color copying is desired to be performed at low cost. ing.
Further, in a one-drum type color image forming apparatus for forming an image of each color on the same drum, the number of rotations of the drum required for development requires four rotations for full color, but only two or three rotations for two color. , Can increase the output speed
[0004]
[Patent Document 1] JP-A-2002-247390
[Patent Document 2] JP-A-11-187279
[0005]
[Problems to be solved by the invention]
Conventionally, the determination of the automatic color select (ACS) is of two types: full color and monochrome. Therefore, when an ACS determination is performed on a character document in which the character to be emphasized is a color character, a monochrome determination is almost always performed, and since the character is copied in monochrome, the character to be copy-emphasized is not copied as a color character. , The text I wanted to emphasize was confusing.
[0006]
Therefore, the user needs to select the two-color copy by his / her own selection, and the frequency of using the ACS is reduced.
Therefore, an object of the present invention is to provide a two-color image forming method and a color image forming apparatus which enable selection of two-color processing in auto color select (ACS).
[0007]
[Means for Solving the Problems]
According to the two-color image forming method of the present invention, an original is determined by an automatic color selection process as to whether the original is a full-color original or a monochrome original. It is determined whether or not the above-described character area exists, and when there is a character area of two or more colors in the document, the user is caused to select either monochrome processing or two-color processing, and according to the selected result. This is a method of forming an image by performing monochrome processing or two-color processing on a document.
[0008]
According to this method, when it is determined by the auto color selection process that the document is a monochrome document, the character region and the like are separated by region separation, and the number of colors used in the separated character region is specified. If there is only one color, monochrome processing is performed. If it is determined that the document is a character document of two or more colors, for example, if there are two colors, black and another color, the user is allowed to select whether to perform two-color processing or monochrome processing, and according to the selected result. The image can be formed by subjecting the original to monochrome processing or two-color processing.
[0009]
Here, “two-color processing” means that when cyan (C), magenta (M), and yellow (Y) are used as three primary colors, CM, CY, MY, CK, MK, YK, CMK, CYK, or MYK (K represents black). When red (R), green (G), and blue (B) are used as the three primary colors, an image is formed using any combination of RG, GB, BR, RK, BK, BK, RGK, GBK, or RBK. That means.
[0010]
As described above, even when the document is determined to be a monochrome document by the automatic color selection process, the user can select the two-color process. It can be formed by color characters of the same color or color characters of other colors.
In the procedure in which the user selects the type of processing, if the user selects two-color processing, the user is caused to select either monochrome processing or two-color processing except for the character area, and the user selects monochrome processing. In such a case, the character area is formed by two-color processing, and the image is formed by monochrome processing except for the character area. When the user selects the two-color processing, the entire document is subjected to two-color processing to form the image. (Claim 2).
[0011]
According to this method, in a document in which the characters to be emphasized are colored characters, the character region is subjected to two-color processing and image formation is performed by monochrome processing other than the character region according to the user's selection, thereby enhancing only the character region. Characters can be formed with colored characters. Therefore, only characters can be emphasized.
In the procedure in which the user selects the type of processing, before the user selects two-color processing, a color having a large amount of remaining toner, a frequently used color in a document, or a previously frequently selected color is selected. It can be presented to the user and selected as a default (claim 3).
[0012]
As described above, by presenting the user with a default color that has a large amount of toner, a color that is frequently used in a document, or a color that is frequently selected, the user can select (1) enable the remaining amount of toner. The user can select a color that can be used for the original, (2) a color that can reproduce a color as faithful as possible in the original, or (3) a color that is suitable for the original to be used by the image forming apparatus based on past results, without the user's trouble. Can be done.
In the procedure in which the user selects the type of processing, the user may be allowed to select an arbitrary color (claim 4). When the user wants to select a color other than the color presented as a default, a color according to the user's preference can be selected.
[0013]
In the procedure of forming an image by performing the two-color processing, it is preferable that an emphasis process can be performed on any one color portion of the target character. For example, when two colors, such as black and another color, exist in a document, the “other colors” can be further emphasized and displayed.
When the user selects two-color processing in the procedure of selecting the type of processing, if the user selects a two-color processing, a color having a large amount of remaining toner, a frequently used color in a document, or a color frequently selected in the past. , Two colors having a large color difference may be presented to the user as defaults and selected (claim 6). This makes it possible to obtain an easy-to-read image in which the color difference clearly appears when two-color processing is performed.
[0014]
In the procedure in which the user selects the type of processing, it is preferable that the relationship between the process selected by the user and the color characteristics of the document is stored, and the relationship is reflected in the character area determination threshold based on this relationship. ). This makes it possible to appropriately determine whether the document is a text document or a document that is not a text document, thereby preventing a deviation in the determination result.
Further, a color image forming apparatus according to the present invention is the same as the two-color image forming method according to claim 1 (claim 8).
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic sectional view showing an internal configuration of a digital color copying machine 1 according to one embodiment of the present invention.
The digital color copying machine 1 applies single-color toners of cyan (C), magenta (M), yellow (Y) and black (K) to paper based on color image data of a document read by a document reading unit 2. By superimposing, a monochrome, two-color or full-color image can be formed by a so-called electrophotographic method.
[0016]
An original to be read by the original reading unit 2 is set on a contact glass 3 arranged on the upper surface of the digital color copying machine 1 so that the image faces downward. A cover 4 that can be opened and closed is disposed above the contact glass 3 so that the cover 4 can be opened and closed so that documents can be set one by one on the contact glass 3. I have.
The original reading unit 2 includes a light source 21 for illuminating the original set on the contact glass 3 from below, a CCD image sensor 22 for detecting reflected light from the original and converting the reflected light into an electric signal, The first, second, and third reflecting mirrors 231 to 233 for guiding the reflected light to the detection surface of the CCD image sensor 22, and for forming an optical image of the document on the detection surface of the CCD image sensor 22 A lens 24. Main scanning of the document is achieved by electrical scanning in the CCD image sensor 22.
[0017]
The light source 21 and the first reflecting mirror 231 are held by a first holding member 251, and the second and third reflecting mirrors 232 and 233 are held by a second holding member 252. The two holding members 251 and 252 are movable along the lower surface of the contact glass 3 in the left-right direction (sub-scanning direction) in FIG. The first and second holding members 251 and 252 move in the same direction by the rotation of the stepping motor so that the speed of the second holding member 252 becomes half the speed of the first holding member 251. ing. The sub-scan of the original set on the contact glass 3 is performed by the movement of the light source 21 and the reflecting mirrors 231 to 233 accompanying the movement of the first and second holding members 251, 252.
[0018]
On the detection surface of the CCD image sensor 22, reading lines 22R, 22G, and 22B for detecting each color of red (R), green (G), and blue (B) are provided at predetermined positions along the main scanning direction. It extends at intervals (for example, a distance of four lines). Light emitted from the light source 21 is reflected on the original, and the reflected light is reflected by the reflecting mirrors 231 to 233 and is incident on the detection surface of the CCD image sensor 22. The digital color copying machine 1 is provided with an image signal based on each color component (RGB) detected on each of the reading lines (red reading line 22R, green reading line 22G, blue reading line 22B) of the CCD image sensor 22. Is input to the control unit 5 (see FIG. 2).
[0019]
The control unit 5 performs one color, two colors, three colors, or all colors selected from cyan (C), magenta (M), yellow (Y), and black (K) based on the input image signal. Is generated, and each digital image data is supplied to the laser scanning unit 6 (LSU). The laser scanning unit 6 separately irradiates the irradiation light based on the given digital image data toward the surface of the substantially cylindrical photoconductor 71 provided in the image forming unit 7.
[0020]
The image forming section 7 contains a main charger 72 for charging the surface of the photoconductor 71 and toners of respective colors of cyan, magenta, yellow and black in addition to the photoconductor 71. The image forming apparatus includes developing devices 73C, 73M, 73Y, and 73BK for forming toner images of respective colors, and a cleaning device 73 for removing toner remaining on the surface of the photoconductor 71 after the transfer of the toner image.
The surface of the substantially cylindrical transfer drum 75 contacts the surface of the photoconductor 71. The transfer drum 75 is formed such that its outer peripheral length is longer than the length of a sheet to be used. A transfer device 76 is provided in the transfer drum 75 at a position facing the photoconductor 71. In the digital color copying machine 1, the paper is wound around the transfer drum 75 rotating clockwise in FIG. 1, and passes through the transfer position (between the photosensitive member 71 and the transfer drum 75) once to four times. Each color toner image sequentially formed on the surface of the photoconductor 71 can be transferred one by one to a sheet by the operation of the transfer device 76.
[0021]
More specifically, during image formation, first, the surface of the photoconductor 71 rotating counterclockwise in FIG. 1 is uniformly charged by the discharge of the main charger 72. Irradiation light based on digital image data of a document read by the document reading unit 2 is radiated from the laser scanning unit 6 onto the charged surface of the photoconductor 71, so that the surface of the photoconductor 71 is selectively provided. Upon exposure, an electrostatic latent image corresponding to any one of cyan, magenta, yellow, and black is formed on the surface of the photoconductor 71. Then, on the surface of the photoreceptor 71 on which the electrostatic latent image is formed, toner is adhered by a developing device corresponding to the one-color toner, and a one-color toner image to be transferred to paper is formed.
[0022]
The paper to be used can be set in, for example, a paper cassette 8 or a manual tray 9. In the digital color copying machine 1, the paper is guided from each of the paper cassette 8 and the manual tray 9 to the image forming unit 7. A branched paper transport path 10 is arranged so as to be able to perform the operation.
The paper cassette 8 can store a plurality of papers, for example, and can feed out the stored papers one by one to the paper transport path 10 by a pickup roller 81. On the other hand, the sheets set one by one on the manual feed tray 9 are sent out to a sheet transport path 10 by a sheet feeding roller 91.
[0023]
The sheet sent from the sheet cassette 8 or the manual feed tray 9 to the image forming unit 7 through the sheet conveyance path 10 is temporarily stopped when the leading end thereof reaches the registration roller 11. Then, the rotation of the registration roller 11 is adjusted such that the timing at which the one-color toner image formed on the surface of the photoreceptor 71 comes to a position facing the transfer drum 75 and the timing at which the paper reaches the transfer position coincide. Will be resumed. At this time, static electricity is applied to the surface of the transfer drum 75 by the discharge of the discharge device 12 arranged opposite to the surface of the transfer drum 75, and the paper sent from the registration roller 11 is transferred to the transfer drum 75 by the electrostatic force. It can be wound around. The sheet sent from the registration roller 11 is wound around the transfer roller 75 and moves to the transfer position, and the one-color toner image formed on the surface of the photoconductor 71 is transferred to the sheet.
[0024]
Subsequently, when the transfer of another color is continued, the photosensitive member 71 after the transfer of the toner image is uniformly charged again by the main charger 72 after the toner remaining on the surface thereof is collected by the cleaning device 73. You. On the charged surface of the photoconductor 71, an electrostatic latent image corresponding to a toner image of a color to be formed next is formed by irradiation light from the laser scanning unit 6. Toner is attached to the surface of the photoreceptor 71 on which the electrostatic latent image is formed by a developing device corresponding to the color, and a toner image of the next one color to be transferred to paper is formed. Then, the toner image formed on the surface of the photoconductor 71 is wrapped around the transfer drum 75 and is again transferred to the sheet that has reached the transfer position.
[0025]
In this manner, the paper is wound around the transfer drum 75 and passes through the transfer position one to four times, and the toner image is transferred onto the paper every time the paper passes the transfer position, so that the cyan, magenta, yellow, and black are removed. The toner images of the selected one to four colors are transferred onto the paper (in the case of two or more colors, overlapping).
When the toner images of one to four colors are transferred to the sheet, the discharge device 12 discharges the static electricity on the surface of the transfer drum 75, and the sheet is separated from the transfer drum 75. Then, the toner adhered to the surface of the transfer drum 75 after the paper is separated is collected by the cleaning brush device 77.
[0026]
The toner image-transferred sheet separated from the transfer drum 75 is transported to the fixing device 14 on the surface of the rotating endless transport belt 13. Then, the sheet subjected to a predetermined fixing process by the fixing device 14 is discharged to a sheet discharge unit 17 disposed outside the apparatus via a conveying roller 15 and a discharge roller 16.
FIG. 2 is a block diagram for explaining the flow of image processing in the present invention.
The digital color copying machine 1 includes a control unit 5 including a microcomputer and the like. The control unit 5 includes a color image reading circuit 51, an input correction circuit 52, an area separation circuit 53, a UCR / black generation circuit 54, a color / monochrome original discrimination circuit 55, a character area judgment circuit 56, a spatial filter processing circuit 57, and an output floor. The tone processing circuit 58 and the like are functionally provided.
[0027]
Further, a signal is input to the control unit 5 from an operation unit 18 disposed on the upper surface of the digital color copying machine 1. The user operates the operation unit 18 to start the image forming operation in the digital color copying machine 1 or to select whether to process in monochrome, two-color, or full-color. can do. In addition, the user can select a threshold value for determining whether or not a character area is present in the document at a ratio equal to or greater than the threshold value, for example, in the form of “character determination strong / medium / weak”.
[0028]
When red (R), green (G), and blue (B) image signals are input from the CCD image sensor 22 to the control unit 5, the control unit 5 stores the image signals in a predetermined medium such as a CD-ROM or a hard disk in advance. Various processing is performed in each processing circuit using the program software provided.
Specifically, first, the color image reading circuit 51 captures the input image signals of each color and converts the red, green, and blue image signals into digital image data of cyan, magenta, and yellow (for example, 256 floors). The input signal is quantized and converted into a tone and transmitted to the input correction circuit 52. The input correction circuit 52 performs line correction for correcting the shift of the capture timing of each color, and the optical system such as the light source 21 has different light distribution characteristics between the center and the end in the main scanning direction (both ends in the main scanning direction). In addition to shading correction processing for correcting variations in the sensitivity of the reading line due to having a characteristic of lowering the luminance of the read line, gamma correction processing for giving a gradation characteristic proportional to the density of the original, digital images Processing for enlarging or reducing data in the sub-scanning direction, processing for enlarging or reducing data in the main scanning direction, and the like are performed.
[0029]
The area separation processing circuit 53 extracts a graphic area such as a character area, a photograph area (halftone area), and a graph from the original image, separates the image area into respective image signals, and sends the image signals to the UCR / black generation circuit 54. .
The UCR / black generation circuit 54 performs black generation processing by extracting only the same component (level) from cyan, magenta, and yellow and replacing it with a black component. Thus, black (BK) digital image data is added to the digital image data supplied to the laser scanning unit 6.
[0030]
The color / monochrome original discrimination circuit 55 judges whether the original is full color or monochrome using ACS (auto color select) processing.
The character area determination circuit 56 determines whether or not the ratio of characters in the document is greater than or equal to the threshold, and whether or not the ratio of characters of two or more colors is greater than or equal to the threshold in the document.
The spatial filter processing circuit 57 performs a process of converting a document image into an image of only the selected color when performing two-color processing. In addition, filter processing (so-called edge enhancement processing, smoothing processing, etc.) is performed.
[0031]
The digital image data processed by each of the above circuits is subjected to output gradation processing by an output gradation processing circuit 58, and is sent to the laser scanning unit 6 through an output device 59 after the output gradation processing. . The output gradation processing includes, for example, intermediate value processing (so-called error diffusion processing, dither processing, and the like).
Hereinafter, the two-color setting procedure in the color / monochrome original discrimination circuit 55 and the character area judgment circuit 56 will be described with reference to flowcharts.
[0032]
FIG. 3 is a flowchart showing the entire setting procedure. When image data is input to the control unit 5 (step S1), it is determined whether the original is full-color or monochrome using ACS (auto color select) processing (step S2). A two-color original document in which only characters to be emphasized are colored characters may be determined to be full color or monochrome according to the criterion. If it is determined that the character is monochrome, the character area determination circuit 56 determines whether or not there are two or more characters in the character area (step S3). The criterion for the presence of characters of two or more colors is based on whether or not the ratio of characters of two or more colors in the character area is higher than a predetermined threshold. If the document does not exist, since the document is a true monochrome document, monochrome processing is performed (step S11). If there are two or more colors, the user operates the operation unit 18 to select whether to process in monochrome or two colors (step S4). If the selected processing is monochrome, monochrome processing is performed. If the selected process is a two-color process, the user selects whether to process a portion other than characters (for example, a photograph or a pattern portion) in monochrome or in two colors (step S6). If two-color is selected, two-color processing is performed on the entire document (step S10). If monochrome is selected, two-color processing is performed only on the character portion, and monochrome processing is performed on the portion other than the character (step S9). Note that the user may use the result already selected in step S4 instead of selecting again in step S6.
[0033]
If the document is determined to be full color in step S2, it is determined whether or not a character area is present in the document at a rate equal to or greater than a threshold (step S13). An original such as a full-color photograph or a color poster, which has a small character area and does not have a threshold or more, is subjected to full-color processing (step S12). The threshold may be set by the user. In the case of a document having a large number of character areas such as a business document using a large number of color characters and having a threshold value or more, it is determined whether there are two or more characters in the character area (step S14). If there is, the user selects whether to process the entire original in full color or in two colors (step S15). If the selected color is two-color, two-color processing is performed on the entire document (step S10). If the selected color is full color, full color processing is performed on the entire document (step S12).
[0034]
In the two-color processing (step S10), one color other than black that is most frequently used and black, or two colors other than black that is most frequently used, or two colors other than black in the character portion or other portions are used. Using black, the spatial filter processing circuit 57 generates digital image data to be supplied to the laser scanning unit 6 so as to reproduce the gradation of the document as faithfully as possible. For example, if cyan and yellow are selected, the cyan part of the original is reproduced using cyan or cyan and black toner, and the yellow part of the original is reproduced using yellow or yellow and black toner. The magenta portion is reproduced as faithfully as possible with the gradation of the original by using cyan and yellow or cyan, yellow and black toner.
[0035]
As described above, when the monochrome is determined by the ACS (auto color select) processing, and when the character area includes two or more colors such as black and other colors, the user performs the monochrome processing or the two-color processing. Can be selected. In addition, the user may select whether to perform monochrome processing or two-color processing with respect to portions other than characters, or use the selection result of character portions.
In addition, when the character area is determined to be full color by the ACS (auto color select) processing, and the character area has two or more colors such as black and other colors, the user selects whether to perform two-color processing or full-color processing. can do.
[0036]
In the flowchart of FIG. 3 described above, in the procedure of the user selecting monochrome, two-color, or full-color (steps S4, S6, and S15), the selected process and the characteristics of the document are stored as a history, and the next and subsequent times are stored. It is also possible to reflect it in the criterion for determining the original (steps S3 and S13).
FIG. 4 is a functional block diagram for explaining a procedure for storing the selected process and the characteristics of the document and reflecting the selected process and the subsequent reference in the determination of the document (partly overlapping with the procedure of the flowchart in FIG. 3). are doing).
[0037]
In this procedure, first, the ACS processing unit (S2) determines whether the original is full color or monochrome. If it is determined that the image is monochrome, the character area determination unit (S3) performs the determination. This determination is the same as the above-described procedure (step S3) of determining whether or not the ratio of characters of two or more colors exists in the document at or above the threshold. If there is, the user selection unit (S4) selects whether to process in monochrome or two colors. Monochrome processing or two-color processing is performed according to the selection (S11, S10). If the character area determination unit (S3) determines that there are no characters of two or more colors, monochrome processing is performed (S11). The feature extraction unit (S17) stores the process selected by the user and the feature (color distribution and the like) of the document at that time in association with each other.
[0038]
On the other hand, when the ACS processing section (S2) determines that the original is full color, the character area determination section (S13) determines whether the ratio of the character area is equal to or greater than the threshold. If there is more than the threshold, the user selection unit (S15) selects whether to process in full color or in two colors. According to the selection, full-color processing or two-color processing is performed (S12, S10). If not, a full color process is performed (S12). The feature extracting unit (S18) stores the process selected by the user and the feature (color distribution etc.) of the original at that time in association with each other.
[0039]
The feature extracting unit (S17, S18) stores the number of times selected for each of the monochrome, two-color, and full-color processes, and when the user selects any of the processes, sends the selected information to the operation unit 18. The process with the larger number of times is initially displayed as the default. As a result, the process with the larger number of selections is selected from the beginning, and the operation burden on the user can be reduced. If the user's selection operation has not been performed for a certain period, the process may be performed in the mode initially displayed.
[0040]
Further, the feature extraction unit (S17, S18) statistically processes the process selected by the user and the feature of the original at that time, and changes the determination threshold in the character region determination unit (S3, S13). For example, the color distribution of a document for which monochrome processing has been selected in the user selection unit (S4) and the color distribution of a document for which two-color processing has been selected are calculated, and a character area determination unit is calculated based on the color distribution. The threshold is reflected in (S3). The method of setting the threshold is as follows. The threshold value of the original for which monochrome processing is selected in step S4 is shifted so that it is determined that there is no character area of two or more colors with high probability. The original for which two-color processing is selected in step S4 is high probability. Is used to move the threshold so that it is determined to be a character area of two or more colors.
[0041]
With this proper threshold setting, it can be appropriately determined whether or not the document is a character document of two or more colors. For example, for a document having a considerably large number of character areas of two or more colors, the user rarely selects monochrome processing in step S4, and two or more color areas in which the user selects monochrome processing in step S4. The probability of going from the step S3 directly to the monochrome processing in the step S11 increases for a document with extremely few characters. Therefore, at the time of step S4, “two-color processing” can be set by default on the operation unit.
[0042]
The color distribution of the document for which the full-color processing has been selected in the user selection unit (S14) and the color distribution of the document for which the two-color processing has been selected are calculated, and the threshold value of the character area determination unit (S13) is determined based on these. To reflect. The method of setting the threshold is as follows. The threshold value is shifted so that the document in which the full-color processing is selected in step S15 is determined to have a high probability that there is no character area of two or more colors, and the document in which the two-color processing is selected in step S15 has a high probability. Is used to move the threshold so that it is determined to be a character area of two or more colors.
[0043]
With this proper threshold setting, it can be appropriately determined whether or not the document is a character document of two or more colors. For example, the user rarely selects full-color processing in step S15 for a document having a considerably large number of character areas of two or more colors, and a character area of two or more colors in which the user selects full-color processing in step S15. The probability of going from the step S14 directly to the full-color processing of the step S12 for a document with extremely small amount of is increased. Therefore, at the time of step S15, “two-color processing” on the operation unit can be set as default.
[0044]
As a result, at the time of the determination by the character area determination unit (S3, S14), the determination of the original can be appropriately performed, and the deviation of the determination result can be prevented.
In the flowchart of FIG. 3 so far, when the two-color processing is selected, the two-color copy is performed by selecting a frequently used color among the original colors. However, when the two-color processing is selected, one or two colors having a large remaining amount of toner among the YMC colors are automatically selected and presented to the user. If permission is obtained, the one or two colors are selected. Two-color copying may be performed using two colors or the color and black.
[0045]
FIG. 5 shows a flowchart in the case where a combination of two colors is automatically selected and presented to the user. First, the remaining amount of the YMCK color toner is measured (step T1). Two colors having a large remaining amount of toner are selected from the YMCK colors (step T2). Then, a combination of two colors is determined based on the remaining amount of toner. For example, when there are many K toners and C toners, and next there are M toners, a combination of C and M, a combination of C and K, a combination of M and K, and the like are determined.
[0046]
When the user selects two colors (steps S4, S6, and S14), the determined combination of the two colors is presented and permission is requested (step T4). Select (Step T9). If there is no permission from the user, two frequently used colors are selected from the character area of the document (step T5). Then, a combination of the two colors is determined based on the frequency of use (step T6), the combination of the two colors is presented, and permission is requested (step T7). If the user has permission, the presented two colors are selected (step T7). (Step T9), the selected color is recorded (Step T10). The spatial filter processing circuit 57 converts the document image into two colors from the selected YMCK or a combination of the two colors and black (step T11).
[0047]
If there is no user permission in step T7, the user inputs a combination of two colors desired by the user through the operation unit (step T8), records the selected color (step T10), and converts the original image by the spatial filter processing circuit 57. The input YMCK is converted into two colors or a combination thereof with black (step T11). In the description of FIG. 5 so far, when the user selects the two-color copy, the user is presented with two colors in the document (step T5) or two colors in consideration of the remaining amount of toner (step T3). However, two colors that have been used so far (the number of times recorded in step T10) may be presented and the user may select the color.
[0048]
As described above, by presenting the user with two colors of the YMCK color, which have a large amount of remaining toner, two colors with a high frequency of characters in the document, or two colors with a high selection frequency, the user can select (1) The user can select a color that can effectively use the remaining amount of toner, (2) a color that can reproduce two colors as faithfully as a document, or (3) a color that is suitable for use conditions of the digital color copier 1 based on past results. The user can be made to make a selection without the hassle of the above.
[0049]
Next, a description will be given, with reference to a flowchart, of a procedure in which when the two-color processing is selected, the user can also select edge enhancement, hollowing, and the like.
FIG. 6 is a flowchart including processes such as edge enhancement and hollowing. When performing two-color processing, the control unit 5 displays on the operation unit 18 a question asking the user whether to select one color or two colors when YMCK or two colors are included. The user selects whether or not to perform an emphasis process on a character whose color is changed when performing the two-color process (step U2). If it is selected to perform the emphasizing process, the spatial filter processing circuit 57 performs an emphasizing process such as edge emphasis or hollowing out (step U4). If it is selected not to perform the enhancement processing, the spatial filter processing circuit 57 skips the enhancement processing and converts the original image into the input one color, two colors, or these and black (step U5).
[0050]
As described above, since the user can select an emphasis process such as edge emphasis or hollowing, emphasis can be made more than other characters.
In the current two-color selection procedure, the user is caused to select two colors with a large amount of remaining toner, two colors with a high character frequency in a document, or two colors with a high selection frequency. However, for these two colors, L close to human intellectual sensation ^* a ^* b ^* The color difference may be calculated by converting to a system, and two colors may be specified in descending order of the color difference, presented to the user, and selected by the user.
[0051]
FIG. 7 is a flowchart showing a procedure for selecting two colors in descending order of color difference.
First, a combination of two colors based on the remaining amount of toner is extracted (steps V1 and V2), two colors that are frequently used in the document are extracted (step V3), and a feature extraction unit (FIG. 4, S17, S18). ), Two colors that have been used so far are extracted (steps V4 and V5).
Then, the CMY values of the image generated using these two extracted colors are converted into tristimulus values XYZ that have been once standardized. ^* a ^* b ^* It is converted into a value (step V6).
[0052]
L ^* = 116 ³ √Y-16
a ^* = 500 ( ³ √X- ³ (Y)
b ^* = 200 ( ³ √Y- ³ √Z)
Converted L ^* a ^* b ^* The color difference is calculated based on the value (step V7). Here, the color difference is L ^* a ^* b ^* It is the distance between two points in space. Those having a color difference equal to or less than a certain value are excluded (step V8), and the color differences are compared (step V9). As a result of the comparison, two colors having large color differences are arranged in order, and presented to the user as a default (step V10). Then, L ^* a ^* b ^* Reconvert the values to CMY values.
[0053]
In the above processing, L ^* a ^* b ^* Instead of adopting the system, L ^* u ^* v ^* A system may be adopted to obtain the color difference in the Luv space.
If the two colors presented to the user agree, the spatial filter processing circuit 57 converts the original image into the selected two colors and / or black. If the user does not agree with the presented two colors, the user inputs a combination of the two colors from the operation unit. In this case, the spatial filter processing circuit 57 converts the document image into the two colors and / or black based on the two colors input by the user.
[0054]
As described above, the images are displayed in the operation unit 18 arranged in descending order of the color difference, and are selected by the user, so that when copying in two colors, the user can obtain an easy-to-read copy image in which the color difference clearly appears. it can.
The embodiments of the present invention have been described above, but the embodiments of the present invention are not limited to the above embodiments. For example, the same procedure is adopted when two-color processing is performed using not only a CMY system but also an RGB system, another color space Luv system, a Lab system, a YUV system, or the like. In addition, various changes can be made within the scope of the present invention.
[0055]
【The invention's effect】
As described above, according to the present invention, when it is determined that a character document is a two-color character, the user is prompted to select whether to form an image in two colors or to form an image in monochrome or full color. Therefore, two-color characters can be emphasized, and an image can be formed at lower cost than in full-color printing.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing an internal configuration of a digital color copying machine 1 according to an embodiment of the present invention.
FIG. 2 is a block diagram illustrating a flow of image processing according to the present invention.
FIG. 3 is a flowchart illustrating a basic setting procedure of two-color processing.
FIG. 4 is a functional block diagram for explaining a procedure for storing a selected process and a feature of a document and reflecting the feature in a determination standard of a document after the next time.
FIG. 5 is a flowchart showing a procedure for automatically selecting a combination of two colors and presenting the combination to a user.
FIG. 6 is a flowchart including processes such as edge enhancement and hollowing out.
FIG. 7 is a flowchart illustrating a procedure for selecting two colors in descending order of color difference.
[Explanation of symbols]
5 control part
18 Operation unit
51 color image reading circuit
52 input correction circuit
53 area separation circuit
54 UCR / Black Generation Circuit
55 Color / monochrome original discrimination circuit
56 Character area judgment circuit
57 Spatial Filter Processing Circuit
58 Output gradation processing circuit

Claims (8)

A two-color image forming method for forming an image by performing two-color processing on a document,
(A) It is determined whether a document is a full-color document or a monochrome document by an automatic color selection process.
(B) When it is determined that the document is a monochrome document, it is determined whether or not a character area of two or more colors exists in the document,
(C) when a text area of two or more colors exists in the document, the user is allowed to select either monochrome processing or two-color processing;
(D) A two-color image forming method, wherein a document is subjected to monochrome processing or two-color processing according to the selected result to form an image. In the above procedure (c), when the user selects the two-color processing, the user is caused to select either the monochrome processing or the two-color processing for the area other than the character area. An image is formed by performing two-color processing on the area and performing monochrome processing except for the character area, and when the user selects the two-color processing, performing image processing by performing two-color processing on the entire original. 2. The method for forming a two-color image according to item 1. In the procedure (c), before the user selects two-color processing, a color with a large amount of remaining toner, a frequently used color in a document, or a previously frequently selected color is set as a default for the user. The two-color image forming method according to claim 1 or 2, wherein the two-color image is presented. 4. The two-color image forming method according to claim 1, wherein the user can select an arbitrary color in the step (c). 5. The method according to claim 1, wherein in the step (d) of performing image formation by performing two-color processing, an emphasis process can be performed on any one color portion of the target character. 6. 2. The two-color image forming method according to 1. When the user selects two-color processing, two colors having a large color difference among colors having a large amount of remaining toner, frequently used colors in a document, or previously frequently selected colors are presented to the user as defaults. 4. The two-color image forming method according to claim 3, wherein the selection is made by selecting the color image. 2. The method according to claim 1, wherein in the step (c), a relationship between a process selected by the user and a color characteristic of the document is stored, and based on the relationship, the relationship is reflected in the determination threshold in the step (b). The two-color image forming method according to claim 6. A color image forming apparatus having a two-color forming mode for performing two-color processing on a document to form an image,
(A) first determining means for determining whether a document is a full-color document or a monochrome document by an automatic color selection process;
(B) second determining means for determining whether a text area of two or more colors exists in the document when the document is determined to be a monochrome document;
(C) selecting means for allowing a user to select either monochrome processing or two-color processing when a document has a character area of two or more colors;
(D) an image forming means for performing image processing by subjecting the document to monochrome processing or two-color processing in accordance with the selected result.

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