JP2013035146A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology which alleviates the discontinuity of the thin line with a thin line clearly formed; and alleviate reverse in visibility between a thin line and a slightly thin line.SOLUTION: The flags related with selected dot data are determined (Step S230). When a thin line flag=F and middle line flag=F are related with the selected dot data (Step S230, thin line flag=F, middle line flag=F), color conversion of the dot data is performed using LUT for normal lines (Step S240). When the thin line flag=F and middle line flag=T are related with the selected dot data (Step S230, thin line flag=F, middle line flag=T), color conversion of the dot data is performed using LUT for middle lines (Step S250). When a thin line flag=T and middle line flag=F are related with the selected dot data (Step S230, thin line flag=T, middle line flag=F), color conversion of the dot data is performed using LUT for thin lines (Step S260).

Description

  The present invention relates to an image forming apparatus.

  When an image image and a character / line drawing image (hereinafter referred to as “thin line”) are mixed in the print target, a high-quality image is formed with emphasis on gradation and the image line is formed. Is known to form clearly by reinforcing the contours (for example, Patent Document 1).

JP 2007-307891 A

When the above prior art is judged to be a thin line, the outline is clearly formed, so that the print result may differ from the original image appearance. For example, there is a case where a reverse phenomenon occurs in which a fine line is formed more clearly than a line having a large line width. In particular, among images classified as image images, this problem is likely to occur due to a relationship between a line slightly thicker than a thin line (hereinafter referred to as “slightly thin line”) and a thin line. In particular, the above problem is likely to occur in a thin line of light color due to the characteristic of the processing of clearly forming the outline.
The present invention is intended to solve this problem. The appearance of fine lines and slightly fine lines is reversed while thin lines are clearly formed to reduce line breaks (a phenomenon in which lines appear to be broken). The purpose is to provide technology to reduce the amount of work.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1]
An image forming apparatus that converts drawing element data including drawing start coordinate information, drawing end coordinate information, color information, and thickness information into image forming data, and forms an image using the image forming data. ,
The drawing element data includes a thin line classification whose thickness specified by the thickness information is less than a first predetermined value, and an intermediate line less than a second predetermined value greater than or equal to the first predetermined value and greater than the first predetermined value. A classification unit that classifies into three or more stages of classification and a thick line classification greater than or equal to the second predetermined value;
The drawing element data classified into the intermediate line classification is converted into the image forming data for forming an image with a color darker than the density specified by the color information, while being classified into the thin line classification The image formation for forming an image with a color in which the drawing element data is darker than the density specified by the color information and is darker than the drawing element data classified in the intermediate line classification An image forming apparatus comprising: a data conversion unit that converts data into business data.
According to this application example, since the thinnest image is formed with the highest density, line breakage can be reduced. In addition, since the density is gradually changed in three or more stages, it is possible to reduce the appearance reversal. Note that “increasing the density” here means “making it appear darker”. Further, the “color information” referred to here may be information of only brightness (information for monochrome printing) or may include information of at least one of saturation and hue (information for color printing). In addition, the image corresponding to the drawing element data classified as the thickest may be formed with a density higher than the density specified by the color information, or formed according to the density specified by the color information. May be. In addition, “a color that is darker than the drawing element data classified in the middle line classification” means a color that has been darkened by an increase greater than the increase in the density of the drawing element data classified in the middle line classification. It is.

[Application Example 2]
An image forming apparatus according to Application Example 1,
The data conversion unit converts the drawing element data into the image forming data using a halftone process, and changes the dot generation rate in the halftone process, whereby the intermediate line classification and the thin line classification An image forming apparatus that converts the drawing element data classified into (1) into the output image data for forming an image with a color darker than a density specified by the color information.
According to this application example, it is possible to reduce line breakage by using halftone processing and to reduce the appearance reversal.

[Application Example 3]
In the image forming apparatus described in Application Example 2,
The image forming apparatus, wherein the data conversion unit changes a dot generation rate in the halftone process by using a relationship prepared in advance according to a thickness.
Note that the “preliminary relationship” may be, for example, a lookup table used when converting from RGB to CMYK according to the thickness, or a dither mask or a value used for error diffusion depending on the thickness. It may be adjusted.

[Application Example 4]
In the image forming apparatus described in Application Example 2,
The data conversion unit uses a relationship prepared in advance according to the thickness for the drawing element data classified into the thin line classification by the classification unit and the drawing element data classified into the thick line classification. For the drawing element data classified into the intermediate line classification, an image forming apparatus that changes a dot occurrence rate in the halftone process by using a result calculated from the relationship.
Note that the “preliminary relationship” may be, for example, a lookup table used when converting from RGB to CMYK according to the thickness, or a dither mask or a value used for error diffusion depending on the thickness. It may be adjusted.

1 is a schematic diagram of a printing apparatus 10. FIG. 5 is a flowchart showing output image data creation processing. The flowchart which shows a rasterization process. 6 is a flowchart showing color conversion processing. The graph which compared the CMYK value converted based on the same RGB value for every thickness of a drawing element.

[1. Hardware configuration (Figure 1)]
FIG. 1 is a schematic configuration diagram of the printing apparatus 10. The printing apparatus 10 is a color inkjet type, and is mounted on the carriage 80, a mechanism that transports the print medium P by the paper feed motor 74, a mechanism that reciprocates the carriage 80 in the axial direction of the platen 75 by the carriage motor 70, and the carriage 80. A mechanism for forming dots by driving the print head 81 to eject ink, a control unit 30 for controlling objects to be controlled (paper feed motor 74, carriage motor 70, and print head 81), a computer and a storage medium (illustrated) And an image data supply unit 91 that acquires the input image data and supplies the input image data to the control unit 30.

  The carriage 80 carries ink cartridges 82 to 85 for color ink. The ink cartridge 82 contains cyan ink C, the ink cartridge 83 contains magenta ink M, the ink cartridge 84 contains yellow ink Y, and the ink cartridge 85 contains black ink K. In the print head 81 below the carriage 80, nozzle rows corresponding to the inks described above are formed. When the ink cartridges 82 to 85 are mounted on the carriage 80 from above, ink can be supplied from the ink cartridges 82 to 85 to the print head 81.

  The control unit 30 includes a CPU 40, a ROM 51, a RAM 52, and an EEPROM 60. The CPU 40 develops and executes a control program stored in advance in the ROM 51 in the RAM 52, thereby controlling paper feeding and reciprocation of the carriage 80 and driving the print head 81 to eject ink onto the print medium P. To control. An ink ejection program (driver) is prepared for each nozzle.

  The input image data supplied by the image data supply unit 91 is composed of a combination of drawing element data as vector data. Vector data represents a drawing element by any one of basic figures. Examples of basic figures include a polygonal line (including line segments), a polygon, an ellipse (including a circle), a Bezier curve, and the like. These basic figures include drawing start coordinate information, drawing end coordinate information, color information (RGB values), and thickness information (numerical value indicating line width: unit mm).

  The EEPROM 60 stores a color conversion LUT 61. The color conversion LUT 61 converts the RGB format color information included in the drawing element data into an ink amount set indicating the amount of ink (C, M, Y, K) contained in each of the ink cartridges 82 to 85. There are three types of tables according to the thickness of the drawing element (details will be described later).

[2. Output image data creation process (Fig. 2)]
FIG. 2 is a flowchart showing output image data creation processing. This output image data creation process is a process executed mainly by the CPU 40 to create output image data from the input image data. The input image data is supplied from the image data supply unit 91 to the control unit 30. This is a process that is executed when

[2-1. Rasterization processing (Fig. 3)]
When the output image data creation processing is started, rasterization processing as a subroutine thereof is started (step S100), and one of the rendering element data constituting the supplied input image data is selected (not rasterized) (step S100). Step S110). It should be noted that the vector data with the drawing start coordinates placed thereon is selected with priority. If the upper and lower positions are the same, the vector data with the drawing start coordinates arranged on the left is preferentially selected.

  Next, the selected drawing element data is rasterized, that is, converted from the vector format to the raster format to form dot data (step S120). Subsequently, the thickness of the selected drawing element is determined based on the thickness information included in the vector data (step S130).

  When the thickness of the selected drawing element corresponds to 3 pixels or more (step S130, 3 pixels or more), the thin line flag = FALSE and the intermediate flag = FALSE are set for each dot data formed in step S120 (step S130). S140).

  The thin line flag and the intermediate flag are associated with all the dot data, and for each dot data, it is a thin line area, an intermediate area slightly thicker than the thin line area, or a normal area thicker than the intermediate area. This information is used in color conversion processing (to be described later with reference to FIG. 4) in order to distinguish between the two.

  The “3 pixel length” necessary for determining “whether the thickness of the drawing element corresponds to 3 pixels or more” is a length that is three times the width of one pixel. That is, it is equal to the number of pixels in the orthogonal direction of the line extending in the pixel arrangement direction (vertical direction or horizontal direction). Therefore, the number of pixels in the orthogonal direction of the diagonally extending line does not necessarily match.

  Since the initial value of both the fine line flag and the intermediate flag is FALSE, in step S140, both flags are not actually changed, and the initial values are maintained.

  On the other hand, when the thickness of the selected drawing element corresponds to 2 pixels (step S130, 2 pixels), the thin line flag = FALSE and the intermediate flag = TRUE are set for each dot data formed in step S120 (step S130). S150). As in the case of 3 pixels, “the length of 2 pixels” is a length obtained by doubling the width of 1 pixel.

  When the thickness of the selected drawing element corresponds to 1 pixel (step S130, 1 pixel), the thin line flag = TRUE and the intermediate flag = FALSE are set for each dot data formed in step S120 (step S130). S160).

  After executing any of steps S140 to S160, it is determined whether all the drawing element data has been rasterized (step S170). If unrasterized drawing element data remains (step S170, NO), the process returns to step S110, and steps S110 to S170 are repeated until all the drawing element data are rasterized. When all the drawing element data is rasterized (step S170, YES), the rasterization process is finished.

[2-2. Color conversion process (Fig. 4)]
Subsequently, the intercolor change process is started (step S200), and one of the dot data formed in the rasterization process that has not been color-converted is selected (step S210). This selection order follows the procedure of starting from the dot data arranged at the uppermost left, proceeding to the right, and moving to the leftmost dot data one step lower when reaching the rightmost.

  Subsequently, the flag associated with the selected dot data is determined (step S230). When the fine line flag = FALSE and the intermediate flag = FALSE are associated (step S230, fine line flag = FALSE, intermediate flag = FALSE), dot data color conversion (RGB →) using the normal LUT in the color conversion LUT 61 CMYK) (step S240). The normal LUT is a color conversion LUT that emphasizes color reproducibility.

  On the other hand, when the fine line flag = FALSE and the intermediate flag = TRUE are associated (step S230, fine line flag = FALSE, intermediate flag = TRUE), the color conversion of the dot data is performed using the intermediate LUT in the color conversion LUT 61. (Step S250). The intermediate LUT is a color conversion LUT in which the value indicating the ink amount of each of CMYK is 1.25 times that of the normal LUT.

  When the fine line flag = TRUE and the intermediate flag = FALSE are associated (step S230, fine line flag = TRUE, intermediate flag = FALSE), dot data color conversion is performed using the fine line LUT in the color conversion LUT 61. (Step S260). The thin line LUT is a color conversion LUT in which the value indicating the ink amount of each CMYK is 1.2 times that of the intermediate LUT, that is, 1.5 times that of the normal LUT.

  After executing any one of the above-described steps S240 to S260, it is determined whether all the dot data has been color-converted (step S270). If there is dot data that has not yet been converted (step S270, NO), the process returns to step S210, and steps S210 to S270 are repeated until color conversion is performed on all dot data. When all the dot data is color-converted (step S270, YES), the color conversion process is finished.

  Subsequently, halftone processing is performed using the color-converted dot data (step S300), and the output image data creation processing ends. Data output through the halftone process, that is, data that is an output result of the output image data creation process is output image data.

  The printing apparatus 10 executes printing (image formation) by instructing the control target (paper feed motor 74, carriage motor 70, and print head 81) based on the output image data thus created.

  As described above, according to the printing apparatus 10, for example, when the same RGB values are used, a drawing element with a thickness of 2 pixels is a dot in halftone processing more than a drawing element with a thickness of 3 pixels or more. Incidence will increase. Therefore, even when the same RGB values are used, a drawing element having a thickness of 2 pixels is printed darker than a drawing element having a thickness of 3 pixels or more. Similarly, a drawing element having a thickness of 1 pixel is printed darker than a drawing element having a thickness of 2 pixels.

  As a result, it is possible to reduce the disconnection of a drawing element having a thickness of 1 pixel. On the other hand, since the CMYK values are changed in three stages of 1 pixel, 2 pixels, 3 pixels or more, the reversal phenomenon in which the darkness and hue appear to be reversed can be reduced. For example, when the original RGB value is the same, the drawing element having a thickness of 1 pixel looks darker than the drawing element having a thickness of 2 pixels or more, or the thickness is 1 pixel. This is a phenomenon in which the hue that should be the same between the drawing element and the drawing element having a thickness of 2 pixels or more appear differently.

  This reversal phenomenon is likely to be perceived especially in the relationship between thin drawing elements, that is, the thickness between 1 pixel and 2 pixels. Therefore, in this embodiment, although the density of a drawing element having a thickness of 2 pixels is increased, the thickness is increased between 1 pixel and 2 pixels by decreasing the density increase method compared to the case of 1 pixel. The reversal phenomenon is reduced.

[3. Correspondence between embodiment and application example]
Step S100 (more specifically, step S130) corresponds to the classification unit, and steps S200 and S300 correspond to software for realizing some aspects of the data conversion unit. The color conversion LUT 61 corresponds to the “preliminarily prepared relationship”, and each dot data after the halftone process corresponds to the image forming data.

[4. Other Embodiments]
The present invention is not limited to the above-described embodiments, and can be implemented in various forms within the technical scope of the invention. For example, additional components in the embodiment can be omitted from the embodiment. The additional components referred to here are elements corresponding to matters not specified in the substantially independent application example. For example, the following embodiments may be used.

  In the embodiment, the drawing elements are classified on the basis that the thickness is 1 pixel, 2 pixels, 3 pixels or more, but other criteria may be used. For example, a criterion of 2 pixels or less, 3 pixels, 4 pixels or more, or 1 pixel, 2 and 3 pixels, 4 pixels or more may be used. The method of changing the concentration may be four or more steps. For example, the density may be changed stepwise by classifying as 1 pixel, 2 pixels, 3 pixels, 4 pixels or more.

  Since the ease of perception of a line break depends on the resolution of the printed image, the thickness that serves as the reference value for classification may be changed according to the resolution. The higher the resolution, the harder it is to perceive line breaks in a 1-pixel drawing element, but how to change it may be determined as appropriate by experiments or the like.

  The criteria for classification may be based on a method based on thickness, while taking into account other requirements. For example, under a condition where it is difficult to perceive a line break, a configuration in which a thin line LUT or an intermediate LUT is not used may be used. For example, since a line with originally high density is hardly perceived, a normal LUT may be used without determining the thickness. In addition, when it is difficult to perceive the reverse phenomenon, for example, when the drawing elements corresponding to the thin line LUT and the drawing elements corresponding to the intermediate LUT are printed at positions separated from each other, the intermediate LUT can be used instead. Alternatively, a normal LUT may be used.

  A configuration may be adopted in which the use of a plurality of color conversion LUTs is stopped based on a user instruction or the like. For example, when it is necessary to reduce the amount of ink used rather than the quality of the printed image (when there is an instruction from the user or when the remaining amount of ink is low), all the drawing elements are color-converted by the normal LUT You may make it do. When high-speed printing is required, color classification may be performed on all drawing elements by the normal LUT without performing classification based on thickness.

  Instead of storing the intermediate LUT, it may be calculated from the normal LUT and the thin line LUT. For example, the average of the normal LUT and the thin line LUT may be taken. Further, the intermediate LUT and the thin line LUT may be calculated from the normal LUT without storing the thin line LUT in addition to the intermediate LUT. For example, the value acquired from the normal LUT may be multiplied by a constant (for example, 1.25 times for 2 pixels and 1.5 times for 1 pixel).

The relationship between the thin line LUT, the intermediate LUT, and the normal LUT may be the following as well as those described in the embodiment.
Each value of the intermediate LUT may be any value as long as the object can be achieved by realizing an intermediate density between the two.
-The values of CMYK need not be changed at the same ratio. For example, only K may be changed by a different ratio, or each of CMYK may be changed by a different ratio.

The dot generation rate may be changed not in the color conversion LUT but in halftone processing. Specific examples of the method include the following.
In the case of using the dither method, for example, the dither matrix having different values may be used according to the thickness of the drawing element so that the dot generation rate increases as the drawing element becomes thinner.
In the case of using the error diffusion method, for example, the dot generation rate may be increased as the drawing element becomes thinner by correcting the diffusing error according to the thickness of the drawing element.

  It may be configured to ensure that the reverse phenomenon does not occur. Specifically, experiments are performed on all values of parameters related to line breakage and reversal phenomenon (for example, line width, hue, brightness, saturation, etc.), and line breakage prevention and reversal phenomenon are based on the experimental results. Design an LUT that is compatible with both prevention and prevention. Then, when performing color conversion, it is possible to ensure that the reverse phenomenon does not occur by selecting an appropriate LUT based on the parameters. In the case of monochrome printing, it is not necessary to consider hue and saturation, so that LUT design and selection are facilitated.

This process may be applied only to lines drawn in a light color. Specific examples of the method include the following.
A determination may be made as to whether the color of the thin line is a light color based on threshold values for brightness, saturation, hue, etc., and the process may be applied only to the thin line determined to be a light color.
The process may be applied only to colors that are the same as the predetermined color.
As described above, the processing is limited to light lines, so that processing targets can be narrowed down and processing can be performed at high speed.

In addition, the following forms may be used.
In the embodiment, in classifying the drawing elements, the line width specified by the length (mm) is converted into the number of pixels after rasterization and compared with the reference value determined by the number of pixels. You may classify | categorize by comparing with a reference value with length without converting into.
-The printer may be for monochrome printing. Further, a laser printer or a thermal printer may be used.
-Halftone processing may not be used. For example, binarization may be used.
-The color density may be adjusted by controlling the size of the ink dots.
A RIP (raster image processor) may be used.

DESCRIPTION OF SYMBOLS 10 ... Printing apparatus 30 ... Control unit 40 ... CPU
51 ... ROM
52 ... RAM
60 ... EEPROM
61 ... Color conversion LUT
DESCRIPTION OF SYMBOLS 70 ... Carriage motor 74 ... Paper feed motor 75 ... Platen 80 ... Carriage 81 ... Print head 82-85 ... Ink cartridge 91 ... Image data supply part

Claims (4)

An image forming apparatus that converts drawing element data including drawing start coordinate information, drawing end coordinate information, color information, and thickness information into image forming data, and forms an image using the image forming data. ,
The drawing element data includes a thin line classification whose thickness specified by the thickness information is less than a first predetermined value, and an intermediate line less than a second predetermined value greater than or equal to the first predetermined value and greater than the first predetermined value. A classification unit that classifies into three or more stages of classification and a thick line classification greater than or equal to the second predetermined value;
The drawing element data classified into the intermediate line classification is converted into the image forming data for forming an image with a color darker than the density specified by the color information, while being classified into the thin line classification The image formation for forming an image with a color in which the drawing element data is darker than the density specified by the color information and is darker than the drawing element data classified in the intermediate line classification An image forming apparatus comprising: a data conversion unit that converts data into business data. The image forming apparatus according to claim 1,
The data conversion unit converts the drawing element data into the image forming data using a halftone process, and changes the dot generation rate in the halftone process, whereby the intermediate line classification and the thin line classification An image forming apparatus that converts the drawing element data classified into (1) into the output image data for forming an image with a color darker than a density specified by the color information. The image forming apparatus according to claim 2,
The image forming apparatus, wherein the data conversion unit changes a dot generation rate in the halftone process by using a relationship prepared in advance according to a thickness. The image forming apparatus according to claim 2,
The data conversion unit uses a relationship prepared in advance according to the thickness for the drawing element data classified into the thin line classification by the classification unit and the drawing element data classified into the thick line classification. For the drawing element data classified into the intermediate line classification, an image forming apparatus that changes a dot occurrence rate in the halftone process by using a result calculated from the relationship.