JP2004034636A - Image formation apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To contrive a high image quality by suppressing degradation of pictures which is conventionally brought about when an underlayer paper appears along an outline at a border of a letter and a background in the case where a black letter is overlapped with the background (BOP). <P>SOLUTION: A pure black is used for drawing a character part with no background as illustrated. A drawing process of the same condition is carried out to the background and the letter to be overlapped with the background for a BOP region part, and a process black is used. The BOP region is trapped. A CMY dither common to various PDLs is applied to a CMY intermediate code after color matching for the region, and data formed in one bit is developed to a CMY plane. Then, under color removal/black generation (removing an equivalent quantity CMY which composes K and generating K) is carried out. At this time, mask values for tailoring data are used for CMY and K, respectively. When printing is carried out by drawing data acquired by synthesizing each CMYK plane obtained by the process to the background and the letter, K of the letter overrides on CMY of the background, so that an image quality degradation can be suppressed. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention uses CMYK (C: Cyan, M: Magenta, Y: Yellow, K: Black) by a print command expressed in a printer description language (PDL), such as is found in a printing apparatus or printing system such as a color printer. ), Which generates drawing data of each component and forms a color image based on the drawing data, particularly in an image including a black overprint (printing characters over a sketch) as a print command. The present invention relates to the image forming apparatus including means for avoiding possible deterioration of image quality and achieving high image quality.
[0002]
[Prior art]
A color printer is widely known as one of image forming apparatuses for forming a color image on a recording medium such as printing paper based on color image data.
In a color printer, an instruction is given to a command based on color image information including characters (documents) and image data included in a print command expressed in a printer description language (PDL) transmitted from a host computer. The image forming process (printing) is performed according to the set printing process conditions.
In the above-described color printer, a color image is formed by using four colors of CMYK (C: Cyan, M: Magenta, Y: Yellow, K: Black), and the image is formed by an electrophotographic method. The printer that performs the forming process also employs the four-color system. In the four-color system, the color image data included in the PDL print command received by the printer is usually represented by three-color data of RGB (R: RED, G: GREEN, B: BLUE). In the printer controller, the PDL processing unit generates drawing data used for image formation from input data expressed in RGB. In the generation process, rendering processing is performed on RGB data (processing for developing data into a two-dimensional pixel array) Is performed, CMY dither is applied to perform 1-bit conversion (raster operation: accompanied by ROP). On the other hand, ROP is performed on character data using K: Black.
[0003]
By the way, a black over print (hereinafter, referred to as “BOP”) in which characters are overlaid on a sketch (background image) and printed is sometimes instructed by a print command. When the drawing data is generated in response to the BOP instruction, the CMYK drawing data for forming the color image is rendered by the above-described method. At this time, according to the conventional processing method, the character data is converted from the character data. With respect to a pixel region of a character in the K plane on which the generated drawing data is expanded, a process of extracting a sketch in the same region has been performed. That is, the pixel data of the CMY plane corresponding to the pixel position of the K plane on which the character is drawn is excluded, and the drawing data of the sketch is not generated in this portion. When a color image is formed using drawing data generated by such a method, the toner attached to the base (printing paper) in the character portion is only K toner. No K toner adhered.
[0004]
[Problems to be solved by the invention]
However, when the above-described conventional method is applied to the BOP and the printing process is performed, an undesired problem with respect to the quality of an image occurs in that the background appears along the outline of the character at the boundary between the character drawn in black and the sketch. There are cases. This occurs in the image forming process. This process is executed by the print engine based on the drawing data created on the CMYK plane. In the existing process, development is performed for each color of CMYK, and the image of each component color is superimposed on an intermediate medium or printing paper. It depends on the method of matching. When forming an image by this method, it is difficult to keep the same operating conditions, and an image of each component color may be shifted depending on a change in the conditions. When a shift that occurs in such an image forming process occurs between a character and a sketch, since only the K toner is attached to the area where the character is drawn as described above, the base (printing paper) is exposed. As a result, image quality is degraded.
SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems of the related art, and has as its object to provide an image forming apparatus that forms a color image in accordance with a black overprint instruction included in a print command expressed in a printer description language. (For example, in a printer, a multifunction copier equipped with a printer and a facsimile function, etc.), a background (print paper) It is another object of the present invention to provide an image forming apparatus having a function of avoiding deterioration of image quality due to appearance of a character along a contour of a character and enabling high image quality.
[0005]
[Means for Solving the Problems]
According to the first aspect of the present invention, a color image composed of character data included in a print command expressed in a printer description language and preliminary image data in which the character data overlaps is converted and processed, and drawing data of each component of four colors of CMYK is converted. An image forming apparatus comprising: a drawing data generating unit for generating; and an image forming unit for forming a color image based on the generated drawing data, wherein the drawing data generating unit includes an intermediate unit for the color image expressed in a printer language. After performing color conversion to CMY components as processing, rendering is performed with 1 bit on each plane of CMY, a function of performing under color removal processing and generation of a K component on the rendered CMY plane, Based on the obtained CMYK plane data and the K plane data generated from the character image, An image forming apparatus having a function of generating drawing data.
[0006]
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the drawing data generating unit temporarily represents an area occupied by the sketch image data on the processing target image using a K plane, When the under color removal processing and the K component generation for the CMY plane are performed, the area information of the sketch image data of the K plane is referred to.
[0007]
According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the drawing data generating means expresses data indicating the area by setting data for masking an area other than the area occupied by the preliminary image data. , A masking operation is performed when under color removal processing and K component generation are performed.
[0008]
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the data of the CMY plane subjected to the under color removal processing is adjusted by a predetermined masking operation. It is characterized by the following.
[0009]
According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, data used for masking is determined based on a total amount control value of color components.
[0010]
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, undercolor removal processing and K component generation are performed on the CMY plane, and a predetermined K plane data is generated. The data is adjusted by the above masking operation.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will be described based on the following embodiments shown in the accompanying drawings.
In the embodiment described below, an example is described in which a color printer is used as the image forming apparatus of the present invention, and a computer as a host device is connected to the color printer via a communication interface.
FIG. 1 is a diagram schematically illustrating a printer system according to the present embodiment, and the embodiment system will be described with reference to FIG. The printer system illustrated in FIG. 1 includes a host computer 100 that transmits a print request, a host computer 100 connected to the host computer 100 via a communication interface (network), and a color image according to a print command received from the host computer 100 via the communication interface. The system is configured by the printer 101 forming the printer. In addition, this system is color-compatible (that is, generates drawing data of each of the four CMYK components based on data for forming a color image included in a print command), and has a sketch (background image). This is a system that has a function corresponding to black over print (BOP), which prints characters overlaid on them. Note that the basic configuration of a system such as this example in which the host computer 100 is connected to the printer 101 via a communication interface is that which is generally employed by a conventional general printer system. Since the components are provided on the printer side, a detailed configuration on the host computer 100 side is omitted.
[0012]
The printer 101 receives a print command transmitted from the host computer 100 via the communication interface, performs a process of generating drawing image data according to the content of the command, and receives the generated drawing image data and prints it on a print sheet. A print engine including an image forming unit for forming an image and a paper supply / discharge unit is provided. The printer controller has a system control function for controlling the entire system of the printer 101 in addition to the above-described function of generating the drawing image data. FIG. 2 is a schematic diagram of a hardware configuration of the printer controller. As shown in FIG. 2, the printer controller has a CPU 215, a program ROM 211, a font ROM 212, a DRAM 213, an NVRAM 214, a host I / F 217, an engine I / F 214, and an operation panel 216.
The CPU 215 of the printer controller executes a print process according to a print command received from the host computer 100 (or an instruction from the operation panel 216). The outline of the processing flow is to interpret and process a print command expressed in the printer description language (PDL) received by the host I / F 217 by a print program stored in the program ROM 211 and generate drawing image data on the DRAM 213. I will do it. The generated drawing image data is transmitted to the image forming engine through the engine I / F 214, the image is formed (visualized) on the printing paper by the existing electrophotographic process, and output as a printing result.
[0013]
Here, the processing steps from generating a print command expressed in PDL received from the host I / F 217 to generating a drawing image on the DRAM 213 will be described in detail.
FIG. 3 shows a block of a processing program in the printer controller. As shown in the figure, a PDL unit 220 that operates on the OS 250 as a program necessary for controlling the operation of the entire system of the printer 101 including the processing of print data and the image forming (printing) process is shown in FIG. , A print control unit 230 and a host control unit 240.
The processing of the print command is performed by the PDL unit 220. FIG. 4 shows the configuration of the PDL unit 220 in more detail. As shown in FIG. 4, a parser 221, a display list 222, and a renderer 223 are elements.
The processing function of the PDL unit 220 will be described with reference to FIG. 4. When a print command from the host computer 100 is received by the host I / F 217, the PDL unit 220 interprets the contents of the print data indicated in the command. Then, the result is temporarily expanded in the display list 222 in the form of an intermediate language (intermediate code). Thereafter, the renderer 223 further develops the intermediate language into drawing image data. The processing of this series of print data is performed in band units (processing units when a method of dividing one page into a plurality of bands in order to increase the processing efficiency and proceeding with the processing for each band) is used. When a plurality of parsers 221 are provided so as to be compatible with print commands of different types of PDL (for example, PCL / PS), an intermediate code common to languages such as PCL / PS is used. This is because it is considered that the code size of the renderer (development unit) 223 can be efficiently suppressed and developed by dropping the code into the (display list 222).
[0014]
Next, the rendering process of the PDL unit including the processing unit unique to the present invention will be described.
The PDL unit 220 has a processing function corresponding to a print command of a color image. When a print command expressed by a PDL of a three-color model of RGB (8 bits) is input by a generally adopted method, the RGB is input. By applying color matching, that is, gamma (γ) to the data, the data is corrected to device-dependent RGB data, and the RGB data after color matching is converted to CMY data. Rendering is performed based on the CMY data. The rendering involves a raster operation (ROP) that applies dither according to the value to each color data and converts the data into one bit. In the case of a CMYK 4-color model printer, it is possible to perform ROP on either CMY data or data that has been converted into CMYK data. If this is done, compatibility with the ROP of the RGB three-color model may not be maintained, so the ROP is performed on CMY data here.
[0015]
Next, the rendering process of the PDL unit in the present embodiment will be described in detail according to a flow.
The renderer 223 of this example implements a black over print (BOP) -compatible processing function for printing characters by overlaying a sketch. This processing function is activated to perform the processing in the BOP mode when the PDL parser 221 of the printer controller that receives the print command interprets the command and recognizes that a BOP is specified therein.
In the renderer 223, the process in the BOP mode performs a process of generating drawing image data in a mode different from the process of a normal color image. In the normal color image processing mode, the same processing is applied to the entire area of one page without changing the processing conditions in order to generate each of the CMYK drawing image data. On the other hand, in the BOP mode, different processing is applied to a region where only character data is drawn and a region where a BOP where characters are overlaid on a sketch is performed.
FIG. 7 illustrates the principle of this drawing method. As shown in the drawing, a process using pure Black: K is performed to draw a character in a region where there is no sketch, and in a region where a character is overlaid on the sketch (BOP), the sketch and the character to be overlapped therewith have the same conditions. A drawing process is performed (a process Black is used for drawing a character by applying BC / UCR masking described later).
In this example, trapping is applied in order to specify an application area of the processing for generating the different drawing image data, and the trapped area and the other areas are respectively shown in FIG. The different drawing processing shown can be executed.
[0016]
FIG. 5 is a diagram for explaining the processing flow in the renderer.
The example shown in FIG. 5 is a processing flow in the BOP mode, in which trapping is performed to generate different drawing image data for an area where only characters are printed and an area where printing is performed by the BOP as described above. It shows a procedure. (1) to (5) in the figure correspond to descriptions (1) to (5) relating to the following processing procedure.
In this example, the data processed by the renderer 223 is converted into CMY data through device-dependent RGB values by performing color matching by applying γ to the 8-bit RGB data already input in the processing steps so far. It is intermediate code data. Further, although image formation (printing) based on the drawing image data is performed for each page, band processing is performed in the process of the rendering image data generation processing of the renderer 223, so rendering is performed on each color plane in band units.
[0017]
With reference to FIG. 5, the processing in the BOP mode will be described along the following processing procedures (1) to (5).
(1) Secure buffer for trapping
In the BOP mode, first, a memory area of the trapping buffer is secured in the DRAM 213. The print command to be processed in the BOP mode is expressed in RGB three-color PDL. In the present system, when input to the renderer 223, the CMY intermediate code data is obtained through color matching. ROP to the CMY plane is performed based on Therefore, the area of the CMY plane is secured in the DRAM 213. At this time, since the ROP to the K plane is not performed, the K plane is not opened in the normal operation mode. However, in the BOP mode, the K plane is opened as a trapping buffer memory area, and the trapping operation is performed. A buffer for performing operations such as (detailed later) and the like is secured, so that it is not necessary to secure an extra memory area for trapping, thereby improving the efficiency of memory use. In the normal mode (as opposed to the BOP mode), the drawing on the K plane is performed after the ROP on the CMY plane, so the K plane is first opened at that time.
[0018]
(2) ROP to CMY plane
Next, ROP is performed on the secured CMY plane based on the CMY intermediate code data. In this ROP, CMY dither commonly used with various types of PDL is applied to the intermediate code data of CMY, that is, by using a dither pattern corresponding to the value for each CMY data, the CMY plane is converted into 1 bit. Perform operations to expand data. Here, since the operation is in the BOP mode, this operation is performed for each of the target sketch and the character, and the following processing is performed.
▲ 3 ▼ Draw bitmap for trapping
Trapping is performed by temporarily writing data that distinguishes the area requiring BOP printing from the other areas on the K plane secured in (1) above, and performs an operation to generate drawing data for each area. It will be used for the operation of the processing (detailed later). In the trapping bitmap generated by writing the data for distinguishing the areas, the area of only the characters for which pure black is to be guaranteed is black (pixel data is set to “1”), and the area where BOP is to be performed is white. (Set the pixel data to “0”). FIG. 6 shows a specific example of the trapping bitmap. As illustrated in the figure, the drawing image data of the K plane for the original picture (the area indicated by hatching indicates the part where the character is overlaid on the sketch) is the area where only the character is drawn in the BOP mode. The area to be drawn in BOP is painted in black and white. In the vector gray assurance mode, character drawing data is generated entirely.
[0019]
4) Generation of CMY drawing image data (UCR processing)
Under color removal (UCR) processing is performed on the 1-bit data developed on the CMY plane by the rendering in the above (2). At this time, with reference to the trapping bitmap temporarily stored in the buffer (K plane) in the above (3), it is determined whether or not to apply the UCR mask processing. In other words, the region where only the characters are printed (the region other than the BOP) is not adjusted by the UCR (Trap) mask, and the region where the BOP is required to be printed is adjusted by the UCR (Trap) mask. CMY drawing image data to be generated.
In this embodiment, the generation of the CMY drawing image data is performed according to the following equation:
CMY drawing value = (UCR value) AND ((UCR mask value) OR (Trap mask value))
The CMY drawing image data to be generated is calculated by performing an arithmetic operation according to the following.
This CMY drawing value is calculated based on the UCR value remaining after removing the undercolor. The (UCR value) in the above arithmetic expression is obtained by removing the under color from the 1-bit input Gray value developed on the CMY plane by the rendering in (2) above (that is, by generating K to form K, etc.). This is the value (CMY data) remaining after removing the amount of CMY). At this time, the data replaced with the K value as a result of the under color removal generates K drawing image data to be described later (this is referred to as “BG” processing).
[0020]
The (UCR mask value) in the above equation is used to adjust the UCR value to an appropriate value in an area where the Trap mask value is “0”, that is, in an area where white is painted as an area where BOP printing is required. . For example, when the total amount is regulated for the toner usage amount, the UCR mask value can use the values exemplified in the following [Example 1] and [Example 2] according to the total amount regulated value. Note that the regulation value of the toner use amount is expressed in% when the maximum use amount of CMYK per unit area is 400% (= 100% × 4). Further, in a matrix representing the following mask values, each row corresponds to CMY.
[Example 1: 280% regulation]
{0x45454545, 0x2a2a2a2a, 0x15151515, 0x8a8a8a8a},
{0x2a2a2a2a, 0x15151515, 0x8a8a8a8a, 0x45454545},
{0x15151515, 0x8a8a8a8a, 0x45454545, 0xa2a2a2a2}
[Example 2: 200% regulation]
{0xbbbbbbbbb, 0xdddddddd, 0xeeeeeeee, 0x777777777},
{0xddddddddd, 0xeeeeeeee, 0x777777777, 0xbbbbbbbbb},
{0xeeeeeee, 0x777777777, 0xbbbbbbbbb, 0xdddddddddd}
[0021]
5) Generation of K drawing image data (BG processing)
As described in the UCR process of (4) above, the under color removal (UCR) process is performed on the 1-bit data (rendering process of (2) above) developed on the CMY plane. The removal of the CMY values means that a K value equivalent to the under color is simultaneously generated as drawing image data at the pixel position (this is referred to as BG: Black Generation).
Therefore, at the time of the above (4) under color removal (UCR) processing, the K value is set at the pixel position in place of the removed under color CMY value. At this time, the K value is temporarily stored in the buffer in the above (3). With reference to the trapping bitmap, it is determined whether to apply the BG mask process. In other words, an area where only characters are printed (an area other than the BOP) is set to a pure black without adjustment using the BG mask, and an area where the BOP needs to be printed is adjusted using the BG mask to obtain the desired K. Enable to generate drawing image data.
In this embodiment, the generation of the K drawing image data is performed by the following arithmetic expression:
K drawing value = (BG value) AND ((BG mask value) OR (Trap mask value))
By performing the arithmetic operation according to, the K drawing image data to be generated is calculated.
The K drawing value is calculated based on the BG value generated simultaneously with the UCR. Note that the (BG value) in the above arithmetic expression is generated by setting the pixel position from which the undercolor has been removed in the 1-bit input Gray value developed on the CMY plane by the rendering in (2) above as K data. Become.
[0022]
The (BG mask value) in the above equation is used to adjust the BG value to an appropriate value in a region where the Trap mask value is “0”, that is, in a region where white is painted as a region where BOP printing is required. . For example, the BG mask value is prepared as a value having a value corresponding to a predetermined adjustment value when adjusting the amount of B toner used, and is set to a value that can be called a process black with respect to a pure black. Have an adjustment value for As the mask value, a value shown in the following [BG mask value (example)] can be used. The matrix values of the masks illustrated below are printed by Black in which K data is arranged in a grid pattern.
[BG mask value (example)]
{0xcccccccc, 0xcccccccc, 0x333333333, 0x333333333}
In the BOP area where characters are superimposed and printed on the sketch, data is generated from both the sketch and the characters as K drawing image data generated through the above-described BG processing. Needs to combine the K drawing image data from both, and develop and output it on one K plane.
[0023]
【The invention's effect】
(1) Effects corresponding to the first aspect of the invention
After performing color conversion into CMY components as an intermediate process for a PDL print command input, the CMY planes are rendered with one bit, and the rendered CMY planes are subjected to under color removal (UCR) processing and K component generation. (BG) and a function of generating drawing data based on CMYK plane data obtained from a color image and K plane data generated from a character image, thereby drawing characters in a sketch. In this case, since the image is formed (printed) with the character K on the sketch CMY, even if a misalignment occurs between the character and the sketch in the image forming process, the image is covered by the sketch CMY and drawn in black. It is possible to avoid that the base is exposed at the boundary between the drawn character and the sketch and it appears along the outline of the character, and the image quality is higher than in the conventional technology It is possible to achieve.
(2) Effects corresponding to the inventions of claims 2 and 3
In addition to the effect of the above (1), the area occupied by the sketch is temporarily expressed using the K plane, and this is referred to when performing the under color removal processing on the CMY plane and the generation of the K component. Since it is not necessary to secure a separate memory area in the memory (DRAM) to indicate the BOP area, the memory can be used efficiently. Further, since the mask indicating the BOP area is set on the K plane and the masking operation is used, it is possible to easily perform the under color removal processing and the generation of the K component.
(3) Effects corresponding to the inventions of claims 4 and 5
In addition to the effects of the above (1) and (2), the CMY plane data is adjusted by a masking operation using a predetermined mask. Various adjustments such as adjustment of the amount of use set based on the regulation value can be performed, and printing can be performed under appropriate conditions.
(4) Effects corresponding to the invention of claim 6
In addition to the effects of the above (1) to (3), the data of the K plane is adjusted by a masking operation using a predetermined mask. Therefore, K can be adjusted by appropriately selecting a mask value. Printing can be performed under various conditions.
[Brief description of the drawings]
FIG. 1 is a diagram schematically illustrating a printer system according to an embodiment of the present invention.
FIG. 2 is a schematic diagram illustrating a hardware configuration of a printer controller provided in the printer of the system according to the present invention.
FIG. 3 is a diagram showing a block of a processing program in the printer controller of FIG. 2;
FIG. 4 is a diagram showing in more detail functions of a PDL unit in the processing program of FIG. 3;
FIG. 5 is a view for explaining a processing flow in the renderer shown in FIG. 4;
FIG. 6 is a diagram for explaining trap data written to a K plane in a BOP mode.
FIG. 7 is a diagram for explaining the principle of a drawing method adopted by the present invention.
[Explanation of symbols]
100: host computer, 200: printer,
211: Program ROM, 213: DRAM,
215: CPU, 217: Host I / F,
218 ... Engine I / F, 220 ... PDL part,
221, a parser, 222, a display list,
223 ... Renderer.

Claims (6)

Drawing data generating means for converting and processing a color image composed of character data included in a print command expressed in a printer description language and preliminary image data in which the character data overlaps, and generating drawing data of each component of CMYK 4 colors; And an image forming apparatus for forming a color image based on the generated drawing data, wherein the drawing data generating means performs color processing on CMY components as an intermediate process for the color image expressed in a printer language. After performing the conversion, rendering is performed on each CMY plane with 1 bit, a function of performing under color removal processing and generation of a K component on the rendered CMY plane, and data of the CMYK plane obtained from the color image And drawing data to be used in the image forming means based on the K-plane data generated from the character image. An image forming apparatus comprising the features of. 2. The image forming apparatus according to claim 1, wherein the drawing data generating unit temporarily represents, using a K plane, an area occupied by the sketch image data on the processing target image, and removes an undercolor from the CMY plane. An image forming apparatus characterized in that when processing and generation of a K component are performed, region information of sketch image data of a K plane is referred to. 3. The image forming apparatus according to claim 2, wherein the drawing data generation unit expresses the data indicating the area by setting data for masking an area other than the area occupied by the underlay image data, and performs the undercolor removal processing and the K processing. An image forming apparatus, wherein a masking operation is performed when generating a component. 4. The image forming apparatus according to claim 1, wherein the data of the CMY plane subjected to the undercolor removal processing is adjusted by a predetermined masking operation. . 5. The image forming apparatus according to claim 4, wherein data used for masking is determined based on a total amount regulation value of color components. 6. The image forming apparatus according to claim 1, wherein undercolor removal processing and K component generation are performed on the CMY plane, and data is adjusted by performing a predetermined masking operation on the generated K plane data. An image forming apparatus, comprising:

Images