JP2018142851A - Image processing apparatus and control method and program of image processing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adjust density difference of first and second objects to be drawn over, based on the size or the thickness of a line of the first object, when drawing a color image while converting into a grayscale image.SOLUTION: An image processing apparatus has extraction means for extracting a first object and a second object to be drawn on the first object from the print data of color image, determination means for determining the minimum value of density difference of the first and second objects extracted by the extraction means, based on the size of the second object, or the thickness of a line constituting the second object, and generation means for generating image data of plain color in which the density difference of the first and second objects is larger than the minimum value of density difference determined by the determination means.SELECTED DRAWING: Figure 8

Description

  The present invention relates to an image processing apparatus, an image processing apparatus control method, and an image processing system, and more particularly, to an image processing apparatus that converts color image print data into monochrome image print data, an image processing apparatus control method, and a program.

  In an image processing apparatus, color image print data may be printed by a monochrome printer or printed in a monochrome mode. In this case, the print data of the color image is converted into gray scale data based on a predetermined conversion formula in the printer.

  In a color image, a colored character may be drawn on top of a colored graphic. For example, when a character is input into a colored cell by spreadsheet software, or when a character is input inside a colored figure. When performing monochrome printing of these image data, the image processing apparatus converts color image print data into gray scale image print data.

  However, depending on the set character color, graphic color, and density of each color, it may be difficult to distinguish the graphic color and the character color as the background when converted to grayscale data. This is because the density of the graphic color and the character color after gray scale conversion are close to each other. For example, if the image after the color image is converted to gray scale is as shown by 1601 in FIG. 16, the gray density of the graphic and the character is close, and it is difficult for the user to distinguish the graphic and the character.

  Japanese Patent Application Laid-Open No. 2004-151867 describes that, in a region where a graphic and a character overlap, if the difference between the gray density of the graphic after conversion to gray scale and the gray density of the character is less than a predetermined threshold, the difference becomes a predetermined value. It is described that the image processing apparatus performs correction. As a result, the gray density difference between the graphic and the character becomes the same value as the predetermined threshold value, and the user can easily distinguish the graphic and the character.

JP 2002-262108 A

  In Patent Document 1, the density difference necessary for distinguishing between a graphic that becomes a background after grayscale conversion and a character or graphic object drawn on the graphic is the size of the character or graphic drawn on the background. It is constant regardless of the thickness of the sheath line.

  However, in general, in a gray scale image, a difference in gray density necessary for a human to distinguish a background graphic and a line or character drawn on the graphic differs depending on the size of the character or the thickness of the line. 1601 and 1603 in FIG. 16 are drawings in which the letters “A” are drawn in grays having a slightly lower density than the rectangular grays in rectangles drawn in the same grays. The small character size 1601 makes it difficult to distinguish between a rectangle and a character. On the other hand, 1603 having a large character size can distinguish between a rectangle and a character. This is because a large character is drawn with a thicker line than a small character.

  The image processing apparatus determines a gray density difference necessary for distinguishing between a figure as a background and a character or line object drawn on the figure based on a large character size. As a result, in characters drawn with small characters and thin lines, the difference between the gray density of the background figure and the gray density of the letters and figures drawn on top of the figure is not sufficient. And cannot distinguish between figures.

  On the other hand, if the density difference necessary to distinguish the background from characters and figures is determined based on the small character size, even if gray density correction is not necessary for large characters and figures drawn with thick lines, the characters And the density of the figure will be corrected.

  Here, the gray density is once replaced with lightness for explanation. A high gray density indicates that the lightness is low, and a light gray density indicates that the lightness is high. FIG. 17 is a diagram in which characters having the same size but different brightness are drawn on a gray having a brightness of 200. FIG. The brightness of each character is 195, 190, 180, 170 from the left. Since the character drawn in FIG. 17 has a sufficiently large character size, the user can distinguish the background graphic from the character without density correction. However, if the threshold value for determining whether or not to correct the gray density is set to 30, the above four characters are all drawn in gray having the same lightness 170. Therefore, the user cannot know that these four characters were originally different color characters.

  In the present invention, when a color image is converted into a grayscale image and drawn, the density difference between the first and second objects drawn in an overlapping manner is determined based on the size of the first object or the thickness of the line. The purpose is to adjust.

  The image processing apparatus according to the present invention is an image processing apparatus capable of generating single-color image data based on print data of a color image, wherein the first object and the first object are generated from the print data of the color image. Extraction means for extracting a second object drawn over the object, and the minimum value of the density difference between the first object and the second object extracted by the extraction means is the size of the second object. Or a determining means for determining based on a thickness of a line constituting the second object, and a density difference between the first object and the second object is a density difference determined by the determining means. Generating means for generating the single-color image data larger than the minimum value.

  In the present invention, when a color image is converted into a grayscale image and drawn, the density difference between the first and second objects drawn in an overlapping manner is determined based on the size of the first object or the thickness of the line. Can be adjusted.

FIG. 2 is a block diagram illustrating a functional configuration of a printer in the present embodiment. 1 is a block diagram showing a configuration of a print system in the present embodiment. 6 is a flowchart illustrating monochrome print processing according to the present embodiment. It is a flowchart which shows the detail of the data processing shown in FIG. 6 is a flowchart showing details of the drawing process shown in FIG. 4. 5 is a flowchart showing details of gray conversion processing shown in FIG. 4. It is a figure which shows an example of the color gray conversion LUT in this Embodiment. It is a flowchart which shows the detail of the brightness correction process shown in FIG. It is a figure which shows an example of the character size minimum brightness difference LUT used for the process which acquires the minimum brightness difference. It is a figure which shows an example of the gray lightness conversion LUT used for the process which calculates | requires the brightness of a character and a figure. 10 is a flowchart showing details of a character density (Gray) correction process shown in FIG. 8. FIG. 12 is a conceptual diagram when the brightness of a graphic is higher than the brightness of a character in the character density (Gray) correction process shown in FIG. 11. It is an image figure of the brightness of the character and figure before and after performing the brightness correction shown in FIG. FIG. 12 is a conceptual diagram when the brightness of a graphic is lower than the brightness of a character in the character density (Gray) correction process shown in FIG. 11. It is an image figure of the brightness of the character and figure before and after replacement of the brightness shown in FIG. It is a conceptual diagram which shows the replacement process of the brightness difference with respect to the character object of a different character size in this Embodiment. It is a figure which shows the example in which the character of different gray density is drawn by superimposing on the figure of a certain gray density in this Embodiment.

(Example)
Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

<Print system configuration including image processing apparatus>
In the present embodiment, a printer that prints image data on a sheet will be described as an example of the image processing apparatus. Needless to say, the image processing apparatus is not limited to the above-described apparatus, and includes various apparatuses such as a multifunction peripheral having a plurality of functions.

  The image processing apparatus according to this embodiment is a laser beam printer or an ink jet printer that enables monochrome printing based on color image print data. The printer is connected to a host computer and constitutes a printing system. The configuration of the print system will be described below with reference to FIG.

  First, the hardware configuration of the host computer 200 connected to the printer 214 will be described.

  In FIG. 2, the host computer 200 is activated when the CPU 201 executes an application program stored in a program ROM 203. Then, the CPU 201 reads out data from the font ROM 204 that stores font data and the data ROM 205 that stores various data, and executes processing. The RAM 202 is used as a main storage area or work area for the CPU 201.

  The host computer 200 includes input / output devices such as a keyboard (KB) 211 and a display (CRT: Cathode Ray Tube) 212, and an interface with an external memory 213 and the like. These devices are controlled by the CPU 201 via the system bus 206 via device controllers such as a keyboard controller (KBC) 207, a display controller (CRTC) 208, and a memory controller (MC) 209, respectively.

  Further, the host computer 200 inputs / outputs data to / from the printer 214 via the print controller (PRCT) 210.

  Next, the hardware configuration of the printer 214 will be described.

  The printer 214 controls each device connected to the system bus 220 when the CPU 215 executes a control program stored in the program ROM 217 or the external memory 226.

  In addition, the CPU 215 outputs an image signal to a printing unit (printer engine) 224 connected via a printing unit I / F (interface) 222. The printer 214 includes a RAM 216 used as a main storage area and an output information expansion area of the CPU 215, a font ROM 218 that stores font information, and a data ROM 219 that stores various data information.

  The external memory 226 supplies font data, form data, an emulation program, and the like to the CPU 215 via the memory controller (MC) 223. The operation unit 225 includes an input device such as a switch and a touch panel for setting the operating environment of the printer 214 and a display device such as a display. The display device is used to display setting data and user information stored in the RAM 216, and the input device is used to receive an operation by the user.

  Next, an outline of a functional configuration of the printer 214 will be described with reference to FIG.

  First, the functional configuration of the printer 214 includes a video controller 110 that generates image data for printing based on input print data, and a printer engine unit that forms a visible image on a recording medium based on the image data for printing. 109.

  The video controller 110 includes a reception buffer 102, a command determination unit 103, a command analysis unit 104, a color tone control unit 105, a command execution unit 106, and a page memory 107. The video controller 110 is controlled by the CPU 215. The CPU 215 controls the video controller 110 by reading out a program stored in the ROM 217, developing it in the RAM 216, and executing it.

  The printer engine unit 109 receives the image data generated by the video controller 110 via the output control unit 108. The printer engine unit 109 is controlled by the CPU 215 and controls the printing unit 224. The CPU 215 controls the printer engine unit 109 by calling a program in which the behavior of the printer engine unit 109 is written from the ROM 217 to the RAM 216 and executing it.

  Hereinafter, processing performed when the printer 214 receives print data from the host computer 200 will be described.

  The interface 101 receives print data sent from the host computer 200 via the input unit 221 and sends the print data to the reception buffer 102. The print data is PDL (Page Description Language) data indicating image data to be printed on a sheet.

  The reception buffer 102 stores the print data received from the interface 101 in the RAM 216. The reception buffer 102 stores the character pattern itself as a character object, the character code of the character included in the received print data, and the like in the RAM 216. If the received print data is a graphic object, the reception buffer 102 stores graphic attributes such as contour coordinate points and colors indicating the shape in the RAM 216.

  The command determination unit 103 reads the print data stored in the reception buffer 102 and determines the PDL type of the print data.

  Thereafter, the command analysis unit 104 analyzes the print data according to the determined type of PDL. The printer 214 has a command analysis unit 104 for each command type. In the present embodiment, one of them is shown as an example. The analyzed command is converted into intermediate data in a format that can be easily processed by the command execution unit 106 in the subsequent stage.

  The command execution unit 106 executes the command converted into the intermediate data, generates raster data that is a set of pixel data, and stores the generated raster data in the page memory 107.

  When it is determined that the command analyzed by the command analysis unit 104 has a color attribute, the color tone control unit 105 executes color tone control that changes the color information on the intermediate data generated by the command analysis unit 104. Processing performed by the color tone control unit 105 will be described later with reference to FIGS. 6, 8, and 11.

  The output control unit 108 creates a video signal based on the raster data, and sends the video signal to the printer engine unit 109 as a laser drive signal for controlling on / off of the laser beam. The printer engine unit 109 controls the laser light applied to the photosensitive drum using the video signal received from the output control unit 108 as a laser drive signal. The photosensitive drum is charged in advance with a negative charge, and the negative charge in the region irradiated with the laser light disappears. Therefore, a potential difference is generated between the region irradiated with the laser beam on the photosensitive drum and the region not irradiated with the laser beam, and a latent image is formed. A visible image is formed on the photosensitive drum by attaching a positively charged toner to the photosensitive drum on which the latent image is formed.

  As described above, the printer 214 according to the present embodiment only needs to be able to perform monochrome printing based on color image print data. Accordingly, the toner color included in the printer engine unit 109 may be a single black color or a plurality of colors.

<Outline of color processing>
Hereinafter, color processing performed when the printer 214 to which the present embodiment is applied processes print data having color attributes, for example, print data of an RGB format color image will be described. Here, it is assumed that the printer 214 is a color printer having four color developing units for YMCK. The printer 214 converts the RGB color information of each pixel of the image data into a YMCK format for printing. Thereafter, the printer 214 generates image data composed of one YMCK color (plane). Therefore, the image data for printing is 4 pieces of image data composed of Y, image data composed of M, image data composed of C, and image data composed of K for each pixel in one page. It has image data for a plane. The printer engine unit 109 performs print processing for each color developer (toner).

  On the other hand, it is assumed that the printer 214 is a monochrome printer that allows only monochrome image formation. The printer 214 has only a black developing unit, and the printer 214 converts RGB color information of each pixel of the color image data into a gray scale based on a predetermined conversion formula. Gray scale image data formed with black toner is composed of lightness information indicating the brightness of the color. Data expressed in gray scale is composed of one plane of image data for one page. Each pixel of the image data has a density signal representing a specific gray density.

  When the printer 214 is a color printer and is set to print in monochrome, the printer 214 performs color processing with gray scale conversion, as in the monochrome printer.

  As described above, when monochrome printing a color image, the video controller 110 associates the density of each pixel with the output level (0 to 255) in the printer engine and outputs it as a video signal. Note that the monochrome printer performs multi-value recording as in the case of the color printer, and performs binary recording depending on whether the engine unit strikes dots. The printer 214 outputs grayscale halftone data as a multivalued image or a binary image according to the recording format.

  When outputting the multi-value print data received from the host computer 200 as a binary image, the printer 214 performs a process of converting the received multi-value image into a binary image. Assume that the printer 214 uses a known method such as a dithering method in which a predetermined threshold is provided for each pixel and the output value is divided into two by comparing the pixel density with the threshold as the binarization process.

  Here, a character density (Gray) correction process performed when the printer 214 according to the present embodiment converts a color image into gray scale will be described with reference to a schematic diagram.

  FIG. 16 is a schematic diagram after gray scale conversion is performed on a color image in which a character object “A” is drawn on a square graphic object. Reference numerals 1601 and 1603 indicate before the brightness of the character is adjusted, and 1602 and 1604 are views after executing the brightness correction process (S609) described in the present embodiment.

  In this embodiment, after the color image print data is converted to gray scale print data, the color tone control unit 105 obtains the difference in lightness between the drawing of the graphic object and the character object drawn in an overlapping manner. If the gray brightness difference between the graphic object and the character object is smaller than the threshold value, the color tone control unit 105 corrects the lightness of the character so that the gray brightness difference between the graphic object and the character is equal to or greater than the threshold value. On the other hand, if the lightness difference between the graphic and the character gray is equal to or greater than the threshold, the color tone control unit 105 does not correct the lightness of the character.

  In this embodiment, the color tone control unit 105 determines the threshold value based on the size of the character object. For example, FIGS. 16 (a) 1601 and (b) 1603 are both drawn by superimposing a character object “A” having a brightness of 175 on a rectangular graphic object having a brightness of 165. Since the character object in FIG. 16A is drawn with a character size of 10 points, the lightness difference between the figure and the character is at least 20 from the character size lightness difference LUT shown in FIG. Therefore, the color tone control unit 105 executes a character density (Gray) correction process for increasing the brightness of the character so that the brightness difference between the figure 1601 and the character is 20. A grayscale image 1602 after the character density (Gray) correction process is executed.

  On the other hand, the character object in FIG. 16B is drawn with a character size of 100 points. When the character size is 100 points from the character size lightness difference LUT in FIG. 9, the minimum lightness difference necessary for distinguishing characters from the background graphic is 5. Since the brightness difference between the graphic and the character in FIG. 16B is 10, the color tone control unit 105 does not perform the character density (Gray) correction process. Therefore, the printed gray scale image 1604 is the same image as 1603.

  The printer 214 in this embodiment changes a threshold value for determining whether or not to correct the gray density of the character according to the character size. As a result, even when the character size is small, the printer 214 can print an image that allows the user to easily distinguish a graphic from a character. Further, the printer 214 decreases the above threshold value for characters having a large character size. This can reduce the occurrence of printing with the same gray density when characters having different colors in the color image state are converted to gray scale and printed.

<Monochrome print processing>
As described above, the printer 214 of the present embodiment can receive color image print data from the host computer 200 and perform monochrome printing based on the color image print data. Hereinafter, a monochrome printing process based on color image print data executed by the printer 214 in this embodiment will be described.

  FIG. 3 is a flowchart showing a series of processes of a monochrome print operation until color image print data is sent from the host computer 200 to the printer 214 and a visible image is formed on the recording medium by the printer engine unit 109. A program for executing the processing described in this flowchart is stored in the ROM 217, and the processing is realized by the CPU 215 executing the program.

  First, the video controller 110 receives color image print data from the host computer 200 via the input unit 221 and stores it in the RAM 216 (S301). Then, the video controller 110 performs data processing described later with reference to FIG. 4 (S302).

  After the video controller 110 completes the process described in S302, the output control unit 108 converts the raster image generated in S302 into a video signal for the printer engine unit 109 and outputs the video signal (S303).

  The printer engine unit 109 forms a visible image on the recording medium based on the received video signal (S304). Thereafter, the printer engine unit 109 discharges the recording medium on which the visible image is formed (S305).

  The video controller 110 determines whether printing has ended based on whether a print end command has been received from the printer engine unit 109 or whether the print data has ended (S306). If it is determined that printing has been completed, the video controller 110 ends the printing operation. If the printing is not finished, the video controller 110 repeats the processing from S301 to S306.

  FIG. 4 is a flowchart showing details of data processing performed by the video controller 110 in S302 of FIG.

  First, the command analysis unit 104 initializes a variable n indicating the number of character drawing commands included in the print data (S401). The variable n is a variable for recording the number of character drawing commands among the data read from the reception buffer 102 by the command analysis unit 104 in the drawing process (S408) described later. The variable n is stored in the RAM 216, and the command analysis unit 104 sets the variable n to 0 in S401.

  Next, the command analysis unit 104 initializes a variable m indicating the number of graphic drawing commands included in the print data (S402). The variable m is a variable indicating how many graphics drawing commands are included in the data read from the reception buffer 102 by the command analysis unit 104 in the drawing process (S408) described later. The variable m is stored in the RAM 216, and the command analysis unit 104 sets the variable m to 0 in S402.

  Next, the command determination unit 103 reads a command from the print data stored in the reception buffer 102, and sends the command to the command analysis unit 104 (S403). The command read by the command determination unit 103 in S403 is a command for instructing to draw a graphic object or a character object from print data and drawing, or a command for instructing a print setting or a paper discharge method.

  The command determination unit 103 determines whether reading of all commands included in the print data has been completed (S404). The print data includes commands indicating the start and end of the page. If the command read from the reception buffer 102 is a command indicating the end of the page, the command determination unit 103 advances the process to S405 described later. On the other hand, when the print data is being read, the command analysis unit 104 executes a process of S406 described later.

  When the print data is being read, the command analysis unit 104 determines whether the command received from the command determination unit 103 is a drawing command accompanied by a character / graphic development process to the page memory 107 (S406). .

  When the command received from the command determination unit 103 is not a drawing command, the command analysis unit 104 creates intermediate data and returns the process to S403 (S407). Commands that are not drawing commands are, for example, commands related to paper discharge and commands related to settings such as single-sided printing and double-sided printing. On the other hand, when the command received from the command determination unit 103 is a drawing command, the command analysis unit 104 performs the drawing process described later with reference to FIG. 5 and then returns the process to S403 (S408). By performing S403 to S408, it is possible to extract character objects and graphic objects included in the print data.

  When the command determination unit 103 determines that all the commands included in the print data for one page have been read, the command analysis unit 104 and the color tone control unit 105 perform gray conversion processing described later with reference to FIG. 6 (S405). In step S <b> 405, the color tone control unit 105 converts the color image print data into single color print data.

  After the gray conversion process described in S405 is completed, the command execution unit 106 generates raster data, which is a set of pixel data, based on the intermediate data created by the command analysis unit 104.

  FIG. 5 is a flowchart showing details of the drawing process executed by the command analysis unit 104 in S408 of FIG. The processing described in this flowchart is realized by the CPU 215 executing a program stored in the ROM 217.

  The command analysis unit 104 determines whether or not the drawing command received from the command determination unit 103 is a character object drawing command (S501).

  When the drawing command received from the command determination unit 103 is a character object drawing command, the command analysis unit 104 stores the character color in the character color buffer of the RAM 216 (S502).

  The command analysis unit 104 stores the character size of the character object in the character size buffer of the RAM 216 (S503). Next, the command analysis unit 104 stores the position of the text box of the character object in the character position buffer (S504). The position of the text box is information indicating where the character is drawn on the page. In step S <b> 504, the command analysis unit 104 stores, for example, the upper left coordinates of the text box for displaying characters in the RAM 216. The character color is, for example, an RGB signal value included in the command.

  Then, the command analysis unit 104 updates the value of the variable n stored in the RAM 216 to a value increased by one from the current value (S505). Thereafter, the command analysis unit 104 generates intermediate data corresponding to the command received from the command determination unit 103 (S511).

  If the drawing command received from the command determination unit 103 in S501 is not a character drawing command, the command analysis unit 104 determines whether the drawing command is a drawing command for a graphic object (S506).

  When the command received from the command determination unit 103 is a drawing command for a graphic object, the command analysis unit 104 stores the color of the graphic object in the graphic color buffer of the RAM 216 (S507). Thereafter, the command analysis unit 104 stores the width and size of the graphic object in the graphic size buffer of the RAM 216 (S508). Then, the command analysis unit 104 stores the drawing position of the graphic object in the graphic position buffer (S509).

  Then, the command analysis unit 104 updates the value of the variable m stored in the RAM 216 to a value that is increased by one from the current value (S510). Thereafter, the command analysis unit 104 generates intermediate data corresponding to the command received from the command determination unit 103 (S511).

  On the other hand, if the command received by the command analysis unit 104 from the command determination unit 103 in S506 is not a graphic drawing command, the command analysis unit 104 generates intermediate data corresponding to the received command (S511). The command determined not to be a graphic drawing command in S506 is a command for drawing an image such as a photograph, for example. Note that either the processing of S501 or S506 may be performed first or may be performed in parallel.

  FIG. 6 is a flowchart showing details of the gray conversion process shown in step S405 of FIG. A program for executing the processing described in this flowchart is stored in the ROM 217, and the processing is realized by the CPU 215 executing the program.

  The command analysis unit 104 determines whether there is a drawing command having color information in each command group converted to intermediate data (S601). When there is a drawing command including color information, the command analysis unit 104 executes the process of S602. On the other hand, when there is no drawing command including color information, the command analysis unit 104 ends the gray conversion process (S405), and the command execution unit 106 executes the process shown in S409 of FIG.

  When there is character or graphic drawing data having color information in the drawing data, the command analysis unit 104 sets the value of the variable n indicating the number of characters in the print data stored in the RAM 216 to the final number of characters processed. The value is stored in the RAM 216 (S602).

  The command analysis unit 104 stores the value of the variable m indicating the number of graphics in the print data stored in the RAM 216 in the RAM 216 as the final value of the processing number of graphics (S603).

  Next, the color tone control unit 105 acquires a color gray conversion LUT for converting color information (RGB) into density information (Gray) from the external memory 226 (S604). Here, the color gray conversion LUT is a table shown in FIG. 7, and is a lookup table (LUT) having RGB signal values as input values and density information (Gray) as output values. The color gray conversion LUT shown in FIG. 7 indicates that the gray density is 56 when R is 50, G is 50, and B is 100.

  For example, the color gray conversion LUT may have an output value obtained by calculating density information (Gray) using the NTSC method with respect to uniform color information (RGB).

  Then, the color tone control unit 105 initializes a variable i indicating the number of processed character objects (S605).

  The color tone control unit 105 calculates a character density (Gray) from the color information (RGB) of the i-th character object using the color gray conversion LUT. Then, the color tone control unit 105 stores the calculated character density (Gray) in the character density buffer of the RAM 216 (S606). The character density (Gray) calculated in S606 will be described as Gray_bf_txt in the following description.

  Next, the color tone control unit 105 initializes a variable j indicating the number of graphic objects processed (S607).

  The tone control unit 105 reads the color information (RGB) of the jth graphic object from the graphic color buffer of the RAM 216. Then, the color tone control unit 105 converts the read color information (RGB) into a graphic density (Gray). The color tone control unit 105 stores the obtained graphic density (Gray) in the graphic density buffer of the RAM 216 (S608). The calculated graphic density (Gray) is described as Gray_bf_back in the description below.

  Then, the color tone control unit 105 executes brightness correction processing described later with reference to FIG. 8 (S609). The color tone control unit 105 determines whether the variable j matches the value of m indicating the number of graphics stored in the RAM 216 by the command analysis unit 104 in S603 (S610). If the variable j is different from the number m of figures included in the print data, the tone control unit 105 increases the value of the variable j by one and returns the process to S608 (S612).

  If the variable j is the same as the number m of images included in the print data, the tone control unit 105 determines whether the variable i is the same as the number n of characters included in the print data (S611). If the value of the variable i is not the same as the number of characters n included in the print data, the color tone control unit 105 increases the value of the variable i by one and returns the process to S606 (S613).

  When the variable i is the same as the number n of characters included in the print data, the tone control unit 105 ends the gray conversion process described in this flowchart, and the command execution unit 106 performs the process described in S409 in FIG.

  FIG. 8 is a flowchart showing details of the brightness correction processing executed by the color tone control unit 105 in S609 of FIG. 6 which is a feature of the present embodiment. The processing described in this flowchart is realized by the CPU 215 executing a program stored in the ROM 217 or the like.

  The color tone control unit 105 determines whether the i-th character and the j-th figure overlap (S801). In S801, the size and position of the character acquired in S503 and S504 of the drawing process of FIG. 5 and the size and position of the graphic acquired in S508 and S509 are compared to determine whether the character and the graphic overlap. When the area where the character is drawn is entirely covered by the area where the graphic is drawn, the color tone control unit 105 determines that the character and the graphic overlap.

  When the color tone control unit 105 determines that the character and the figure do not overlap, the color tone control unit 105 ends the processing described in this flowchart, and advances the processing to S610 in FIG.

  When the color tone control unit 105 determines that the character and the figure overlap, the color tone control unit 105 obtains the character size minimum brightness difference LUT shown in FIG. 9 from the external memory 226 (S802).

  The character size minimum brightness difference LUT is a one-dimensional table stored in the external memory 226 in advance. The index x is a value serving as a headline for managing the data of each row. The character size Pt [x] indicates the font size of the character object. The minimum brightness difference (min_ΔL * [x]) is the minimum brightness difference necessary for the user to distinguish between a graphic and a character when a graphic object is drawn with a character size Pt [x] superimposed on it. is there.

  From the character size minimum brightness difference LUT shown in FIG. 9, for example, if the character size is a character of 10 pt, the user can distinguish between the character and the background if there is a brightness difference between the figure in the background and the character. Recognize. From FIG. 9, the minimum lightness difference (min_ΔL * [x]) increases as the character size decreases, and the minimum lightness difference (min_ΔL * [x]) decreases as the character size increases. This is because the smaller the character size, the smaller the area of the character or the thinner the lines that make up the character, so that the user cannot distinguish the graphic from the character unless the brightness difference between the graphic and the character increases. On the other hand, a character having a large character size has a large character area, and the line width constituting the character is thick, so that the user can distinguish the character even if the density difference between the graphic and the character is small.

  Next, the color tone control unit 105 obtains the minimum lightness difference (min_ΔL * [x]) necessary for the character size of the i-th character using the character size minimum lightness difference LUT acquired in S802 (S803). The color tone control unit 105 obtains the minimum brightness difference (min_ΔLUT * [x]) in the character size of the i-th character by linearly interpolating the minimum brightness difference LUT acquired in S802.

  For example, when the character size is 5 pt, the color tone control unit 105 sets the input character size (Ptinput) to 5. The color tone control unit 105 determines the index [x] (0 <x <N) so that Pt [x] <Ptinput <Pt [x + 1] holds. Here, since Pprint is 5, x is 0 and x + 1 is 1.

  As shown in FIG. 9, when the character size Pt [0] is 1 point, the minimum brightness difference min_ΔL * [0] is 30. When the character size Pt [1] is 10 points, the minimum brightness difference min_ΔL * [1] at that time is 20. The tone control unit 105 substitutes the above value into the following formula (1) to obtain the minimum brightness difference min_ΔL * [x] of the i-th character. When Ptput is 5 points, the minimum brightness difference is 25.6.

Ｓ８０３において、色調制御部１０５がｉ番目の文字について、ユーザが図形と文字を区別するために必要な明度差（最低明度差）を文字サイズに基づいて決定する。最低明度差は、後に説明する文字濃度（Ｇｒｅｙ）修正処理を色調制御部１０５が実行するか否かの閾値として用いられる。

In step S <b> 803, the color tone control unit 105 determines a brightness difference (minimum brightness difference) necessary for the user to distinguish a graphic from a character for the i-th character based on the character size. The minimum brightness difference is used as a threshold value for determining whether or not the color tone control unit 105 executes a character density (Grey) correction process described later.

  Next, the color tone control unit 105 acquires the gray lightness conversion LUT shown in FIG. 10 from the external memory 226 (S804). The gray lightness conversion LUT is a lightness conversion table for converting gray density to lightness. The index y is a value serving as a headline for managing the data of each row. Gray (Gry [y]) is the value of the density signal of the grayscale image to be input. The lightness (L * [y]) indicates the lightness that is output for the density signal (Gry [y]).

  It is assumed that the gray lightness conversion LUT is stored in the external memory 226 in advance. However, the gray lightness conversion LUT prints image data having a plurality of density signals (Gray) with the printer 214 in advance, and converts the lightness (L *) value obtained by measuring the chart with a colorimeter to the gray lightness conversion. It is good also as the brightness (L * [y]) of LUT.

  Next, the color tone control unit 105 converts the density of the i-th character into lightness using the gray lightness conversion LUT acquired in S804 (S805). The color tone control unit 105 obtains the lightness (L * _txt) of the character from the character density (Gray_bf_txt) obtained in S606.

  For example, when the character density Gray_bf_txt is 30, the color tone control unit 105 sets the input gray data (Gryinput) to 30. The color tone control unit 105 determines the index (y) (0 <y <M) so that Gry [y] <Gryinput <Gry [y + 1] holds. Here, since Gryinput is 30, y is 1 and y + 1 is 2. From FIG. 10, the density signal Gry [1] is 17, and the lightness L * [1] at that time is 22. The density signal Gry [2] is 34, and the lightness L * [2] at that time is 25. The color tone control unit 105 obtains the brightness of the i-th character by substituting these values into the following equation (2). When Gryinput is 30, the brightness is 24.3.

次に、色調制御部１０５はＳ８０４で取得したグレイ明度変換ＬＵＴを用いてｊ番目の図形の濃度を明度に変換する（Ｓ８０６）。色調制御部１０５は、Ｓ６０８で求めた図形濃度（Ｇｒａｙ＿ｂｆ＿ｂａｃｋ）からｊ番目の図形の明度（Ｌ＊＿ｂａｃｋ）を求める。Ｓ８０６において色調制御部１０５が行う処理は、Ｓ８０５で行う処理と同様であるため、説明を省略する。

Next, the color tone control unit 105 converts the density of the j-th figure into lightness using the gray lightness conversion LUT acquired in S804 (S806). The color tone control unit 105 obtains the brightness (L * _back) of the j-th figure from the figure density (Gray_bf_back) obtained in S608. Since the process performed by the color tone control unit 105 in S806 is the same as the process performed in S805, description thereof is omitted.

  Next, the color tone control unit 105 calculates the absolute value (ΔL * _abs) of the difference between the character brightness (L * _txt) obtained in S805 and the figure brightness (L * _back) obtained in S806 by the following equation (3). Obtain (S807).

ΔL ^* _abs = | L ^* _txt− L ^* _back Expression (3)
Next, the color tone control unit 105 determines whether or not the absolute value (ΔL * _abs) of the brightness difference between the character and the figure obtained in S807 is less than the minimum brightness difference (min_ΔL *) acquired in S803 (S808). ).

  When the absolute value (ΔL * _abs) of the brightness difference between the character and the figure is less than the minimum brightness difference (min_ΔL *), the color tone control unit 105 executes the process of S809 described later. On the other hand, if the absolute value (ΔL * _abs) of the lightness difference between the character and the figure is equal to or greater than the minimum lightness difference (min_ΔL *), the color tone control unit 105 ends the processing described in this flowchart and then proceeds to S610 in FIG. Execute the process.

  Next, when the absolute value (ΔL * _abs) of the lightness difference between the character and the figure is less than the minimum lightness difference (min_ΔL *), the color tone control unit 105 executes a character density (Gray) correction process described later (S809). . After the color tone control unit 105 ends the process of S809, the color tone control unit 105 ends the process described in this flowchart and executes the process of S610 of FIG.

  Next, the character density (Gray) correction process in S809 of FIG. 8 will be described with reference to FIGS.

  First, the case where the gray brightness of the figure after gray conversion is larger than the gray brightness of the character, that is, the case where the figure is drawn in lighter gray than the character will be described with reference to FIGS.

  FIG. 12 schematically shows the brightness of characters and figures. The vertical axis represents lightness (L *). lim_L * _max is the maximum value of the lightness L * [M] of the gray lightness conversion LUT shown in FIG. 10, and lim_L * _min is the minimum value of the lightness ΔL * [0] of the gray lightness conversion LUT shown in FIG. For example, in FIG. 10, lim_L * _max is 70 and lim_L * _min is 20. min_ΔL * is the minimum lightness difference min_ΔL * [x] obtained in S803, L * _txt is the lightness of the character, and L * _back is the lightness of the figure. Also, the white circles in the figure indicate the brightness of the character after the character density (Gray) correction process of S809 in FIG.

  FIG. 13 shows grayscale images before and after the character density (Gray) correction process. Reference numerals 1301, 1303, 1305, and 1307 denote gray scale images before the character density (Gray) correction process, and reference numerals 1302, 1304, 1306, and 1308 denote gray scale images after the character density (Gray) correction process. FIGS. 13A to 13D correspond to FIGS. 12A to 12D, respectively.

  FIG. 12A shows a case where the lightness of the character is lower than that of the graphic, and the value obtained by subtracting the minimum lightness difference (min_ΔL *) from the lightness (L * _back) of the graphic is not less than lim_L * _min. In this case, the color tone control unit 105 corrects the lightness (L * _txt) of the character to a value (white circle in the drawing) obtained by subtracting the minimum lightness difference (min_ΔL *) from the lightness (L * _back) of the graphic. In FIG. 12A, the color tone control unit 105 executes a process for reducing the brightness of the character. That is, as shown by 1301 and 1302 in FIG. 13A, the gray density of the character is adjusted so that the character density is high.

  FIG. 12B shows a case where the lightness of the character is lower than that of the graphic, and the value obtained by subtracting the minimum lightness difference (min_ΔL *) from the lightness (L * _back) of the graphic is less than lim_L * _min. If the value obtained by adding the minimum lightness difference (min_ΔL *) to the lightness (L * _back) of the graphic is equal to or smaller than lim_L * _max, the color tone control unit 105 converts the lightness (L * _txt) of the character into the lightness (L * _back) of the graphic. ) Plus a minimum brightness difference (min_ΔL *). That is, as shown at 1303 and 1304 in FIG. 13B, the gray density of the character is adjusted so that the character density becomes light.

  FIGS. 12C and 12D show the case where the lightness of the character is lower than that of the graphic, and the value obtained by subtracting the minimum lightness difference (min_ΔL *) from the lightness (L * _back) of the graphic is smaller than lim_L * _min. Further, FIGS. 12C and 12D show a case where the value obtained by adding the minimum lightness difference (min_ΔL *) to the lightness (L * _back) of the figure is larger than lim_L * _max. At this time, the color tone control unit 105 compares the absolute value of the difference between lim_L * _max and the brightness of the graphic, and the absolute value of the difference between lim_L * _min and the brightness of the graphic. If the absolute value of the difference between lim_L * _max and the brightness of the graphic is equal to or greater than the absolute value of the difference between lim_L * _min and the brightness of the graphic, the tone control unit 105 corrects the brightness of the character to lim_L * _max. That is, as shown in FIG. 13C, the character color is corrected to the maximum value of the lightness (L * [y]) of the gray conversion LUT, and the gray density of the character is adjusted to be light. When the absolute value of the difference between lim_L * _max and the brightness of the figure is less than the absolute value of the difference between lim_L * _min and the brightness of the figure, the tone control unit 105 corrects the brightness of the character to lim_L * _min. That is, as shown in FIG. 13D, the character color is corrected to the minimum value of the lightness (L * [y]) of the gray conversion LUT and adjusted so that the character density is high.

  Next, the case where the gray brightness of the graphic after gray conversion is smaller than the gray brightness of the character, that is, the case where the graphic is drawn in a darker gray than the character will be described with reference to FIGS.

  FIG. 14 schematically shows the brightness of characters and figures. Since the respective symbols are the same as those in FIG.

  FIG. 15 shows grayscale images before and after the character density (Gray) correction process. 1501, 1503, 1505, and 1507 are gray scale images before the character density (Gray) correction process, and 1502, 1504, 1506, and 1508 are gray scale images after the character density (Gray) correction process. 14A to 14D correspond to FIGS. 15A to 15D, respectively.

  FIG. 14A shows a case where the lightness of the character is higher than the lightness of the graphic, and the value obtained by adding the minimum lightness difference (min_ΔL *) to the lightness (L * _back) of the graphic is less than or equal to lim_L * _max. The color tone control unit 105 corrects the lightness (L * _txt) of the character to a value obtained by adding the lightness (L * _back) of the graphic and the minimum lightness difference (min_ΔL *). That is, as shown in FIG. 15A, the color tone control unit 105 corrects the character density so as to reduce the character density.

  FIG. 14B shows a case where the brightness of the character is higher than the brightness of the figure, and the value obtained by adding the minimum brightness difference (min_ΔL *) to the brightness of the figure (L * _back) is larger than lim_L * _max. At this time, if the value obtained by subtracting the minimum lightness difference (min_ΔL *) from the lightness (L * _back) of the graphic is equal to or larger than lim_L * _min, the lightness (L * _txt) of the character is calculated from the lightness (L * _back) of the graphic. The value is corrected by subtracting the minimum brightness difference (min_ΔL *). That is, as shown in FIG. 15B, the color tone control unit 105 performs correction to increase the character density.

  FIGS. 14C and 14D show the case where the lightness of the character is higher than that of the graphic, and the value obtained by subtracting the minimum lightness difference (min_ΔL *) from the lightness (L * _back) of the graphic is smaller than lim_L * _min. Further, FIGS. 14C and 14D show a case where the value obtained by adding the minimum lightness difference (min_ΔL *) to the lightness (L * _back) of the graphic exceeds lim_L * _max. At this time, the color tone control unit 105 compares the absolute value of the difference between lim_L * _max and the brightness of the graphic, and the absolute value of the difference between lim_L * _min and the brightness of the graphic. If the absolute value of the difference between lim_L * _max and the brightness of the figure is equal to or greater than the absolute value of the difference between lim_L * _min and the brightness of the figure (L * _back), the tone control unit 105 corrects the brightness of the character to lim_L * _max. . That is, the color tone control unit 105 corrects the character color to the maximum value of the lightness (L * [y]) of the gray conversion LUT as shown in FIG. 15C to reduce the gray density of the character. If the absolute value of the difference between lim_L * _max and the brightness of the figure is less than the absolute value of the difference between lim_L * _min and the brightness of the figure, the tone control unit 105 corrects the brightness (L * _txt) of the character to lim_L * _min. . That is, the color tone control unit 105 corrects the character color to the minimum value of the lightness (L * [y]) of the gray conversion LUT as shown in FIG. 15D to increase the character density.

  Details of the character density (Gray) correction processing described in S809 of FIG. 8 will be described using the flowchart of FIG. A program for executing the processing described in this flowchart is stored in the ROM 217, and the processing described in this flowchart is realized by the CPU 215 reading and executing the program.

  First, the color tone control unit 105 refers to the gray lightness conversion LUT acquired in step S804 in FIG. 8, and sets the lightness value with an index of 0 as the lightness lower limit (lim_L * _min). Further, the color tone control unit 105 sets the lightness value with the largest index of the gray lightness conversion LUT as the lightness upper limit value (lim_L * _max) (S1101). For example, the color tone control unit 105 sets the lightness lower limit (lim_L * _min) to 20 and the lightness upper limit (lim_L * _max) to 70 with reference to the gray lightness conversion LUT of FIG.

  Next, the color tone control unit 105 determines whether or not the lightness (L * _back) of the graphic obtained in S806 of FIG. 8 is equal to or higher than the lightness (L * _txt) of the character obtained in S805 of FIG. 8 (S1102). ). When the lightness (L * _back) of the figure is equal to or higher than the lightness (L * _txt) of the character, the color tone control unit 105 executes the process of S1103 described later.

  On the other hand, when the lightness (L * _back) of the figure is less than the lightness (L * _txt) of the character, the color tone control unit 105 executes the process of S1108 described later.

  When the lightness (L * _txt) of the character is less than the lightness (L * _back) of the graphic, the tone control unit 105 subtracts the minimum lightness difference (min_ΔL *) from the lightness (L * _back) of the graphic. It is determined whether it is equal to or greater than the lower limit value (lim_L * _min) (S1103). Here, the brightness (L * _back) of the figure is obtained by the color tone control unit 105 in S806 of FIG. Further, the minimum lightness difference (min_ΔL *) is obtained by the color tone control unit 105 in S803 of FIG.

  When the value obtained by subtracting the minimum lightness difference (min_ΔL *) from the lightness (L * _back) of the graphic is equal to or larger than lim_L * _min, the color tone control unit 105 calculates the lightness (L * _txt) of the character from the lightness of the graphic. The value is corrected to the subtracted value (S1114). The process of S1114 is a process corresponding to FIG. 12 (A) and FIG. 13 (A).

  When the value obtained by subtracting the minimum lightness difference (min_ΔL *) from the lightness (L * _back) of the figure is less than lim_L * _min, the color tone control unit 105 performs the following processing. The color tone control unit 105 determines whether or not the value obtained by adding the minimum lightness difference (min_ΔL *) to the lightness (L * _back) of the graphic is equal to or smaller than lim_ΔL * _max (S1104).

  When the total value of the lightness (L * _back) and the minimum lightness difference (min_ΔL *) of the figure is larger than lim_ΔL * _max, the color tone control unit 105 executes processing of S1105 described later.

  On the other hand, when the value obtained by adding the minimum lightness difference (min_ΔL *) to the lightness (L * _back) of the graphic is equal to or smaller than lim_ΔL * _max, the color tone control unit 105 executes the following processing. The color tone control unit 105 corrects the lightness (L * _txt) of the character to a value obtained by adding the minimum lightness difference (min_ΔL *) to the lightness (L * _back) of the graphic (S1112). The process of S1112 corresponds to FIGS. 12B and 13B.

  Next, when the value obtained by adding the minimum lightness difference (min_ΔL *) to the lightness (L * _back) of the graphic is larger than lim_L * _max in S1104, the color tone control unit 105 executes the following processing.

  The color tone control unit 105 obtains an absolute value (tmp_max) of a value obtained by subtracting the brightness (L * _back) of the figure from the upper limit value (lim_L * _max) of the brightness. Further, the color tone control unit 105 obtains an absolute value (tmp_min) of a value obtained by subtracting the lower limit value (lim_L * _min) of the brightness from the brightness (L * _back) of the figure. Then, the color tone control unit 105 compares the values of tmp_max and tmp_min, and determines whether tmp_max is greater than or equal to tmp_min (S1105).

  When tmp_max is equal to or greater than tmp_min, the color tone control unit 105 corrects the lightness (L * _txt) of the character to lim_L * _max (S1106). The process of S1106 corresponds to FIGS. 12C and 13C.

  When tmp_max is less than tmp_min, the color tone control unit 105 corrects the lightness (L * _txt) of the character to lim_L * _min (S1113). The process of S1113 corresponds to FIGS. 12D and 13D.

  After executing any one of S1106, S1112, S1113, and S1114, the tone control unit 105 converts the lightness of the corrected character into a gray density (S1107). In step S1107, the color tone control unit 105 performs linear interpolation using the gray lightness conversion LUT illustrated in FIG. 10, and converts the lightness of the character into a gray density. The tone control unit 105 stores the gray density of the character in the character density buffer of the RAM 216.

  The processing when the brightness of the figure (L * _back) is less than the brightness of the character (L * _txt) in S1102 will be described below. The color tone control unit 105 determines whether the value obtained by adding the minimum lightness difference (min_ΔL *) to the lightness (L * _back) of the graphic is equal to or smaller than lim_L * _max (S1108). When the value obtained by adding the minimum brightness difference to the brightness of the graphic is equal to or smaller than lim_ΔL * _max, the color tone control unit 105 executes the following processing. The color tone control unit 105 corrects the lightness (L * _txt) of the character to a value obtained by adding the minimum lightness difference (min_ΔL *) to the lightness (L * _back) of the graphic (S1110). The process of S1110 corresponds to FIGS. 14A and 15A.

  On the other hand, when the value obtained by adding the minimum lightness difference (min_ΔL *) to the lightness (L * _back) of the graphic is larger than lim_L * _max, the color tone control unit 105 executes the process of step S1109. The color tone control unit 105 determines whether the value obtained by subtracting the minimum lightness difference (min_ΔL *) from the lightness (L * _back) of the graphic is equal to or larger than lim_L * _min (S1109).

  When the value obtained by subtracting the minimum lightness difference (min_ΔL *) from the lightness (L * _back) of the figure is equal to or larger than lim_L * _min, the color tone control unit 105 executes the following processing. The color tone control unit 105 corrects the lightness (L * _txt) of the character to a value obtained by subtracting the minimum lightness difference (min_ΔL *) from the lightness (L * _back) of the graphic (S1111). The processing described in S1111 corresponds to FIGS. 14D and 15D.

  In S1109, when the value obtained by subtracting the minimum lightness difference (min_ΔL *) from the lightness (L * _back) of the figure is less than lim_L * _min, the color tone control unit 105 executes the processing from S1105 onward. The processes after S1105 correspond to FIGS. 14C, 14D, and 15C, 15D. The subsequent processing is the same as the case where the lightness (L * _back) of the graphic is higher than the lightness (L * _txt) of the character, and thus the description thereof is omitted.

  In S1101 of FIG. 11, the color tone control unit 105 sets the maximum value of lightness (L * _max) and the minimum value of lightness (L * _min) based on the gray lightness conversion LUT. In step S1101, the color tone control unit 105 may use a predetermined maximum brightness value lim_L * _max and minimum brightness value lim_L * _min without referring to the gray brightness conversion LUT.

  As described above, according to the present embodiment, the minimum brightness difference is determined according to the character size for characters and graphics drawn in an overlapping manner, and the character density is adjusted so that the brightness difference between the characters and the figure is more than that. can do. That is, for single-color graphics and characters drawn in layers, the minimum density difference between the graphics and characters is determined according to the character size, and the character density is set so that the density difference between the characters and graphics is equal to or greater than the determined minimum density difference. adjust. As a result, the user can distinguish the background and the character regardless of the character size, and the color of the character and the character represented by different colors in the color image state are represented by the same gray. Can be suppressed.

  In the present embodiment, the lightness L * _txt of the color for drawing a character and the lightness L * _back of the color for drawing a graphic can be separated by a minimum lightness difference min_ΔL *. In addition, when the brightness that is separated from the brightness L * _back of the figure by the minimum brightness difference min_ΔL * is not a brightness color that can be drawn by the printer 214, the color control unit 105 causes the text brightness and the text brightness to be separated as much as possible. Determine the brightness. As a result, even if the brightness difference between the graphic and the character cannot be taken sufficiently, the brightness difference between the graphic and the character is increased as much as possible, and the printer 214 adjusts the density of the character so that the user can easily distinguish between the graphic and the character.

  In this embodiment, after the gray density is converted to lightness, it is determined whether the lightness difference between the character object and the graphic object is equal to or greater than the minimum lightness difference, and the color tone control unit 105 adjusts the lightness of the character object. . Instead of converting the gray density into lightness, it may be determined whether the density difference between the character object and the graphic object is equal to or greater than a predetermined density difference, and the density of the character object may be adjusted.

(Other examples)
In the present embodiment, the case has been described as an example in which a character object is drawn on the graphic object with the graphic object as the background. The present invention may be applied to a case where a graphic object of a line drawing image including only lines is drawn with a graphic object as a background. In this embodiment, when the printer 214 executes the processing written for the character object on the graphic object of the line drawing image, the density difference between the line drawing image drawn on the background graphic and the background graphic is increased. Can be corrected. In this case, the ROM 219 or the external memory 226 of the printer 214 stores a table for managing the line width and the minimum brightness difference (min_ΔL *) of the lines constituting the graphic object of the line drawing image. This table is a table corresponding to the character size brightness difference LUT shown in FIG. 9 of the present embodiment. This table is set such that the minimum brightness difference becomes smaller and the minimum brightness difference becomes smaller as the line width of the line constituting the graphic object becomes smaller and the line width becomes thicker.

  When the graphic object serving as the background and the graphic object of the line drawing image are drawn to overlap, the color tone control unit 105, based on the above table, determines the minimum lightness difference (min_ΔL *) based on the thickness of the line constituting the line drawing image. ) This processing is processing corresponding to S803 in FIG. 8 of the present embodiment. Other processes are the same as those in the case where the character object is replaced with the graphic object of the line drawing image in the present embodiment, and thus the description thereof is omitted. By doing this, it is possible to change the threshold value for determining whether or not to correct the lightness difference between the background and the line, according to the line width constituting the line drawing image drawn on the graphic object serving as the background. . When the line constituting the line drawing image is thin, the user can distinguish the background from the line drawing image by increasing the brightness difference between the background and the line. On the other hand, a line drawing image drawn with a thick line can suppress a plurality of line drawing images drawn with different colors with respect to the background from being drawn with the same gray density.

  In the present embodiment, the case where the density of the character is adjusted when the density difference between the background graphic and the character is less than the minimum brightness difference has been described. The density of the figure as the background may be adjusted. Further, the density of both the figure and the character as the background may be adjusted so that the brightness difference between the figure and the character is equal to or greater than the minimum brightness difference.

  Although the present invention has been described in detail based on the preferred examples thereof, the present invention is not limited to these specific embodiments, and various forms within the scope of the present invention are also included in the present invention. included. Moreover, you may combine suitably a part of above-mentioned embodiment.

  And this invention is implement | achieved also by performing the following processes. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, etc.) of the system or apparatus reads the program code. It is a process to be executed. In this case, the program and the storage medium storing the program constitute the present invention.

Claims (14)

An image processing apparatus capable of generating monochrome image data based on print data of a color image,
Extracting means for extracting a first object and a second object drawn on the first object from the color image print data;
Based on the minimum value of the density difference between the first object and the second object extracted by the extracting means, based on the size of the second object or the thickness of the line constituting the second object. A determination means to determine
Generating means for generating the monochrome image data in which the density difference between the first object and the second object is larger than the minimum value of the density difference determined by the determining means. Processing equipment. The image processing apparatus includes:
Conversion means for converting the first object and the second object extracted by the extraction means into a single-color object;
The determination unit is configured to determine the first object and the second object based on the size of the first object and the second object converted by the conversion unit or the thickness of a line constituting the second object. The image processing apparatus according to claim 1, wherein the minimum value of the density difference of the second object is determined. The first object is a graphic object, and the second object is a character object;
The determining means determines the minimum value of the density difference between the first object and the second object to a smaller value as the size of the second object increases.
The minimum value of the density difference between the first object and the second object is determined to be a larger value as the size of the second object becomes smaller. Image processing device.   When the density difference between the first object and the second object is smaller than the minimum value of the density difference determined by the determination means, the generation means is at least one of the first object and the second object. When the monochrome image data with one density adjusted is generated, and the density difference between the first object and the second object is larger than the minimum value of the density difference determined by the determination means, the first 4. The image processing apparatus according to claim 1, wherein the monochrome image data is generated without adjusting a density difference between the second object and the second object. 5. The image processing apparatus includes a table that associates a minimum value of a density difference between the first object and the second object and a size of the second object or a thickness of a line constituting the second object. A storage means for storing;
5. The determination unit according to claim 1, wherein the determination unit determines a minimum value of a density difference between the first object and the second object based on the table stored in the storage unit. The image processing apparatus according to one item. The image processing apparatus includes: a gray conversion unit that converts the first object of color and the second object of color into gray scale;
Brightness conversion means for converting the density of the first object and the second object converted to gray scale by the gray conversion means into lightness;
The determining means determines a minimum value of a brightness difference between the first object and the second object based on a size of the second object or a thickness of a line constituting the second object. And
The generation unit includes the monochrome image in which the brightness difference between the first object and the second object converted to gray scale by the gray conversion unit is larger than the minimum value of the brightness difference determined by the determination unit. The image processing apparatus according to claim 1, wherein data is generated.   The lightness conversion unit converts the density of the first object and the second object into lightness based on a lightness conversion table that associates the density of a single color with the lightness of a single color. Image processing device.   The said generation means adjusts the density | concentration of a said 2nd object to the value which deducted the minimum value of the density difference determined by the said determination means from the density | concentration of the said 1st object. The image processing apparatus according to any one of the above.   When the value obtained by subtracting the minimum value of the density difference determined by the determining unit from the first object is smaller than a predetermined first value, the generating unit determines the density of the second object. The image processing apparatus according to claim 8, wherein the image processing apparatus is adjusted to a value obtained by adding the minimum value of the density difference to the density of the first object.   The generation means is a case where a value obtained by subtracting a minimum value of the density difference determined by the determination means from the first object is smaller than the first value, and further, the density of the first object is When the value obtained by adding the determined minimum value of the density difference exceeds a predetermined second value, the density of the second object is set to the first value among the first value and the second value. The image processing apparatus according to claim 9, wherein the density is adjusted to a value far from the density of one object.   Based on information on the position where the first object is drawn on the sheet and the size of the first object, and information on the position where the second object is drawn on the sheet and the size of the second object, The image processing apparatus according to claim 1, further comprising a determination unit that determines whether or not the first object and the second object are drawn in an overlapping manner.   The image processing apparatus according to claim 1, wherein the second object is a graphic object composed of lines. A control method for an image processing apparatus capable of generating single-color image data based on print data of a color image,
An extraction step of extracting a first object and a second object drawn on the first object from print data of a color image;
The lowest density difference between the first object and the second object based on the size of the second object extracted in the extraction step or the thickness of the line constituting the second object. A decision step for determining a value;
A generation step of generating monochrome image data in which a density difference between the first object and the second object is larger than a minimum value of the density difference determined in the determination step based on the print data of the color image; And a method for controlling the image processing apparatus.   A program for causing a computer to execute the control method of the image processing apparatus according to claim 13.

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