Method and device for acquiring tone value of printed matter
Technical Field
The invention relates to the technical field of printing, in particular to a method and a device for acquiring a tone value of a printed matter.
Background
In the field of color printing and reproduction, the amount of ink printed on a printing material is usually expressed by tone value, which is an important parameter for controlling the printing quality. Meanwhile, the change of the tone value corresponds to the visual representation of the change of the brightness or the shade of the image of the printed matter and corresponds to the gradation change of the printed image.
In the conventional print quality control, the tone value of the printed matter is calculated mainly by the density value, and the calculation of the tone value of the printed matter is generally performed using davis's formula (Murray-Davies) or yale-Nielson's formula (Yule-Nielson). However, with the development of digital printing technology, color management technology is generally adopted in the printing process, the color value of a known printing ink sample is used for performing printing color prediction, and the color transmission of the whole printing process and the color of a printed matter are controlled through color management. The density value is a calculated amount by measuring the light absorption of the ink, cannot express the color feeling of an object, is not compatible with the currently commonly used CIE color system, cannot be used for evaluating the printing quality and calculating the color difference, and cannot be used for color conversion by using a density measured value in a color management process, namely the density value cannot be used in a color management system of a digital printing technology.
In order to meet the requirements of the current digital printing process and color management, in the newly established international standard ISO 12647 of the printing process control series, the calculation of tone values of printed products by CIEXYZ tristimulus values is specified, but the method needs to use different tristimulus values and different relational expressions for inks of different primary colors for calculation, and the method is not suitable for the printed products of spot color inks.
Therefore, the method for acquiring the tone value of the printed matter used in the existing digital printing technology is complicated in calculation process and poor in applicability.
Disclosure of Invention
The invention provides a method and a device for acquiring a tone value of a printed matter, and aims to solve the problems that the calculation process is complicated and the applicability is poor in the conventional method for acquiring the tone value of the printed matter in the digital printing technology.
In a first aspect, the present invention provides a method for obtaining a tone value of a printed matter, the method comprising: acquiring a first brightness value of a printing stock of a target printed matter and a second brightness value of solid printing ink corresponding to each single-color printing ink in the target printed matter; calling a preset measurement and control strip, determining a target color block corresponding to each monochromatic ink in the target printed matter in the preset measurement and control strip, and determining a third luminosity value of the monochromatic ink printed matter with the screen dots corresponding to the monochromatic ink according to the target color block; and determining the tone value of the target printed matter according to the first brightness value, the second brightness value, the third brightness value and a preset tone value relational expression.
Further, the process of determining the tone value of the target printed matter according to the first brightness value, the second brightness value, the third brightness value and a preset tone value relational expression specifically includes: determining a tone value corresponding to each monochromatic ink in the target printed matter according to a first brightness value, a second brightness value and a third brightness value corresponding to each monochromatic ink and the preset tone value relational expression;
wherein α represents the tone value corresponding to any one of the single color inks in the target printed matter,
a first lightness value corresponding to the single-color ink,
a second lightness value corresponding to the single-color ink,
and a third luminosity value corresponding to the single-color ink is shown.
Further, a process of calling a preset measurement and control strip, determining a target color block corresponding to each monochromatic ink in the target printed matter in the preset measurement and control strip, and determining a third brightness value of the monochromatic ink printed matter with the screen dots corresponding to the monochromatic ink according to the target color block specifically comprises the following steps: and calling a preset measurement and control strip, determining a target color block corresponding to each monochromatic ink in the target printed matter in the preset measurement and control strip, acquiring the color value of the target color block, and taking the lightness component of the color value as a third lightness value of the monochromatic ink printed matter with the dots corresponding to the monochromatic ink.
In a second aspect, the present invention also provides an apparatus for obtaining a tone value of a printed matter, the apparatus comprising: the brightness value acquisition module is used for acquiring a first brightness value of a printing stock of a target printed matter and a second brightness value of solid printing ink corresponding to each single color ink in the target printed matter; the brightness value determining module is used for calling preset measuring and controlling strips, determining a target color block corresponding to each monochromatic ink in the target printed matter in the preset measuring and controlling strips, and determining a third brightness value of the monochromatic ink printed matter with the screen dots corresponding to the monochromatic ink according to the target color block; and the tone value determining module is used for determining the tone value of the target printed matter according to the first brightness value, the second brightness value, the third brightness value and a preset tone value relational expression.
Further, the tone value determination module is specifically configured to: determining a tone value corresponding to each monochromatic ink in the target printed matter according to a first brightness value, a second brightness value and a third brightness value corresponding to each monochromatic ink and the preset tone value relational expression;
wherein α represents the tone value corresponding to any one of the single color inks in the target printed matter,
a first lightness value corresponding to the single-color ink,
a second lightness value corresponding to the single-color ink,
and a third luminosity value corresponding to the single-color ink is shown.
Further, the brightness value determination module is specifically configured to: and calling a preset measurement and control strip, determining a target color block corresponding to each monochromatic ink in the target printed matter in the preset measurement and control strip, acquiring the color value of the target color block, and taking the lightness component of the color value as a third lightness value of the monochromatic ink printed matter with the dots corresponding to the monochromatic ink.
The technical scheme provided by the embodiment of the invention has the following beneficial effects: the invention provides a method and a device for acquiring a tone value of a printed matter. The method is suitable for calculating the tone values of printed matters of CMYK four-color ink and printed matters of spot color ink, the calculated tone values have a linear relation with the lightness and color sensation of human eyes, the requirement of the uniformity of the visual sensation of the human eyes is met, and the calculation process of the tone values is simpler and the applicability is better.
Drawings
In order to more clearly explain the technical solution of the present application, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious to those skilled in the art that other drawings can be obtained according to the drawings without any creative effort.
Fig. 1 is a schematic flowchart of a method for obtaining a tone value of a printed product according to an embodiment of the present invention;
fig. 2 is a block diagram of an apparatus for obtaining a tone value of a printed product according to an embodiment of the present invention.
Detailed Description
The printed matter is a visual product and is viewed through human vision, so that the color of the printed matter needs to accord with the color vision rule of human eyes, and the change of the tone value can be preferably in a linear relation with the human vision feeling. The evaluation of the quality of the printed matter generally includes two aspects, namely, whether the color of the printed matter conforms to the color vision rule of human eyes, namely, the perception rule of the human eyes on the color, and whether the difference between the color of the printed matter and a target value (or a standard value), namely, a color difference value. Both of the two evaluations must meet the perception requirements of human eyes according to the perception rules of human eyes on colors. Therefore, in the process of controlling the quality of the printed matter, the tone value of the printed matter is obtained by using the calculation method of the tone value of the printed matter according with the human eye color vision rule, and then the printing color of the printed matter is controlled to be more in accordance with the human eye color vision rule, so that the method has important significance for improving the printing quality of the printed matter.
In the CIELAB uniform color space, the lightness of a color is represented by L values consistent with lightness perception, and the color perception is represented by opponent color colorimetric values a and b consistent with color perception, so that the color perception of the system is closer to the visual perception. For printed matter, the L value is the nonlinear transformation of the brightness factor Y of the printed matter and represents the change relation of human eye brightness perception, and the change relation reflects the absorption and reflection amount of the printing ink to the illuminating light and can reflect the change of the quantity of the printing ink. Therefore, the gradation value of the printed matter obtained by calculating the L value of the uniform lightness feeling can reflect the change rule of the lightness of the printing color in vision and reflect the size of the printing ink amount.
Based on this, the present invention provides a method and an apparatus for obtaining a tone value of a printed matter, and details of embodiments of the present invention are described below with reference to the accompanying drawings.
Referring to fig. 1, fig. 1 is a schematic flowchart illustrating a method for obtaining a tone value of a printed product according to an embodiment of the present invention. As can be seen from fig. 1, the method includes:
step 101, acquiring a first brightness value of a printing stock of a target printed matter and a second brightness value of solid printing ink corresponding to each single color ink in the target printed matter.
The target printed matter refers to a printed matter of which the tone value is to be acquired currently, and any printed matter of which the tone value is to be acquired can be taken as the target printed matter. The second lightness value of the printed solid ink corresponding to each monochromatic ink in the target print refers to the lightness value of the solid ink print of that monochromatic ink. A solid ink print of each single color ink refers to a print obtained by covering a substrate (e.g., white paper) of the target print with 100% of the single color ink. The single color ink in the target printed matter comprises primary color ink and spot color ink.
The acquisition of the first lightness value of the printing stock of the target printed matter and the second lightness value of the solid printing ink corresponding to each single-color ink in the target printed matter can be realized by the following steps: the method comprises the steps of measuring a color value of a printed material of a target printed matter and a color value of a solid ink printed matter of each monochromatic ink in the target printed matter by using a spectrophotometer, inputting the color value of the printed material of the target printed matter and the color value of the solid ink printed matter of each monochromatic ink in the target printed matter into a device for acquiring a tone value of the printed matter, or automatically reading the color value of the printed material of the target printed matter and the color value of the solid ink printed matter of each monochromatic ink in the target printed matter from the spectrophotometer by the device for acquiring the tone value of the printed matter. In any of the above methods, the apparatus for acquiring the gradation value of the printed matter acquires the color value of the printing material of the target printed matter and the color value of the solid ink printed matter of each of the monochromatic inks in the target printed matter, and then sets the lightness component of the color value of the printing material of the target printed matter as the first lightness value of the printing material of the target printed matter, and sets the lightness component of the color value of the solid ink printed matter of each of the monochromatic inks in the target printed matter as the second lightness value of the solid ink for printing corresponding to the monochromatic ink.
102, calling preset measurement and control strips, determining a target color block corresponding to each monochromatic ink in the target printed matter in the preset measurement and control strips, and determining a third brightness value of the monochromatic ink printed matter with the screen dots corresponding to the monochromatic ink according to the target color block.
The ink printed matter with the screen dots corresponding to each monochromatic ink in the target printed matter refers to the printed matter obtained by covering the printing stock of the target printed matter with the monochromatic ink in a screen dot proportion of 1% -100%. And presetting a target color block corresponding to each monochromatic ink in the target printed matter in the measurement and control strip, wherein the target color block is a color block printed by the monochromatic ink.
In the specific implementation process, a preset measurement and control strip is called, a target color block corresponding to each monochromatic ink in the target printed matter is determined in the preset measurement and control strip, and a process of determining a third brightness value of the monochromatic ink printed matter with the dots corresponding to the monochromatic ink according to the target color block specifically comprises the following steps: and calling a preset measurement and control strip, determining a target color block corresponding to each monochromatic ink in the target printed matter in the preset measurement and control strip, acquiring the color value of the target color block, and taking the lightness component of the color value as a third lightness value of the monochromatic ink printed matter with the dots corresponding to the monochromatic ink.
Step 103, determining the tone value of the target printed matter according to the first brightness value, the second brightness value, the third brightness value and a preset tone value relational expression.
In specific implementation, the process of determining the tone value of the target printed product according to the first brightness value, the second brightness value, the third brightness value and a preset tone value relational expression specifically includes:
determining the tone value corresponding to each single color ink in the target printed matter according to the first brightness value, the second brightness value and the third brightness value corresponding to each single color ink and the following preset tone value relational expression, namely the relational expression (1):
in the relational expression (1), α represents a tone value corresponding to any one of the single color inks in the target printed matter,
a first lightness value corresponding to the single-color ink,
a second lightness value corresponding to the single-color ink,
and a third luminosity value corresponding to the single-color ink is shown.
And (3) calculating the tone value corresponding to each single-color ink in the target printed matter according to the relational expression (1) to obtain the tone value of the target printed matter.
Next, a specific example is used to compare the tone value of the target printed matter obtained by the method for obtaining the tone value of the printed matter according to the embodiment of the present invention with the tone value of the target printed matter obtained by the density value method and the CIEXYZ tristimulus value method mentioned in the prior art.
In the density value method, the tone value of the target printed matter is calculated by adopting the following relational expression (2):
in the relational expression (2), α represents the tone value of the target printed matter, DsThe solid density of any one of the monochromatic inks in the target printed matter relative to the printing material of the target printed matter, DtIs a measured value of the density of the single-color ink in the target print relative to the substrate of the target print, i.e., the actually measured density value.
In the CIEXYZ tristimulus value method, the tone value of the target printed matter is calculated by using the following relational expressions (3) to (6):
equation (3) is used to calculate the tone value corresponding to the cyan ink in the target print, Xw represents the component of the tristimulus value of the substrate of the target print along the X-axis, Xt represents the component of the tristimulus value of cyan along the X-axis, and Xs represents the component of the tristimulus value of the solid cyan ink along the X-axis.
Equation (4) is used to calculate the tone value corresponding to the magenta ink in the target print, Yw represents the component of the tristimulus value of the substrate of the target print along the Y axis, Yt represents the component of the tristimulus value of magenta along the Y axis, and Ys represents the component of the tristimulus value of the solid magenta ink along the Y axis.
Equation (5) is used to calculate the tone value corresponding to the yellow ink in the target print, Zw represents the component of the tristimulus value of the printing stock of the target print along the Z-axis, Zt represents the component of the tristimulus value of yellow along the Z-axis, and Zs represents the component of the tristimulus value of the solid yellow ink along the Z-axis.
Equation (6) is used to calculate the tone value corresponding to the black ink in the target print, Y ' w represents the component of the tristimulus value of the substrate of the target print along the Y axis, Y't represents the component of the tristimulus value of black along the Y axis, and Y's represents the component of the tristimulus value of the solid black ink along the Y axis.
The specific implementation process comprises the following steps: ink ladder was printed with CMYK four-color process inks and green and red spot color inks at 5% intervals, 21 levels per color. The density values, CIEXYZ tristimulus values and CIELAB color values of each patch were measured separately. The tone values of the target printed matter are respectively calculated by using the density value method of the relational expression (2), the CIEXYZ tristimulus value methods of the relational expressions (3) to (6) and the method for acquiring the tone values of the printed matter, which are provided by the invention, and the calculation results are compared. The solid area data of the target printed matter on the white paper, the CMYK process inks, and the spot green and red inks are shown in table 1 below, the measured values of the CMYK process inks are shown in table 2 below, and the calculation results are shown in table 3 below. The measured data and calculation examples of the green and red spot color inks are shown in table 4 below.
Table 1: solid data of white paper, CMYK process ink and green and red spot color ink of printing stock of target printed matter
In table 1, CMYK process inks only measure complementary color density; theoretically, the spot color ink has no density measurement standard and cannot be used for calculating the tone value, but the channel data corresponding to the maximum solid density value is often used for calculating the tone value in actual production, and the method is only taken as an example and does not represent the correctness of the method; at present, there is no standard for calculating the spot color ink tone by using the CIEXYZ tristimulus values, and here, the color channel (channel corresponding to the maximum density value) of the minimum value in the solid XYZ tristimulus values is selected for calculation, which is also only an example and does not represent the correctness of the method.
Table 2: target print CMYK process ink measurement data
Table 3: tone value of target printed matter calculated by three methods
Table 4: the tone values corresponding to the green and red special color inks in the target printed matter are calculated by the three methods
As can be seen from tables 1 to 4, the method for obtaining the tone values of the printed matter according to the embodiment of the present invention is not only suitable for the printed matter of CMYK four-color inks, but also suitable for the printed matter of spot color inks.
The method for obtaining the tone values of the printed matters provided by the embodiment of the invention can accurately calculate the tone values of the printed matters of CMYK four-color ink and the printed matters of spot color ink, and has simpler calculation process and better applicability.
Corresponding to the method for acquiring the tone value of the printed matter, the invention also provides a device for acquiring the tone value of the printed matter.
Referring to fig. 2, fig. 2 is a block diagram illustrating a structure of an apparatus for obtaining a tone value of a printed product according to an embodiment of the present invention. As can be seen in fig. 2, the apparatus includes: the lightness value acquisition module 201 is configured to acquire a first lightness value of a printing material of a target printed matter and a second lightness value of a solid printing ink corresponding to each monochromatic ink in the target printed matter; the brightness value determining module 202 is configured to retrieve preset measurement and control strips, determine a target color block corresponding to each monochromatic ink in the target printed matter in the preset measurement and control strips, and determine a third brightness value of the monochromatic ink printed matter with the dots corresponding to the monochromatic ink according to the target color block; a tone value determining module 203, configured to determine a tone value of the target printed product according to the first brightness value, the second brightness value, the third brightness value, and a preset tone value relation.
Further, the tone
value determining module 203 is specifically configured to: determining a tone value corresponding to each monochromatic ink in the target printed matter according to a first brightness value, a second brightness value and a third brightness value corresponding to each monochromatic ink and the preset tone value relational expression;
wherein α represents the tone value corresponding to any one of the single color inks in the target printed matter,
a first lightness value corresponding to the single-color ink,
a second lightness value corresponding to the single-color ink,
and a third luminosity value corresponding to the single-color ink is shown.
Further, the brightness value determination module 202 is specifically configured to: and calling a preset measurement and control strip, determining a target color block corresponding to each monochromatic ink in the target printed matter in the preset measurement and control strip, acquiring the color value of the target color block, and taking the lightness component of the color value as a third lightness value of the monochromatic ink printed matter with the dots corresponding to the monochromatic ink.
By adopting the device for acquiring the tone value of the printed matter provided by the embodiment of the invention, each step of the method for acquiring the tone value of the printed matter can be implemented, and corresponding beneficial effects are achieved. The device for acquiring the tone value of the printed matter provided by the embodiment of the invention can calculate the tone value of the printed matter of the primary color ink and also can calculate the tone value of the printed matter of the spot color ink, the calculated tone value has a linear relation with the visual sensation of human eyes, and the calculation process is simpler and the applicability is better.
In a specific implementation, the present invention further provides a computer storage medium, where the computer storage medium may store a program, and the program may include some or all of the steps in the embodiments of the method for obtaining a tone value of a printed product provided by the present invention when executed. The storage medium may be a magnetic disk, an optical disk, a read-only memory (ROM) or a Random Access Memory (RAM).
Those skilled in the art will readily appreciate that the techniques of the embodiments of the present invention may be implemented as software plus a required general purpose hardware platform. Based on such understanding, the technical solutions in the embodiments of the present invention may be essentially or partially implemented in the form of a software product, which may be stored in a storage medium, such as ROM/RAM, magnetic disk, optical disk, etc., and includes several instructions for enabling a computer device (which may be a personal computer, a server, or a network device, etc.) to execute the method according to the embodiments or some parts of the embodiments.
The same and similar parts in the various embodiments in this specification may be referred to each other. In particular, for the embodiment of the apparatus for obtaining the tone value of the printed matter, since it is basically similar to the embodiment of the method, the description is simple, and the relevant points can be referred to the description in the embodiment of the method.
The above-described embodiments of the present invention should not be construed as limiting the scope of the present invention.