JP5619216B2 - Image processing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an image processing apparatus that reads image data from an original and an image forming apparatus that forms an image based on the read image data, and more particularly to a technique for preventing the show-through of the original.

Conventionally, when an image processing device such as a scanner device, a copier, a facsimile device, or a multifunction device is used to read only an image on the front side of an original with images formed on the front and back sides, the image on the back side of the original is read as the read image. It is a problem that so-called “show-through” occurs. For this reason, the show-through is generally suppressed by reducing the density of the entire image of the document. However, in this case, there arises a problem that the density of the original image of the document is lowered instead of the show-through portion.
On the other hand, for example, in Patent Document 1, a density histogram that shows the relationship between density and frequency in two dimensions is calculated, and the density with the highest frequency is recognized as the density of the background color, and the density near the density of the background color. It has been proposed to prevent show-through by uniformly converting the color to the same level as the base color.
FIG. 9 shows an example of the density histogram. As shown in FIG. 9, the density histogram calculates the density frequency for each predetermined range included in the image data and shows the relationship between the density and the frequency. In the example shown in FIG. 9, it can be seen that the frequency in the range from 0 to 15 is the highest.

Japanese Patent Laid-Open No. 11-187266

However, according to the technique disclosed in Patent Document 1, even when there are a plurality of colors that occupy a large area in the image data of the document, it is possible to prevent show-through based only on the density of one of the most frequently used colors. Since the processing is performed, there arises a problem that the show-through cannot be prevented for other portions.
Specifically, when the original is a book original composed of two pages of left and right pages, the background color may be different for each page, but in order to prevent show-through depending on one of the background colors. Therefore, there is a problem that the show-through cannot be prevented on the other page, or the color changes greatly.
Accordingly, the present invention has been made in view of the above circumstances, and an object thereof is to prevent show-through without impairing the color reproducibility of an image for each page even when the original is a book original. It is an object of the present invention to provide an image processing apparatus and an image forming apparatus that can perform the above processing.

To achieve the above object, the present invention provides an image reading means for reading image data from a document, and a high frequency value that satisfies a preset high frequency condition in which the frequency included in the image data read by the image reading means is set. And a data conversion unit that executes data conversion processing for converting the image data so as to make a value in the vicinity of the high frequency value substantially uniform to the high frequency value. A book manuscript judging means for judging whether or not the manuscript is a book manuscript, and reading by the image reading means when the book manuscript judging means judges that the manuscript is a book manuscript. Image data dividing means for dividing the received image data into image data for each page of the book document, wherein the data conversion means comprises the book document When it is determined that the original is a book original by the determining means, the data conversion processing is individually executed for the image data for each page divided by the image data dividing means, and the original is not a book original. If determined, the image conversion apparatus is configured to execute the data conversion process on the entire image data read by the image reading unit.
The present invention may also be understood as an image forming apparatus including the image processing apparatus and an image forming unit that forms an image based on each of the color component data converted by the data conversion unit.
According to the present invention, when the original is a book original, the data conversion process is executed individually for each of the image data divided for each page, so that the color reproducibility of the image is impaired for both pages. Show-through can be prevented without any problem.

For example, the data conversion means includes a high-frequency specifying means for specifying a high-frequency value in which the frequency included in the image data satisfies a preset high-frequency condition, and a high-frequency value specified by the high-frequency specifying means. Density conversion information generating means for generating density conversion information used for converting the image data to make the value in the vicinity of the high frequency value substantially uniform, the value in the vicinity of the high frequency value. It is conceivable that the image data representing the image is converted based on the density conversion information generated by the density conversion information generating means.
Here, the image reading means reads the image of the document as color image data including a plurality of color component data. Further, the high-frequency specifying unit specifies a high-frequency color satisfying a high-frequency condition in which a frequency included in the image of the document is preset among a plurality of colors expressed by the plurality of color component data. Is. Further, the density conversion information generating means corresponds to each high-frequency color specified by the high-frequency specifying means, and the color component to make the color in the vicinity of the high-frequency color substantially uniform to the high-frequency color. Individual density conversion information used to convert each data is generated. The data conversion means generates each color component data for the color image data expressing colors in the vicinity of the high frequency color by the individual density conversion information generation means corresponding to the high frequency color. Conversion is performed based on the individual density conversion information. As a result, each of the color component data is converted based on the individual density conversion table generated corresponding to the high frequency color for color image data expressing one or a plurality of colors near the high frequency color. Therefore, even when there are a plurality of colors that are frequently included in the image of the document, that is, even when there are a plurality of locations where it is considered that show-through has occurred in the scanned image of the document, The show-through in each of the plurality of colors can be prevented. The color component data is converted based on the individual density conversion table only for the color image data representing colors in the vicinity of the high frequency color, and the color image data representing other colors is Since the color component data is not converted based on the individual density conversion table, the color reproducibility of the entire image is not impaired.

Further, the high-frequency specifying means includes the plurality of colors expressed by the plurality of color component data into the color group for each color within a predetermined range, and is included in the document image. First color histogram calculation means for calculating a first color histogram indicating the frequency for each color group, and a preset value based on the first color histogram calculated by the first color histogram calculation means. A high-frequency color group extracting unit that extracts a high-frequency color group that is equal to or higher than a predetermined frequency, and a high-frequency color group extracted by the high-frequency color group extraction unit for each color included in the high-frequency color group Second color histogram calculation means for calculating a second color histogram indicating the frequency, and based on the second color histogram calculated by the second color histogram calculation means, the high frequency It is contemplated that is to identify the most frequent color in each group as the high frequency satisfying high frequency color.
As a result, the processing load can be remarkably reduced as compared with the case where histograms are calculated for all colors.

  By the way, the book manuscript judgment unit automatically determines whether or not the manuscript is a book manuscript in response to an operation input to a predetermined operation unit, and automatically based on image data read from the manuscript. A determination method switching for switching between automatic determination means for determining whether or not the original is a book original, and whether the manual determination means or the automatic determination means determines whether or not the original is a book original Means. For example, the determination method switching means switches whether the manual determination means or the automatic determination means determines whether or not the original is a book original in accordance with an operation input to a predetermined operation means. .

  According to the present invention, when the original is a book original, the data conversion process is executed individually for each of the image data divided for each page, so that the color reproducibility of the image is impaired for both pages. Show-through can be prevented without any problem.

1 is a block diagram showing a schematic configuration of a multifunction machine X according to an embodiment of the present invention. FIG. 3 is a block diagram showing a main configuration of an image processing unit 4 of the multifunction machine X according to the embodiment of the present invention. The figure for demonstrating an example of a color histogram. The figure for demonstrating an example of the separate density | concentration conversion table produced | generated by the density | concentration conversion process performed with the multifunctional machine X which concerns on embodiment of this invention. The figure for demonstrating an example of the separate density | concentration conversion table produced | generated by the density | concentration conversion process performed with the multifunctional machine X which concerns on embodiment of this invention. 6 is a flowchart for explaining an example of a procedure of density conversion processing executed by the multifunction machine X according to the embodiment of the present invention. 6 is a flowchart for explaining an example of a book document determination process executed by the multifunction machine X according to the embodiment of the present invention. The figure for demonstrating an example of a book manuscript automatic determination process. The figure for demonstrating an example of a density histogram.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
First, a schematic configuration of the multifunction machine X according to the embodiment of the present invention will be described with reference to FIG.
As shown in FIG. 1, the multifunction machine X is an example of an image processing apparatus and an image forming apparatus according to the present invention, and includes a control unit 1, an operation display unit 2, an image reading unit 3 (image reading unit), an image A processing unit 4, an image forming unit 5, and the like are schematically configured. Note that a copying machine, a scanner device, a facsimile device, and the like having an image reading function also correspond to the image processing apparatus or the image forming apparatus according to the present invention.

The control unit 1 has peripheral devices such as a CPU and ROM, RAM, etc., and the CPU controls the MFP X by executing processing according to a predetermined control program stored in the ROM. Control. The operation display unit 2 has a liquid crystal display, a touch panel, various operation keys, and the like for displaying various types of information on the multifunction machine X and performing input operations by the user.
The image reading unit 3 has a CCD or the like for reading an image of a document placed on a document table (not shown) or a document conveyed by an automatic document feeder (ADF, not shown). Here, the image reading unit 3 converts the original image into R (red), G (green), and B (blue) color component data (hereinafter referred to as R color component data, G color component data, B). Color image data) including color component data). In particular, the image reading unit 3 reads the image as color image data including R, G, and B color component data regardless of whether the document is monochrome or color.
The image processing unit 4 performs, on the color image data read by the image reading unit 3, a density conversion process (see flowcharts of FIGS. 6 and 7) described later, a known gamma correction process, a shading correction process, Various image processing such as smoothing / enhancement processing and CMYK conversion processing is performed. For example, the CMYK conversion process is a process of converting the RGB color component data into color image data composed of CMYK color component data.
When the copying process is executed in the multifunction machine X, the image processing unit 4 inputs the color image data after the image processing to the image forming unit 5. Further, when a scanning process is executed in the multi-function device X, the image processing unit 4 stores the color image data after the image processing in an internal storage means or predetermined information via a network such as a LAN. Send to the processing device.
The image forming unit 5 includes constituent elements of a well-known electrophotographic image forming unit such as a photosensitive drum and a developing device corresponding to each color of CMYK. A monochrome image or a color image is formed based on the color image data after the image processing input from the image processing unit 4.
The multi-function device X configured as described above is characterized by a density conversion process (see flowcharts of FIGS. 6 and 7) executed by the image processing unit 4 and will be described in detail below. To do.

FIG. 2 is a block diagram showing the main functions of the image processing unit 4.
As shown in FIG. 2, the image processing unit 4 includes a density conversion unit 41, a conversion point calculation unit 42, a density conversion table generation unit 43, and the like. The image processing unit 4 performs various image processing such as gamma correction processing, shading correction processing, smoothing / enhancement processing, and CMYK conversion processing on the color image data converted by the density conversion unit 41. However, they are not different from the conventional ones, so the explanation is omitted here.
The density conversion unit 41, the conversion point calculation unit 42, the density conversion table generation unit 43, and the like are electronic circuits having functions described below, or are processed by an arithmetic processing unit such as an MPU. It may be each processing function embodied by.

The density conversion unit 41 converts the R, G, B color component data included in the color image data read by the image reading unit 3 based on a preset density conversion table. In this embodiment, the case of converting R, G, B color component data will be described as an example. For example, after converting RGB data into CMY data, C (cyan), M (magenta) , Y (yellow) image data can be converted in the same manner.
However, the density conversion unit 41 converts each of the R, G, and B color component data with respect to color image data expressing colors near the high-frequency color specified by the conversion point calculation unit 42 as described later. For color image data expressing other colors excluding the high frequency color, the conversion of the R, G, B color component data is not performed.
The conversion point calculation unit 42 selects a high-frequency color (high frequency) satisfying a preset high-frequency condition in which the frequency included in the image of the document among a plurality of colors expressed by the R, G, B color component data is satisfied. Frequency value). Here, the conversion point calculation unit 42 corresponds to high-frequency specifying means.
Then, the conversion point calculation unit 42 is referred to as Pr, Pg, Pb (hereinafter referred to as “conversion points Pr, Pg, Pb”) which are density values of R, G, B color component data expressing the specified high frequency color. ) Is input to the density conversion unit 41 and the density conversion table generation unit 43.

Here, an example of a method for specifying a high-frequency color by the conversion point calculation unit 42 will be described.
First, when the conversion point calculation unit 42 classifies a plurality of colors expressed by R, G, and B color component data into color groups for each color in a predetermined range, the color in the document image is displayed. A first color histogram (three-dimensional histogram) indicating the frequency (number) of pixels for each group is calculated. Here, the conversion point calculation unit 42 when executing such processing corresponds to the first color histogram calculation means.
FIG. 3 shows an example of the first color histogram.
As shown in FIG. 3, when the density values of the R, G, and B color component data constituting the color image data are arranged in three dimensions, the first color histogram has its three-dimensional density values (R, The frequency for each color group including a predetermined range of colors indicated by G, B) is calculated. Specifically, in the example shown in FIG. 3, 4096 colors of 16 × 16 × 16 are represented by 256 × 256 × 256 16,777,216 colors expressed by combinations of values of R, G, and B color component data. And the frequency of pixels for each color group included in the original image is calculated. In this case, the predetermined range of colors included in each of the color groups is (R, G, B) = (0-15, 0-15, 0-15), (16-31, 0-15, 0-15). ), (32 to 47, 0 to 15, 0 to 15), ... (239 to 255, 239 to 255, 239 to 255).

Next, the conversion point calculation unit 42 extracts a high-frequency color group in which the frequency included in the image of the document is equal to or higher than a predetermined frequency, based on the first color histogram. To do. Here, the conversion point calculation unit 42 when executing such processing corresponds to high-frequency color group extraction means. The predetermined frequency is set in advance, for example, in order to determine that the color occupies an area where the show-through is significant in the document image.
In this way, the conversion point calculation unit 42 does not specify only the most frequent color group, but extracts the high frequency color group that is equal to or higher than the predetermined frequency. There are cases where multiple samples are extracted.

Thereafter, the conversion point calculation unit 42 calculates a second color histogram indicating the frequency of each color included in the high-frequency color group for each high-frequency color group. Here, the conversion point calculation unit 42 when executing such processing corresponds to second color histogram calculation means.
For example, as shown in FIG. 3, the first color histogram represents 256 × 256 × 256 16,777,216 colors represented by the values of the R, G, B color component data, and 16 × 16 ×. When the frequency is classified into 16 4096 color groups and the frequency for each color group is calculated, the second color histogram is obtained for each of 16 × 16 × 16 4096 colors included in the color group. The frequency is calculated.
Then, the conversion point calculation unit 42 specifies the most frequent color as the high-frequency color satisfying the high-frequency condition for each high-frequency color group based on the second color histogram. At this time, when a plurality of the high-frequency color groups are extracted as described above, a plurality of high-frequency colors are also specified here.
As described above, the conversion point calculation unit 42 first calculates the first color histogram of the coarse level, and then extracts one or a plurality of color groups having a predetermined frequency or more from the first color histogram. More detailed second color histogram is calculated only for the color group. For this reason, the processing load is significantly reduced as compared with the case of calculating a histogram indicating the frequencies of all colors (16,777,216 colors in the above example) from the beginning.

The density conversion table generation unit 43 corresponds to each high-frequency color specified by the conversion point calculation unit 42, so that the colors near the high-frequency color are substantially uniformed to the high-frequency color. An individual density conversion table (an example of individual density conversion information) used for converting each of the G and B color component data is generated and input to the density converter 41. Here, the density conversion table generating unit 43 corresponds to individual density conversion information generating means.
Here, when there are a plurality of high-frequency colors specified by the conversion point calculation unit 42, the density conversion table generation unit 43 generates a plurality of individual density conversion tables corresponding to each of the RGB color component data. To do. Hereinafter, the individual density conversion tables corresponding to the R, G, B color component data will be referred to as individual density conversion tables Tr, Tg, Tb.

4 and 5 are diagrams illustrating an example of the individual density conversion table generated by the density conversion table generating unit 43 when there are two high-frequency colors specified by the conversion point calculating unit 42. FIG. is there. Of course, the individual density conversion table generated here is increased or decreased according to the number of the high-frequency colors.
FIG. 4 shows the case where the first high-frequency color corresponds to the high-frequency color when the values of the color components of R, G, and B are colors represented by conversion points Pr1, Pg1, and Pb1. An example of the generated individual density conversion table is shown. (A), (b), and (c) are individual density conversion tables Tr1, Tg1, and Tb1 corresponding to R, G, and B color component data, respectively. Is shown.
FIG. 5 shows the case where the second high-frequency color corresponds to the high-frequency color when the values of the color components of R, G, and B are colors represented by conversion points Pr2, Pg2, and Pb2. FIG. 6 shows an example of the individual density conversion table generated in the above manner, and (a), (b), and (c) are individual density conversion tables Tr2 and Tg2 corresponding to the R, G, and B color component data, respectively. , Tb2.

As shown in FIG. 4 (a), the individual density conversion table Tr1 converts the density in a predetermined range centered on the conversion point Pr1 that is the value of the R color component included in the first high-frequency color. It is used when converting so as to make the point Pr1 substantially uniform.
Similarly, as shown in FIGS. 4B and 4C, the individual density conversion tables Tg1 and Tb1 include conversion points Pg1 and B colors which are values of G color components included in the first high-frequency color. This is used when converting a density within a predetermined range centering on the conversion point Pb1, which is a component value, so that the conversion points Pg1 and Pb1 are substantially uniform. Further, the individual density conversion tables Tr2, Tg2, and Tb2 shown in FIG. 5 are generated in the same manner.
The individual density conversion table is shown in FIGS. 4 and 5 as long as it can prevent show-through by approximating the color in the vicinity of the high frequency color and making it substantially uniform. It is not limited to form.

Hereinafter, an example of the procedure of density conversion processing executed by the image processing unit 4 will be described with reference to the flowcharts of FIGS. In the figure, S10, S11,... And S1, S2,.
In the density conversion process, color image data is read from a document by the image reading unit 3, and R, G, B color component data constituting the color image data is input to the image processing unit 4. It is started by the image processing unit 4. Here, the image processing unit 4 when executing such density conversion processing corresponds to image data conversion means.
For example, the control unit 1 or the image processing unit 4 can select whether or not to switch the execution of the density conversion processing, that is, whether to remove the show-through according to a user operation on the operation display unit 2 or the like. It is also possible to have a simple configuration. In addition, the predetermined frequency used as a determination index by the conversion point calculation unit 42 is preferably changeable by the control unit 1 or the image processing unit 4 according to a user operation on the operation display unit 2. .

(Step S10)
First, in step S10, the image processing unit 4 determines whether or not the document read by the image reading unit 3 is a book document. The book document determination process (see FIG. 7) for switching the process contents is executed. Here, the image processing unit 4 when determining whether or not the original is a book original corresponds to the book original determination means. Note that the book document determination process may be executed by the control unit 1.
Here, the book document determination process will be described with reference to FIG.

(Step S11)
The image processing unit 4 performs image reading processing in a book document automatic determination mode that automatically determines whether a document corresponding to color image data read by the image reading unit 3 is a book document. Determine whether or not. The book manuscript is a spread manuscript covering, for example, two pages on the left and right or top and bottom.
Here, whether or not the book manuscript automatic determination mode is executed is determined by the control unit 1 in response to a user operation on the operation display unit 2 (predetermined operation means) at the start of image reading processing or initial setting. Can be switched. The said control part 1 when performing the switching process which concerns here corresponds to the determination method switching means.
If it is determined that the book document automatic determination mode is not being executed (No in S11), the process proceeds to step S111, and if it is determined that the book document automatic determination mode is selected ( The process proceeds to step S12.

(Steps S111 to S112)
When the book document automatic determination mode is not executed, in the subsequent step S111, the image processing unit 4 is selected as a book document by a user operation on the operation display unit 2 at the start of an image reading process or the like. Judge whether or not it was. Here, if it is selected to be a book document (Yes side of S111), the process proceeds to step S112. If it is not selected to be a book document (No side of S111), the process will be described later. The process proceeds to step S14. Here, the image processing unit 4 for determining whether or not the document is a book document in accordance with an operation input to the operation display unit 2 (predetermined operation unit) corresponds to a manual determination unit.
In step S112, the image processing unit 4 divides the color image data read by the image reading unit 3 into image data for each page of the book document, and in steps S1 to S9 described later, It is selected that the data conversion process is individually executed for each of the divided image data. Here, the image processing unit 4 when executing the image data dividing process corresponds to an image data dividing unit. For example, the division of the color image data is performed using the center in the longitudinal direction of the color image data as a boundary line.

(Step S12)
On the other hand, when the book document automatic determination mode is being executed, in the subsequent step S12, the image processing unit 4 determines that the document is based on the color image data read from the document by the image reading unit 3. It is automatically determined whether the document is a document. Here, the image processing unit 4 when executing such determination processing corresponds to automatic determination means.
Here, an example of the determination method will be described with reference to FIG. FIG. 8 shows an example of the result of reading color image data from a book document.
As shown in FIG. 8, in a book document covering left and right pages, a gap is generated between the page boundary located near the center in the longitudinal direction and the document table of the image reading unit 3, so that the image reading unit In FIG. 3, the light applied to the original is not normally reflected, and the central portion in the longitudinal direction of the color image data read from the book original is a black image. Therefore, it can be determined that the document is a book document by detecting the presence of the black portion at the center.

For example, for the color image data read by the image reading unit 3, a region having a predetermined length d0 extending from the center in the longitudinal direction to the left and right and a predetermined length d1 in the lateral direction is set as the determination target region R. Then, the average density in the lateral direction is calculated for each line in the entire longitudinal direction of the determination target region R. Further, based on the average density of the predetermined width d2 at both ends of the determination target region R, a threshold value K for determining whether or not it is a page boundary is set. For example, the average density in the predetermined width d2 on both sides is further averaged, and a density obtained by subtracting a predetermined value from the value (low density is black) is set as the threshold K, or the value It is conceivable to set a predetermined percentage of the density as the threshold value K.
When the threshold value K is set, the color image data is determined by determining whether or not the number of pixels exceeding the threshold value K exceeds the preset upper limit value in the determination coping area R. It is determined whether or not a page boundary (a black image having a predetermined width) exists, that is, whether or not the document is a book document. The same applies when the book document covers two pages in the vertical direction. Of course, the method for determining whether or not the document is a book document is not limited to this, and for example, the density gradually decreases from the left and right in the longitudinal direction toward the center in the determination target region R. It may be determined that the document is a book document by detecting the presence of a black image extending substantially in the short side direction in the vicinity of the center of the color image data in the longitudinal direction. Further, the thickness of the document may be detected based on an angle of a document pressing plate that presses the document placed on the document table, and may be determined as a book document when the thickness is equal to or greater than a predetermined value.

(Steps S13 to S14)
In step S13, it is determined whether or not the book document is determined in step S12. If it is determined that the document is a book document (Yes side in S13), the process proceeds to S112. If it is determined that the document is not a book document (No side in S13), the process is step. The process proceeds to S14.
In step S14, the image processing unit 4 does not divide the color image data read by the image reading unit 3, and performs data conversion processing on the entire color image data as one in steps S1 to S9 described later. Choose to run.
As described above, in the multi-function device X, in step S10, the contents of data conversion processing (S1 to S9) to be described later are switched depending on whether or not the original is a book original. Specifically, if it is determined in step S13 or S111 that the document is a book document, data conversion processing (S1 to S9) is individually performed on the image data for each page divided in step S112. If it is determined that the original is not a book original, data conversion processing (S1 to S9) is executed for the entire color image data.
Hereinafter, returning to FIG. 6, the data conversion process performed on each of the color image data or the divided image data will be described.

(Steps S1-S4)
First, in steps S1 to S4, the conversion point calculation unit 42 of the image processing unit 4 executes the process for specifying the high-frequency color in the document image as described above. Specifically, as described above, the conversion point calculation unit 42 calculates the first color histogram (see FIG. 3) (S1), and sets a predetermined predetermined value based on the first color histogram. Color groups that are equal to or higher than the frequency are extracted (S2). Then, the conversion point calculation unit 42 calculates the second color histogram for each extracted color group (S3), and specifies the most frequently used color for each color group (S4).
At this time, if it is determined that the book document is a book document by the book document determination process, the high-frequency color is individually specified for each of the divided image data, and if it is determined that the book document is not a book document, The high-frequency color is specified for the entire color image data. That is, in the case of a book document, the conversion point calculation unit 42 calculates the first color histogram (see FIG. 3) for each of the two divided image data (S1), and based on the first color histogram. A color group having a predetermined frequency or more set in advance is extracted (S2). Then, the conversion point calculation unit 42 calculates the second color histogram for each extracted color group (S3), and specifies the most frequently occurring high-frequency color for each color group (S4).

(Steps S5 to S6)
Next, in step S5, the density conversion table generation unit 43 of the image processing unit 4 corresponds to the individual density conversion table (FIG. 4, FIG. 4) corresponding to each high-frequency color specified by the conversion point calculation unit. 5), and the individual density conversion table is input to the density converter 41.
In step S6, the density conversion unit 41 of the image processing unit 4 converts the individual density conversion table and the R, G, B color component data representing the high-frequency color input from the conversion point calculation unit 42. Based on the conversion points Pr, Pg, and Pb, density conversion of color image data for each pixel of the read original image is started.

(Step S7)
Specifically, first, in step S7, the density conversion unit 41 determines whether or not the color image data represents a color near one of the high-frequency colors.
At this time, if the original is a book original, is it color image data representing any color in the vicinity of the high-frequency color corresponding to the page of the divided image data for each of the divided image data? It is determined whether or not. Therefore, for example, it is not determined whether the divided image data corresponding to the left page is a color in the vicinity of the high-frequency color on the right page.
Here, when it is determined that the color in the vicinity of any one of the high-frequency colors is expressed (Yes side in S7), the process proceeds to step S8, and the vicinity of any one of the high-frequency colors is detected. If the color is not expressed (No side of S7), the process proceeds to step S9. For example, as shown in FIGS. 4 and 5, any one of the high-frequency color expressed by the conversion points Pr1, Pg1, and Pb1 and the high-frequency color expressed by the conversion points Pr2, Pg2, and Pb2 When color image data of a neighboring color is input (Yes side of S7), the process proceeds to step S8.
Therefore, for color image data that does not represent any color in the vicinity of the high-frequency color, conversion of R, G, B color component data based on the individual density conversion table in step S8 described later is not performed. . Of course, the density conversion may be performed based on a predetermined conversion table or the like set in advance as an initial value.

(Step S8)
On the other hand, in step S8, each of the R, G, and B color component data is associated with the high-frequency color in order to make the color in the vicinity of the high-frequency color substantially uniform to the high-frequency color. In step S5, conversion is performed based on the individual density conversion table generated by the density conversion table generating unit 42.
For example, when color image data of a color in the vicinity of the high frequency color expressed by the conversion points Pr1, Pg1, and Pb1 shown in FIG. 4 is input, the color image data is generated in the step S5 corresponding to the high frequency color. Based on the individual density conversion tables Tr1, Tg1, and Tb1, the R, G, and B color component data are converted. Similarly, when color image data of a color in the vicinity of the high-frequency color represented by the conversion points Pr2, Pg2, and Pb2 shown in FIG. 5 is input, the color image data is generated in step S5 corresponding to the high-frequency color. The R, G, B color component data are converted based on the individual density conversion tables Tr2, Tg2, Tb2.

(Step S9)
Thereafter, the density conversion unit 41 determines whether or not the processing of steps S7 to S8 has been executed for all the color image data of one original read by the image reading unit 3 (S9). Here, until all the processes are completed (No in S9), the process is returned to Step S7. When all the processes are completed (Yes in S9), the density conversion process is completed and the image processing unit 4 The next color image data is awaited.
The image processing unit 4 performs various image processes such as a gamma correction process, a shading correction process, a smoothing / enhancement process, and a CMYK conversion process on the color image data converted by the density conversion process. , The color image data after the image processing is input to the image forming unit 5. At this time, if the color image data is divided into the divided image data, the image processing unit 4 combines the divided image data as one color image data.
Here, the case where the color histogram (see FIG. 3) of the color image data is used in the steps S1 to S5 has been described as an example, but the density histogram (FIG. 9) may be used as in the conventional case. It can be considered as an example.

As described above, in the multifunction device X, the color image data representing the color in the vicinity of one or a plurality of the high-frequency colors specified in step S4 is generated corresponding to the high-frequency colors. Since each of the color component data is converted based on the individual density conversion table, when there are a plurality of colors frequently included in the original image, that is, the show-through of the read original image. Even in the case where there are a plurality of places where it is considered that the occurrence of the occurrence of show-through, it is possible to prevent show-through in each of the plurality of colors.
The color component data is converted based on the individual density conversion table only for the color image data representing colors in the vicinity of the high frequency color, and the color image data representing other colors is Since the color component data is not converted based on the individual density conversion table, the color reproducibility of the entire image is not impaired.
In addition, when the document read by the image reading unit 3 is a book document, the read image data is divided into two pages of image data included in the book document, and each of the divided image data after the division is divided. The conversion points are individually calculated for the image data, the individual density conversion table is created, and image data conversion processing is performed. Therefore, even if the background color of each page of the book document is different, the show-through can be appropriately prevented without deteriorating the color reproducibility for each page.

By the way, the density correction processing (FIGS. 6 and 7) described in the embodiment has been described as being executed independently of the gamma correction processing in the image processing unit 4. On the other hand, the density correction process may also be a gamma correction process.
In this case, the density conversion table generation unit 42 generates an individual gamma table (an example of individual density conversion information) corresponding to each of the R, G, B color component data corresponding to each of the high frequency colors. Then, the individual gamma table is input to the density conversion unit 41. Similar to the individual density conversion table (see FIGS. 4 and 5), the individual gamma table generated at this time is an input that can substantially uniformize the color in the vicinity of the high frequency color to the high frequency color. This realizes output characteristics. When the original is a book original, the individual gamma table is individually created for each page included in the book original.
The density conversion unit 41, with respect to color image data representing any color in the vicinity of the high frequency color, for each of the R, G, B color component data included in the color image data. For the color image data that is subjected to gamma correction processing based on the individual gamma table generated by the density conversion table 42 and expresses other colors, the R, G, and B colors included in the color image data are used. For each component data, for example, a gamma correction process is performed based on an initial gamma table set as an initial value. When the original is a book original, gamma correction processing is individually executed for each of the divided image data by the individual gamma table corresponding to the page of the divided image data.
As a result, the image processing unit 4 prevents show-through by performing density conversion based on the individual density conversion table for color image data representing colors in the vicinity of the high-frequency color in the gamma correction processing. can do.

1: Control unit 2: Operation display unit 3: Image reading unit 4: Image processing unit 5: Image forming unit 41: Density conversion unit 42: Conversion point calculation unit 43: Density conversion table generation unit S1, S2,... (Step) numbers S10, S11,...: Processing procedure (Step) numbers Tr1, Tr2, Tg1, Tg2, Tb1, Tb2: Density conversion tables Pr1, Pr2, Pg1, Pg2, Pb1, Pb2: Conversion point X: Multifunction machine

Claims (3)

An image reading unit that reads color image data including a plurality of color component data from a document, and a high frequency value that satisfies a preset high frequency condition that is included in the color image data read by the image reading unit is specified A data conversion means for executing a data conversion process for converting the color image data so that a value in the vicinity of the high-frequency value is substantially uniform to the high-frequency value; and whether or not the document is a book document. A book document determination unit for determining, and when the book document determination unit determines that the document is a book document, the color image data read by the image reading unit is used as a color image for each page of the book document. Image data dividing means for dividing the data into data,
When the data conversion means determines that the original is a book original by the book original determination means, the data conversion processing is individually performed on the color image data for each page divided by the image data division means. An image processing apparatus that executes the data conversion process on the entire color image data read by the image reading unit when the original is determined not to be a book original;
One or a plurality of high-frequency colors satisfying a preset high-frequency condition in which the data conversion means includes a frequency included in the image of the color image data among a plurality of colors represented by the plurality of color component data Corresponding to each of the high-frequency colors specified by the high-frequency specification means, the color component data to make the color in the vicinity of the high-frequency color substantially uniform to the high-frequency color Density conversion information generating means for generating one or a plurality of sets of individual density conversion information used for converting each of the color image data representing colors in the vicinity of the high-frequency color. color component data respectively, which converts on the basis of the individual density conversion information of each set which has been generated in the previous Kiko degree conversion information generating means in response to the high frequency color,
The color group included in the image of the original when the high-frequency specifying unit classifies the plurality of colors represented by the plurality of color component data into color groups for each color within a predetermined range. First color histogram calculation means for calculating a first color histogram indicating the frequency of each, and a predetermined frequency set in advance based on the first color histogram calculated by the first color histogram calculation means For each high-frequency color group extracted by the high-frequency color group extraction means for extracting the high-frequency color group, and for each high-frequency color group extracted by the high-frequency color group extraction means, the frequency for each color included in the high-frequency color group is calculated. Second color histogram calculation means for calculating a second color histogram to be shown, and for each of the high-frequency color groups based on the second color histogram calculated by the second color histogram calculation means. Most possible frequent one or more colors is to identify as the high frequency satisfying high frequency color Te image processing apparatus according to claim. The book manuscript determination means sets a region having a predetermined length in the longitudinal direction and the short direction from the center of the color image data as a determination target region, and a predetermined width at both ends in the longitudinal direction of the determination target region. An average density in the lateral direction is calculated for each line, and a threshold value for determining a boundary between pages is set based on the average density of the predetermined width, and the number of pixels exceeding the threshold value is within the determination target area. The image processing apparatus according to claim 1, wherein it is determined whether or not the document is a book document depending on whether or not a predetermined upper limit value is present.   3. An image forming apparatus comprising: the image processing apparatus according to claim 1; and an image forming unit that forms an image based on each of the color component data converted by the data conversion unit.

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