JP2008087224A - Printing apparatus, printing method, and printing program - Google Patents

Abstract

A printing apparatus capable of efficiently executing correction processing and color conversion processing is provided.
A determination unit (core module 80) that determines whether or not to perform correction processing on image data, and a calculation unit (correction parameter calculation unit 20i) that calculates a correction parameter if it is determined to perform correction processing. The first correction means (image correction module 82) that executes the correction process of the image data based on the calculated correction parameter, and if it is determined not to perform the correction, the image data is corrected based on the fixed correction parameter. Color conversion processing based on a three-dimensional lookup table for second correction means (image correction module 82) that executes correction processing and image data that has been corrected by the first or second correction means Conversion means (color conversion module 84) for performing the above-described processing, and printing means (printing mechanism 50) for printing the color-converted image data on the printing paper. .
[Selection] Figure 2

Description

  The present invention relates to a printing apparatus, a printing method, and a printing program.

  2. Description of the Related Art Color printers are widely used as output devices that output color image data created using an image device such as a computer or color image data captured by an imaging device such as a digital camera.

  In recent years, as shown in Patent Document 1, for example, printing is performed after performing correction processing on image data so that the color of human skin becomes a natural color. Such correction processing is generally executed based on the obtained statistical information by sampling RGB color system image data to generate statistical information.

JP-A-11-008773 (abstract, claim)

  In a color printer, color image data is expressed using, for example, a CMYK (Cyan Magenta Yellow Black) color system. On the other hand, in digital cameras, computers, and the like, color image data is expressed using an RGB (Red Green Blue) color system. Therefore, when printing image data generated by a digital camera, a computer, or the like with a color printer, it is necessary to convert the color system. When converting these color systems, the conversion is generally performed with reference to a look-up table indicating the correspondence between the RGB color system and the CMYK color system.

  By the way, even when the above-described correction processing is not executed, conventionally, for the purpose of improving the appearance of the image, a special table is used as the above-described lookup table (the color is converted into a better-looking color at the time of color conversion). It was done to use. In other words, color conversion processing has been performed using two types of lookup tables for each of cases where there is no correction and whether there is correction.

  However, the lookup table needs to be prepared according to the combination of the type of printing paper, the type of ink, and the resolution. Therefore, in order to prepare a look-up table that can cope with these combinations for each case without correction and with correction, there is a problem that it is necessary to secure a storage area for storing the table. Moreover, the cost increase by that also becomes a problem.

  The present invention has been made based on the above circumstances, and the object of the present invention is to provide a printing apparatus, a printing method, a printing method, and a printing device capable of efficiently executing correction processing and color conversion processing. It is intended to provide a program.

  In order to achieve the above-described object, the printing apparatus of the present invention is determined to determine whether or not to perform correction processing on image data to be subjected to print processing, and to be determined to perform correction processing by the determination device. In such a case, the calculation unit that calculates the correction parameter for the image data, the first correction unit that executes the correction process of the image data based on the correction parameter calculated by the calculation unit, and the correction unit perform the correction process. If it is determined that there is no correction, the second correction unit that executes the correction process of the image data based on the fixed correction parameter, and the image data that has been corrected by the first or second correction unit Conversion means for performing color conversion processing based on the common color conversion information, and printing means for printing the image data color-converted by the conversion means on printing paper. To. Therefore, it is possible to provide a printing apparatus that can efficiently execute the correction process and the color conversion process.

  In addition to the above-described invention, in the printing apparatus according to another invention, the second correction unit executes a correction process for increasing at least one of brightness, contrast, and saturation. For this reason, even if it is a case where correction processing is not performed, a good-looking print image can be obtained.

  In addition to the above-described invention, in the printing apparatus of another invention, the second correction unit executes the correction process by changing the characteristic of the tone curve indicating the input / output characteristic. For this reason, various effects of the image can be given by changing the tone curve.

  In addition to the above-described invention, in the printing apparatus of another invention, the second correction unit has a correction parameter corresponding to the type of printing paper, and the correction is made according to the printing paper to be printed. The parameter is selected. For this reason, it is possible to obtain a good-looking print image regardless of what kind of printing paper is used.

  In addition to the above-described invention, the printing device according to another invention includes a plurality of color conversion information in the conversion unit, and the type of ink used by the printing unit, the type of printing paper, and / or the printing resolution. Depending on the color conversion information, the color conversion information is selected. For this reason, it is possible to obtain a good-looking print image regardless of the type of ink, the type of printing paper, and the printing resolution.

  In addition to the above-described invention, the printing apparatus according to another aspect of the invention calculates the correction parameter based on information obtained by sampling the image data, and the fixed correction parameter is the image data. Independent fixed parameters. For this reason, when correction is performed, optimal correction is performed based on the image data, and even when correction based on the image data is not performed, correction that improves the appearance of the image is performed based on a fixed parameter. Can do.

  Further, the printing method of the present invention determines whether or not to perform the correction process on the image data to be subjected to the printing process, and calculates the correction parameter for the image data when it is determined to perform the correction process. The image data correction process is executed based on the calculated correction parameter. On the other hand, if it is determined that the correction process is not performed, the image data correction process is executed based on the fixed correction parameter. The image data that has been subjected to the correction process based on the correction parameter or the fixed correction parameter is subjected to the color conversion process based on the common color conversion information, and the color-converted image data is printed on the printing paper. Like to do. Therefore, it is possible to provide a printing method capable of efficiently executing the correction process and the color conversion process.

  Further, the printing program of the present invention provides a determination unit that determines whether or not the computer performs correction processing on image data to be printed, and when the determination unit determines that correction processing is to be performed. Is determined to be not subjected to the correction process by the calculation means for calculating the correction parameter for the image data, the first correction means for executing the correction process of the image data based on the correction parameter calculated by the calculation means, and the determination means. In this case, the second correction unit that executes the correction process of the image data based on the fixed correction parameter, the common color conversion for the image data that has been corrected by the first or second correction unit. Function as conversion means for performing color conversion processing based on information, and printing means for printing image data color-converted by the conversion means on printing paper To. Therefore, it is possible to provide a printing program that can efficiently execute the correction process and the color conversion process.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is an external view showing a configuration example of a printing apparatus according to an embodiment of the present invention. As shown in FIG. 1, a printing apparatus 10 is a so-called composite printing apparatus in which a scanner device, a printing device, and a copying device are integrated. Here, the printing apparatus 10 includes a case 11 that covers the entire apparatus, a paper feeding device (not shown) that supplies printing paper, a scanner device that includes a transparent contact glass 13 on which a document is placed, a carriage 14, and the like. And a printing unit (not shown) for printing on the printing paper. The printing method and the printing program of the present invention will be described as operations of the printing apparatus 10.

  The case 11 is a substantially rectangular box, and a lid 12 that can be freely opened and closed is provided on the upper portion thereof. When the lid 12 is opened, the contact glass 13 on which the document is placed appears. Inside the contact glass 13, there is a carriage 14 provided with a light source 60 a and a light receiving unit 60 b described later. By moving the carriage 14 in the sub-scanning direction (the direction indicated by the arrow in the figure), the information printed on the document is read as image data. The scanner device is a so-called flat bed type (original fixed type) scanner that reads a fixed original while the carriage 14 moves in the sub-scanning direction.

  An LCD (Liquid Crystal Display) 40a is disposed at the center of the front surface of the case 11, and a touch panel 30b is disposed so as to overlap therewith. In addition, various operation buttons 30a are arranged in the vicinity thereof. The LCD 40a displays the menu, operation content, operation status, error content, and the like of the printing apparatus 10, and the operation button 30a is pressed when selecting the menu of the printing apparatus 10 or the like.

  The case 11 is provided with a discharge port 17 in the lower part of the front surface so that printed printing paper can be discharged. In addition, a card slot 18 is provided in the center of the right side of the front surface of the case 11 so that, for example, a memory card 70 for recording image data taken by a digital camera (not shown) can be detachably stored. It has become. In this example, the card slot 18 is provided with a lid 18a. When the memory card 70 is inserted, the lid 18a is opened and closed. The memory card 70 stores, for example, image data compressed in the JPEG format as a lossy compression method or the TIFF format as a lossless compression method.

  A paper feeding device (not shown) is provided on the back side of the case 11 and stocks printing paper and supplies printing paper one by one into the printing device 10 as needed.

  FIG. 2 is a block diagram illustrating an electrical configuration example of the printing apparatus 10. As shown in this figure, the printing apparatus 10 includes a main control unit 20, an information input unit 30, an information output unit 40, a print mechanism 50, and a scan mechanism 60 as main components.

  The main control unit 20 includes an input / output control unit 20a, a card I / F (Interface) 20b, a control unit 20c, a memory 20d, an image processing unit 20e, a printer control unit 20f, a buffer 20g, a scanner control unit 20h, and a correction. The parameter calculation unit 20i, a 3D-LUT (3 Dimensional Look Up Table) 20j as color conversion information, and a fixed correction parameter 20k are main components and are input from the information input unit 30. Based on the information, the information output unit 40, the print mechanism 50, the scan mechanism 60, and the like are controlled.

  More specifically, the input / output control unit 20a is an interface that appropriately converts the data representation format when information is exchanged between the information input unit 30 and the information output unit 40. When the memory card 70 is inserted, the card I / F 20b executes processing for reading image data from the memory card 70 and writing image data. The memory card 70 is constituted by, for example, a flash memory, and stores image data taken by a digital camera (not shown), for example.

  The control unit 20c is configured by, for example, a CPU (Central Processing Unit), and controls each unit of the apparatus based on a program 20d1 stored in the memory 20d. The image processing unit 20e performs a decoding process, an image correction process, and the like on the image data supplied from the control unit 20c. The printer control unit 20f controls the print mechanism 50 to print image data or the like on printing paper. The buffer 20g temporarily stores the image data supplied to the printer control unit 20f, and temporarily stores the image data supplied from the scanner control unit 20h. The scanner control unit 20h controls the scanning mechanism 60 and executes processing for optically reading image data printed on the printing paper.

  The correction parameter calculation unit 20i as a calculation unit calculates a correction parameter according to an instruction when automatic correction processing for image data is set. That is, the correction parameter calculation unit 20i is a parameter calculated based on information obtained as a result of sampling the image data. As will be described later, the 3D-LUT 20j is a table that is referred to when image data is color-converted, and has information for converting the RGB color system to the CMYK color system. The fixed correction parameter 20k has a predetermined fixed correction parameter.

  The information input unit 30 uses the operation buttons 30a and the touch panel 30b as main components, and generates and outputs information based on user operations. Here, the operation button 30a is a button arranged on an operation panel or the like, and generates and outputs information corresponding to a user operation. The touch panel 30b is arranged so as to be superimposed on an LCD (Liquid Crystal Display) 40a, and position information corresponding to the operated position is output by operating the touch panel 30b based on information displayed on the LCD 40a. .

  The information output unit 40 includes the LCD 40a and the lamp 40b as main components, and outputs information to be presented to the user. Here, the LCD 40a is superimposed on the touch panel 30b as described above, and displays the image data and the like supplied from the control unit 20c. The lamp 40b is arranged on an operation panel or the like, and indicates predetermined information to the user by turning on / off under the control of the control unit 20c.

  A printing mechanism 50 as a printing unit includes a recording head 50a, a scanning unit 50b, and a paper transport unit 50c as main components, and prints image data supplied from the control unit 20c on a printing paper. Here, for example, the recording head 50a appropriately discharges ink of each color corresponding to CMYK from a plurality of nozzles, and prints an image corresponding to printing paper. The scanning unit 50b moves the recording head 50a in the main scanning direction (direction orthogonal to the nozzle row of each color). The paper transport unit 50c moves the printing paper in the sub-scanning direction (direction parallel to the nozzle rows for each color).

  The scanning mechanism 60 has a light source 60a, a light receiving unit 60b, and a scanning unit 60c as main components, optically reads an image printed on a document, and generates and outputs corresponding image data. Here, the light source 60a is composed of, for example, a cold cathode tube, and irradiates white light onto an area of the original to be read. The light receiving unit 60b is configured by a CCD (Charge Coupled Device) or the like that receives the light irradiated by the light source 60a and reflected by the document and converts it into a corresponding electrical signal. The scanning unit 60c moves the light receiving unit 60b in the sub-scanning direction (direction perpendicular to the longitudinal direction of the light receiving unit (the direction of the arrow in FIG. 1)).

  FIG. 3 shows functional blocks realized by the cooperation of the program 20d1 as the software shown in FIG. 2 and hardware including the control unit 20c. As shown in this figure, the functional blocks include a core module 80, a resolution conversion module 81, an image correction module 82, a color conversion module 84, a gradation number conversion module 85, an interlace module 86, and correction parameter calculation units 20i, 3D- It has an LUT 20j and a fixed correction parameter 20k.

  Here, the core module 80 serving as a determination unit is a module serving as a core (core) of each module, and a process described later is executed by connecting the modules by this module. The resolution conversion module 81 is a module that performs processing for converting the resolution of the image data supplied from the core module 80 into a resolution for printing by the print mechanism 50. The correction parameter calculation unit 20i is the same as that shown in FIG. 2, and calculates parameters for correcting image data. The image correction module 82 as the first correction unit and the second correction unit is a module that performs correction processing on the image data based on the correction parameter supplied from the correction parameter calculation unit 20 i or the fixed correction parameter 20 k. .

  The fixed correction parameter 20k supplies a fixed correction parameter stored in advance to the image correction module 82 when it is set not to execute the correction process as a printing condition. That is, the fixed correction parameter 20k is a predetermined parameter and is an independent parameter that does not depend on the image data. The color conversion module 84 as conversion means refers to the 3D-LUT 20j and executes processing for converting image data expressed in the RGB color system into the CMYK color system. The 3D-LUT 20j is the same as that shown in FIG. 2, and has information (details will be described later) necessary for executing color conversion. The gradation number conversion module 85 is a module that executes processing for converting the image data (256 gradation data) subjected to color conversion by the color conversion module 84 into the gradation number that can be expressed by the print mechanism 50. .

  The interlace module 86 is a module that performs processing for rearranging image data in consideration of the order in which dots are formed by the recording head 50a when the image data is printed by the print mechanism 50.

  Next, the operation of the above embodiment will be described. Below, with reference to FIG. 4, after demonstrated the outline | summary of operation | movement of embodiment of this invention, detailed operation | movement is demonstrated based on FIGS.

  First, the outline of the operation of the embodiment of the present invention will be described with reference to FIG. FIG. 4A is a diagram for explaining the outline of the operation according to the embodiment of the present invention. As shown in this figure, in the embodiment of the present invention, first, the presence / absence of image correction is determined (P10), and when correction processing is executed (Y), the correction parameter calculation unit 20i responds to the image data. The correction parameters are calculated (P11), and image correction processing is executed by the image correction module 82 (P12). Then, the image data subjected to the image correction processing is subjected to color conversion by referring to the 3D-LUT 20j (P15) by the color conversion module 84 (P16). On the other hand, when the correction process is not executed, the correction process is executed by the image correction module 82 with reference to the fixed correction parameter 20k (P14) (P13). Then, the image data subjected to the image correction is subjected to color conversion by referring to the 3D-LUT 20j (P15) by the color conversion module 84 (P16) as in the case described above.

  FIG. 4B is a diagram for explaining the outline of the conventional operation. As shown in this figure, in the conventional method, first, the presence / absence of image correction is determined (P20), and when correction processing is executed (Y), correction parameters corresponding to the image data are calculated (P21). Then, image correction processing is executed (P22). Then, the image data subjected to the image correction process is subjected to color conversion with reference to the 3D-LUT for correction process (P23) (P24). On the other hand, when the correction process is not executed, the correction process is not executed, and the 3D-LUT for no correction is referred to (P26) and color conversion is performed (P25). Note that the 3D-LUT for no correction executes image quality improvement processing in combination with color conversion processing, so that a good-looking print image is obtained by using this LUT.

  From these comparisons, in the conventional method shown in FIG. 4B, when executing the correction process, the color conversion process is executed with reference to the 3D-LUT for correction, while the correction process is executed. When not executed, the color conversion processing is executed with reference to the 3D-LUT for no correction. For this reason, two types of 3D-LUTs with and without correction are required. Since the 3D-LUT needs to be prepared according to the type of printing paper, the type of ink, and the like, considering these combinations, a large number of 3D-LUTs are required, and the storage capacity of the memory is required.

  On the other hand, in the embodiment of the present invention shown in FIG. 4A, the image quality improvement processing executed by the conventional 3D-LUT for no correction is replaced by image correction processing (P13) by the image correction module 82. Yes. This makes it possible to use a common 3D-LUT with and without correction, so that the 3D-LUT without correction in the case of FIG. 4B can be omitted. The required storage capacity of the memory can be reduced.

  Next, the detailed operation of the embodiment of the present invention will be described with reference to FIG. FIG. 5 shows processing executed when predetermined image data stored in the memory card 70 is selected and printing is instructed in the embodiment shown in FIG. In the following processing, the program 20d1 stored in the memory 20d shown in FIG. 2 is executed, and the program 20d1 as software cooperates with hardware including the control unit 20c. Realized.

  Step S10: When the user selects predetermined image data stored in the memory card 70 by operating the operation button 30a or the touch panel 30b, the control unit 20c acquires the image data from the memory card 70, and the LCD 40a To display. Specifically, the control unit 20c acquires image data subjected to JPEG compression from the memory card 70, and supplies the image data to the image processing unit 20e. The image processing unit 20e decodes the supplied image data by performing Huffman decompression, inverse quantization processing, inverse DCT (Discrete Cosine Transform) processing, color conversion (conversion from YCC to RGB), and the like. To do. Then, the image data is thinned according to the display size of the LCD 40a, and the obtained image data is converted into a video signal, which is then supplied to the LCD 40a via the input / output control unit 20a for display.

  Step S11: When the user understands that the image is the target image by referring to the image displayed on the LCD 40a, the control unit 20c displays a graphical user interface (GUI) on the LCD 40a, and displays the print condition. Receive settings. That is, the control unit 20c receives settings for print resolution, print paper type, ink type, necessity of image correction, and the type thereof. More specifically, as the print resolution, the number of dots to be printed per unit length is specified. In general, the higher the resolution, the higher the print quality, but the time required for printing tends to increase. Normally, a value set as a standard is used as the print resolution. However, the printer can also set the print resolution as necessary. As the type of printing paper, the type of printing paper set in the printing apparatus 10 is set. In principle, it is necessary to set the product name of the printing paper for the type of printing paper, but if the standard printing paper is recommended by the printer manufacturer, select a setting such as “Glossy Paper” or “Exclusive Glossy Paper”. You can also In this embodiment, one of “plain paper” and “exclusive paper” is selected. As the ink type, the type of ink currently installed in the printing apparatus 10 is set. Since the ink type is described on the side of the ink cartridge, this value is input. Some ink cartridges have an IC chip embedded therein, and some information such as ink type and date of manufacture is stored in the IC chip. When the printing apparatus 10 is compatible with an ink cartridge having an IC chip mounted thereon and information in the IC chip can be read from the mounted ink cartridge, the ink type information is automatically read.

  The necessity of image correction and the type thereof are selected, for example, from “with correction processing” and “without correction processing” as image correction. Here, the correction process means that the printing apparatus 10 automatically executes the correction process based on the attribute information of the image data. As attribute information, statistical value information obtained by directly sampling image data can be used. Other than this, for example, information included in the header of PIM (Print Image Matching) information and Exif (Exchangeable Image File Format) can be used. Further, manual correction processing in which the user directly sets the correction content by manual operation may be included in “with correction processing”. On the other hand, “no correction process” means that the above-described correction process is not executed. The information input as described above is supplied to the core module 80.

  Step S12: The resolution conversion module 81 performs a process of converting the resolution of the image data selected by the process of Step S10 into a resolution when the print mechanism 50 prints on the printing paper (hereinafter referred to as “printing resolution”). Execute. Specifically, when the resolution of the image data is lower than the printing resolution, the resolution conversion module 81 performs linear interpolation to generate new data between adjacent image data, and conversely, when the resolution is higher than the printing resolution. First, the resolution of the image data is converted to the printing resolution by thinning out the data at a certain rate.

  Step S13: The core module 80 refers to the printing conditions acquired in step S11 to determine whether or not “correction processing is present” is set. If the correction processing is present, step S16 is performed. Otherwise, go to step S14. For example, if no correction processing is set, the process proceeds to step S14.

  Step S14: The image correction module 82 acquires a parameter corresponding to the printing condition from the fixed correction parameter 20k. Here, the fixed correction parameter is a parameter for performing processing that substitutes for the color conversion processing that is executed using the non-correction 3D-LUT shown in FIG.

  FIG. 6 is a diagram showing the contents of the fixed correction parameter 20k for each of plain paper and dedicated paper. As shown in this figure, on plain paper, the contrast is unchanged (+0), the lightness is increased by “34”, and the saturation is increased by “5”. The tone curve indicating the input / output characteristics is adjusted so that the input (IN) “45” and “195” are mapped to the output (OUT) “182” and “36”, respectively. FIG. 7A shows a tone curve used for correction of plain paper. In this figure, the horizontal axis indicates the input of gradation values (IN), and the vertical axis indicates the output of gradation values (OUT). The tone curve indicating the input / output characteristics is a curve that passes through the coordinates (45, 36) and the coordinates (195, 182). Thereby, an image in which the brightness of the intermediate portion is suppressed is obtained.

  On the other hand, in the special paper, the contrast is increased by “2”, the lightness is increased by “27”, and the saturation is increased by “5”. The tone curve is adjusted so that “195” of the input (IN) is mapped to “182” of the output (OUT). FIG. 7B shows a tone curve of gradation values used for correction of dedicated paper. The tone curve indicating the input / output characteristics is a curve passing through the coordinates (195, 182). Thereby, an image in which the brightness above the intermediate portion is suppressed is obtained.

  Note that the content of the correction processing described above is an example, and the present invention is not limited to such content. For example, the contrast, brightness, and saturation correction values may be set to values other than those shown in FIG. Further, not all of the contrast, brightness, and saturation may be corrected, but correction may be performed by any one or a combination of these. Further, with respect to the tone curve shown in FIG. 7, the curve shown is merely an example, and may have other characteristics. Alternatively, the correction using the tone curve may not be performed. Whether or not the correction is optimal is determined by the characteristics of the paper, the characteristics of the ink, and the like, so various modes are conceivable. In addition, since whether or not it is optimal depends on the user's preference, the fixed correction parameter 20k may be freely edited by the user.

  Step S15: The image correction module 82 performs a correction process on the image data based on the fixed correction parameter 20k acquired in step S14. Specifically, based on the fixed correction parameter 20k (see FIG. 6) acquired in step S14, correction is performed to increase the contrast, brightness, and saturation of the image data, and in accordance with the tone curve shown in FIG. Adjust the image brightness.

  Correction for increasing the contrast can be realized by converting the pixel value using a tone curve having S-shaped input / output characteristics. The correction for increasing the brightness can be realized, for example, by increasing the pixel value by a specified value and outputting it for all the pixels in the image. As correction for increasing the saturation, for example, the pixel values before correction are R, G, B, the pixel values after correction are R ′, G ′, B ′, and the luminance is Y (= 0.30R + 0.59G + 0). .11B) and the correction coefficient is α (> 1), the relationship between R ′, G ′, B ′ and R, G, B is expressed by the following equation. The saturation can be increased by setting the correction coefficient α in accordance with the value shown in FIG.

R ′ = R + (R−Y) × α (1)
G ′ = G + (G−Y) × α (2)
B ′ = B + (BY) × α (3)

  Further, the correction by the tone curve can be corrected based on a table having the same characteristics as the tone curve shown in FIG. Note that the correction processing described above is an example, and correction processing other than these may be performed, or correction processing may be executed by a method other than the above-described correction processing.

  At this time, when printing the image data, the image correction module 82 decodes the image data (Huffman decompression and inverse quantization) if rotation of the image is necessary (rotation), and rotates information ( A process of acquiring an address indicating the leftmost block of the image in the image data is also executed.

  Through the above processing, the image quality of the image data can be improved as in the case of the 3D-LUT for no correction shown in FIG.

  Step S16: The correction parameter calculation unit 20i calculates a correction parameter. That is, the correction parameter calculation unit 20i performs Huffman decompression, inverse quantization, inverse DCT calculation, and color conversion processing (processing for converting the YCC color system to RGB / HSB) on the image data. Calculate the histogram of the image data. Then, a correction parameter is calculated based on the histogram. Specifically, the correction parameter calculation unit 20i calculates, for example, a correction parameter that makes the skin color of a person as a subject close to a color (memory color) stored in advance.

  Step S17: The image correction module 82 performs a correction process on the image data based on the correction parameter calculated in step S16. Specifically, processing for correcting the brightness, contrast, saturation, hue, and the like of the image data is executed based on the correction parameter calculated in step S16.

  At this time, when printing the image data, the image correction module 82 obtains rotation information (address indicating the leftmost block of the image in the image data) when the image needs to be rotated. Are also executed.

  Step S18: The color conversion module 84 performs color conversion processing on the image data that has been corrected by the image correction module 82 with reference to the 3D-LUT 20j.

  FIG. 8 is a diagram conceptually showing a 3D-LUT (color conversion table). If each gradation value of RGB is taken on each axis of a three-dimensional orthogonal coordinate, each gradation value of RGB can take a value from 0 to 255. Therefore, as shown in FIG. It can be expressed as coordinates inside the cube. Such a cube is called a color solid. The 3D-LUT is a numerical table in which color solids are subdivided into a grid and the gradation values of each color of CMYK are stored at each grid point. By referring to the 3D-LUT, the color conversion process can be performed quickly as follows. For example, when converting colors whose R, G, B gradation values are represented by RA, GA, BA, respectively, the point A of the coordinates (RA, GA, BA) in the color solid is considered and the point A is included. Find a small cube (dV). Then, by reading out the gradation values of each color of C, M, Y, K stored in each vertex of this cube and performing interpolation for each color from the read gradation values, C, M, Y at point A , K gradation values can be calculated.

  Depending on the type of ink used for printing and the combination with the printing paper, the color of the ink may differ slightly. Therefore, color conversion processing is performed with reference to a suitable 3D-LUT according to the combination of the ink and the printing paper. It is desirable to do.

  Further, as described with reference to FIG. 8, in the color conversion process, the gradation values stored in the grid points are interpolated for each color, so that the gradation values of C, M, Y, and K are calculated. The color conversion accuracy tends to increase as the interval between the lattice points decreases, that is, as the number of lattice points stored in the 3D-LUT increases. In particular, it is desirable to use a 3D-LUT having a large number of grid points for each combination with a standard ink type for dedicated printing paper used when printing a high-quality image.

  Also, a 3D-LUT dedicated to a specific image device can be used. That is, when printing a color image taken using an image device such as a digital camera, a higher quality image can be printed by using a dedicated 3D-LUT for the following reasons. . That is, when printing a color image taken using an image device such as a digital camera, the color of the printed image may differ slightly depending on the model of the image device taken. This is because the characteristics of the elements that detect R, G, and B colors from the video to be photographed and convert them into RGB image data may differ depending on the type of image equipment. Similarly, the detectable light intensity and wavelength range may vary depending on the model of the imaging device. Therefore, the range of colors (gamut) that can be reproduced as a printed image may differ depending on the model that captures the image. Normally, color image data that has been corrected once to a standard characteristic called sRGB is handled in order to reduce the difference in characteristics among these devices, but some correction errors are mixed or expressed during correction. The possible gamut may become narrower. On the other hand, if the image device that captured the color image is specified, color conversion can be performed so that the color as captured is reproduced, so that a high-quality image can be printed. Become.

  The color conversion module 84 selects an optimal 3D-LUT from the 3D-LUT 20j according to the printing conditions acquired in step S11, and executes a color conversion process based on the selected 3D-LUT. As a result, color conversion processing according to printing conditions is executed, and image data expressed in the RGB color system is converted into the CMYK color system.

  Step S19: The gradation number conversion module 85 performs a process for reducing the gradation number on the image data that has undergone color conversion. That is, the image data after color conversion is data having 256 gradation widths for each color. In contrast, the printing mechanism 50 according to the present embodiment can take only one of the states of “forming dots” and “not forming dots”. That is, the print mechanism 50 of this embodiment can only express two gradations locally. Therefore, it is necessary to convert image data having 256 gradations into image data expressed in 2 gradations that the print mechanism 50 can express.

  As a method of converting the number of gradations of image data, various methods such as a method called an error diffusion method and a method called a systematic dither method are known. In the error diffusion method, an error caused by converting the number of gradations of a certain pixel is diffused to surrounding pixels, and when the gradation number conversion of surrounding pixels is performed, the diffused error is minimized. This is a method for converting the number of gradations. When the gradation number conversion process is performed using the error diffusion method, the gradation number conversion process is performed so as to reduce the error, so that a high-quality image is generally obtained. In the systematic dither method, a threshold value of 0 to 255 is uniformly set for each pixel of a matrix called a dither matrix, and the magnitude relationship between the image data and the threshold value set in the dither matrix is compared, and the image In this method, a dot is formed for a pixel having a larger data and a dot is not formed for a pixel having a larger threshold. The gradation number conversion module 85 executes processing for converting the gradation number based on any one of these methods.

  Step S20: The interlace module 86 performs interlace processing on the image data that has been subjected to tone number conversion. That is, as described above, the print mechanism 50 prints an image by forming dots at appropriate timing while the recording head 50a that discharges ink of each color is main-scanned and sub-scanned on the printing paper. That is, dots are not necessarily formed in the order of image data. Therefore, it is necessary to rearrange the image data in the order to be transferred to the print mechanism 50 while considering the order in which dots are formed by the print mechanism 50. The interlace module 86 executes such a process called an interlace process.

  Step S21: The interlaced image data is temporarily stored in the buffer 20g and then supplied to the printing mechanism 50 via the printer control unit 20f and printed on printing paper. That is, the print mechanism 50 acquires image data for one scanning line from the printer control unit 20f, and ejects ink of a corresponding color by the recording head to record it on the printing paper. At this time, the scanning unit 50b moves the recording head 50a in the main scanning direction (a direction orthogonal to the nozzle row for ejecting ink), and the paper transport unit 50c moves the printing paper in the sub-scanning direction (a direction parallel to the nozzle row). Move to. By repeating such an operation, the image data is printed on the printing paper.

  As described above, according to the embodiment of the present invention, the image data improvement processing that has been conventionally performed using the non-correction 3D-LUT is performed by the image correction processing using the fixed correction parameter 20k. Since the replacement is made, the size of the 3D-LUT 20j can be reduced. For this reason, the required amount of memory for storing the 3D-LUT 20j can be reduced. This contributes particularly to reducing the cost of a so-called stand-alone type printing apparatus that can print image data without connecting a host computer.

  Further, in the embodiment of the present invention, the improvement processing of the image data that has been executed using the 3D-LUT for no correction is replaced by the image correction processing using the fixed correction parameter 20k. An image correction process that is a process can be used. The trouble of adding a new program module can be omitted.

  The above embodiment is merely an example, and there are various other modified embodiments. For example, in the above embodiment, the memory card 70 is inserted into the card I / F 20b and image data is read out. For example, a digital camera (not shown) is connected to the input / output control unit 20a by a cable (not shown). The image data may be read out via the cable. Further, the table shown in FIG. 7 may be stored in the memory of the digital camera.

  In the above embodiments, the case where the RGB color system is converted to the CMYK color system as the color conversion process has been described as an example. However, the present invention can be applied to other color conversions. Needless to say. For example, it may be a CMY color system, or a color system obtained by adding LM (Light Magenta) and LC (Light Cyan) to CMYK.

  In the above embodiment, the gradation number conversion module 85 converts 256 gradations into two gradations with or without dots. For example, three gradations of large dots, medium dots, and small dots are used. It is also possible to convert to four gradations consisting of a combination of two dots, or to convert to other gradations.

  In the above embodiment, the fixed correction parameter adjusts contrast, lightness, and saturation according to the type of printing paper, and performs adjustment by tone curve. These may be adjusted according to the resolution.

  In the above embodiment, the 3D-LUT is selected according to the combination of ink type and printing. For example, as another element, the 3D-LUT is considered in consideration of the print resolution and the like. May be selected.

  In the above embodiment, the description has been given by taking the composite type printing apparatus as an example, but the present invention is applied to a normal printing apparatus (printing apparatus of a type connected to a personal computer). be able to. In addition, the present invention can be applied to a normal stand-alone printing apparatus that is not a composite type.

  In the above embodiment, the processing illustrated in FIG. 5 is executed in the printing apparatus 10, but can be executed in, for example, a host computer connected to the printing apparatus 10.

  The above processing functions can be realized by a computer. In this case, a program describing the processing contents of the functions that the printing apparatus should have is provided. By executing the program on a computer, the above processing functions are realized on the computer. The program describing the processing contents can be recorded on a computer-readable recording medium. Examples of the computer-readable recording medium include a magnetic recording device, an optical disk, a magneto-optical recording medium, and a semiconductor memory. Examples of the magnetic recording device include a hard disk device (HDD), a flexible disk (FD), and a magnetic tape. Examples of the optical disc include a DVD (Digital Versatile Disk), a DVD-RAM, a CD-ROM (Compact Disk ROM), and a CD-R (Recordable) / RW (ReWritable). Magneto-optical recording media include MO (Magneto-Optical disk).

  When distributing the program, for example, portable recording media such as a DVD and a CD-ROM in which the program is recorded are sold. It is also possible to store the program in a storage device of a server computer and transfer the program from the server computer to another computer via a network.

  The computer that executes the program stores, for example, the program recorded on the portable recording medium or the program transferred from the server computer in its own storage device. Then, the computer reads the program from its own storage device and executes processing according to the program. The computer can also read the program directly from the portable recording medium and execute processing according to the program. In addition, each time the program is transferred from the server computer, the computer can sequentially execute processing according to the received program.

1 is an external view showing an external appearance of a printing apparatus according to an embodiment of the present invention. It is a figure which shows the structural example of the printing apparatus which concerns on embodiment of this invention. It is an example of the functional block implement | achieved in embodiment shown in FIG. It is a figure which shows the outline | summary of operation | movement of embodiment of this invention and the conventional method. It is an example of the flowchart performed in embodiment shown in FIG. It is a figure which shows the content of the correction process for every printing paper. It is a figure which shows an example of a tone curve. It is a figure for demonstrating the outline | summary of 3D-LUT.

Explanation of symbols

  10 printing apparatus, 20i correction parameter calculation unit (calculation means), 20j 3D-LUT (three-dimensional lookup table), 50 printing mechanism (printing means), 80 core module (determination means), 82 image correction module (first Correction means, second correction means), 84 color conversion module (conversion means)

Claims (8)

Determining means for determining whether or not to perform correction processing on image data to be printed;
A calculation means for calculating a correction parameter for the image data when the determination means determines that correction processing is to be performed;
First correction means for executing correction processing of image data based on the correction parameter calculated by the calculation means;
A second correction unit that executes a correction process on the image data based on a fixed correction parameter when the determination unit determines that the correction process is not performed;
Conversion means for performing color conversion processing on the image data subjected to correction processing by the first or second correction means based on common color conversion information;
Printing means for printing the image data subjected to color conversion on the printing paper by the conversion means;
A printing apparatus comprising:   The printing apparatus according to claim 1, wherein the second correction unit executes a correction process for increasing at least one of brightness, contrast, and saturation.   The printing apparatus according to claim 1, wherein the second correction unit executes correction processing by changing a characteristic of a tone curve indicating input / output characteristics.   2. The second correction unit has a correction parameter corresponding to the type of printing paper, and selects the correction parameter according to the type of printing paper to be printed. The printing apparatus as described.   The conversion unit has a plurality of the color conversion information, and selects the color conversion information according to the type of ink used by the printing unit, the type of the printing paper, and / or the printing resolution. The printing apparatus according to claim 1, wherein: The correction parameter is calculated by the calculation means based on information obtained by sampling the image data,
The fixed correction parameter is a fixed parameter independent of the image data.
The printing apparatus according to claim 1. Determine whether to perform correction processing on the image data to be printed,
If it is determined that correction processing is to be performed, a correction parameter for the image data is calculated,
Based on the calculated correction parameter, the image data correction process is executed,
On the other hand, when it is determined that the correction process is not performed, the image data correction process is executed based on the fixed correction parameter,
Applying color conversion processing based on common color conversion information to image data that has been subjected to correction processing based on the calculated correction parameter or fixed correction parameter,
Print color-converted image data on printing paper,
A printing method characterized by the above. Computer
Determination means for determining whether or not to perform correction processing on image data to be printed;
A calculation unit that calculates a correction parameter for the image data when the determination unit determines that the correction process is to be performed;
First correction means for executing correction processing of image data based on the correction parameter calculated by the calculation means;
A second correction unit that executes a correction process on the image data based on a fixed correction parameter when the determination unit determines that the correction process is not performed;
Conversion means for performing color conversion processing based on common color conversion information on the image data subjected to correction processing by the first or second correction means;
Printing means for printing the image data subjected to color conversion by the conversion means on a printing paper;
A computer-readable printing program characterized in that it functions as a computer program.

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