JP2004320190A - Conversion table creation method, printing method, conversion device, and printing device - Google Patents

Abstract

An object of the present invention is to provide a method of creating a color conversion table with a small color shift of gray.
A method for creating a conversion table for converting a gray value to a non-gray value, comprising the steps of: determining a predetermined value in an L * a * b * color space as a converted non-gray value; Determining a white point in the L * a * b * color space such that the white point belongs to the same quadrant to which the predetermined value belongs in the a * b * color plane, Defining a target axis such that at least a value on the target axis between the predetermined value and the white point belongs to a quadrant; Creating a conversion table for converting to a non-gray value on an axis.
[Selection diagram] FIG.

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a conversion table creation method, a printing method, a conversion device, and a printing device.
[0002]
[Background technology]
The achromatic color in the RGB space is theoretically a value on the L * axis in the L * a * b * space. However, in consideration of human visual characteristics, it is empirically known that achromatic color in the RGB space is more natural to humans when it is shifted from the L * axis in the L * a * b * space. Have been.
[0003]
As a color conversion method considering such human visual characteristics, there is a method disclosed in JP-A-2002-118762 (Patent Document 1). The color conversion method disclosed in Patent Document 1 enables more faithful color reproduction by shifting the gray axis from the logical L * axis in the L * a * b * space.
[0004]
[Patent Document 1]
JP-A-2002-118762
[Problems to be solved by the invention]
However, in the conventional color conversion method disclosed in Patent Literature 1, the gray axis is not determined in consideration of the relationship between the white point and the medium lightness. This causes a problem that an appropriate gray color is not reproduced on a print medium.
[0006]
Therefore, an object of the present invention is to provide a conversion table creation method, a printing method, a conversion device, and a printing device that can solve the above-described problems. This object is achieved by a combination of features described in the independent claims. The dependent claims define further advantageous embodiments of the present invention.
[0007]
[Means for Solving the Problems]
To achieve the above object, according to a first aspect of the present invention, there is provided a method for creating a conversion table for converting a gray value into a non-gray value, wherein L * a * b * Determining a predetermined value in the color space; and converting the L * a * b * color so that the converted non-gray value belongs to the same quadrant as the predetermined value in the a * b * color plane. Determining a white point in space; and a target axis passing through the predetermined value and the white point, wherein the target axis is set so that at least a value on the target axis between the predetermined value and the white point belongs to the quadrant. Defining a conversion table for converting a gray value on the L * axis to a non-gray value on the target axis. To. Accordingly, at least between the predetermined value and the white point, the non-gray value does not belong to a plurality of quadrants across the a * axis and / or the b * axis, so that the non-gray value is a color represented by the non-gray value. Gray color fluctuation can be suppressed. As a result, a non-gray color of the input image can be appropriately reproduced.
[0008]
Further, the conversion table creating method further includes a step of determining a black point in the L * a * b * color space as a non-gray value after the conversion so as to belong to the quadrant. Preferably, the target axis is further defined such that the value between the black point and the white point passes through the point and belongs to the quadrant. Thereby, in the L * a * b * color space, the color fluctuation of the non-gray color from the white point to the black point can be suppressed.
[0009]
According to a second aspect of the present invention, a step of converting a gray value on the L * axis in an input image into a non-gray value on a target axis based on the conversion table created by the conversion table creation method. And printing the input image on a print medium based on the converted non-gray value. Thus, at least between the predetermined value and the white point, non-gray color fluctuation of the input image reproduced on the print medium can be suppressed. That is, the non-gray color of the input image can be appropriately reproduced on the print medium.
[0010]
The printing method further includes a step of creating a conversion table corresponding to each of the plurality of types of print media, and a step of selecting a conversion table based on the type of print medium on which the input image is printed. Preferably, the step of converting to gray values converts gray values on the L * axis in the input image to non-gray values on the target axis based on the selected conversion table. As a result, a conversion table suitable for the type of print medium can be selected, so that a non-gray color of the input image can be reproduced on the print medium with less color fluctuation.
[0011]
Preferably, the printing method further includes a step of preparing white ink for printing the input image, and the step of determining the white point preferably determines the white point based on the color of the white ink. Accordingly, the white point and the gray target can be set in the same quadrant according to the color of the white ink to be used, so that the non-gray color fluctuation of the input image can be suppressed.
[0012]
Further, the step of determining the white point is such that the white point belongs to the quadrant when the input image printed on the print medium is observed under the standard light D50 and when the input image is observed under the standard light A. It is preferable to determine the white point as follows. Thus, even when the printed input image is viewed under a plurality of viewing environments, a non-gray color of the input image can be reproduced with little color fluctuation.
[0013]
According to a third aspect of the present invention, there is provided a method for creating a conversion table for converting a gray value into a non-gray value, wherein a white point in an L * a * b * color space is defined as the converted non-gray value. Determining the converted non-gray values in the L * a * b * color space as the converted non-gray values so that they belong to the same quadrant to which the white point belongs in the a * b * color plane. Defining a predetermined value; and defining a target axis passing through the white point and the predetermined value, wherein at least a value on the target axis between the white point and the predetermined value belongs to a quadrant. And a step of creating a conversion table for converting gray values on the L * axis into non-gray values on the target axis. To provide. This makes it possible to suppress the non-gray color fluctuation of the input image at least between the predetermined value and the white point.
[0014]
Preferably, in the step of determining a white point, the white point is determined based on a color of the print medium. Thus, the white point and the gray target can be set in the same quadrant according to the color of the print medium to be used, so that the non-gray color fluctuation of the input image can be suppressed.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described through embodiments of the present invention with reference to the drawings, but the following embodiments do not limit the invention according to the claims and are described in the embodiments. Not all combinations of features are essential to the solution of the invention.
[0016]
FIG. 1 is a block diagram illustrating a hardware configuration of a printer system 1 according to the embodiment of the present invention. As shown in FIG. 1, the printer system 1 may be a host device 10 and a communication network (LAN, the Internet, a dedicated line, a packet communication network, a combination thereof, or the like, including both wired and wireless communication). ), And a printer device 20 configured to be able to communicate with the host device 10 via the printer.
[0017]
The host device 10 is configured to include hardware such as a CPU (processor), a ROM, a RAM, an I / O controller, and a communication interface. The CPU is configured to be able to access each unit via an internal bus. I have.
[0018]
The host device 10 has the same function as an information processing device such as a normal personal computer. For example, the host device 10 accepts various inputs from a user via an I / O controller or the like / input / output means 11 for outputting information, and transmits / receives various data to / from another device via a communication interface. A communication unit 12, a printer driver unit 13 for controlling a printer, and the like are provided (see FIG. 2). Each of these units is functionally realized by the CPU executing a program stored in a ROM or a RAM in the host device 10 or an external storage medium.
[0019]
Here, the printer driver 13 included in the host device 10 has the same functional configuration as a normal printer driver. For example, a print job is created based on a predetermined printer control language in response to a print request from an application program running on the host device 10, and the print job is transmitted to the printer device 20.
[0020]
However, as will be described later, the printer driver unit 13 of the present embodiment has a predetermined value in the L * a * b * color space, which is a non-gray value after conversion, and a predetermined value in the a * b * color plane. A non-gray value on the target axis passing through a white point belonging to the same quadrant as the quadrant to which the value belongs, wherein at least a value on the target axis between the predetermined value and the white point belongs to the quadrant; * It differs from the conventional configuration in that it is configured to be able to refer to a conversion table (see FIG. 2) that associates gray values on the axis.
[0021]
The printer device 20 includes a paper feed mechanism that supplies print paper, which is an example of a print medium, into a printer, a print engine that performs printing, and a power mechanism that includes a paper discharge mechanism that discharges print paper outside the printer. Is provided. The print engine includes a paper feed mechanism, a carriage mechanism, a print head, an ink cartridge that stores a plurality of colors of ink including white ink, and the like.
[0022]
As the print engine, various print engines such as a serial printer that prints in units of one character, a line printer that prints in units of lines, and a page printer that prints in units of pages, such as an ink jet printer, can be used.
[0023]
It is an information processing unit including a CPU (processor), a ROM, a RAM, an LCD panel and an LCD controller, a communication interface, and the like that controls these power mechanism units to perform a printing operation. The CPU is configured to be able to access each unit via an internal bus, and controls a power mechanism to actually perform a printing operation according to a print job sent from the host device 10 via a communication interface, for example. Let Note that the power mechanism unit may independently include a CPU. In this case, the CPU of the power mechanism unit communicates with the CPU of the information processing unit via a parallel interface or the like to control the print engine. The printing operation is performed.
[0024]
The configuration and operation of the printer 20 are basically the same as the configuration and operation of the conventional printer (see FIG. 2). For example, the printer device 20 includes a receiving unit 21 that receives a print job described in a predetermined printer control language such as PostScript, analyzes the print job, and generates a raster-format print image for one band or one page. Analyzing / image generating means 22 for storing the print image in a predetermined unit (for example, for one pass) from the image buffer to the print engine based on the control command in the print job, and controlling the print engine. And a print control unit 23 for executing printing. Each of these units is functionally realized by the CPU executing a program stored in a ROM or a RAM in the printer device 20 or an external storage medium.
[0025]
Hereinafter, a procedure for creating a conversion table for converting a gray value to a non-gray value and a printing procedure in the printer system 1 will be described with reference to a flowchart. Note that each step (including partial steps without reference numerals) can be executed in an arbitrary order or in parallel without changing the processing contents.
[0026]
FIG. 3 is a flowchart for creating a conversion table referred to by the printer driver unit 13. FIG. 4 is a diagram showing a target axis in the L * a * b * color space. In the L * a * b * color space, the L * axis represents lightness, and the values on the a * axis and the b * axis represent chromaticity indicating hue and saturation. In the L * a * b * color space, values on the L * axis are gray values indicating a gray color having no chromaticity, and values other than on the L * axis are colors corresponding to the values of a * and b *. Non-gray values with degrees. First, a procedure for creating a conversion table for converting a gray value into a non-gray value will be described with reference to FIGS.
[0027]
First, a gray target which is an example of a non-gray value after conversion in the L * a * b * color space is set (S110). The gray target is a non-gray value in the a * b * color plane that satisfies 0 <L <100 in the L * a * b * color space, and is set in consideration of metamerism. In the present embodiment, the gray target is a non-gray value after conversion in the a * b * color plane near L = 50 in the L * a * b * color space.
[0028]
Next, a white point which is an example of the non-gray value after conversion in the L * a * b * color space is set (S120). In the present embodiment, the white point is a non-gray value in the a * b * color plane near L = 100 (for example, about L = 95) in the L * a * b * color space. The a * b * color plane is divided into four quadrants by the a * axis and the b * axis, while the white point is the quadrant to which the gray target belongs in the a * b * color plane (the hatched quadrant in FIG. 4). Are set to belong to the same quadrant as.
[0029]
The white point may be set based on the color of printing paper on which an input image is printed in a printing process (see FIG. 7) described later. This makes it possible to set a white point suitable for reproducing the gray value of the input image on the printing paper to be used.
[0030]
Further, the white point may be set based on the color of white ink used in a printing process (see FIG. 7) described later. For example, when a print engine (see FIG. 1) is provided with a plurality of types of white inks such as a pigment-based white ink and a dye-based white ink, among the plurality of types of white inks, an a * b * color plane is used. The value of the white ink whose value belongs to the same quadrant as the gray target may be set as the white point. Thereby, when reproducing the gray color of the input image using the white ink filled in the ink cartridge (see FIG. 1), the color fluctuation of the gray color can be suppressed. Further, it is possible to set a white point suitable for reproducing the gray color of the input image without considering the influence of the color of the printing paper used. For this reason, the color fluctuation of the gray color of the input image can be suppressed, and the gray color can be appropriately reproduced.
[0031]
Further, the white point may be determined based on an observation environment in which an input image printed in a printing process (see FIG. 7) described later is observed. For example, the white point is set to belong to the same quadrant as the gray target in the a * b * color plane, assuming that the printed input image is viewed under standard light D50 and standard light A. You. Thus, even when the printed input image is viewed under a plurality of viewing environments, a white point suitable for reproducing the gray color of the input image can be set. For this reason, the color fluctuation of the gray color of the input image can be suppressed, and the gray color can be appropriately reproduced.
[0032]
In the present embodiment, after setting the gray target, the white point is set in the same quadrant to which the gray target belongs in the a * b * plane, but after setting the white point, the white point is set in the a * b * plane. A gray target may be set in the same quadrant to which the white point belongs. At this time, the white point may be determined based on the color of printing paper or white ink on which the input image is printed in a printing process (FIG. 7) described later. Specifically, for example, the color of printing paper or white ink that can be used in the printing process is set as a white point as it is. Thus, the white point and the gray target can be set in the same quadrant on the a * b * plane in accordance with the color of the printing paper, so that the gray color shift of the input image can be suppressed.
[0033]
Next, a black point is set as an example of the non-gray value after conversion in the L * a * b * color space (S130). In the present embodiment, the black point is a non-gray value in the a * b * color plane near L = 0 (for example, about L = 5) in the L * a * b * color space. The black point is set to belong to the same quadrant (the hatched quadrant in FIG. 4) to which the gray target and the white point belong in the a * b * color plane.
[0034]
Next, a target axis is set to pass through the white point, the gray target, and the black point (S140). The target axis is set such that non-gray values on the target axis between the white point and the black point belong to the same quadrant as the white point, gray target, and black point. Thus, the target axis can be prevented from intersecting with the a * axis or the b * axis in the L * a * b * color space, so that the color fluctuation of the gray value of the printed input image can be suppressed. .
[0035]
The target axis may be set to be a curve passing through the white point, the gray target, and the black point, or may be set to be one or more straight lines passing through the white point, the gray target, and the black point. . At this time, the target axis may be set to be a straight line substantially parallel to the L * axis.
[0036]
Alternatively, after defining an axis passing through the white point, the gray target, and the black point, the axis may be shifted to be the target axis. In this case, it is preferable to shift the line in a direction away from one or both of the a * axis and the b * axis. As a result, a sufficient margin between the a * axis and the b * axis and the target axis can be ensured. Color fluctuation of an image can be suppressed. However, if the L * axis is too far away from the L * axis, the chromaticity of the non-gray value on the target axis becomes strong, and the gray color may not be properly reproduced on the print medium. For this reason, it is desirable to shift the axis from the L * axis within a range where the gray color can be appropriately reproduced on the print medium.
[0037]
Next, a conversion table for converting gray values on the L * axis into non-gray values on the target axis is created (S150). The conversion table includes gray values on the L * axis before conversion and non-gray values after conversion. In the present embodiment, the conversion table is configured to include an RGB value as an example of a gray value and a CMYK value as an example of a non-gray value (see FIG. 5). That is, the conversion table is a conversion table that obtains CMYK values indicating non-gray values on the target axis for RGB values where R value = G value = B value. In the example shown in FIG. 5, each RBG value and CMYK value is represented by 8 bits (0 to 255).
[0038]
Preferably, the conversion table is configured to include corresponding gray values and non-gray values for non-gray values on the target axis other than the white point, the gray target, and the black point. In this embodiment, the conversion table is configured to convert the gray values on the L * axis into 17 non-gray values on the target axis, including a white point, a gray target, and a black point. Here, the non-gray values making up the conversion table belong to the same quadrant on the a * b * color plane.
[0039]
Further, a plurality of conversion tables may be created. For example, the conversion table may be created for each type of printing paper, such as plain paper, glossy paper, or matte paper, used in a printing process (see FIG. 7) described below. Thereby, since a conversion table suitable for the printing paper on which the input image is printed can be selected, the color fluctuation of the printed input image can be further suppressed.
[0040]
FIG. 6 is a flowchart illustrating a procedure for adjusting the gray balance of the conversion table. When an input image is printed based on the created conversion table, an image printed by a machine difference of a printing apparatus or the like, an ink used, or a printing paper may not always be reproduced in an intended color. Therefore, in the present embodiment, as necessary, a predetermined image is printed based on the created conversion table, and by measuring the color of the printed predetermined image, the gray balance of the value forming the target axis is adjusted. Adjustments are made to reduce the effects of machine differences between printing devices and the like so that the intended colors can be reproduced.
[0041]
First, a gray patch is printed on a print medium based on the created conversion table (S210). Then, the color of the gray patch on the print medium is measured (S220) and compared with the color indicated by the non-gray value on the corresponding target axis (S230). If the difference between the color of the measured gray patch and the color indicated by the non-gray value on the target axis is larger than a predetermined value (No in S230), the gray balance is adjusted based on the color of the measured gray patch. (S240), the conversion table is updated (S250). Then, by performing the same processing based on the updated conversion table (S210 to S230), the difference between the color of the gray patch measured again and the color indicated by the value on the target axis is determined from the predetermined value. If it has become smaller (Yes in S230), the adjustment of the gray balance of the non-gray values constituting the conversion table ends. Even when adjusting the gray balance, it is desirable to adjust the white point after adjustment and the gray target so that they belong to the same quadrant.
[0042]
FIG. 7 is a flowchart illustrating a procedure for printing an input image on a print medium based on the conversion table. The process of printing an input image on a print medium by the printer system 1 will be described with reference to FIGS. Upon receiving a print request from an external or an application program running on the host device, the printer driver unit 13 of the host device 10 executes the following processing.
[0043]
The printer driver 13 receives the RGB values for each pixel of the input image for which the print request has been made (S310), and determines whether the received RGB values are gray values (S320). If the printer driver unit 13 determines that the received RGB values are gray values (Yes at S320), the printer driver unit 13 refers to the incorporated conversion table (see FIG. 2) and converts the gray values to non-gray values on the target axis. It is converted (S330, see arrow in FIG. 4 and FIG. 5). On the other hand, if the printer driver 13 determines that the received RGB values are not gray values (S320, No), the printer driver 13 converts the RGB values other than the values on the L * axis into CMYK values incorporated in the printer driver 13. The received RGB values are converted into CMYK values with reference to another conversion table (S320, No). Then, the printer driver unit 13 generates the print image of the input image based on the converted CMYK values by repeating the above-described operation for all the pixels of the input image (S310 to S330) (S340). In the present embodiment, the printer driver unit 13 refers to different conversion tables when the received RGB values are gray values and non-gray values. However, the conversion table referred to when the RGB values are gray values is used. The conversion table referred to when the RGB values are non-gray values may be a single conversion table.
[0044]
Then, the printer driver unit 13 creates a print job based on the generated print image and transmits the print job to the printer device 20 via the communication network (see FIG. 1). In the printer device 20, when receiving the print job from the printer driver unit 13, the information processing unit controls the print head based on the ink ejection amount described in the print job and prints the input image on print paper (S350). ).
[0045]
In the present embodiment, the printer driver 13 determines the amount of ink to be ejected by the print head of the printer 20 and sends it to the printer 20. In other examples, the printer driver 13 transmits the amount of ink to the printer 20. The generated print image may be transmitted, and the information processing unit of the printer device 20 may determine the discharge ink amount of the print head based on the print image.
[0046]
The examples and application examples described through the above embodiments of the present invention can be used in appropriate combination or with modifications or improvements depending on applications. The present invention is limited to the description of the above embodiments. Not something. It is apparent from the description of the appended claims that embodiments in which such combinations or changes or improvements are made can be included in the technical scope of the present invention.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a hardware configuration of a printer system 1 according to an embodiment of the present invention.
FIG. 2 is a block diagram illustrating a functional configuration of a host device 10 and a printer device 20.
FIG. 3 is a flowchart for creating a conversion table incorporated in the printer driver unit 13;
FIG. 4 is a diagram illustrating a target axis in an L * a * b * color space.
FIG. 5 is a diagram illustrating an example of a conversion table.
FIG. 6 is a flowchart illustrating a procedure for adjusting a gray balance of a conversion table.
FIG. 7 is a flowchart illustrating a procedure for printing an input image on a print medium based on a conversion table.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Printer system, 10 ... Host device, 11 ... Input / output means, 12 ... Communication means, 13 ... Printer driver means, 20 ... Printer device 21 ... Receiving means, 22: analysis / image generation means, 23: print control means

Claims (10)

A method of creating a conversion table that converts gray values to non-gray values,
Determining a predetermined value in the L * a * b * color space as the converted non-gray value;
Determining a white point in the L * a * b * color space such that the converted non-gray value belongs to the same quadrant to which the predetermined value belongs in the a * b * color plane;
A target axis passing through the predetermined value and the white point, defining a target axis such that at least a value on the target axis between the predetermined value and the white point belongs to the quadrant;
Creating a conversion table for converting gray values on the L * axis into non-gray values on the target axis. Determining a black point in the L * a * b * color space as a non-gray value after the conversion so as to belong to the quadrant;
The method of claim 1, wherein the step of defining the target axis further comprises: defining the target axis such that a value between the black point and the white point passes through the black point and belongs to the quadrant. Conversion table creation method. Converting a gray value on the L * axis in the input image into a non-gray value on the target axis based on the conversion table created by the conversion table creating method according to claim 1;
Printing the input image on a print medium based on the converted non-gray value. Creating the conversion table corresponding to each of a plurality of types of print media;
Selecting the conversion table based on a type of a print medium on which the input image is printed, further comprising:
The step of converting to the non-gray value converts the gray value on the L * axis in the input image into the non-gray value on the target axis based on the selected conversion table. 4. The printing method according to claim 3, wherein: Further comprising preparing white ink for printing the input image,
The printing method according to claim 3, wherein the step of determining the white point determines the white point based on a color of the white ink. The step of determining the white point is performed when the input image printed on the print medium is observed under the standard light D50 and when the input image is observed under the standard light A. The printing method according to claim 3, wherein the white point is determined so as to belong to a quadrant. A method of creating a conversion table that converts gray values to non-gray values,
Determining a white point in the L * a * b * color space as the converted non-gray value;
A predetermined value in the L * a * b * color space as the converted non-gray value such that the converted non-gray value belongs to the same quadrant to which the white point belongs in the a * b * color plane. Determining the value of
A target axis passing through the white point and the predetermined value, and defining a target axis such that at least a value on the target axis between the white point and the predetermined value belongs to the quadrant;
Creating a conversion table for converting gray values on the L * axis into non-gray values on the target axis. Converting a gray value on the L * axis in an input image into a non-gray value on the target axis based on the conversion table created by the conversion table creating method according to claim 7;
Printing the input image on a print medium based on the converted non-gray value,
The printing method, wherein the step of determining the white point determines the white point based on a color of the print medium. A conversion device for converting an input gray value into a non-gray value,
A target passing through a predetermined value in the L * a * b * color space, which is the non-gray value after the conversion, and a white point belonging to the same quadrant to which the predetermined value belongs in the a * b * color plane Axis, wherein at least a value on the target axis between the predetermined value and the white point corresponds to a non-gray value on the target axis belonging to the quadrant and a gray value on the L * axis. A storage unit for storing the conversion table,
A conversion unit configured to convert the input gray value into the non-gray value based on the conversion table. A conversion device according to claim 9,
A printing unit configured to print the input image on a print medium based on the non-gray value converted by the conversion device.

Images