CN109808306B - Method and device for determining linearization curve of printing equipment - Google Patents
Method and device for determining linearization curve of printing equipment Download PDFInfo
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Abstract
The application provides a method and a device for determining a linearization curve of printing equipment, wherein the method comprises the following steps: acquiring alternative linearization curves corresponding to the Nielsen coefficients according to a plurality of preset Nielsen coefficients; acquiring a composite color target image corresponding to each Nielsen coefficient according to each alternative linearization curve and a preset sampling point set; acquiring measured density data of each composite color target image and three-color field measured density data; determining a target Nielsen coefficient according to the measured density data, the three-color field measured density data and the printing standard density data of each composite color target image; and determining a target linearization curve according to the target Nielsen coefficient. The method realizes the automatic determination of the Nielsen coefficient value, ensures that the generated target linearization curve conforms to the printing standard, thereby achieving the aim of scientifically and accurately generating the equipment linearization curve and laying a foundation for further color management.
Description
Technical Field
The application relates to the technical field of printing, in particular to a method and a device for determining a linearization curve of printing equipment.
Background
With the development of technologies such as digital proofing and digital printing, the role of color management in printing production is becoming more and more important. Therefore, it is a hot research to improve printing efficiency by combining color management with new printing techniques. In the existing printing process, because the original output state of the ink jet output equipment is not linear, the output printed product has unsatisfactory gradation and gradation, has the problems of ink piling, color cast and the like, and is not suitable for further color management. In order to improve print quality, output device linearization is therefore required.
The equipment linearization is based on the characteristics of paper and ink, optimizes the ink amount of each single channel of the output equipment, controls the tone and the level of a printed product and provides a foundation for the establishment of an equipment characteristic file. The equipment linearization becomes a key step in the printing production process, and has important significance for truly reproducing the original manuscript and obtaining a high-quality printed product. Therefore, how to conveniently and accurately calculate the linearization curve is a technical problem to be solved in the printing color management.
Disclosure of Invention
The application provides a method and a device for determining a linearization curve of printing equipment, which aim to overcome the defects that the determined linearization curve of the printing equipment does not meet the printing standard and the like due to poor accuracy of a Nielsen coefficient in the prior art.
In a first aspect, the present application provides a method for determining a linearization curve of a printing device, including:
acquiring alternative linearization curves corresponding to the Nielsen coefficients according to a plurality of preset Nielsen coefficients;
acquiring a composite color target image corresponding to each Nielsen coefficient according to each alternative linearization curve and a preset sampling point set;
acquiring measured density data and three-color field measured density data of each composite color target image;
determining a target Nielsen coefficient according to the measured density data of each composite color target image, the three-color field measured density data and the printing standard density data;
and determining a target linearization curve according to the target Nielsen coefficient.
Another aspect of the present application provides a device for determining a linearization curve of a printing apparatus, including:
the first acquisition module is used for acquiring alternative linearization curves corresponding to the Nielsen coefficients according to a plurality of preset Nielsen coefficients;
the second acquisition module is used for acquiring a composite color target image corresponding to each Nielsen coefficient according to each alternative linearization curve and a preset sampling point set;
the third acquisition module is used for acquiring the measured density data of each composite color target image and the three-color field measured density data;
the first processing module is used for determining a target Nielsen coefficient according to the measured density data of each composite color target image, the three-color field measured density data and the printing standard density data;
and the second processing module is used for determining a target linearization curve according to the target Nielsen coefficient.
According to the method and the device for determining the linearization curve of the printing equipment, aiming at the requirement of equipment linearization in printing color management, based on the printing standard density curve, the target linearization curve which is most matched with the printing standard density curve is selected from the alternative linearization curves corresponding to the Nielsen coefficients, so that the automatic determination of the Nielsen coefficient value is realized, the generated target linearization curve is ensured to accord with the printing standard, the aim of scientifically and accurately generating the equipment linearization curve is fulfilled, and a foundation is laid for further color management.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to these drawings without inventive exercise.
Fig. 1 is a schematic flowchart of a method for determining a linearization curve of a printing apparatus according to an embodiment of the present disclosure;
fig. 2 is a schematic structural diagram of a device for determining a linearization curve of a printing apparatus according to an embodiment of the present application.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
Example one
The embodiment provides a method for determining a linearization curve of a printing device, which is used for determining the linearization curve of the printing device. The implementation subject of the embodiment is a device for determining a linearization curve of a printing device, and the device can be arranged in a terminal device such as a server, a PC, a tablet computer, and the like.
As shown in fig. 1, a schematic flow chart of a method for determining a linearization curve of a printing device provided in this embodiment is provided, where the method includes:
And 102, acquiring a composite color target image corresponding to each Nielsen coefficient according to each alternative linearization curve and a preset sampling point set.
And 103, acquiring the measured density data of each composite color target image and the three-color field measured density data.
And step 104, determining a target Nielsen coefficient according to the measured density data, the three-color field measured density data and the printing standard density data of each composite color target image.
And 105, determining a target linearization curve according to the target Nielsen coefficient.
Specifically, a plurality of nielsen coefficients may be preset according to experience, and the plurality of preset nielsen coefficients are adopted to obtain a candidate linearization curve corresponding to each nielsen coefficient, that is, each nielsen coefficient corresponds to one candidate linearization curve. After each alternative linearization curve is obtained, a preset sampling point set is determined, the preset sampling point set is selected from an input point set of a printing standard density curve, the printing standard density curve is an international standard curve, and the input point set is a known and determined standard point set, which is not described herein again. After the preset sampling point set is determined, acquiring a composite color target image corresponding to each nielsen coefficient according to each alternative linearization curve and the preset sampling point set, and specifically acquiring the composite color target image corresponding to each nielsen coefficient by printing. After the composite color target images corresponding to the nielsen coefficients are obtained, the measured density data of the composite color target images and the three-color field measured density data can be obtained, and can be obtained through measurement. And determining a target Nielsen coefficient according to the measured density data, the three-color field measured density data and the printing standard density data of each composite color target image, wherein the printing standard density data are input point sets of the printing standard density curve and corresponding output point sets thereof, and are known data of international standards. After the target nielsen coefficients are determined, a target linearization curve can be determined according to the target nielsen coefficients, and specifically, a candidate linearization curve corresponding to the target nielsen coefficients is determined as the target linearization curve.
The method for determining the linearization curve of the printing device provided by the embodiment selects the target linearization curve most matched with the printing standard density curve from the candidate linearization curves corresponding to the nielsen coefficients based on the printing standard density curve according to the requirement of device linearization in printing color management, so that the nielsen coefficient value is automatically determined, and the generated target linearization curve is ensured to meet the printing standard, thereby achieving the purpose of scientifically and accurately generating the device linearization curve and laying a foundation for further color management.
Example two
This embodiment further supplements the method for determining the linearization curve of the printing apparatus provided in the first embodiment.
As a practical manner, on the basis of the first embodiment, optionally, the step 101 may specifically include:
and 2011, acquiring a target map of the color of the ladder ruler according to a preset input point set.
Step 2012, obtaining the step measurement density of the step color target map and the maximum step measurement density.
And 2013, obtaining corresponding standard reference density according to the maximum measurement density of the ladder ruler and a plurality of preset Nielsen coefficients.
Specifically, the following formula (1) is adopted to obtain the corresponding standard reference density:
wherein D issFor maximum measurement density of the ladder bar, N is the Nelsen coefficient, XiRepresenting the value of the ith input point In the predetermined set of input points, DiA value X representing the ith input point In the predetermined set of input points IniCorresponding standard reference density values.
And step 2014, fitting according to the ladder ruler measured density and the standard reference density to obtain a candidate linearization curve corresponding to each Nielsen coefficient.
As another implementable manner, on the basis of the first embodiment, optionally, the step 104 may specifically include:
step 2021, determining the calculated standard density of each point in the preset sampling point set according to the measured density data of each composite color target map, the three-color field measured density data, and the printing standard density data corresponding to the preset sampling point set.
Step 2022, determining the average difference ratio of each point in each preset sampling point set corresponding to each alternative linearization curve according to the calculated standard density of each point in the preset sampling point set and the measured density data of the composite color target map corresponding to the preset sampling point set.
Step 2023, determining a target nielsen coefficient according to the average difference ratio of each point in each preset sampling point set corresponding to each alternative linearization curve.
Optionally, step 2021 may specifically include:
step 2031, obtaining the printing standard density data corresponding to the preset sampling point set.
Step 2032, calculate the ratio between the three color solid measured density and the print standard density curve top density.
Step 2033, determining the calculation standard density of each point in the preset sampling point set according to the ratio between the three-color field measurement density and the top density of the printing standard density curve.
Specifically, according to a printing standard density curve input point set InS and a printing standard density curve, obtaining printing standard density data OutS, and presetting a sampling point set as n points selected from InS and marking as a set InD;
acquiring printing standard density data corresponding to a preset sampling point set from the OutS;
the ratio between the tristimulus field measured density and the print standard density curve vertex density was calculated according to the following equation (3):
rate＝(OutMfruit of Chinese wolfberry-OutSzq)/(OutSjq-OutSzq)z,j∈[2,r-1]OutSzq≤OutMFruit of Chinese wolfberry≤OutSjq(3)；
Wherein: OutMFruit of Chinese wolfberryDensity was measured for CMY tristimulus fields; OutSjqAnd OutSzqThe vertex density of j and z curves in the printing standard density curve set OutS, wherein z is j-1;
calculating the calculated standard density Std of each point in the preset sampling point set by adopting the following formula (4) according to the ratio between the three-color solid measured density and the top density of the printing standard density curve:
wherein t represents the ith point value Z in the point set InS and the preset sampling point set InDiIndex number of point corresponding to value, OutSjt、OutSztThe printing standard density values of the t points in the j-th and z-th printing standard density point sets in the printing standard density data set OutS are represented, and the relation between z and j is as follows: and z is j-1.
Optionally, step 2022 may specifically include:
step 2041, calculating the difference ratio of each point in the preset sampling point set according to the calculated standard density of each point in the preset sampling point set and the measured density data of the composite color target map corresponding to the preset sampling point set.
Specifically, each alternative linearization curve corresponds to the calculated standard density of the preset sampling point set and the measured density data conforming to the color target map, so that the calculated difference ratios are also multiple groups, and each group corresponds to one alternative linearization curve.
Step 2042, calculating to obtain the average difference ratio corresponding to each alternative linearization curve according to the difference ratio of each point in the preset sampling point set.
Specifically, according to the calculated standard density of each point in the preset sampling point set and the measured density data of the composite color target map corresponding to the preset sampling point set, the following formula (5) is adopted to calculate the difference ratio △ E of each point in the preset sampling point seti：
△Ei＝fabs(Stdi-OutMji)/Stdii∈[1,n](5)；
Wherein: stdiCalculating the standard density, OutMj, for each point in a predetermined set of sampling points InDiThe measured density corresponding to the InD midpoint i in OutMj is obtained, and n represents the number of the concentrated sampling points of the preset sampling points;
the average difference ratio △ E corresponding to each Nelsen's coefficient is obtained according to the following formula (6)meanj：
△Emeanj＝(△E1+…△Ei+…+△En)/n i∈[1,n](6)。
Wherein, △ EmeanjThe average difference ratio corresponding to the jth nielsen coefficient is shown.
Optionally, step 2023 may specifically include: and determining the Nielsen coefficient corresponding to the average difference ratio with the minimum value as the target Nielsen coefficient.
Specifically, the nielsen coefficient with the smallest average difference ratio is the target nielsen coefficient. And the alternative linearization curve corresponding to the target Nielsen coefficient is the target linearization curve.
The method for determining the linearization curve of the printing device provided by the embodiment selects the target linearization curve most matched with the printing standard density curve from the candidate linearization curves corresponding to the nielsen coefficients based on the printing standard density curve according to the requirement of device linearization in printing color management, so that the nielsen coefficient value is automatically determined, and the generated target linearization curve is ensured to meet the printing standard, thereby achieving the purpose of scientifically and accurately generating the device linearization curve and laying a foundation for further color management. And generating a plurality of linear curves by traversing a Nielsen coefficient method, outputting a plurality of sampling point composite color targets with different gradation levels, calculating the standard density of the sampling points by combining the CMY three-color field measurement density and the printing standard density, and selecting the optimal Nielsen coefficient value by calculating the difference ratio of the standard density of the sampling points and the measurement density. Wherein the output effect of different nielsen coefficient values can be known in advance by the traversal method; the standard density of the sampling points is calculated according to the printing standard density, and the standard density is more in accordance with the printing standard specification, so that the calibrated equipment can be ensured to be in accordance with the printing standard, and the purpose of controlling the integral contrast of the color image is achieved.
EXAMPLE III
This embodiment further details the determination method of the linearization curve of the printing apparatus provided in the above embodiment.
The method specifically comprises the following four steps:
step one, obtaining a plurality of linearization curves corresponding to a plurality of Nielsen coefficients
Setting k printing device linearization curves is represented by the following expression:
In＝{X1,X2,......,Xi,......,Xm} Xi∈[0,100]
Out＝{Out1,Out2,......,Outj,......,Outk} j∈[1,k]
Outj＝{Y1,Y2,......,Yi,......,Ym} Yi∈[0,100]
wherein: in denotes the set of input points (In percent), m denotes the number of In, XiA value representing an input point; out represents a k linear curve output point set; outjRepresenting the set of output points of the linearization curve of the j-th plant, YiRepresents the jth linearizationIn the curve XiThe corresponding output value.
The process of specifically obtaining the k linear curve is as follows:
(1) printing ladder ruler color target picture
The ladder color target map is composed of ladder rules of each color of the printing equipment, and the color values In the ladder rules are composed of m sampling color blocks In a point set In.
(2) Obtaining the measurement density of the ladder ruler by measuring the color target diagram of the ladder ruler
The output surface gradient scale measurement density curves of all colors are represented by point sets In and D ', and the surface gradient scale measurement density point set D' of all colors is represented as follows:
D'＝{D'1，D'2，......，D'i，......，D'm}，i∈[1,m]
wherein, D'iX In the representative point setiThe corresponding ladder ruler measures the density value.
Measuring the color target diagram of the ladder ruler to obtain a set D' of the measured density points of the ladder ruler of each color surface and the maximum measured density D of the ladder ruler of each color surfaces。
(3) Calculating standard reference density according to the maximum measured density and a plurality of preset Nielsen coefficients
A single piece of standard reference density curve data may be represented by a set of points In and D, which is represented as follows:
D＝{D1，D2，......，Di，......，Dm}，i∈[1,m]
wherein D isiX In the representative point setiCorresponding standard reference density values.
DiObtained by calculation from the following formula (1):
wherein D issThe maximum measurement density of the tread scale of each color obtained by the measurement is N, which is a Nielsen coefficient.
Presetting a plurality of Nielsen coefficients, such as Nielsen coefficient N, which is taken as:
calculating a plurality of standard reference density output values according to formula (1), wherein a set of standard reference density output value points is expressed as follows:
wherein Dj represents a standard reference density set corresponding to the jth Nielsen coefficient value of a certain color surface of the printing equipment.
(4) Fitting to obtain k linear curves
Fitting according to the measured density data D' of the ladder ruler and the jth standard reference density set Dj to obtain a linearized curve Oj。
The specific fitting formula is as follows (2):
wherein, YiThe obtained jth linear curve data is obtained;
Djirepresents the jth reference density point set XiCorresponding reference density value, D'pAnd D'p-1Respectively represent X In the input point set InpAnd Xp-1Measuring the density value of the corresponding ladder ruler;
the values of i and p satisfy the following relations:
D'p≤Dji≤D'p-1。
step two, printing a composite color target chart by using the obtained multiple standby linearization curves
After k spare linearization curves are obtained, the k spare linearization curves are adopted to print a composite color target chart, and the specific process is as follows:
set the print standard density curve input point set to lnS (which is a known set of standard points):
InS＝{S1,S2,......,Si,......,Sq} Si∈[0,100]
wherein: siRepresenting the input point value (in percent) and q the number of input points.
The standard set of input points lnS corresponds to a set of output points for r different vertex densities, denoted as OutS (known as International Standard), and is expressed as follows:
OutS＝{OutS1,OutS2,......,OutSj,......,OutSr} j∈[1,r]
wherein: r is the number of the printing standard density curves, q is the number of output points of each printing standard density curve, and OutSj represents the printing standard density set of the input point set InS of the printing standard density curve under the vertex density of the jth printing standard density curve; OutSjiThe ith input point value S in the representative point set InSiAnd (4) presetting sampling points as n points selected from the point set InS according to corresponding values of a density point set OutSj at the top point of the jth printing standard density curve, and marking the preset sampling points as InD.
(1) Preset sample point selection
Selecting n points from the input point set lnS of the print standard density curve as preset sampling points, and recording as a preset sampling point set InD, which is expressed as follows:
InD＝{Z1,Z2,......,Zi,......,Zn} Zi∈[0,100]
wherein Z isiRepresenting the CMY input values (in percentage) for each sample point, and n represents the number of preset sample points.
(2) Printing composite color target picture
An input point set InD and CMY three-color solid color blocks (namely color blocks with CMY three color values of 100) are used for establishing an output color target diagram.
Outputting the composite color target chart with the obtained k alternative linearization curves and measuring to obtain a measured density data set OutM and a CMY three-color field-measured density value OutMFruit of Chinese wolfberry. OutM is represented as follows:
OutM＝{OutM1,OutM2,...,OutMj,...OutMk} j∈[1,k]
wherein: OutMj represents a measurement density set corresponding to a preset sampling point output by different alternative linearization curves;
OutMjirepresenting Z in a set of predetermined sampling points InDiThe corresponding value at OutMj.
Step three, calculating the calculation standard density of the preset sampling point set
Calculating the calculation standard density corresponding to the preset sampling point set InD, wherein the specific process is as follows:
(1) density ratio calculation
The ratio between the CMY three-color solid measurement density and the print standard density curve vertex density is calculated using the following formula (3):
rate＝(OutMfruit of Chinese wolfberry-OutSzq)/(OutSjq-OutSzq)z,j∈[2,r-1]OutSzq≤OutMFruit of Chinese wolfberry≤OutSjq(3)
Wherein: OutMFruit of Chinese wolfberryDensity is measured in the field for the three colors CMY, i.e., the three colors obtained above;
OutSjqand OutSzqThe vertex densities of the j-th and z-th curves in the print standard density curve set OutS, where z is j-1.
(2) Determining a calculated standard density of a set of predetermined sampling points from a ratio
Setting the calculation standard density corresponding to the preset sampling point set InD as a point set Std:
Std＝{Std1,Std2,...,Stdi,...Stdn} i∈[1,n]
wherein StdiRepresenting Z in a set of predetermined sampling points InDiCorresponding calculated Standard Density value, StdiThe following formula (4) is used for calculation:
wherein: t represents Z in the point set InS and the preset sampling point set InDiValue-corresponding node index number, OutSjt、OutSztAnd the printing standard density values of the t nodes in the j-th and z-th printing standard density point sets in the printing standard density curve set OutS are represented, and the relation between z and j is as follows: and z is j-1.
Step four: nielsen coefficient selection
The method mainly comprises the step of selecting a Nielsen coefficient value by calculating the difference ratio between the standard density and the measured density through calculating sampling points.
(1) Calculating a difference ratio
And calculating the average difference ratio of each point between a calculation standard density set Std corresponding to the preset sampling point set InD and a certain measurement density set OutMj.
The single node difference value ratio △ E is calculated according to the following formula (5)i:
△Ei＝fabs(Stdi-OutMji)/Stdii∈[1,n](5)
Wherein: stdiCalculating the standard density, OutMj, for each node of InDiAnd n represents the number of sampling points for the measurement density corresponding to each node i of InD in OutMj.
The density difference ratio △ E obtained by the above calculationiThe average was obtained according to the following formula (6) to obtain △ Emeanj。
△Emeanj＝(△E1+…△Ei+…+△En)/n i∈[1,n](6)
(2) Determining the value of the Nelsen coefficient
Respectively calculating the average difference ratio of each node corresponding to the k linearization curves according to the method, and recording as a set △ Emean：
△Emean＝{△Emean1,△Emean2,...,△Emeanj,...,△Emeank} j∈[1,k]
Assumption set △ EmeanMinimum value of △ EmeanjAnd the Nielsen coefficient value corresponding to the difference ratio is the obtained Nielsen coefficient.
In the present embodiment, the output device used is an EPSON Stylus Pro 7910 digital printer, the paper is a pantoke 170 g high-grade sub-photo paper, and the measuring device is EyeOne-isi from alice. Alternatively, other practical output devices, paper sheets or measuring devices are possible, and the embodiment is only exemplary and not limiting.
Setting the number of input points as m to 30, and adopting the following data in the preset input point set:
In＝{0.0,1.0,2.0,3.0,4.0,6.0,8.0,10.O,12.0,15.0,17.0,20.0,24.0,28.0,32.0,36.0,40.0,44.0,48.0,52.0,56.0,61.0,65.0,70.0,75.0,80.0,85.0,90.0,95.0,100.0}
firstly, using the above-mentioned preset input point set, a color target map of a color scale is printed, and the color target map is composed of C, M, Y, K color surface scales, as shown in table 1:
TABLE 1
| Cyan surface node C | C1 | C2 | C3 | … | C28 | C29 | C30 |
| Pint M | M1 | M2 | M3 | … | M28 | M29 | M30 |
| Yellow surface node Y | Y1 | Y2 | Y3 | … | Y28 | Y29 | Y30 |
| Node K with black surface | K1 | K2 | K3 | … | K28 | K29 | K30 |
Namely, color block diagrams printed by the printing inks of the different colors with the preset input point proportion are adopted in sequence, which is the prior art and is not described herein again.
Measuring each color block of the color target diagram of the ladder ruler by using a measuring instrument to obtain a ladder ruler measurement density point set D' of each color block in each color surface and a maximum measurement density D of the ladder ruler of each color surfaces。
D'＝{D'1，D'2，......，D'i，......，D'30}，i∈[1,30]
For example, the maximum measurement densities of the scale for C, M, Y, K obtained in this embodiment are 1.72, 1.73, 1.22, and 1.74, respectively.
Optionally, after obtaining the maximum measurement density of the ladder rule according to the measurement, the maximum density can be set according to experience, and then the maximum measurement density D of the ladder rule finally usedsFor the lesser of the measurement acquisition and the empirical setting, e.g. the empirically set maximum densities of the scales are 1.80, 1.10, 1.80, respectively, the final maximum measured density D of the scale iss1.72, 173, 1.10, 1.74.
The following maximum measured Density D of a color ScalesFor example, the determination of a target linearization curve for a color system is described. The specific determination process of each other color system is the same as that of the color system, except that the maximum measurement density of the adopted step ruler is different.
In this embodiment, 25 nielsen coefficients are preset as follows:
the maximum measured density D of the final used ladder rule obtained abovesE.g. maximum measured density D of a scale of cyan CsIs 1.72, and the values of the 25 Nelsen coefficients are respectively substituted into the formula (1), and the standard reference density point set D is obtained by calculation.
Wherein Dj represents a standard reference density set corresponding to the jth Nielsen coefficient value of a certain color surface of the printing equipment. That is, D includes standard reference density sets corresponding to 25 nielsen coefficients, and each standard reference density set includes 30 standard reference densities corresponding to 30 input points in the preset input point set.
Substituting each Dj in the standard reference density D and the measured density data D' into the above equation (2) to obtain 25 sets Out of output points:
Out＝{Out1,Out2,......,Outj,......,Out25} j∈[1,25]
Outj＝{Y1,Y2,......,Yi,......,Y30} Yi∈[0,100]
and fitting according to a preset input point set In and an output point set Out to obtain 25 alternative linearization curves.
The set of standard input points InS of the printing standard density curve includes q ═ 25 standard sampling points, as follows:
InS＝{(0,0,0),(2,1,1),(4,3,3),(6,4,4),(8,5,5),(10,7,7),(15,11,11),(20,15,15),(25,19,19),(30,23,23),(35,27,27),(40,31,31),(45,36,36),(50,40,40),(55,45,45),(60,50,50),(65,55,55),(70,60,60),(75,66,66),(80,72,72),(85,78,78),(90,84,84),(95,92,92),(98,97,97),(100,100,100)}
selecting one of highlight, dark tone and middle tone from the printing standard density curve input point set lnS as a preset sampling point set InD, namely:
InD＝{(25,19,19),(50,40,40),(75,66,66)}
an output composite color target map is prepared by using the three-color solid color patches (100,100,100) of the preset sampling point set InD and CMY, as shown in Table 2:
TABLE 2
Wherein InD25, InD50, InD75 respectively represent dot percentages CMY (25,19,19), CMY (50,40,40) and CMY (75,66,66) of the color patch, N0.5 represents the output of the color patch using a linearization curve corresponding to a Nielsen coefficient value of 0.5; CMY100 represents a CMY three-color solid color block.
Outputting the composite color target chart by adopting the obtained 25 alternative linearization curves and measuring to obtain a measured density data set OutM and a CMY three-color field-measured density value OutMFruit of Chinese wolfberry。
For example, the three-color OutM obtained in this embodiment is used for on-site measurement of densityFruit of Chinese wolfberryIs 1.95.
The OutS corresponding to the standard input point set InS of the print standard density curve (the print standard density curve used in this embodiment includes 20 curves, i.e., r is 20) is:
since each point in the preset sampling point set InD is a point in InS, it can be known from the preset sampling point set according to the standard input point set that (25,19,19), (50,40,40) and (75,66,66) in the preset sampling point set InD correspond to S in InS respectively9、S14And S19. I.e. InD corresponds to OutSj in OutS9、OutSj14And OutSj19，j∈[1,20]。
From the print standard density corresponding to the InD and the CMY three-color solid measured densities obtained above, a ratio between the CMY three-color solid measured densities and the top density of the print standard density curve is calculated using formula (3). The top density of the printed standard density curve is OutSj25。
rate＝(OutMFruit of Chinese wolfberry-OutSz25)/(OutSj25-OutSz25)z,j∈[2,r-1]OutSz25≤OutMFruit of Chinese wolfberry≤OutSj25(3)
Wherein z is j-1.
For example, a three-color OutM density measurement in the fieldFruit of Chinese wolfberryAt 1.5, the vertex densities of two adjacent printed standard density curves are 1.4 and 1.7, respectively, OutSz25Is 1.4, OutSj251.7, the ratio between the tristimulus solid field measured density and the print standard density curve vertex density is:
rate＝(OutMfruit of Chinese wolfberry-OutSz25)/(OutSj25-OutSz25)＝(1.5-1.4)/(1.7-1.5)＝0.5 z,j∈[2,r-1]
Then Z in the preset sampling point set InDiCorresponding calculated standard density value StdiCan adoptEquation (4). I.e. due to OutSz25≤OutMFruit of Chinese wolfberry≤OutSj25: from equation (4) we can obtain:
Stdi＝rate*OutSjt+(1-rate)*OutSzt
for each point (25,19,19), (50,40,40) and (75,66,66) in the InD, the corresponding calculated standard densities are:
Std1＝rate*OutSj9+(1-rate)*OutSz9
Std2＝rate*OutSj14+(1-rate)*OutSz14
Std3＝rate*OutSj19+(1-rate)*OutSz19。
if OutMFruit of Chinese wolfberry≤OutS125And then:
Std1＝OutS19
Std2＝OutS114
Std3＝OutS119。
if OutMFruit of Chinese wolfberry≥OutS2025Then, then
Std1＝OutS209
Std2＝OutS2014
Std3＝OutS2019。
For example, the calculated standard densities corresponding to each point in the predetermined sampling point set InD determined in this embodiment are 0.255, 0.540, and 0.980, respectively.
After the calculation standard density corresponding to each point in the preset sampling point set InD is determined, the average difference value ratio △ E of each point between the calculation standard density set Std corresponding to the preset sampling point set InD and a certain measurement density set OutMj is further determinedmeanjI.e. the average difference ratio corresponding to the jth nielsen coefficient, or the average difference ratio corresponding to the jth alternative linearization curve.
△E1＝fabs(Std1-OutMj1)/Std1
△E2＝fabs(Std2-OutMj2)/Std2
△E3＝fabs(Std3-OutMj3)/Std3
△Emeanj＝(△E1+△E2+△E3)/3。
Respectively calculating and obtaining an average difference ratio set △ E corresponding to the 25 alternative linearization curves according to the methodmeanNamely:
△Emean＝{△Emean1,△Emean2,...,△Emeanj,...,△Emean25} j∈[1,25]
as shown in table (3), for the average difference ratio obtained in this example:
TABLE 3
If set △ EmeanMinimum value of △ EmeanjAnd the Nielsen coefficient corresponding to the average difference ratio is the target Nielsen coefficient. Namely, the alternative linearization curve corresponding to the target Nielsen coefficient is the target linearization curve. As shown in table 2, it can be seen that if the average difference ratio is at least 0.055 and the nielsen coefficient corresponding thereto is 1.3, the candidate linearization curve corresponding to the nielsen coefficient 1.3 is the target linearization curve corresponding to the color system.
The target linearization curve corresponding to cyan determined by the maximum measurement density Ds of the scale in cyan is determined, and the target linearization curve corresponding to the maximum measurement density Ds of the scale in other color systems can be determined. The specific process is the same as the cyan process and will not be described herein.
The method for determining the linearization curve of the printing device provided by the embodiment selects the target linearization curve most matched with the printing standard density curve from the candidate linearization curves corresponding to the nielsen coefficients based on the printing standard density curve according to the requirement of device linearization in printing color management, so that the nielsen coefficient value is automatically determined, and the generated target linearization curve is ensured to meet the printing standard, thereby achieving the purpose of scientifically and accurately generating the device linearization curve and laying a foundation for further color management. And generating a plurality of linear curves by traversing a Nielsen coefficient method, outputting a plurality of sampling point composite color targets with different gradation levels, calculating the standard density of the sampling points by combining the CMY three-color field measurement density and the printing standard density, and selecting the optimal Nielsen coefficient value by calculating the difference ratio of the standard density of the sampling points and the measurement density. Wherein the output effect of different nielsen coefficient values can be known in advance by the traversal method; the standard density of the sampling points is calculated according to the printing standard density, and the standard density is more in accordance with the printing standard specification, so that the calibrated equipment can be ensured to be in accordance with the printing standard, and the purpose of controlling the integral contrast of the color image is achieved.
Example four
The present embodiment provides a device for determining a linearization curve of a printing apparatus, which is used to execute the method for determining a linearization curve of a printing apparatus in the first embodiment.
As shown in fig. 2, a schematic structural diagram of the device for determining a linearization curve of a printing apparatus is provided in this embodiment. The printing device linearization curve determining apparatus 40 includes a first obtaining module 41, a second obtaining module 42, a third obtaining module 43, a first processing module 44, and a second processing module 45.
The first obtaining module 41 is configured to obtain, according to a plurality of preset nielsen coefficients, an alternative linearization curve corresponding to each nielsen coefficient; the second obtaining module 42 is configured to obtain a composite color target map corresponding to each nielsen coefficient according to each alternative linearization curve and a preset sampling point set; the third obtaining module 43 is configured to obtain measured density data of each composite color target image and three-color field measured density data; the first processing module 44 is used for determining a target nielsen coefficient according to the measured density data, the three-color field measured density data and the printing standard density data of each composite color target image; the second processing module 45 is configured to determine a target linearization curve according to the target nielsen coefficient.
The specific manner in which the respective modules perform operations has been described in detail in relation to the apparatus in this embodiment, and will not be elaborated upon here.
According to the determining device of the printing equipment linearization curve provided by the embodiment, aiming at the requirement of equipment linearization in printing color management, based on the printing standard density curve, the target linearization curve which is most matched with the printing standard density curve is selected from the candidate linearization curves corresponding to the plurality of nielsen coefficients, so that the automatic determination of the nielsen coefficient value is realized, the generated target linearization curve is ensured to accord with the printing standard, the aim of scientifically and accurately generating the equipment linearization curve is fulfilled, and a foundation is laid for further color management.
EXAMPLE five
This embodiment further supplements the determining apparatus for the linearization curve of the printing apparatus provided in the fourth embodiment.
As a practical manner, on the basis of the fourth embodiment, optionally, the first obtaining module 41 may include: the device comprises a first obtaining submodule, a second obtaining submodule, a determining submodule and a fitting submodule.
The first obtaining submodule is used for obtaining a color target map of the ladder ruler according to a preset input point set; the second obtaining submodule is used for obtaining the ladder ruler measurement density and the ladder ruler maximum measurement density of the ladder ruler color target map; the determining submodule is used for determining the standard reference density corresponding to each Nielsen coefficient according to the maximum measurement density of the ladder ruler and a plurality of preset Nielsen coefficients; and the fitting submodule is used for fitting according to the measurement density of the ladder ruler and the standard reference density to obtain an alternative linearization curve corresponding to each Nielsen coefficient.
As another implementable manner, on the basis of the fourth embodiment, optionally, the first processing module 44 may include a first processing sub-module, a second processing sub-module and a third processing sub-module.
The first processing submodule is used for determining the calculation standard density of each point in a preset sampling point set according to the measured density data of each composite color target image, three-color field measured density data and printing standard density data corresponding to the preset sampling point set; the second processing submodule is used for determining the average difference value ratio corresponding to each Nielsen coefficient according to the calculation standard density of each point in the preset sampling point set and the measurement density data of the composite color target image corresponding to the preset sampling point set; and the third processing submodule is used for determining the target Nielsen coefficients according to the average difference ratio corresponding to each Nielsen coefficient.
Optionally, the first processing sub-module is specifically configured to: acquiring printing standard density data corresponding to a preset sampling point set; calculating the ratio between the three-color solid measured density and the top density of the printing standard density curve; and determining the calculation standard density of each point in the preset sampling point set according to the ratio of the three-color solid measured density to the top density of the printing standard density curve.
Optionally, the second processing sub-module is specifically configured to: calculating the difference ratio of each point in the preset sampling point set according to the calculated standard density of each point in the preset sampling point set and the measured density data of the composite color target map corresponding to the preset sampling point set; and calculating to obtain the average difference ratio corresponding to each Nielsen coefficient according to the difference ratio of each point in the preset sampling point set.
Optionally, the third processing sub-module is specifically configured to: and determining the Nielsen coefficient corresponding to the average difference ratio with the minimum value as the target Nielsen coefficient.
In addition, the respective implementable modes in the embodiment may be implemented individually or in combination in any combination, and are not limited herein.
The specific manner in which the respective modules perform operations has been described in detail in relation to the apparatus in this embodiment, and will not be elaborated upon here.
According to the determining device of the printing equipment linearization curve provided by the embodiment, aiming at the requirement of equipment linearization in printing color management, based on the printing standard density curve, the target linearization curve which is most matched with the printing standard density curve is selected from the candidate linearization curves corresponding to the plurality of nielsen coefficients, so that the automatic determination of the nielsen coefficient value is realized, the generated target linearization curve is ensured to accord with the printing standard, the aim of scientifically and accurately generating the equipment linearization curve is fulfilled, and a foundation is laid for further color management. And generating a plurality of linear curves by traversing a Nielsen coefficient method, outputting a plurality of sampling point composite color targets with different gradation levels, calculating the standard density of the sampling points by combining the CMY three-color field measurement density and the printing standard density, and selecting the optimal Nielsen coefficient value by calculating the difference ratio of the standard density of the sampling points and the measurement density. Wherein the output effect of different nielsen coefficient values can be known in advance by the traversal method; the standard density of the sampling points is calculated according to the printing standard density, and the standard density is more in accordance with the printing standard specification, so that the calibrated equipment can be ensured to be in accordance with the printing standard, and the purpose of controlling the integral contrast of the color image is achieved.
Those of ordinary skill in the art will understand that: all or part of the steps for implementing the method embodiments may be implemented by hardware related to program instructions, and the program may be stored in a computer readable storage medium, and when executed, the program performs the steps including the method embodiments; and the aforementioned storage medium includes: various media that can store program codes, such as ROM, RAM, magnetic or optical disks.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present application.
Claims (12)
1. A method for determining a linearization curve for a printing device, comprising:
acquiring alternative linearization curves corresponding to the Nielsen coefficients according to a plurality of preset Nielsen coefficients;
acquiring a composite color target image corresponding to each Nielsen coefficient according to each alternative linearization curve and a preset sampling point set;
acquiring measured density data of each composite color target image and field measured density data of cyan, magenta and yellow colors;
determining a target Nielsen coefficient according to the measured density data of each composite color target image, the measured density data of the cyan, magenta and yellow three-color fields and the printing standard density data;
and determining a target linearization curve according to the target Nielsen coefficient.
2. The method according to claim 1, wherein the obtaining of the candidate linearization curve corresponding to each nielsen coefficient according to a preset plurality of nielsen coefficients comprises:
acquiring a color target map of a ladder ruler according to a preset input point set;
obtaining the ladder ruler measurement density and the ladder ruler maximum measurement density of the ladder ruler color target map;
determining a standard reference density corresponding to each Nielsen coefficient according to the maximum measurement density of the ladder ruler and the preset plurality of Nielsen coefficients;
and fitting according to the measurement density of the ladder ruler and the standard reference density to obtain a candidate linearization curve corresponding to each Nielsen coefficient.
3. The method of claim 1, wherein determining a target nielsen coefficient from the measured density data, the cyan, magenta, yellow solid field measured density data, and the print standard density data for each of the composite color target maps comprises:
determining the calculation standard density of each point in the preset sampling point set according to the measured density data of each composite color target map, the measured density data of the three colors of cyan, magenta and yellow on the spot and the printing standard density data corresponding to the preset sampling point set;
determining the average difference ratio corresponding to each Nielsen coefficient according to the calculated standard density of each point in the preset sampling point set and the measured density data of the composite color target image corresponding to the preset sampling point set;
and determining the target Nielsen coefficients according to the average difference ratio corresponding to each Nielsen coefficient.
4. The method of claim 3, wherein determining the calculated standard density of each point in the preset sampling point set according to the measured density data of each composite color target map, the measured density data of the three colors cyan, magenta and yellow, and the printing standard density data corresponding to the preset sampling point set comprises:
acquiring printing standard density data corresponding to a preset sampling point set;
calculating the ratio of the measured density of the three colors of cyan, magenta and yellow to the top density of the printing standard density curve;
and determining the calculation standard density of each point in the preset sampling point set according to the ratio of the measured density of the real areas of the cyan, the magenta and the yellow to the vertex density of the printing standard density curve.
5. The method according to claim 3, wherein the determining the average difference ratio corresponding to each Nielsen coefficient according to the calculated standard density of each point in the preset sampling point set and the measured density data of the composite color target map corresponding to the preset sampling point set comprises:
calculating the difference ratio of each point in the preset sampling point set according to the calculated standard density of each point in the preset sampling point set and the measured density data of the composite color target map corresponding to the preset sampling point set:
and calculating to obtain the average difference ratio corresponding to each Nielsen coefficient according to the difference ratio of each point in the preset sampling point set.
6. The method of claim 3, wherein determining the target Nelsen coefficients according to the average difference ratio corresponding to each Nelsen coefficient comprises:
and determining the Nielsen coefficient corresponding to the average difference ratio with the minimum value as the target Nielsen coefficient.
7. An apparatus for determining a linearization curve for a printing device, comprising:
the first acquisition module is used for acquiring alternative linearization curves corresponding to the Nielsen coefficients according to a plurality of preset Nielsen coefficients;
the second acquisition module is used for acquiring a composite color target image corresponding to each Nielsen coefficient according to each alternative linearization curve and a preset sampling point set;
the third acquisition module is used for acquiring the measured density data of each composite color target image and the measured density data of the cyan, magenta and yellow three colors on the spot;
the first processing module is used for determining a target Nielsen coefficient according to the measured density data of each composite color target image, the measured density data of the three colors of cyan, magenta and yellow and the printing standard density data;
and the second processing module is used for determining a target linearization curve according to the target Nielsen coefficient.
8. The apparatus of claim 7, wherein the first obtaining module comprises:
the first obtaining submodule is used for obtaining a color target map of the ladder ruler according to a preset input point set;
the second obtaining submodule is used for obtaining the ladder ruler measurement density and the ladder ruler maximum measurement density of the ladder ruler color target map;
the determining submodule is used for determining the standard reference density corresponding to each Nielsen coefficient according to the maximum measurement density of the ladder ruler and the preset plurality of Nielsen coefficients;
and the fitting submodule is used for fitting according to the measurement density of the ladder ruler and the standard reference density to obtain an alternative linearization curve corresponding to each Nielsen coefficient.
9. The apparatus of claim 7, wherein the first processing module comprises:
the first processing sub-module is used for determining the calculation standard density of each point in the preset sampling point set according to the measured density data of each composite color target image, the measured density data of the three colors of cyan, magenta and yellow on site and the printing standard density data corresponding to the preset sampling point set;
the second processing submodule is used for determining the average difference value ratio corresponding to each Nielsen coefficient according to the calculated standard density of each point in the preset sampling point set and the measured density data of the composite color target map corresponding to the preset sampling point set;
and the third processing submodule is used for determining the target Nielsen coefficients according to the average difference ratio corresponding to each Nielsen coefficient.
10. The apparatus according to claim 9, wherein the first processing submodule is specifically configured to:
acquiring printing standard density data corresponding to a preset sampling point set;
calculating the ratio of the measured density of the three colors of cyan, magenta and yellow to the top density of the printing standard density curve;
and determining the calculation standard density of each point in the preset sampling point set according to the ratio of the measured density of the real areas of the cyan, the magenta and the yellow to the vertex density of the printing standard density curve.
11. The apparatus according to claim 9, wherein the second processing sub-module is specifically configured to:
calculating the difference ratio of each point in the preset sampling point set according to the calculated standard density of each point in the preset sampling point set and the measured density data of the composite color target map corresponding to the preset sampling point set;
and calculating to obtain the average difference ratio corresponding to each Nielsen coefficient according to the difference ratio of each point in the preset sampling point set.
12. The apparatus according to claim 9, wherein the third processing sub-module is specifically configured to: and determining the Nielsen coefficient corresponding to the average difference ratio with the minimum value as the target Nielsen coefficient.
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| JP2003011397A (en) * | 2001-06-20 | 2003-01-15 | Scitex Digital Printing Inc | Method of defining printer media and inking intensity compatibility |
| CN102848747A (en) * | 2011-06-28 | 2013-01-02 | 北大方正集团有限公司 | Recalibration method and device for ink-jet printing equipment |
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