JP2008086033A - Image processing apparatus, drawing data processing method, and program for executing the method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable achromatic color processing without causing the deterioration of image quality in drawing data generation (conversion into CMYK) for a source image such as a scanner image constituted of only a full color image without an instruction of an image object type. <P>SOLUTION: An image color converting part 3 performs color conversion from RGB inputted from a host into CMYK for printing, a color conversion determining part 31 instructs for each pixel which of a K conversion part 33 (using only K) or a CMYK conversion part 32 should be employed. The color conversion determining part instructs the conversion part to be applied to achromatic/chromatic colors pixel determination and an achromatic color pixel. This instruction checks whether or not a chromatic color pixel exists in neighborhood pixels around a target pixel, regards the chromatic pixels as constituent pixels of a photographic image if any, and applies CMYK 4-color conversion. This leads to that gray pixels contained in the photographic image maintain gradation continuity with the neighborhood pixels, and that black characters and black ruled lines are clearly drawn in K monochrome. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image processing apparatus such as a printer that generates drawing data in order to draw a figure in accordance with a figure drawing command based on full-color image data, and a drawing data processing method, and more specifically, at the time of achromatic color conversion, The image processing apparatus, the drawing data processing method, and the program for executing the method, which can select a K single color conversion condition using only K and a normal conversion condition using CMYK to improve the quality of a print output image Further, the present invention relates to a printing apparatus (for example, a printer) and a host apparatus on which the program is installed.

In an image processing apparatus such as a printer that generates drawing data in order to draw a figure in accordance with a figure drawing command based on full-color image data, in the process of generating drawing data based on an original image represented by RGB data The printer performs color conversion to CMYK data for color printing.
In this color conversion, conversion methods corresponding to the following two types of drawing methods are conventionally applied as conversion processing for achromatic colors (white and gray including black). For example, when color printing a page with mixed characters, graphs, and photographs as seen in a business document, the achromatic color (hereinafter referred to as “gray”) refers to the K color material. The gray portion of the photographic image is preferably printed with a mixed color of CMYK four color materials, and K single color conversion and CMYK four color conversion are performed corresponding to these drawing methods.

  Such correspondence is likely to become thicker if four color materials are used for the gray of characters and graph parts. For example, in the case of a color laser printer, the ink bleeds due to scattering of toner, and in the case of an inkjet printer, a large amount of ink is used. Use of this will cause problems such as paper slipping and lighting. On the other hand, when a K single color material is used only in the gray portion when gradation like a photograph is required, the gray portion and the chromatic color portion that is almost similar to gray are different drawing methods of K single color and CMYK four colors, respectively. Because of this, the border is conspicuous and a “mottled pattern” may occur, degrading the image quality.

The following patent documents 1 and 2 can be shown as conventional examples proposed for solving such image quality degradation.
In Patent Document 1 below, gray is determined from the color components of the image area of the same color in the image data to be subjected to color conversion, and gray processing is performed in which color conversion is performed on the gray-determined data using K single-color conversion conditions. In addition, when it is determined that the type (drawing object) of the image area is not text, processing according to an operation condition such as not applying the gray processing to the area is performed, and further, the type of the area is set. It is shown that the gray judgment standard is changed accordingly.

In other words, the method exemplified in Patent Document 1 can use gray processing (printed in K single color) only for characters as processing corresponding to the type of region if the type of region of the target image data can be known. It is to make. That is, in the conventional PDL (printer description language) for printers such as PostScript based on Windows (registered trademark) GDI, characters, graphs, and photographs can be identified almost at the language level. Based on these assumptions, it is possible to avoid the image quality degradation caused by gray processing by applying gray processing that performs color conversion according to the K single color conversion condition corresponding to the type of the identified area. It can be said that.
Further, in Patent Document 2 below, in order to use a determination criterion optimum for the type of document when performing gray determination that can be used for the same purpose as Patent Document 1, each component data of the input color image is used. The threshold value of the gray determination to be performed is changed, and high image quality can be obtained.

JP 9-27915 A JP-A-7-184075

  However, in Patent Document 1, gray is determined from the color components in the image area of the same color in the image data, and gray processing (color conversion is performed under K single color conversion conditions) is applied thereto (main invention: claim 1). The gray determination and the gray processing are based on a fixed correspondence relationship, and it is impossible to prevent the deterioration such as the “mottled pattern” generated in the photographic image for which the gray determination is made. Further, when it is determined that the type of the area is not text, the process is performed in accordance with the condition that the gray process is not applied to the area (Claim 7). However, it is necessary to determine the type of the area based on the area identification data included in the PDL data, and the digital camera image or the scanner image. For image data (for example, digital camera images and scanner images, especially scanner image data read from a manuscript that contains a mixture of characters, photos, pictures, etc.) consisting of full-color images. Thus, identification is not easy, and it is difficult to improve the image quality of such a target image.

As a method for solving this problem, there is a conventional method that uses hardware image area separation processing means such as found in some copiers (for example, an ASIC chip is used for the image area separation processing circuit). However, mounting on low-cost products is difficult in terms of cost, and a software solution is desired. At the same time, since the processing speed is required, it is difficult in terms of processing speed to realize the conventional image area separation processing as it is on the software.
The present invention has been made in view of the above-described problems of the prior art proposed to solve image quality degradation caused by gray processing performed in a drawing data generation process for drawing a figure in accordance with a figure drawing command based on full-color image data. The purpose (problem) is to generate drawing data (convert to CMYK) for image data composed only of a full color image such as a scanner image, for example, where the type of target image such as a photographic image is not instructed. ) Also enables achromatic processing without image quality degradation. Another object of the present invention is to realize such achromatic processing by a simpler method that does not require special hardware as in the above-described conventional image area separation processing circuit.

The invention according to claim 1 is an image processing apparatus having drawing data processing means for generating graphic drawing data in accordance with a graphic drawing command based on full-color image data, wherein the drawing data processing means includes each pixel of full-color original image data. Chromatic determination means for determining whether a pixel is a chromatic color or an achromatic color, image feature determination means for determining whether each pixel of the original image data has a feature of a pixel constituting a photographic image, and A color conversion unit that can convert original image data into CMYK data for color printing under different conversion conditions, and a pixel that has been determined to be achromatic by the color determination unit, and a photographic image is configured by the image feature determination unit A conversion condition instruction for instructing the color conversion means a normal conversion condition using CMYK as the conversion condition for a pixel determined to have pixel characteristics. An image processing apparatus characterized by comprising a stage.
The invention according to claim 2 is an image processing apparatus having drawing data processing means for generating graphic drawing data in accordance with a graphic drawing command based on full-color image data, wherein the drawing data processing means includes each pixel of full-color original image data. Chromatic determination means for determining whether a pixel is a chromatic color or an achromatic color, image feature determination means for determining whether each pixel of the original image data has a feature of a pixel constituting a photographic image, and A color conversion unit that can convert original image data into CMYK data for color printing under different conversion conditions, and a pixel that has been determined to be achromatic by the color determination unit, and a photographic image is configured by the image feature determination unit For a pixel determined not to have pixel characteristics, K color conversion conditions that use only K and do not use CMY as the conversion condition are specified to the color conversion means. An image processing apparatus characterized by comprising a conversion condition instructing means for.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the color determining means determines that the color is achromatic when the RGB component data values are equal.
According to a fourth aspect of the present invention, in the image processing apparatus according to the first or second aspect, the color determining means determines that the color is achromatic when the difference between the RGB component data values is within a predetermined threshold value. It is characterized by that.
According to a fifth aspect of the present invention, in the image processing apparatus according to any one of the first to fourth aspects, the different conversion conditions in the color conversion means are a K single color conversion condition that uses only K and does not use CMY, and CMYK. The normal conversion conditions to be used are used, and these are the color conversion conditions to be applied to the pixels determined to be achromatic colors.
The invention of claim 6 is a drawing data processing method for generating graphic drawing data in accordance with a graphic drawing command based on full-color image data, and determines whether each pixel of the full-color original image data is chromatic or achromatic. A color determination procedure, an image feature determination procedure for determining whether or not each pixel of the original image data has a feature of a pixel constituting a photographic image, and a pixel determined as an achromatic color in the color determination procedure. A conversion condition instruction procedure for instructing the color conversion to a normal conversion condition using CMYK as the conversion condition for the pixel determined to have the characteristics of the pixels constituting the photographic image by the image feature determination procedure; And a color conversion procedure for converting the original image data into CMYK data for printing in accordance with the instruction.
The invention of claim 7 is a drawing data processing method for generating graphic drawing data in accordance with a graphic drawing command based on full-color image data, and determines whether each pixel of the full-color original image data is chromatic or achromatic. A color determination procedure, an image feature determination procedure for determining whether or not each pixel of the original image data has a feature of a pixel constituting a photographic image, and a pixel determined as an achromatic color by the color determination procedure. For the pixels determined not to have the characteristics of the pixels constituting the photographic image by the image feature determination procedure, K color conversion conditions that use only K and do not use CMY are used as the conversion conditions. And a conversion condition instruction procedure for instructing the drawing data, and a color conversion procedure for converting the original image data into K data for printing in accordance with the instruction. It is a method.
According to an eighth aspect of the present invention, in the drawing data processing method according to the sixth or seventh aspect, the coloring determination procedure determines that the color is achromatic when the RGB component data values are equal.
According to a ninth aspect of the present invention, in the drawing data processing method according to the sixth or seventh aspect, the coloring determination procedure determines that the color is achromatic when the difference between the RGB component data values is within a predetermined threshold value. It is characterized by doing.
A tenth aspect of the present invention is the drawing data processing method according to any one of the sixth to ninth aspects, wherein the color conversion condition applied to the pixel determined to be an achromatic color uses only K and does not use CMY. K single color conversion conditions and normal conversion conditions using CMYK are used.
The invention of claim 11 is a program for causing a computer to execute each processing procedure of the drawing data processing method according to any one of claims 6 to 10.
A twelfth aspect of the present invention is a computer-readable recording medium on which the program according to the eleventh aspect is recorded.
According to a thirteenth aspect of the present invention, there is provided a printing apparatus in which the program described in the eleventh aspect is installed in a printer controller.
According to a fourteenth aspect of the present invention, there is provided a host device comprising a computer equipped with a printer driver including the program according to the eleventh aspect.

(1) Effects corresponding to the inventions of claims 1, 2, 6 and 7 Drawing data processing for generating CMYK figure drawing data for color printing by color-converting the original image data in accordance with a figure drawing command based on full-color image data , It is determined whether or not each pixel is an achromatic color, and the target pixel has a characteristic of a pixel constituting a photographic image when color conversion to CMYK is performed on the pixel determined to be an achromatic color. By specifying the color conversion condition depending on whether or not, it is possible to apply the conversion condition suitable for the image type indicating the image feature in units of pixels, and this has conventionally occurred due to achromatic processing. It is possible to improve the image quality without causing image quality degradation such as a “mottled pattern” that occurs at the boundary between the gray portion and the chromatic color portion that is almost gray.
(2) Effects corresponding to the inventions of claims 3, 4, 8, and 9 Since an achromatic color is determined when the RGB component data values are equal, the determination process can be easily performed.
Further, since the achromatic color is determined when the difference between the RGB component data values is within a predetermined threshold value, a color range of minute saturation that cannot be confirmed by human eyes is also determined as an achromatic color. As a result, it becomes possible to avoid the manifestation of image quality degradation and to improve image quality.
(3) Effects corresponding to the inventions of claims 5 and 10 As color conversion conditions applicable to pixels determined to be achromatic colors, K single color conversion conditions that do not use CMY and normal conversion conditions that use four colors of CMYK Since it is used, the gray color of the photographic image is made almost gray by maintaining the gradation continuity with the surrounding chromatic color pixels by applying the color conversion condition of CMYK 4 colors to the achromatic color pixel of the photographic image. Prevents the occurrence of a “mottled pattern” that occurs at the border with a nearby chromatic color part, and makes it possible to form a clear image with K single color for achromatic pixels such as black characters and black ruled lines in graphs. .
(4) Effects corresponding to inventions of claims 11 and 12 A program for causing a computer to execute each processing procedure of the drawing data processing method according to any one of claims 6 to 10 is installed in a computer of an image processing apparatus. By doing so, any one of the effects (1) to (3) can be easily realized.
(5) Effects corresponding to the invention of claim 13 A program for causing a computer to execute each processing procedure of the drawing data processing method according to any one of claims 6 to 10 is installed in a printer controller of a printing apparatus. Thus, any one of the effects (1) to (3) can be realized in the printing apparatus.
(6) Effect corresponding to invention of claim 14 By mounting a program for causing a computer to execute each processing procedure of the drawing data processing method according to any one of claims 6 to 10, the computer of the host device It is possible to realize any one of the effects (1) to (3) in the host apparatus that issues a drawing command to a printing apparatus that does not have a color conversion processing function.

The present invention will be described based on the following embodiments shown with the accompanying drawings.
In each of the following embodiments, a K single color conversion condition that uses only K when performing color conversion on achromatic pixels in drawing data processing for generating figure drawing data in accordance with a figure drawing command based on source full-color image data. In addition, it is possible to change the setting of the conversion condition according to the image feature that each pixel of the original (source) image data has as an attribute, which of the normal conversion conditions using CMYK and CMYK is used, and to improve the image quality of the output image An embodiment relating to an image processing apparatus and a drawing data processing method of the present invention for the purpose will be described.
Here, an example in which the drawing data processing according to the present invention is performed on a printer in a generalized printer system (that is, a system including a printer that performs a printing process according to a print command received from a host computer) will be described. When drawing data processing according to the present invention is performed on the printer side, it can be performed as processing of a printer controller provided in the printer, as in some existing laser printers. Further, as in the case of some existing ink jet printers, when processing is performed on the host computer side, it can be implemented by installing functions necessary for processing in the printer driver. When implemented by a printer controller or a printer driver, necessary functions are provided by installing a program for causing the computer (CPU) that drives them to execute each processing procedure of the drawing processing method described in the following embodiment. Can be realized.

“Embodiment 1”
In this embodiment, in the achromatic color conversion, an image that each pixel of the original (source) image data has as an attribute which one of the K single color conversion condition using only K and the normal conversion condition using CMYK is used. Instructions are given according to the characteristics, and the basic means necessary to improve the image quality of the printed output image are shown. The high image quality aimed at by this embodiment is, for example, in printed matter such as characters, graphics, photographs, etc. mixed in business documents, black characters and black ruled lines of graphs are clearly K single color, A gray pixel included in a part of a photographic image is to maintain gradation continuity with surrounding pixels using CMYK.

FIG. 1 is a diagram illustrating a schematic configuration of a printer according to the present embodiment. The present embodiment will be described with reference to the same drawing.
A printer 1 illustrated in FIG. 1 includes a printer controller 2 that processes data necessary for performing print processing in accordance with a print command received from a PC (personal computer) 7 serving as a host device, and controls each operation unit of the printer. The printer engine 4 performs printing on a medium such as paper by drawing data output from the printer controller 2.
The printer controller 2 includes an interpreter 10, a development processing unit 11, an image color conversion unit 3, and a graphic drawing processing unit as elements necessary for data processing from generation of an input print command to generation of drawing data to be output to the printer engine 4. 12. As memory used in the data processing process, an image memory (1) 20 for RGB image data, an image memory (2) 34 for CMYK image data, a page memory 23, and a CPU 14 are provided. When the interpreter 10, the development processing unit 11, the image color conversion unit 3, and the graphics drawing processing unit 12 are realized by hardware, the CPU 14 controls each of these image processing units to perform processing / operation. When implemented by software, the interpreter 10, the development processing unit 11, the image color conversion unit 3, and the graphic drawing processing unit 12 are functions implemented by software driven by the CPU.

The operation of each element unit of the printer illustrated in FIG. 1 will be described below along the flow of drawing data.
The host PC 7 generates color image data and transfers it to the printer controller 2 of the printer 1 as a print command of PDL data, for example. In this embodiment, the color image data generated as original (source) image data by the host PC 7 is expressed in RGB, and the host-side printer driver does not convert it to CMYK data for printing, but does not convert it to RGB. The image data is transmitted to the printer side as it is.
The color image data input as a print command to the printer controller 2 is input to the interpreter 10, where the format, PDL data, etc. are decoded and passed to the expansion processing unit 11. The development processing unit 11 develops the intermediate format data obtained in the previous stage into bitmap data by sequentially processing the data through a compression process of color image data compression as necessary, and then for RGB image data. Are stored in the image memory (1) 20.

  Next, the RGB image data is input to the image color conversion unit 3 and color-converted into CMYK data for printing. The image color conversion unit 3 can use different conversion conditions, and operates by a method of changing the conversion condition to be applied according to the instruction. In the image color conversion unit 3, color conversion conditions are determined by the color conversion determination unit 31 for each pixel with respect to the RGB image data developed in the bitmap stored in the image memory (1) 20, and the determined conditions are applied. The instructions are given. Details of the operation of the color conversion determination unit 31 will be described later.

  In the present embodiment, the different color conversion conditions are two conditions of K single color conversion using only K performed by the K conversion unit 33 without using CMY and normal conversion using CMYK four colors performed by the CMYK conversion unit 32. The conversion method based on the K single color condition is a method that can be applied when the input RGB is determined to be an achromatic color, and prints using only the K color material. For example, “K = 1.0−R, C = M = Y = 0.0 "as a conversion condition. Also, the conversion method based on the CMYK4 color condition is to print using the CMYK4 color material, and uses a generally known method of calculating each color by “BG / UCR (black generation / undercolor removal)”. It is possible to implement. At the time of color conversion for a pixel determined to be an achromatic color, either the K single color condition or the CMYK four color condition is applied in accordance with an instruction from the color conversion determination unit 31.

  The CMYK image data after color conversion is temporarily stored in the image memory (2) 34, and the graphic drawing processing unit 12 expands the graphic into bitmap data for each CMYK based on the data stored in the memory. The image is drawn in the page memory 23. When the processing for the drawing command for one page is completed according to the processing of the drawing data performed in this way, the contents of the page memory 23 are output to the printer engine 4 that prints on a recording medium such as paper.

Here, the operation of the color conversion determination unit 31 will be described in more detail.
The color conversion determination unit 31 determines, for each pixel, which one of the K single color condition and the CMYK four color condition is to be used as the conversion condition when the achromatic color is converted, and the K conversion unit 33 or the CMYK conversion unit 32 determines the conversion condition. Perform conversion operation.
The color conversion determination unit 31 according to the present embodiment performs chromatic determination to determine an achromatic color / chromatic color. For pixels determined to be an achromatic color, an image feature that the pixel has as an attribute has a pixel constituting the photographic image. A two-step decision is made to check whether or not the feature is present. As a result of the determination made in this way, an instruction is given according to the CMYK four-color condition for pixels that are achromatic and have the characteristics of the pixels constituting the photographic image. On the other hand, the K single color condition is instructed.

  Of course, the drawing data processing based on the CMYK four-color condition is applied to the chromatic color pixel. In addition, since it is necessary to perform a determination processing operation for each pixel for the determination of achromatic color, if there is RGB that originally corresponds to each pixel data, such as image data such as a digital camera image or a scanner image, the corresponding processing for each pixel However, if the input data does not have data for each pixel as in the case where the input data is text data or graphics data in the PDL format, it cannot be dealt with immediately. Therefore, as described above, for the text and graphics drawing objects indicated in the graphic drawing command, the expansion processing is performed on the basis of the color designation data instructed by the objects, so that the bitmap data is obtained. After the expansion, the implementation is enabled by the correspondence of applying the color determination processing to each pixel.

In the achromatic / chromatic color determination process, a standard for determining achromatic colors (white and gray including black) is set. If this criterion is satisfied, the achromatic color is determined, and pixels that cannot be determined as achromatic are regarded as chromatic colors. , By the method.
In this embodiment, the achromatic color determination condition determines that the pixel is an achromatic color when the data values of the respective components in the input RGB are equal, that is, when the condition R = G = B is satisfied.
Further, for pixels that satisfy R = G = B and are determined to be achromatic, it is checked whether or not the pixels constituting the photographic image have the characteristics of the pixels. In this process, when it is instructed that the original image data to be processed is a photographic image as the type of image data, it is possible to easily obtain this information by checking the presence or absence of this instruction. It is.
For example, the image data type can be instructed by a user through an input operation such as a key. In this case, it can be known that the image is a photographic image by the presence or absence of an operation input.

  Further, it is possible to know that the pixel is to be handled as a photographic image by examining the area information specified for the drawing object indicated by the graphic drawing command. Since it is planned to set each drawing object of text, graphics, and image (the “image” shown here corresponds to a photographic image) in a PDL drawing command generally used. It is possible to check based on the designation of a photo (image) object obtained as a result of analysis of the drawing command.

“Embodiment 2”
In the “embodiment 1”, in the chromatic determination, the data value of each component is R = G = B, that is, when there is no hue (saturation), the achromatic color is determined. According to the standard, if there is very little saturation that cannot be confirmed by human eyes, it will not be determined as an achromatic color.
An example of this is when there is an error in the color calculation even though it should originally be an achromatic color. If the minute saturation caused by such an error exists in a part of the gray gradation, that is the achromatic color. In some cases, a phenomenon in which only that portion becomes chromatic color and the gradation becomes a mottled pattern occurs. In addition, even in data to which an irreversible compression format such as JPEG is applied, a case where an achromatic color becomes a minute chromatic color in a compression / decompression calculation process can be cited as an example of causing such image degradation. Furthermore, in the case of normalizing RGB, which depends on the characteristics of the device, to an integer value of 0 to 255 in a scanner read image, a digital camera photographed image, etc., a case where the achromatic color portion becomes a minute chromatic color may be considered.
Therefore, in the achromatic color determination, a color range of minute saturation that cannot be confirmed by human eyes is also determined as an achromatic color, thereby avoiding the manifestation as deterioration of the image quality and enabling high image quality. That is, achromatic color determination is performed so that R≈G≈B, which is a color that includes a minute chromatic color that cannot be determined by human eyes, is also determined as a gray pixel.

As a method for performing this determination, the method can be implemented by using a method of performing threshold processing on a color difference between two arbitrary colors in RGB.
That is, if the threshold is T, the following inequality:
| RG | ≦ Trg, | GB | ≦ Tgb, | BR | ≦ Tbr
RGB satisfying the above is determined as an achromatic color.
The above inequality is a general expression, and an example of an embodiment assuming that Trg, Tgb, and Tbr have different values according to the characteristics of the device has been shown. Of course, for simplicity, Trg = Tgb = Tbr.

“Embodiment 3”
In the “embodiment 1”, if the pixel is determined to be an achromatic color and has the characteristics of the pixel constituting the photographic image, the CMYK four-color condition is designated for this pixel. It is also possible to detect whether or not a pixel constituting a photographic image has a characteristic by checking a drawing object indicated by the graphic drawing command. However, this method is based on the premise that a drawing object is specified in the graphic drawing command, and cannot be applied without this premise.

Therefore, in this embodiment, a photographic image is formed by means applicable to image data in which the entire page is composed of only a full color image, such as a digital camera image or a scanner image, without a drawing object instruction. A method for checking whether or not the pixel is a pixel is presented.
In this embodiment, if there is a chromatic color pixel in a predetermined pixel range (n pixels) continuous in the main scanning direction before the target pixel (target pixel) of the original (source) image data, this image feature causes this attention. A method according to the principle that a pixel is regarded as a constituent pixel of a photographic image is used. Therefore, the presence / absence of such a chromatic color pixel is examined for the target pixel. This method is suitable when the original (source) image is raster data. That is, whether or not it can be regarded as a constituent pixel of a photographic image by a simple operation when taking a procedure of sequentially performing drawing data generation processing on pixels input continuously in the main scanning direction as a raster image This is an effective method for realizing the purpose of checking.

  FIG. 2 is a diagram illustrating a method for determining a conversion condition to be applied to each pixel of original (source) image data according to a principle of the present embodiment. The example shown in FIG. 2 exemplifies data of 8 pixels continuous in the main scanning direction indicated by pixel numbers 1 to 8. The input RGB is shown in the upper part. Here, the result of the determination of achromatic / chromatic color for each pixel is shown, and G in the figure is an achromatic color (that is, R = G = B or R≈G≈B). , C indicates a chromatic color (that is, a color other than that determined as an achromatic color G). The lower part shows the result of defining the color conversion condition for each pixel in the upper part according to the determination principle, and K1 in the figure is a K single color condition (for example, K = 1.0−R, C = M = Y = 0.0). 4C indicates a CMYK four-color condition (for example, four colors are calculated by BG / UCR).

In the present embodiment, the range in which the presence / absence of a chromatic color pixel is examined, that is, the number of pixels connected in the main scanning direction (previous) before the target pixel: n = 4. Therefore, in FIG. The rule is that if the pixel has a chromatic color pixel, 4C color conversion is performed, and if not, K1 color conversion is performed. Specifically, pixel number 1 is converted according to the K1 condition because the input RGB is a G (achromatic) pixel and there are no C (chromatic) pixels in the past four pixels (in the smaller pixel number direction). Since the pixel number 2 is an input C pixel, it is unconditionally converted according to the 4C condition. Pixel number 3 is a G pixel, but since there is a C pixel in pixel number 2 included within the past four pixels, conversion is performed according to the 4C condition. Pixel numbers 4, 5, and 6 are the same as pixel number 3. Pixel number 7 is a G pixel, and since there are no C pixels in the past four pixels, conversion is performed according to the K1 condition. Pixel number 8 is the same as pixel number 7.
In accordance with the rules as described above, it is instructed that the pixels (pixel numbers 3, 4, 5, and 6 in the above example) regarded as the pixels constituting the photographic image are converted under the CMYK four-color condition. Note that if this rule is applied to data of all G pixels of the input RGB, all the pixels of the output CMYK are converted according to the K1 condition.

“Embodiment 4”
In the present embodiment, pixels that are determined to be achromatic with respect to image data (such as a digital camera image or a scanner image) in which a drawing object is not specified and the entire page is composed of only a full-color image, and a photograph In order to indicate the CMYK four color conditions when the pixel can be regarded as a pixel constituting an image, a method for checking whether or not the pixel constituting the photo image has a characteristic of the pixel is provided. This point has the same purpose as that of the above-described “Embodiment 3”.

In the present embodiment, as in the above “Embodiment 3”, a predetermined pixel range (n pixels) continuous in the main scanning direction of the target pixel of the original (source) image data as the image feature of the target pixel (target pixel). The pixel range used for the check is the pixel before the pixel of interest in “Embodiment 3”, whereas in this embodiment, the pixel after the pixel of interest is checked. It is characterized by.
According to the present embodiment, the pixel range for checking the presence / absence of a chromatic color pixel is set to the pixel after the target pixel, so that prefetching is required, but the original image is raster data as in “Embodiment 3”. This is a method suitable for the case, and enables a target check to be performed by a simple operation, and a more effective result can be obtained depending on the conditions of the input image.

  FIG. 3 is a diagram illustrating a method for determining a conversion condition to be applied to each pixel of original (source) image data in accordance with the principle of the present embodiment. The example shown in FIG. 3 exemplifies data of 8 pixels connected in the main scanning direction indicated by pixel numbers 1 to 8. The input RGB is shown in the upper part. Here, the result of the determination of achromatic / chromatic color for each pixel is shown, and G in the figure is an achromatic color (that is, R = G = B or R≈G≈B). , C indicates a chromatic color (that is, a color other than that determined as an achromatic color G). The lower part shows the result of defining the color conversion condition for each pixel in the upper part according to the determination principle, and K1 in the figure is a K single color condition (for example, K = 1.0−R, C = M = Y = 0.0). 4C indicates a CMYK four-color condition (for example, four colors are calculated by BG / UCR).

In the present embodiment, the range in which the presence / absence of a chromatic color pixel is checked, that is, the number of pixels connected in the main scanning direction (forward) after the target pixel: n = 4. Therefore, in FIG. The rule is that 4C color conversion is performed if there are chromatic color pixels in the four pixels in the increasing direction, and K1 color conversion is performed if there is no chromatic color pixel. Specifically, pixel number 1 is converted according to the K1 condition because the input RGB is a G (achromatic) pixel and there are no C (chromatic) pixels in the front four pixels (in the larger pixel number direction). Pixel number 2 is the same as pixel number 1.
Pixel number 3 is a G pixel, but since there is a C pixel at pixel number 7 included within the front four pixels, conversion is performed according to the 4C condition. Pixel numbers 4, 5, and 6 are the same as pixel number 3. Pixel number 7 is unconditionally converted under the 4C condition because the input is a C pixel. Pixel number 8 is a G pixel, and the K1 condition is used on the assumption that there are no C pixels in the front four pixels.

In accordance with the rules as described above, it is instructed that the pixels (pixel numbers 3, 4, 5, and 6 in the above example) regarded as the pixels constituting the photographic image are converted under the CMYK four-color condition. Note that if this rule is applied to data of all G pixels of the input RGB, all the pixels of the output CMYK are converted according to the K1 condition.
By combining this embodiment with “Embodiment 3”, the pixel range for checking the presence or absence of a chromatic color pixel can be implemented as a predetermined pixel range continuous in the main scanning direction before and after the pixel of interest. The procedure for determining the conversion condition for each pixel uses the same procedure as in the above-described embodiment and “Embodiment 3”.

“Embodiment 5”
In the present embodiment, image data (such as a digital camera image or a scanner image) in which a drawing object is not specified and the entire page is composed of only a full color image is achromatic and can be regarded as a constituent pixel of a photographic image. In order to indicate the CMYK four color condition in this case, a method for checking whether or not the pixel constituting the photographic image is a pixel having a characteristic is provided. It has the same purpose as “Embodiment 4.”

  In the present embodiment, as in the above “Embodiment 3” and “Embodiment 4”, a predetermined pixel range (n) connected to the target pixel of the original (source) image data as the image feature of the target pixel (target pixel). The pixel range to be examined is a pixel before the pixel of interest in “Embodiment 3”, and a pixel behind the pixel of interest in “Embodiment 4”. On the other hand, the present embodiment is characterized by a predetermined pixel range (for example, 5 × 3 pixels) adjacent to the periphery of the target pixel, and if there is even one C (chromatic color) pixel in this pixel range. 4C (CMYK 4 colors) condition is output.

  According to the present embodiment, the pixel range for checking the presence / absence of a chromatic pixel is set to a predetermined adjacent pixel range centered on the pixel of interest, so that it is more appropriate than “third embodiment” and “fourth embodiment”. It is a method that can obtain a correct judgment result.

  FIG. 4 is a diagram illustrating a method for determining a conversion condition to be applied to each pixel of original (source) image data according to a principle of the present embodiment. The example shown in FIG. 4 exemplifies data of pixels (X, Y) connected in the main / sub-scanning direction shown as X = 1-8 and Y = 1-3. The input RGB is shown in the upper part. Here, the result of the determination of achromatic / chromatic color for each pixel is shown, and G in the figure is an achromatic color (that is, R = G = B or R≈G≈B). , C indicates a chromatic color (that is, a color other than that determined to be an achromatic color G and exists only in (X, Y) = (5, 2) shown by hatching in the figure). The lower part shows the result of defining the color conversion condition for each pixel in the upper part according to the determination principle, and K1 in the figure is a K single color condition (for example, K = 1.0−R, C = M = Y = 0.0). 4C indicates a CMYK four-color condition (for example, four colors are calculated by BG / UCR).

In the present embodiment, a 5 × 3 pixel centered on the target pixel is used as a range for checking the presence or absence of a chromatic color pixel, and a 4C color conversion is performed if a chromatic color pixel exists in the range, and a K1 color conversion is performed if there is no chromatic color pixel. . Specifically, since (X, Y) = (5, 2) is C (chromatic color) and the others are G (achromatic) pixels, a range of 5 × 3 pixels centering on the pixel of interest. The pixel range including the C pixel (5, 2), that is, the pixel range using the 4C condition is a pixel group (X, Y) = (3-7, 1-3) surrounded by a broken line in the drawing. It becomes. Further, since the other pixel ranges do not include C (chromatic color) pixels within the 5 × 3 pixel range, the K1 condition is used.
Note that if this rule is applied to data of all G pixels of the input RGB, all the pixels of the output CMYK are converted according to the K1 condition.

“Embodiment 6”
A processing procedure of a series of drawing data realized by the above-described image processing apparatus will be described based on an embodiment exemplified below.
FIG. 5 is a flowchart showing an example of a drawing data processing procedure according to this embodiment.
With reference to the flowchart shown in FIG. 5, the processing of the drawing data according to the present embodiment will be described step by step. After the host PC 7 and the printer 1 establish a communication state via the communication interface, the printer controller 2 A data processing program is started, and first, a graphic drawing command transmitted from the host PC 7 is received and data is input (S101).

  Next, since the input graphic drawing command is data described in a predetermined format or language such as PDL, the input data is decoded and intermediate drawing data is generated before being expanded into bitmap data. Then, based on the obtained intermediate format data, a process of developing the RGB bitmap data (decoding process of color image data compression as necessary) is performed, and the developed RGB data is temporarily stored in the image memory. Store (S102). This development to bitmap data is a process necessary for performing a procedure peculiar to the present embodiment in which a color conversion condition is designated for each pixel in the subsequent stage.

Thereafter, the color determination is performed on each pixel of the developed RGB bitmap data (S103). The coloring judgment is the following inequality:
| RG | ≦ Trg, | GB | ≦ Tgb, | BR | ≦ Tbr
R, G, and B that are satisfied are determined to be achromatic colors, and other colors are determined to be chromatic colors. Here, the threshold T is set to a predetermined value of 0 or more, and it is possible to cope with such a case that a color including a chromatic color that is so minute that it cannot be determined by the human eye is determined to be an achromatic color. Of course, Trg = Tgb = Tbr It is also possible to take the form of = 0 (that is, R = G = B).

  FIG. 6 shows a flowchart of the coloring determination subroutine. In this flow, it is checked whether or not the above inequality holds (S301). If it is established, it is determined as an achromatic color (S302), and the other is determined as a chromatic color (S303).

Next, a photographic image feature check is performed to check whether or not the pixels determined as achromatic in the previous chromatic determination have the characteristics of the pixels constituting the photographic image (S104). This check is performed in the preceding stage in order to indicate the CMYK four color conditions at the time of color conversion when the pixel is determined to be an achromatic color and can be regarded as a pixel constituting a photographic image.
FIG. 7 is a flowchart of this photographic image feature check subroutine. In this flow, first, it is checked whether or not the target pixel to be checked is an achromatic color (S401). In this process, it is checked whether or not each pixel is an achromatic color by subtracting the result of the color determination performed in the previous stage. If it is not an achromatic color (S401-NO), this flow is exited.

On the other hand, in the case of an achromatic color (S401-YES), it is checked whether or not there is a chromatic color pixel in a predetermined pixel range adjacent to the target pixel (S402).
This photographic image feature check can take different embodiments depending on the method of setting a predetermined pixel range adjacent to the pixel of interest, and can take the following methods (1) to (4).
(1) A predetermined pixel range that continues in the main scanning direction before the target pixel (for example, see the description regarding FIG. 2).
(2) A predetermined pixel range that continues in the main scanning direction after the target pixel (for example, see the description regarding FIG. 3).
(3) Predetermined pixel range in the main scanning direction before and after the target pixel (this is a method using (1) and (2) in combination)
(4) A predetermined pixel range adjacent to the periphery of the pixel of interest (for example, see the description regarding FIG. 4)

  By the way, in the variation of the pixel range setting of (1) to (4) as described above, the pixel range before the target pixel (1) is the method that can simplify the processing most easily, and next (3), the pixel range after the pixel of interest (2), and the pixel range around the pixel of interest (4). This is because the drawing data is processed basically in the order of input, that is, in the order of pixels that are continuous in the main scanning direction. Therefore, the above methods (2) and (3) that require pre-reading, and later This is because the method (4), which also requires pre-reading for the pixels of this line, complicates the processing procedure. In addition, in the pixel range setting variations (1) to (4) described above, the determination accuracy as to whether or not the pixel can be regarded as a pixel constituting the photographic image is in the reverse order of the simplification of the processing described above. The periphery (4) is the method that can increase the accuracy most.

  When the pixel range is set to (2) to (4) above, pre-reading is performed on necessary pixels among the pixels in the range set as the premise, and there is no processing in the coloring determination step (S103). It is necessary to determine chromatic color / chromatic color and obtain a chromatic determination result in advance.

  In the flow of FIG. 7, if any of the above-described methods with different pixel range settings is used to check whether there is a chromatic color pixel in the set pixel range, if any (S402—YES) ), A determination result indicating that the pixel has the characteristics of a photographic image, that is, a pixel that can be regarded as a pixel constituting the photographic image is obtained (S403), and this flow is exited. As a result of the check, if there is no chromatic color pixel (S402-NO), this flow is exited without doing anything.

  Next, a color conversion condition is instructed in order to perform color conversion according to the check result for the pixel whose photographic image feature is checked in the previous stage (S105). In the present embodiment, any one of K single color conversion using only K and not using CMY or conversion using four colors of CMYK can be applied to a pixel determined to be an achromatic color. Here, the two different color conversion conditions are selectively used depending on whether or not the pixel has the characteristics of a photographic image, that is, is a pixel that can be regarded as a pixel constituting the photographic image.

  Therefore, by applying the same color conversion conditions based on the four CMYK colors as the chromatic pixels constituting the image to the achromatic color pixel of the photographic image, the gradation continuity with the surrounding pixels is maintained, and the gray portion is almost the same. Prevents the occurrence of "mottled patterns" that occur at the border with chromatic parts close to gray, and can form a clear image with K single color for achromatic pixels such as black characters and black ruled lines in graphs. To.

  FIG. 8 shows a flowchart of a subroutine for instructing the color conversion condition. In this flow, first, it is checked whether or not the pixel to be checked is an achromatic color (S501). This is done by quoting the result of the color determination performed in the previous stage (S103) to check whether or not each pixel is an achromatic color. If it is not an achromatic color (S501-NO), it is treated as a chromatic color. After instructing the application of the color conversion conditions using the CMYK four colors that are normally used for the image data (S504), this flow is exited.

  On the other hand, as a result of examining whether or not the color is achromatic, if it is achromatic (S501-YES), a photographic image is constructed by quoting the result of the photographic image feature check performed in the previous stage (S104). Whether or not the pixel can be regarded as a pixel is checked (S502). If YES, it is treated as an achromatic pixel of the photographic image, so that the application of the color conversion condition using CMYK four colors is instructed (S504), and then this flow is exited. . If it is not a pixel that can be regarded as a pixel constituting a photographic image (NO in S502), it is treated as an achromatic pixel such as a black character or a black ruled line of a graph. Exit this flow.

Next, color conversion according to the instruction result is performed on the pixel for which the color conversion condition is specified in the previous stage (S106). In the present embodiment, for a pixel for which the K monochrome conversion condition is instructed, for example, “K = 1.0−R, C = M = Y = 0.0” is used as the conversion condition, and only K is used. Then, color conversion without using CMY is performed. In addition, for pixels for which CMYK four-color conversion conditions are instructed, for example, commonly used BG / UCR conversion color conversion is performed.
Next, graphic drawing processing is performed on the CMYK image data obtained by performing color conversion for each pixel in the previous stage (S107). Here, the drawing data is generated in the page memory while developing the figure into bitmap data for each CMYK based on the CMYK image data, and the bitmap is developed using the dither pattern as the pseudo gradation processing. Includes processing.
When the processing for the drawing command for one page is completed according to the series of processing of drawing data performed in this way, the contents of the page memory for each color of CMYK are output to a printer engine that prints on a recording medium such as paper (S108). ), The drawing data processing flow ends.

1 is a diagram illustrating a schematic configuration of a printer according to an embodiment of the present invention. It is a figure explaining the principle (the 1) of the method which checks whether it has the image characteristic which the pixel which comprises a photograph image has, and defines conversion conditions. It is a figure explaining the principle (the 2) of the method which checks whether it has the image characteristic which the pixel which comprises a photograph image has, and determines conversion conditions. It is a figure explaining the principle (the 3) of the method which checks whether it has the image characteristic which the pixel which comprises a photograph image has, and determines conversion conditions. It is a flowchart which shows an example of the process sequence of the drawing data concerning embodiment of this invention. 6 is a flowchart of a “coloration determination” subroutine shown in the drawing data processing procedure of FIG. 5. 6 is a flowchart of a “photo image feature check” subroutine shown in the drawing data processing procedure of FIG. 5. 6 is a flowchart of a “color conversion condition instruction” subroutine shown in the drawing data processing procedure of FIG. 5.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Printer, 2 ... Printer controller, 3 ... Image color conversion part, 31 ... Color conversion determination part, 32 ... CMYK conversion part, 33 ... K conversion part, 34 ... Image memory (2), 10 ... interpreter, 11 ... development processing unit, 12 ... graphic drawing processing unit, 14 ... CPU, 20 ... image memory (1), 23 ... Page memory, 4 ... printer engine, 7 ... host PC.

Claims (14)

An image processing apparatus having drawing data processing means for generating graphic drawing data according to a graphic drawing command based on full-color image data,
The drawing data processing means includes color determination means for determining whether each pixel of full-color original image data is a chromatic color or an achromatic color, and features of pixels in which each pixel of the original image data constitutes a photographic image An image feature determining unit that determines whether or not the image data includes color conversion unit that can convert the original image data into CMYK data for color printing under different conversion conditions, and pixels that are determined to be achromatic by the chromatic determination unit A conversion condition for instructing the color conversion unit to perform a normal conversion condition using CMYK as the conversion condition for a pixel determined by the image feature determination unit to have a feature of a pixel constituting a photographic image. An image processing apparatus comprising an instruction unit. An image processing apparatus having drawing data processing means for generating graphic drawing data according to a graphic drawing command based on full-color image data,
The drawing data processing means includes color determination means for determining whether each pixel of full-color original image data is a chromatic color or an achromatic color, and features of pixels in which each pixel of the original image data constitutes a photographic image An image feature determining unit that determines whether or not the image data includes color conversion unit that can convert the original image data into CMYK data for color printing under different conversion conditions, and pixels that are determined to be achromatic by the chromatic determination unit And a color conversion condition that uses only K as the conversion condition and does not use CMY as the conversion condition for the pixel determined not to have the characteristics of the pixels constituting the photographic image by the image feature determination means. An image processing apparatus comprising conversion condition instruction means for instructing the conversion means.   3. The image processing apparatus according to claim 1, wherein the color determination unit determines an achromatic color when the RGB component data values are equal. 4.   3. The image processing apparatus according to claim 1, wherein the color determining unit determines that the color is achromatic when the difference between the RGB component data values is within a predetermined threshold value. 4. apparatus.   5. The image processing apparatus according to claim 1, wherein the different conversion conditions in the color conversion means are a K single color conversion condition that uses only K and does not use CMY, and a normal conversion condition that uses CMYK, An image processing apparatus characterized in that these are color conversion conditions to be applied to pixels determined to be achromatic colors. A drawing data processing method for generating graphic drawing data according to a graphic drawing command based on full-color image data,
A chromatic determination procedure for determining whether each pixel of the full-color original image data is a chromatic color or an achromatic color, and determining whether each pixel of the original image data has the characteristics of the pixels constituting the photographic image An image feature determination procedure, and a pixel that has been determined to be an achromatic color in the chromatic determination procedure and that has been determined to have a feature of a pixel that constitutes a photographic image by the image feature determination procedure, the conversion condition A rendering condition comprising: a conversion condition instruction procedure for instructing the color conversion as a normal conversion condition using CMYK as a color conversion procedure; and a color conversion procedure for converting the original image data into CMYK data for printing in accordance with the instruction. Data processing method. A drawing data processing method for generating graphic drawing data according to a graphic drawing command based on full-color image data,
A chromatic determination procedure for determining whether each pixel of the full-color original image data is a chromatic color or an achromatic color, and determining whether each pixel of the original image data has the characteristics of the pixels constituting the photographic image An image feature determination procedure and a pixel that has been determined to be achromatic by the chromatic determination procedure and that has been determined not to have a feature of a pixel that constitutes a photographic image by the image feature determination procedure. A conversion condition instruction procedure for instructing the color conversion means to use a K single color conversion condition without using CMY as a condition, and a color conversion procedure for converting the original image data into K data for printing according to the instruction; A drawing data processing method characterized by comprising:   8. The drawing data processing method according to claim 6, wherein the coloring determination procedure determines that the color is achromatic when the RGB component data values are equal.   8. The drawing data processing method according to claim 6, wherein the coloring determination procedure determines an achromatic color when a difference between RGB component data values is within a predetermined threshold value. Data processing method.   10. The drawing data processing method according to claim 6, wherein the color conversion condition to be applied to a pixel determined to be an achromatic color is a K single color conversion condition that uses only K and does not use CMY, and CMYK. A drawing data processing method, characterized in that the normal conversion conditions are used.   A program for causing a computer to execute each processing procedure of the drawing data processing method according to claim 6.   A computer-readable recording medium on which the program according to claim 11 is recorded.   A printing apparatus comprising the program according to claim 11 installed in a printer controller.   A host device comprising a computer on which a printer driver including the program according to claim 11 is mounted.

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