JP7494603B2 - Image forming apparatus and image processing method - Google Patents

Description

The present invention relates to an image forming apparatus and an image processing method.

One of the application functions of image forming devices is the stamp function. The stamp function is a function that combines a stamp of a type specified by the user, such as a page number, copy number (numbering), or print date and time, with the original image and prints it. In conventional image forming devices, the RGB image input from a scanner or the like is converted to a YMCK image, and then the stamp is combined.

Stamp composition is performed in real time by the ASIC (Application Specific Integrated Circuit) while printing. As shown in Figure 8, this is achieved by writing a stamp image corresponding to the specified stamp (the "P.1" part in Figure 8) to the ASIC's built-in RAM, and then specifying the stamp composition coordinates and YMCK values to the ASIC.

For example, Patent Document 1 describes a method of acquiring image data composed of multiple color planes and an attribute plane, drawing an overlay object such as a stamp on the attribute plane, converting the color components expressed in CMY to printing color components expressed in CMYK for pixels where the overlay object is not drawn, and outputting the color components (CMYK values) of the attribute plane for pixels where the overlay object is drawn.

JP 2008-205902 A

However, when writing a stamp image to the ASIC's built-in RAM, stamps with a large data size cannot be used because the ASIC's built-in RAM has data size restrictions. In order to use stamps with a large data size, it is possible to combine the stamp image with the RGB image, convert it to a YMCK image, and then print it, rather than combining the stamp while printing, as shown in Figure 9.

Here, the user can specify the stamp color from among seven colors, for example R, G, B, Y, M, C, and K, and when the stamp is composited after conversion to a YMCK image as in the past, the color corresponding to the user-specified color can be printed in YMCK, as shown in Figure 10. On the other hand, when the stamp is composited into an RGB image and then converted to a YMCK image, the stamp will be composited with RGB corresponding to the user-specified color and then converted to YMCK, as shown in Figure 11.

However, RGB → YMCK color conversion is designed to reproduce the color of the original document, taking into account the characteristics of the input device of the original document image (for example, the CCD characteristics of the scanner) and the YMCK color characteristics of the image forming unit. In other words, when the input is RG = 100% and B = 0%, the color is theoretically yellow due to additive color mixing, but if the original color when RG = 255 and B = 0 appears to be yellow-green, for example, in order to reproduce yellow-green, RGB → YMCK color conversion is performed so that the color becomes a mixture of yellow and cyan after RGB → YMCK conversion. Therefore, even if you try to make a stamp yellow by compounding a stamp with theoretical RGB values (RG = 255, B = 0), it will not become a yellow stamp made of monochrome toner.

The technology described in Patent Document 1 does not combine a stamp with an RGB image and then convert it to a YMCK image, so it does not have the problem that even if a stamp of theoretical values is combined with an RGB image, the color will not be what the user intended after conversion to a YMCK image, and it cannot solve the above problem.

The objective of the present invention is to enable the stamp to be converted to a color intended by the user when combining an RGB image with a stamp and color-converting the RGB image with the combined stamp into a YMCK image.

In order to solve the above problems, the image forming apparatus according to the present invention comprises:
An acquisition means for acquiring an RGB image and designation information of a type, a position, and a color of a stamp to be combined with the RGB image;
a stamp image generating means for generating a stamp image indicating whether each pixel is a stamp pixel forming the stamp or a non-stamp pixel based on the designation information;
a synthesizing means for synthesizing the stamp with the RGB image based on the stamp image using RGB values corresponding to the color designated by the designation information to generate an RGB image with the stamp;
a color conversion means for generating a stamped YMCK image by referring to the stamp image as an attribute plane of the RGB image and applying different color conversion rules to the stamp pixels and the non-stamp pixels in the stamped RGB image;
an adjustment means for performing a tone curve adjustment on the stamped YMCK image;
an image forming means for forming an image on a recording medium based on the stamped YMCK image;
Equipped with
The adjustment means performs the tone curve adjustment only on the non-stamp pixels with reference to the attribute plane .

The image forming apparatus according to the second aspect of the present invention comprises:
An acquisition means for acquiring an RGB image and designation information of a type, a position, and a color of a stamp to be combined with the RGB image;
a stamp image generating means for generating a stamp image indicating whether each pixel is a stamp pixel forming the stamp or a non-stamp pixel based on the designation information;
a synthesizing means for synthesizing the stamp with RGB values corresponding to a color designated by the designation information based on the stamp image to generate a stamped RGB image, and synthesizing the stamp pixels of the stamp image as character pixels on an attribute plane indicating whether each pixel of the RGB image is a character pixel or a non-character pixel;
a color conversion means for generating a stamped YMCK image by applying different color conversion rules to the character pixels and the non-character pixels in the stamped RGB image with reference to the attribute plane;
an image forming means for forming an image on a recording medium based on the stamped YMCK image;
Equipped with.

The invention described in claim 3 is the invention described in claim 2 ,
an adjustment means for performing a tone curve adjustment on the stamped YMCK image,
The adjustment means performs the tone curve adjustment only on the non-character pixels with reference to the attribute plane.

The image processing method according to the fourth aspect of the present invention comprises:
acquiring an RGB image and designation information of the type, position, and color of a stamp to be combined with the RGB image;
generating a stamp image indicating whether each pixel is a stamp pixel forming the stamp or a non-stamp pixel based on the designation information;
a step of synthesizing the stamp with RGB values corresponding to a color designated by the designation information for the RGB image based on the stamp image to generate a stamped RGB image;
a step of generating a stamped YMCK image by referring to the stamp image as an attribute plane of the RGB image and applying different color conversion rules to the stamp pixels and the non-stamp pixels in the stamped RGB image and performing color conversion;
performing a tone curve adjustment on the stamped YMCK image;
Including,
The step of performing tone curve adjustment on the stamped YMCK image refers to the attribute plane and performs the tone curve adjustment only on the non-stamped pixels .

The image processing method according to claim 5 ,
acquiring an RGB image and designation information of the type, position, and color of a stamp to be combined with the RGB image;
generating a stamp image indicating whether each pixel is a stamp pixel forming the stamp or a non-stamp pixel based on the designation information;
a step of synthesizing the stamp with RGB values corresponding to a color designated by the designation information for the RGB image based on the stamp image to generate a stamped RGB image, and synthesizing the stamp pixels of the stamp image as character pixels on an attribute plane indicating whether each pixel of the RGB image is a character pixel or a non-character pixel;
generating a stamped YMCK image by performing color conversion by applying different color conversion rules to the character pixels and the non-character pixels in the stamped RGB image with reference to the attribute plane;
including.

According to the present invention, when a stamp is composited with an RGB image and the RGB image with the composite stamp is color-converted to a YMCK image, it is possible to convert the stamp to a color intended by the user.

1 is a diagram showing a schematic configuration of an image forming apparatus according to an embodiment to which the present invention is applied. 1 is a block diagram showing a main functional configuration of an image forming apparatus; 3 is a flowchart showing the flow of stamp composition and color conversion processing A executed by the control unit of FIG. 2 in the first embodiment. 11A to 11C are diagrams illustrating a flow of stamp compositing in stamp compositing and color conversion processing A. 13 is a diagram showing the correspondence relationship between the stamp color designated by the user, the stamp RGB value corresponding to that color, and the YMCK value after conversion according to RGB→YMCK color conversion rule 2. FIG. 10 is a flowchart showing the flow of stamp composition and color conversion processing B executed by the control unit in FIG. 2 in the second embodiment. 13 is a flowchart showing the flow of stamp composition and color conversion processing C executed by the control unit in FIG. 2 in the third embodiment. FIG. 10 is a diagram illustrating a flow of printing an RGB image by stamp composition in the prior art. 11A and 11B are diagrams illustrating a flow of combining an RGB image with a stamp image, converting the image into a YMCK image, and printing the resulting image. 13 is a diagram showing the correspondence relationship between a user-specified color and a composite color (YMCK value) when a stamp is composited after conversion into a YMCK image. FIG. 13 is a diagram showing the correspondence relationship between a user-specified color and a composite color (RGB value) when an RGB image is composited with a stamp and then color-converted into a YMCK image. FIG.

Below, an embodiment of the image forming apparatus of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples.

First Embodiment
(Configuration of Image Forming Apparatus)
Fig. 1 is a diagram showing a schematic configuration of an image forming apparatus 1 according to a first embodiment of the present invention, Fig. 2 is a block diagram showing a main functional configuration of the image forming apparatus 1.

The image forming apparatus 1 includes a control unit 10 having a CPU 101 (Central Processing Unit), a RAM 102 (Random Access Memory) and a ROM 103 (Read Only Memory), a memory unit 11, an operation unit 12, a display unit 13, an interface 14, a scanner 15, an image processing unit 16, an image forming unit 17, a fixing unit 18 and a conveying unit 19.
The control unit 10 is connected to the memory unit 11, the operation unit 12, the display unit 13, the interface 14, the scanner 15, the image processing unit 16, the image forming unit 17, the fixing unit 18 and the conveying unit 19 via a bus 21.

The CPU 101 reads and executes control programs stored in the ROM 103 or the memory unit 11, and performs various calculation processes.

RAM 102 provides working memory space for CPU 101 and stores temporary data.

The ROM 103 stores various control programs and setting data executed by the CPU 101. Note that a rewritable non-volatile memory such as an EEPROM (Electrically Erasable Programmable Read Only Memory) or a flash memory may be used instead of the ROM 103.

The control unit 10 including the CPU 101, the RAM 102, and the ROM 103 controls each part of the image forming apparatus 1 in accordance with the various control programs described above.
For example, the control unit 10 causes the image processing unit 16 to perform a predetermined image processing on the image data. The control unit 10 also causes the conveying unit 19 to convey a sheet, and causes the image forming unit 17 to form an image on the sheet based on the image data that has been subjected to the image processing.

The storage unit 11 is composed of storage means such as semiconductor memory such as DRAM (Dynamic Random Access Memory) and HDD (Hard Disk Drive), and stores image data acquired by the scanner 15, image data acquired by the interface 14, various setting information such as stamp designation information, etc. Note that this image data, etc. may also be stored in the RAM 102.

The storage unit 11 also stores stamp data of a variety of types of stamps (fixed-form stamps, watermarks, watermark numbering, etc.) that can be used in the stamp function.
The storage unit 11 also stores color conversion rules 1 and 2 (described in detail below) that are used during color conversion from RGB to YMCK.

The operation unit 12 includes input devices such as operation keys and a touch panel arranged over the screen of the display unit 13, and converts input operations on these input devices into operation signals and outputs them to the control unit 10.

The display unit 13 includes a display device such as an LCD (Liquid Crystal Display) and displays an operation screen showing the status of the image forming device 1 and the contents of input operations to the touch panel.

The interface 14 is configured with a NIC (Network interface card) or a serial interface, etc., and transmits and receives data to and from external devices such as a PC (Personal Computer).

The scanner 15 is equipped with a light source, an optical system, and a CCD (Charge Coupled Device) sensor, and reads an original image formed on paper to obtain image data (RGB image) having monochromatic image data for each of the color components R (red), G (green), and B (blue).

The image processing unit 16 includes, for example, a rasterization processing unit, a stamp synthesis unit, a color conversion unit, etc., and performs various image processing on the image data acquired by the scanner 15 or the interface 14 and stored in the memory unit 11 to generate image data (YMCK image) having image data for each color component of Y (yellow), M (magenta), C (cyan), and K (black).

The functions of each part of the image processing unit 16 may be realized by dedicated hardware, but in this embodiment, they are executed by cooperation between the CPU 101 of the control unit 10 and a program stored in the ROM 103. The image processing unit 16, as a stamp compositing unit and color conversion unit, executes stamp compositing and color conversion process A (see FIG. 3) described below, and realizes the functions of the stamp image generating means, compositing means, and color conversion means of the present invention.

The image forming unit 17 forms an image on paper based on the processed image data (YMCK image). The image forming unit 17 has four sets of exposure units 171, photoconductors 172, and development units 173, each corresponding to the color components Y, M, C, and K. The image forming unit 17 also has an intermediate transfer belt 174 as an image carrier, a primary transfer roller 175, and a secondary transfer roller 176.

The exposure unit 171 is equipped with an LD (Laser Diode) as a light-emitting element. The exposure unit 171 drives the LD based on image data, irradiates the charged photoconductor 172 with laser light, and forms an electrostatic latent image on the photoconductor 172 by exposing it. The development unit 173 supplies toner (color material) of a predetermined color (Y, M, C, or K) by a charged development roller onto the exposed photoconductor 172, and develops the electrostatic latent image formed on the photoconductor 172.

Images (monochrome images) formed with Y, M, C and K toners on the four photoconductors 172 corresponding to Y, M, C and K, respectively, are transferred from each photoconductor 172 onto an intermediate transfer belt 174 in a sequentially overlapping manner.
The intermediate transfer belt 174 is a semiconductive endless belt suspended and rotatably supported by a plurality of rollers including the intermediate transfer driving roller 41, and is rotated and driven in association with the rotation of the rollers. The intermediate transfer belt 174 rotates in accordance with the rotation of each roller when a toner image is transferred.

This intermediate transfer belt 174 is pressed against each of the opposing photoconductors 172 by the primary transfer rollers 175. A transfer current corresponding to the applied voltage flows through each of the primary transfer rollers 175. As a result, each toner image developed on the surface of each photoconductor 172 is transferred (primary transfer) sequentially to the intermediate transfer belt 174 by each of the primary transfer rollers 175.

The secondary transfer roller 176 rotates while being pressed against the intermediate transfer belt 174, transferring (secondary transfer) the toner images of each color Y, M, C, and K formed by being transferred onto the intermediate transfer belt 174 onto paper conveyed from the paper feed unit. Residual toner on the intermediate transfer belt 174 is removed by a cleaning unit (not shown).

The fixing unit 18 has an upper fixing member 181 equipped with a heating means, and a lower fixing member 182, and performs a fixing process in which the paper onto which the toner has been transferred is heated and pressurized to fix the toner to the paper.

As shown in FIG. 1, the transport unit 19 includes multiple paper transport rollers that rotate while clamping the paper to transport the paper along a predetermined transport path.

(Operation of Image Forming Apparatus 1)
Next, the operation of the image forming apparatus 1 in the first embodiment will be described.
When a user wishes to copy an image in which a stamp has been added (combined) to an original image, the user operates the operation unit 12 to display a stamp function specification screen (not shown) on the display unit 13 and specifies the type of stamp to be added, the position to add the stamp, and the color of the stamp. Any of R, G, B, Y, M, C, and K can be specified as the stamp color. Multiple types of stamps can be added, and different colors can be specified for each stamp. After specifying the stamp, the user sets the original image in the scanner 15 and has it read. As a result, the scanner 15 reads the original image and obtains an RGB image, and also obtains the specification information of the stamp specified by the operation unit 12.

When the stamp designation information and the RGB image of the document are acquired, the control unit 10 causes the image processing unit 16 to execute stamp composition and color conversion processing A, and generates a YMCK image onto which the stamp is composed.
Fig. 3 is a flow chart showing the flow of stamp compositing and color conversion processing A. Fig. 4 is a diagram showing a schematic flow of stamp compositing in the stamp compositing and color conversion processing A.

First, the image processing unit 16 reads data of the type of stamp specified in the stamp specification information from the memory unit 11, generates a stamp image in which the read stamp is placed at the specified position, and writes it to the RAM 103 as an attribute plane (step S1).
The stamp image is an image of the same size as the acquired RGB image, with stamp pixels (pixels that make up the stamp) storing 1 and non-stamp pixels that are not stamp pixels storing 0. In other words, the stamp image is an image that indicates whether each pixel is a stamp pixel or a non-stamp pixel, and is used as an attribute plane for the RGB image.

Next, the image processing unit 16 sets the variable n to 1 and N to the number of pixels of the RGB image (step S2).

Next, the image processing unit 16 judges whether or not pixel n of the stamp image (attribute plane) is a stamp pixel (step S3).
If it is determined that pixel n of the stamp image is not a stamp pixel (step S3; NO), the image processing unit 16 color-converts pixel n of the RGB image to YMCK values using RGB → YMCK color conversion rule 1 (step S4), and proceeds to step S7.

Here, RGB → YMCK color conversion rule 1 is a rule established so as to reproduce the color of the original document based on the characteristics of the input device of the original document (for example, the CCD characteristics of the scanner 15) and the YMCK color characteristics of the image forming unit 17, and is different from the conversion rule based on the theoretical values of additive color mixing.
For example, if the original color where R, G = 255, B = 0 appears to be yellow-green, conversion rule 1 specifies that in order to reproduce yellow-green, the color after color conversion from RGB to YMCK must be a mixture of yellow and cyan.

On the other hand, if it is determined that pixel n of the stamp image is a stamp pixel (step S3; YES), the image processing unit 16 replaces the RGB values of pixel n of the RGB image with RGB values (called stamp RGB values) corresponding to the color specified in the stamp specification information (step S5). This makes it possible to composite the stamp into the RGB image. Then, pixel n of the RGB image is converted to YMCK values using RGB → YMCK color conversion rule 2 (step S6), and the process proceeds to step S7.

Fig. 5 is a diagram showing the correspondence relationship between the stamp color designated by the user, the stamp RGB value corresponding to that color, and the YMCK value after conversion according to RGB → YMCK color conversion rule 2. As shown in Fig. 5, conversion between the stamp color designated by the user (in the case of Y, M, C, K) and the stamp RGB value is performed based on the theoretical values of additive color mixing and subtractive color mixing. Conversion between the stamp RGB value and the YMCK value combined with the RGB image is also performed based on the theoretical values of subtractive color mixing and additive color mixing.
In this way, color conversion of an RGB image combined with a stamp to a YMCK image is performed for non-stamp pixels using color conversion rule 1 that reproduces the color of the original, and for stamp pixels using color conversion rule 2 that is different from color conversion rule 1 and is based on theoretical values of mixed colors.

In step S7, the image processing unit 16 determines whether or not n≧N (step S7).
If it is determined that n≧N is not true (step S7; NO), the image processing unit 16 increments n by 1 (step S8) and returns to step S3.
If it is determined that n≧N (step S7; YES), the image processing unit 16 ends the stamp composition and color conversion process A.

When the stamped YMCK image is generated by the stamp compositing and color conversion process A, the control unit 10 causes the image forming unit 17 to print the stamped image on paper based on the stamped YMCK image.

In this way, in the first embodiment, the stamp image is used as an attribute plane, and the RGB → YMCK color conversion rules are made independent for when the attribute of each pixel of the RGB image in which the stamp is composited with the RGB image is a stamp pixel and when it is a non-stamp pixel, and for the stamp pixels, RGB → YMCK color conversion is performed based on the theoretical value of mixed colors, making it possible to print an image with a stamp in the color intended by the user.

Second Embodiment
A second embodiment of the present invention will now be described.
In the first embodiment, attention was focused only on the color conversion from RGB to YMCK, but color conversion by tone curve adjustment is also performed after YMCK conversion. In this case, if tone curve adjustment is also applied to the stamp pixels, the stamp color intended by the user cannot be obtained.
Therefore, in the second embodiment, tone curve adjustment is not applied to stamp pixels.

The configuration of the image forming device 1 in the second embodiment is similar to that described in the first embodiment, so the description will be used to explain the operation of the second embodiment below.

When the stamp designation information and the RGB image of the document are acquired, the control unit 10 causes the image processing unit 16 to execute a stamp composition and color conversion process B.
6 is a flowchart showing the flow of the stamp compositing and color conversion process B. The image processing unit 16 executes the stamp compositing and color conversion process B to realize the functions of the stamp image generating means, the compositing means, the color conversion means, and the adjusting means of the present invention.

First, the image processing unit 16 reads data of the type of stamp specified in the stamp specification information from the memory unit 11, generates a stamp image in which the read stamp is placed at the specified position, and writes it to the RAM 103 as an attribute plane (step S11).
The process in step S11 is similar to that in step S1 in FIG.

Next, the image processing unit 16 sets the variable n to 1 and N to the number of pixels of the RGB image (step S12).

Next, the image processing unit 16 judges whether or not pixel n of the stamp image is a stamp pixel (step S13).
If it is determined that pixel n of the stamp image is not a stamp pixel (step S13; NO), the image processing unit 16 converts pixel n of the RGB image to YMCK values using RGB → YMCK color conversion rule 1 (step S14), performs tone curve adjustment (step S15), and proceeds to step S18.

On the other hand, if it is determined that pixel n of the stamp image is a stamp pixel (step S13; YES), the image processing unit 16 replaces the RGB value of pixel n of the RGB image with an RGB value (stamp RGB value) corresponding to the color specified by the stamp specification information (step S16). This allows the stamp to be synthesized with the RGB image. Then, pixel n of the RGB image is color-converted to YMCK values according to RGB->YMCK color conversion rule 2 (step S17), and the process proceeds to step S18.
Color transformation rules 1 and 2 are similar to those explained in the first embodiment, and so the explanation will be used here.

In step S18, the image processing unit 16 determines whether or not n≧N (step S18).
If it is determined that n≧N is not satisfied (step S18; NO), the image processing unit 16 increments n by 1 (step S19) and returns to step S13.
If it is determined that n≧N (step S18; YES), the image processing unit 16 ends the stamp composition and color conversion process B.

The stamp-added YMCK image is generated by the stamp synthesis and color conversion process B, and tone curve adjustment is applied to the area other than the stamp area of the stamp-added YMCK image. The control unit 10 then causes the image forming unit 17 to print the stamp-added image on paper based on the stamp-added YMCK image.

In the second embodiment, a stamp image is used as an attribute plane, and the RGB → YMCK color conversion rules are made independent for when the attribute of each pixel of a stamped RGB image in which a stamp is composited with an RGB image is a stamp pixel and when it is a non-stamp pixel, and for stamp pixels, RGB → YMCK color conversion is performed based on the theoretical value of mixed colors, making it possible to print the stamp in the color intended by the user. Furthermore, after the RGB → YMCK color conversion, tone curve adjustment is performed only on non-stamp pixels, and tone curve adjustment is not performed on stamp pixels. Therefore, it is possible to prevent the stamp from becoming an unintended color due to tone curve adjustment.

Third Embodiment
A third embodiment of the present invention will now be described.
In some image forming devices as actual products, only two types of RGB → YMCK color conversion rules can be defined, one for pixels in character areas and the other for pixels in other (non-character) areas. Therefore, in such image forming devices, it is not possible to define a color conversion rule exclusively for stamp pixels.

The color conversion rule for the text area is designed so that black text is printed in a single color of K toner, without mixing YMC colors as much as possible (K 100% is used around RGB=0). This is because text is often black, and mixing YMC colors results in a brownish color, so this color conversion rule is for printing black text neatly in black.
Therefore, in the third embodiment, the attribute of the stamp pixel is set to character area (character pixel), and the color conversion rule for the character area (third color conversion rule) is set to convert R, G, and B values within a predetermined range (for example, a range of ±15) near 255 or 0 to Y, M, C, and K of 255 or 0. Specifically, the rule is set to convert values within a predetermined range (for example, a range of ±15) of the RGB values before conversion (stamp RGB values) from the values shown in Fig. 5 to the converted YMCK values of Fig. 5. Since the character area has no gradation and is composed of a single color, there is almost no problem even if the YMCK output values change significantly between R, G, and B near 255 or 0 and the rest.
On the other hand, since non-character regions are photographs, gradation graphics, etc., and the RGB values change continuously, if the YMCK output values are significantly changed between a predetermined range value near RGB=255 or 0 and other values, a sudden color change will occur in part of the gradation, so it is not preferable to apply the same color conversion rule as the stamp pixels. Therefore, a color conversion rule different from that for character regions is applied to the pixels in non-character regions (non-character pixels).
Although the color conversion rule for a certain range has been changed in the above, it is also possible to convert to YMCK values using the conversion in FIG. 5 only when R, G, and B are 255 or 0 without setting a range.

That is, in the third embodiment, the memory unit 11 stores a first color conversion rule (similar to the first color conversion rule described in the first embodiment) to be applied to non-character areas, and a third color conversion rule to be applied to character areas.
Other configurations of the image forming apparatus 1 in the third embodiment are similar to those described in the first embodiment, so the description thereof will be used here and the operation of the third embodiment will be described below.

When the stamp designation information and the RGB image of the document are acquired, the control unit 10 causes the image processing unit 16 to execute stamp synthesis and color conversion processing C, generate a YMCK image with a stamp, and perform tone curve adjustment.
7 is a flowchart showing the flow of the stamp compositing and color conversion process C. The image processing unit 16 executes the stamp compositing and color conversion process C to realize the functions of the stamp image generating means, the compositing means, the color conversion means, and the adjusting means of the present invention.

First, the image processing unit 16 reads data of the type of stamp specified in the stamp specification information from the storage unit 11, generates a stamp image in which the read stamp is placed at the specified position, and writes the generated stamp image into the RAM 103 (step S21).
The process of step S21 is similar to that of step S1 in FIG.

Next, the image processing unit 16 sets the variable n to 1 and N to the number of pixels of the RGB image (step S22).

Next, the image processing unit 16 judges whether or not the pixel n of the stamp image is a stamp pixel (step S23).
When it is determined that pixel n of the stamp image is not a stamp pixel (step S23; NO), the image processing unit 16 proceeds to step S26.

When it is determined that pixel n of the stamp image is a stamp pixel (step S23; YES), the image processing unit 16 replaces the RGB value of pixel n of the RGB image with the RGB value (stamp RGB value) corresponding to the color specified by the stamp specification information (step S24). This makes it possible to composite the stamp into the RGB image.
Next, the image processing unit 16 sets the attribute of pixel n in the attribute plane to character pixel (step S25), and proceeds to step S26.

In step S26, the image processing unit 16 determines whether or not the attribute of pixel n is a character pixel (step S26).
If it is determined that the attribute of pixel n is not a character pixel (step S26; NO), the image processing unit 16 converts pixel n of the RGB image to YMCK values using RGB → YMCK color conversion rule 1 (step S27), performs tone curve adjustment (step S28), and proceeds to step S30.

On the other hand, if it is determined that the attribute of pixel n is a character pixel (step S26; YES), the image processing unit 16 converts pixel n of the RGB image to YMCK values using color conversion rule 3 for characters (step S29) and proceeds to step S30.

In step S30, the image processing unit 16 determines whether or not n≧N (step S30).
When it is determined that n≧N is not satisfied (step S30; NO), the image processing unit 16 increments n by 1 (step S31) and returns to step S23.
When it is determined that n≧N (step S30; YES), the image processing unit 16 ends the stamp composition and color conversion process C.

The stamp compositing and color conversion process C generates a stamped YMCK image, and when tone curve adjustment is applied to the stamped YMCK image, the control unit 10 causes the image forming unit 17 to print the stamped image on paper based on the stamped YMCK image.

In the third embodiment, the stamp pixels of the stamp image are composited into the attribute plane as character pixels, and different RGB → YMCK color conversion rules are applied depending on whether the attribute of each pixel of the RGB image is a character pixel or a non-character pixel. Therefore, even if the color conversion rule can only define two types of regions, character regions and other non-character regions, RGB → YMCK color conversion can be performed on the stamp pixels using theoretical values of mixed colors, making it possible to print in the color intended by the user. Furthermore, after the RGB → YMCK color conversion, tone curve adjustment is performed only for non-character pixels, and tone curve adjustment is not performed on character pixels. Therefore, it is possible to prevent the stamp from becoming an unintended color due to tone curve adjustment.

The present invention has been described above based on the above embodiment, but the description in the above embodiment is a preferred example of the image forming device according to the present invention and is not limited to this.

For example, in the above embodiment, the present invention has been described as being applied to a case where a stamp is added to an RGB image obtained by scanning an original image with the scanner 15 and then copied. However, the present invention may also be applied to a case where a stamp is added to an RGB image of an original transmitted from an external device such as a PC and then printed. For example, when a user specifies the type, position, and color of a stamp to be added to the RGB image to be printed on the setting screen of a printer driver of the external device and transmits the RGB image and stamp specification information to the image forming device 1, the interface 14 of the image forming device 1 acquires the RGB image and stamp specification information. The control unit 10 causes the image processing unit 16 to execute the above-mentioned stamp composition/color conversion process A, stamp composition/color conversion process B, or stamp composition/color conversion process C on the acquired RGB image and stamp specification information, and causes the image forming unit 17 to print the generated stamped YMCK image.

In the above embodiment, the present invention has been described as being applied to an electrophotographic image forming apparatus, but the present invention may also be applied to other image forming apparatuses, such as an inkjet type.

In addition, in the above embodiment, the recording medium on which the image is printed is described as being paper, but this is not limited to this and may be an overhead projector sheet, cloth, etc.

In addition, the specific details of the configuration, structure, control content, and order shown in the above embodiment can be modified as appropriate without departing from the spirit of the present invention.

REFERENCE SIGNS LIST 1 Image forming apparatus 10 Control section 11 Memory section 12 Operation section 13 Display section 14 Interface 15 Scanner 16 Image processing section 17 Image forming section 18 Fixing section 19 Conveying section 21 Bus

Claims (5)

An acquisition means for acquiring an RGB image and designation information of a type, a position, and a color of a stamp to be combined with the RGB image;
a stamp image generating means for generating a stamp image indicating whether each pixel is a stamp pixel forming the stamp or a non-stamp pixel based on the designation information;
a synthesizing means for synthesizing the stamp with the RGB image based on the stamp image using RGB values corresponding to the color designated by the designation information to generate an RGB image with the stamp;
a color conversion means for generating a stamped YMCK image by referring to the stamp image as an attribute plane of the RGB image and applying different color conversion rules to the stamp pixels and the non-stamp pixels in the stamped RGB image;
an adjustment means for performing a tone curve adjustment on the stamped YMCK image;
an image forming means for forming an image on a recording medium based on the stamped YMCK image;
Equipped with
The adjustment means performs the tone curve adjustment only on the non-stamp pixels by referring to the attribute plane . An acquisition means for acquiring an RGB image and designation information of a type, a position, and a color of a stamp to be combined with the RGB image;
a stamp image generating means for generating a stamp image indicating whether each pixel is a stamp pixel forming the stamp or a non-stamp pixel based on the designation information;
a synthesizing means for synthesizing the stamp with RGB values corresponding to a color designated by the designation information based on the stamp image to generate a stamped RGB image, and synthesizing the stamp pixels of the stamp image as character pixels on an attribute plane indicating whether each pixel of the RGB image is a character pixel or a non-character pixel;
a color conversion means for generating a stamped YMCK image by applying different color conversion rules to the character pixels and the non-character pixels in the stamped RGB image with reference to the attribute plane;
an image forming means for forming an image on a recording medium based on the stamped YMCK image;
An image forming apparatus comprising: an adjustment means for performing a tone curve adjustment on the stamped YMCK image,
3. The image forming apparatus according to claim 2 , wherein the adjustment means performs the tone curve adjustment only on the non-character pixels by referring to the attribute plane. acquiring an RGB image and designation information of the type, position, and color of a stamp to be combined with the RGB image;
generating a stamp image indicating whether each pixel is a stamp pixel forming the stamp or a non-stamp pixel based on the designation information;
a step of synthesizing the stamp with RGB values corresponding to a color designated by the designation information for the RGB image based on the stamp image to generate an RGB image with a stamp;
a step of generating a stamped YMCK image by referring to the stamp image as an attribute plane of the RGB image and performing color conversion by applying different color conversion rules to the stamp pixels and the non-stamp pixels in the stamped RGB image;
performing a tone curve adjustment on the stamped YMCK image;
Including,
The image processing method includes performing a tone curve adjustment on the stamped YMCK image by referring to the attribute plane and performing the tone curve adjustment only on the non-stamped pixels . acquiring an RGB image and designation information of the type, position, and color of a stamp to be combined with the RGB image;
generating a stamp image indicating whether each pixel is a stamp pixel forming the stamp or a non-stamp pixel based on the designation information;
a step of synthesizing the stamp with RGB values corresponding to a color designated by the designation information for the RGB image based on the stamp image to generate a stamped RGB image, and synthesizing the stamp pixels of the stamp image as character pixels on an attribute plane indicating whether each pixel of the RGB image is a character pixel or a non-character pixel;
generating a stamped YMCK image by performing color conversion by applying different color conversion rules to the character pixels and the non-character pixels in the stamped RGB image with reference to the attribute plane;
An image processing method comprising:

Images