CN107330188B - Split modeling method and system for multicolor halftone equipment facing copied object - Google Patents
Split modeling method and system for multicolor halftone equipment facing copied object Download PDFInfo
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F30/00—Computer-aided design [CAD]
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- H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
- H04N1/40—Picture signal circuits
- H04N1/405—Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels
Abstract
A split-type modeling method and a split-type modeling system for multicolor halftone equipment facing a copied object comprise that the multicolor halftone equipment is split into a plurality of four-color models containing black ink in an enumeration mode; obtaining each four-color model color gamut by a convex hull algorithm by utilizing a Niger primary color ladder ruler prepared in the ink amount limiting modeling process; obtaining the color gamut coverage rate of different four-color model combinations on the image to be copied by using a color gamut judging method, and determining the four-color model combinations on the principle of maximizing the color gamut coverage rate; and determining the final optimal four-color model combination by using a central color difference minimization method aiming at the condition that multiple groups of possible combinations simultaneously meet the condition requirements, and completing the split modeling of the equipment. The invention prepares the color difference sample by means of the ink amount limiting process, realizes the simplification of the whole modeling process of the multicolor halftone equipment under the condition of no additional sample preparation step, and is convenient to implement.
Description
Technical Field
The invention belongs to the technical field of color reproduction of halftone equipment, and particularly relates to a split-type modeling method and system of multicolor halftone equipment for a reproduction object.
Background
Multicolor halftone color reproduction is the mainstream technology in the field of image reproduction. The technology aims to establish a correlation model (namely a color characterization model) between an original image data input control value and an equipment output color value, and further realize accurate control of copy colors. Compared with the traditional four-Color (CMYK) copying technology, the multicolor copying technology has the advantages of wide color gamut, rich levels, clear details and the like.
In the above-mentioned characterization model building process, because the multicolor device has a high ink color dimension, it is often faced with the problem of huge sampling pressure if modeling it as a whole. For this reason, a common method at present is to convert the multi-color device modeling problem into several three-color or four-color sub-device modeling problems. Compared with high-dimensional integral modeling, the split modeling method obviously improves the modeling efficiency of the multicolor equipment color characterization model.
However, in the sub-model modeling aspect, the realization of high-precision characterization modeling is also based on high-density sampling, so that on the basis of the split modeling method, the high-precision modeling of the multi-color device is still a tedious process.
Reference 1: wang B, xu H, luo MR, et al, maintaining acquisition of cellular Yule-Nielsen spectral Neugebauer models for differential ink cards using a primary component analysis, JOSA A2011;28:1429-1435.
Reference 2: liu Q, wan X and Xie D.optimization of spectral printer modified based on a modified cellular yule-Nielsen spectral Neugebauer model.JOSAA2014;31:1284-1294.
Reference 3: wang B, xu H, luo MR, et al, spectral-based color segmentation method for a Multi-inkprinter, chinese Optics Letters 2011;9:063301.
In fact, in practical applications, because the color features of the copy object are all characterized, it is not necessary to model the multicolor device at a full gamut level for specific applications (for example, preparing a copy object with a single color composition such as skin color card, cosmetic color card, antique copy, etc.). Therefore, if the characterization model for the color features of the copied object can be constructed by a specific method, not only the efficiency of the whole characterization modeling can be remarkably improved, but also the modeling precision can be further improved by increasing the sampling density of the specific sub-model modeling samples and the like. However, due to the restriction of subjective and objective factors such as the level of theoretical methods, no effective solution has been proposed in the academic and industrial fields.
Disclosure of Invention
The invention aims to solve the problems in the background art and provides a split modeling method and a split modeling system for a multicolor halftone device facing a copied object.
The technical scheme of the invention is to provide a split modeling method of multicolor halftone equipment facing a copy object, which comprises the following steps:
step 1, splitting a multicolor half-tone device into M four-color models in an enumeration mode, wherein each model contains black ink;
step 2, preparing a T-level Neigber ladder ruler on the basis of the four-color model in the step 1, removing an ink amount overrun sample by a visual observation method, and finishing equipment ink amount limitation on the basis;
step 3, measuring the color information of samples of the Neigber ladder ruler in the step 2 by using color measuring equipment, and removing corresponding color data of the ink amount over-limit samples;
step 4, on the basis of the color data obtained by measurement in the step 3, calculating the color gamut volume of the four-color model in the step 1 by using a convex hull algorithm;
step 5, on the basis of the color gamut volume calculation in the step 4, calculating the color gamut volume of the four-color model combination with the number of the models being N by an enumeration method, wherein N =1,2,3,4; then, for any image to be copied, judging the gamut coverage rate G of the gamut corresponding to each four-color model combination to the image to be copied by using a gamut judgment method;
step 6, determining the four-color model combination according to the principle of maximizing the color gamut coverage rate G of the four-color model combination in the step 5;
step 7, if only one group of model combinations in the step 6 meets the conditions, the model combinations are the optimal split; if the condition that the multiple groups of combinations meet the requirements simultaneously exists in the step 6, firstly, resampling is carried out on the image to be copied, the number of pixels is reduced to Q, then, the average color difference C between the Q pixel points and the color value corresponding to the dot W in the ink volume space of the N four-color model combinations selected in the step 6 is calculated, and the final four-color model combination is selected according to the minimization of the average color difference C, so that the splitting modeling is completed.
Moreover, the Neegber step number T in step 2 should be greater than 20.
Furthermore, the color information measured in step 3 should be spectral reflectance information or chromaticity information.
When the color gamut coverage G is obtained in step 5, the model is setThe number N is tried from small to large, if N = N opt If < 4, G =100%, then no attempt is made to have N > N opt The case of combination. The solution of the color gamut coverage rate G adopts an inhull algorithm, and the value of the inhull algorithm is equal to the ratio of the number of pixels of the image to be copied in the four-color model combined color gamut to the total number of pixels of the image.
In step 7, the number Q of the pixels is greater than 100 and less than Q and less than 200, and the point W in the ink volume space of the four-color model is defined as a point where each dimension of the ink volume takes a value of 50.
In addition, in the step 7, the average color difference C is calculated by using a CIEDE2000 color difference formula and using a D50/2 chromaticity condition.
The invention provides a split modeling system of multicolor half-tone equipment facing to a copy object, which comprises the following modules:
the device enumeration splitting module splits the multicolor halftone device into M four-color models in an enumeration form, wherein each model contains black ink;
the ink amount limiting module is used for preparing a T-level Neigber ladder ruler on the basis of the four-color model in the equipment enumeration splitting module, eliminating an ink amount overrun sample by a visual observation method and finishing equipment ink amount limitation on the basis;
the color measuring module is used for measuring the color information of samples of the Neegber ladder ruler in the ink amount limiting module by using color measuring equipment and eliminating the color data of corresponding ink amount overrun samples;
the color gamut volume calculation module is used for enumerating the color gamut volumes of the four-color models in the splitting module by utilizing a convex hull algorithm calculation device on the basis of the color data measured by the color measurement module;
the gamut coverage rate calculation module is used for calculating the gamut volume of the four-color model combination with the number of N by an enumeration method on the basis of the gamut volume calculation module, wherein N =1,2,3 and 4; then, for any image to be copied, judging the gamut coverage rate G of the gamut corresponding to each four-color model combination to the image to be copied by using a gamut judgment method;
the four-color combination initial selection module determines the four-color model combination according to the principle that the color gamut coverage rate G of the four-color model combination in the color gamut coverage rate calculation module is maximized;
the four-color combination final selection module is used for determining that the four-color combination initial selection module is optimal split if only one group of model combinations in the four-color combination initial selection module meets the condition; if a plurality of groups of combinations in the four-color combination primary selection module meet the requirement at the same time, firstly, resampling the image to be copied to reduce the number of pixels to Q, then, calculating the average color difference C between the Q pixel points and the color values corresponding to the mid points W in the ink volume space of the N four-color models selected by the four-color combination primary selection module, and selecting the final four-color model combination according to the minimization of the average color difference C to finish splitting modeling.
Also, the Neugebauer step number T in the ink level limiting module should be greater than 20.
Moreover, the color information measured in the color measurement module should be spectral reflectance information or chromaticity information.
In addition, when the color gamut coverage rate G is obtained in the color gamut coverage rate calculation module, the number of models N should be tried from small to large, and if N = N opt If < 4, G =100%, then N > N need not be tried opt The case of combination. The solution of the color gamut coverage rate G adopts an inhull algorithm, and the value of the inhull algorithm is equal to the ratio of the number of pixels of the image to be copied in the four-color model combined color gamut to the total number of pixels of the image.
Moreover, the value of the number Q of the pixel points in the four-color combination final selection module is more than 100 and less than 200, the definition of the midpoint W in the ink volume space of the four-color model is the point with the value of each dimension of the ink volume being 50, and the solution of the average chromatic aberration C in the four-color combination final selection module is calculated by adopting a CIEDE2000 chromatic aberration formula and adopting a D50/2 chromatic aberration condition.
Compared with the prior art, the invention has the following beneficial effects:
the split modeling technical scheme of the multicolor halftone equipment facing the copied object creatively utilizes the ink amount limiting modeling process to prepare the color sample, so that the ink amount limiting and split modeling processes of the multicolor halftone equipment are combined into a whole, and the modeling process is simplified. According to the technical scheme, the optimal four-color model combination facing a specific copy object is selected in a targeted manner through a color gamut judgment method, and on the premise of ensuring the color copy precision, the modeling efficiency of the multi-color halftone equipment in the characterization process is remarkably improved. Therefore, the method effectively solves the problem of split modeling of the multicolor halftone equipment facing the copied object, is convenient to implement, and has strong applicability in the technical field of multicolor halftone color copying.
Drawings
FIG. 1 is a flow chart of a modeling method embodiment of the present invention;
FIG. 2 is a block diagram of the modeling system of the present invention.
Detailed Description
The following provides a detailed description of embodiments of the invention, taken in conjunction with the accompanying drawings.
The split modeling method for the multicolor halftone equipment facing the copied object, which is provided by the embodiment shown in fig. 1, can effectively utilize the color samples prepared by the equipment ink amount limiting process to realize efficient split modeling for the multicolor halftone equipment facing the copied object. In the embodiment, a Canon IPF5100 large format printer with seven main Colors (CMYKRGB) is adopted, epson art micro-spray Xuan paper is used as a printing medium, a spectral image of an ancient painting duplicate is used as a duplication object, and the seven main color equipment is disassembled by the equipment disassembling method. Meanwhile, the device splitting methods described in the foregoing references 1 and 3 are referred to as a control. It should be noted that the present invention is not limited to the halftone apparatus, the print medium, and the copy object described above, and the present method is also applicable to other apparatuses and copy objects.
When the technical scheme of the invention is implemented, the technical scheme can be automatically operated by a person skilled in the art by adopting a computer software technology. The method flow provided by the embodiment comprises the following steps:
step 1, splitting a multicolor halftone device into M four-color models in an enumeration form, wherein each model contains black ink; since M is selected from a multicolor halftone device, M is necessarily greater than or equal to 4.
For the seven dominant Color (CMYKRGB) printing apparatus employed in the embodiment, since the black ink K is a mandatory option, the printing apparatus uses one sheetNumber of form-splitting four-color models
Step 2, preparing a T-level Neger ladder ruler based on the four-color model in the step 1, removing an ink amount overrun sample by a visual observation method, and finishing equipment ink amount limitation on the basis, wherein the number T of the Neger ladder ruler levels is more than 20;
in the embodiment, for 20 four-color models obtained by splitting in step 1, 21-grade Neigber ladder rules are prepared one by one. Among them, the Neugebert ladder is well known in the art. Taking monochrome C as an example, its Neegber ladder ruler is: c =0, C =5, C =10, C =15 \ 8230c =100; taking a bicolor C + M as an example, its nexgberg ladder scale is C = M =0, C = M =5, C = M =10, C = M =15. Wherein, only preparation is needed because of the repetition of the corresponding Neuger ladder ruler in 20 four-color models
A combined Neugebert ladder ruler.
In addition, "removing the ink amount overrun sample by a visual observation method and completing the ink amount limitation of the device on the basis of the ink amount overrun sample" is also the prior art, and specific reference can be made to: liu qiang, study of inkjet printing ink volume limiting method based on spectral gamut maximization, spectroscopy and spectral analysis (2013) (in this example, take monochromatic C nie guerber ladder rule as an example, and determine the critical value as 85 if the ink volume overrun problem occurs at C =90 by visual judgment method)
And 3, measuring the color information of the samples of the Neegber ladder ruler in the step 2 by using color measuring equipment, eliminating the corresponding color data of the samples with the ink amount exceeding the limit, and obtaining the color information by measurement as spectral reflectivity information or chromaticity information.
In the embodiment, an X-rite Spectroscopy type scanning spectrophotometer is adopted to measure the Neguerber ladder bar spectral reflectivity information prepared in the step 2, wherein the wavelength range of the spectral reflectivity is 400nm-700nm, and the color information of the sample with the ink amount exceeding the limit is deleted according to the ink amount threshold of each Neguerber primary color ladder bar determined in the step 2.
Step 4, on the basis of the color data obtained by measurement in the step 3, calculating the color gamut volume of the four-color model in the step 1 by using a convex hull algorithm;
in the embodiment, since the spectral reflectance data measured in step 3 has a high dimension (31 dimensions), it is first converted into the LAB chromaticity space under the D50/2 condition by the chromaticity conversion method, and the gamut volumes of the 20 four-color models obtained in step 1 are calculated by using the convex hull algorithm. The conversion from the spectral reflectance space to the chromaticity space and the convex hull algorithm are the prior art, and the following can be specifically seen: schanda J.CIE Colorimetry, wiley Online Library;2007. and Barber CB, dobkin DP, huhdanpaa H.the quick hue algorithms for covex hills.ACM Transactions on chemical Software (TOMS) 1996;22 (4):469-83.
Step 5, on the basis of the color gamut volume calculation in the step 4, calculating the color gamut volume of the four-color model combination with the number of N models by an enumeration method, wherein N =1,2,3,4; then, for any image to be copied, judging the gamut coverage rate G of the gamut corresponding to each four-color model combination to the image to be copied by using a gamut judgment method; in addition, when the gamut coverage G is obtained, the number of models N is tried to be increased from small to large, and when N = N, the number of models N is tried to be increased opt If < 4, G =100%, then N > N need not be tried opt The case of combination. The solution of the color gamut coverage rate G adopts an inhull algorithm, and the value of the inhull algorithm is equal to the ratio of the number of pixels of the image to be copied in the four-color model combined color gamut to the total number of pixels of the image.
In an embodiment, when the number of models N =1, the four color models are combined together
Alternatively, the gamut volume is calculated in step 4 and can be used directly. When the number of models N =2, the four-color models are combined
The species and the like. The ancient drawing duplicate spectral image used in the example was 198 x 465 pixels in size (only usingAs illustrated). When the color gamut coverage rate is obtained, an Inhull algorithm is adopted to calculate whether each pixel point of the image to be copied is in a certain four-color model combination one by one, and the color gamut coverage rate G is defined according to the ratio of the pixel number of the image to be copied in the color gamut of the four-color model combination to the total pixel number of the image. (wherein, the inhall algorithm is the prior art in the field of computer graphics, see D' Errico J. Inhull 2006 http:// www. Mathworks. Com/matlabbcentral/filexchange/10226-inhall.) in actual operation, the number N of models is tried from small to large, and it is found that N is the current state of the art in computer graphics opt If =2, the gamut coverage rate can reach 100%, so that it is not necessary to try N > 2.
Step 6, determining the four-color model combination according to the principle of maximizing the color gamut coverage rate G of the four-color model combination in the step 5;
in the examples, the four color model combinations that satisfy gamut coverage maximization (G = 100%) have 3 groups: CMYK + RGBK, BCGK + MRYK, and RYGK + MRYK.
Step 7, if only one group of model combinations in the step 6 meets the conditions, the optimal split is obtained; if the condition that the multiple groups of combinations simultaneously meet the requirements exists in the step 6, firstly, resampling the image to be copied to reduce the number of pixels to Q, and then calculating Q pixel points and the N four-color model ink volume space middle points W selected in the step 6 i (i =1,2.. N) and selecting a final four-color model combination according to the minimum average color difference C, thereby completing the splitting modeling. Wherein the value of the number Q of the pixel points is more than 100 and less than 200, the point W in the ink volume space is defined as the point with the value of each dimension of the ink volume as 50, and the solution of the average chromatic aberration C is calculated by adopting a CIEDE2000 chromatic aberration formula and adopting a D50/2 chromatic aberration condition.
In step 6, the combination of 3 sets of four color models in total meets the condition of gamut coverage G =100%, so it needs to be screened twice. First, in order to improve the operation efficiency, the original spectral image is reduced from 198 × 465=92070 pixel size to 8 × 19=152 pixel size by sampling every 25 pixel intervals in horizontal and vertical directions. Subsequently, for the 3 sets of four-color model combinations in step 6, the color difference mean values of 152 pixels of the reduced-dimension spectral image and the midpoint of the model are respectively calculated (CIEDE 2000 color difference formula, D50/2 chromaticity condition). Taking the CMYK four-color model as an example, the midpoint of the model, i.e., C = M = Y = K =50 sample points. Wherein, CIEDE2000 color difference formula is prior art, see Luo MR, cui G, rigg B.the depth soft CIE2000 color-difference formula CIEDE2000.ColorResearch & application.2001;26 (5):340-50.
Through calculation, the calculation result of the average color difference between the combination center of the 3 kinds of four-color models and the image to be copied is
CMYK+RGBK：DE2000＝25.9
BCGK+MRYK:DE2000＝19.7
RYGK+MRYK:DE2000＝11.2
Therefore, the RYGK + MRYK four-color model combination is finally selected to complete the final splitting modeling.
To further demonstrate the advantages of the present method in split modeling of a replicated object-oriented multi-color halftone device, the present method is contrasted with the methods used in references 1 and 3 of the present invention. In the contrast method, the CMYKRGB seven-color model is also split into 5 sets of four-color models (CMYK, RMYK, CGYK, CMBK, RGBK) and 5 sets of three-color models (CMY, RMY, CGY, CMB, RGB). However, as is known from the above, the present invention can achieve 100% full coverage of the color gamut of the copied object only by using 2 sets of four-color models, so compared with the comparison method, the method herein can significantly reduce the subsequent modeling workload, thereby improving the modeling efficiency. For example, taking the example of constructing a 5-level sampling CYNSN characterization model, the control method requires printing at least 3750 color samples, whereas the method herein requires printing at least 1250 color samples. In fact, even if the CYNSN model with 6-level sampling is constructed by the splitting method, only 2592 color samples need to be printed, namely, the modeling efficiency can be improved and the modeling precision can be improved by the method of increasing the sampling level and reducing the number of the models. Among them, the cysnn model is a prior art in the field of halftone characterization, and the modeling accuracy thereof is improved by increasing the number of sampling stages, and specifically, the foregoing references 1 to 3 can be referred to.
The invention also provides a split modeling system of the multicolor half-tone equipment facing the copied object, which comprises the following modules:
the device enumeration splitting module splits the multicolor halftone device into M four-color models in an enumeration form, wherein each model contains black ink;
the ink amount limiting module is used for preparing a T-level Neugebert ladder ruler on the basis of a four-color model in the equipment enumeration splitting module, eliminating an ink amount overrun sample by a visual observation method and finishing equipment ink amount limiting on the basis;
the color measuring module is used for measuring the color information of samples of the Neegber ladder ruler in the ink amount limiting module by using color measuring equipment and eliminating the color data of corresponding ink amount overrun samples;
the color gamut volume calculation module is used for enumerating the color gamut volumes of the four-color models in the splitting module by utilizing a convex hull algorithm calculation device on the basis of the color data measured by the color measurement module;
the gamut coverage rate calculation module is used for calculating the gamut volume of the four-color model combination with the number of N by an enumeration method on the basis of the gamut volume calculation of the gamut volume total calculation module, wherein N =1,2,3,4; then, for any image to be copied, judging the gamut coverage rate G of the gamut corresponding to each four-color model combination to the image to be copied by using a gamut judgment method;
the four-color combination primary selection module determines the four-color model combination according to the principle that the color gamut coverage rate G of the four-color model combination in the color gamut coverage rate calculation module is maximized;
the four-color combination final selection module is used for determining that the four-color combination initial selection module is optimal split if only one group of model combinations in the four-color combination initial selection module meets the condition; if a plurality of groups of combinations in the four-color combination initial selection module meet the requirements at the same time, firstly resampling the image to be copied to reduce the number of pixels to Q, then calculating the average color difference C between the Q pixel points and the color value corresponding to the midpoint W in the ink volume space of the N four-color models selected by the four-color combination initial selection module, and selecting the final four-color model combination according to the minimization of the average color difference C to finish splitting and modeling.
Wherein the number T of Neegber steps in the ink quantity limiting module is more than 20.
The color information measured in the color measuring module is spectral reflectivity information or chrominance information.
When the color gamut coverage rate G is obtained in the color gamut coverage rate calculation module, the number N of the models is tried from small to large, and if N = N opt If < 4, G =100%, then no attempt is made to have N > N opt The case of combination. The solution of the color gamut coverage rate G adopts an inhull algorithm, and the value of the inhull algorithm is equal to the ratio of the number of pixels of the image to be copied in the four-color model combined color gamut to the total number of pixels of the image.
The value of the number Q of the pixel points in the four-color combination final selection module is more than 100 and less than 200, and the definition of the midpoint W in the ink volume space of the four-color model is the point with the value of each dimension of the ink volume being 50.
The average color difference C in the four-color combination final selection module is calculated by using a CIEDE2000 color difference formula and a D50/2 chromaticity condition.
The specific implementation of each module corresponds to each step, and details are not repeated in the present invention.
The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.
Claims (10)
1. A split modeling method of a multicolor halftone device facing a copy object is characterized by comprising the following steps:
step 1, splitting a multicolor half-tone device into M four-color models in an enumeration mode, wherein each model contains black ink;
step 2, preparing a T-level Neugebauer ladder based on the four-color model in the step 1, eliminating ink overrun samples by a visual observation method, and completing equipment ink amount limitation on the basis;
step 3, measuring the color information of samples of the Neeger ladder ruler in the step 2 by using color measuring equipment, and eliminating corresponding color data of the ink amount overrun samples;
step 4, on the basis of the color data obtained by measurement in the step 3, calculating the color gamut volume of the four-color model in the step 1 by using a convex hull algorithm;
step 5, on the basis of the color gamut volume calculation in the step 4, calculating the color gamut volume of the four-color model combination with the number of models being N by an enumeration method, wherein N =1,2,3,4; then, for any image to be copied, judging the gamut coverage rate G of the gamut corresponding to each four-color model combination to the image to be copied by using a gamut judgment method;
step 6, determining the four-color model combination according to the principle of maximizing the color gamut coverage rate G of the four-color model combination in the step 5;
step 7, if only one group of model combinations in the step 6 meets the conditions, the optimal split is obtained; if the condition that the multiple groups of combinations meet the requirements simultaneously exists in the step 6, firstly, resampling is carried out on the image to be copied, the number of pixels is reduced to Q, then, the average color difference C between the Q pixel points and the color value corresponding to the dot W in the ink volume space of the N four-color model combinations selected in the step 6 is calculated, and the final four-color model combination is selected according to the minimization of the average color difference C, so that the splitting modeling is completed.
2. A split-modeling method for a multicolor halftone apparatus facing copied objects according to claim 1, wherein T, the niguerber scale number in step 2 is greater than 20.
3. The method for split-modeling a replicated object-oriented multicolor halftone apparatus according to claim 1, wherein the color information measured in step 3 is spectral reflectance information or chrominance information.
4. The split modeling method for a multicolor halftone apparatus for replicated objects according to claim 1, wherein: when the color gamut coverage rate G is obtained in step 5, the number N of models is tried from small to large, and if N = N opt If < 4, G =100%, then N > N need not be tried opt Combined cases, where the solution of gamut coverage G uses the inhull algorithm, the value of whichAnd the ratio of the pixel number of the image to be copied in the four-color model combined color gamut to the total pixel number of the image is equal to the ratio of the pixel number of the image to be copied in the four-color model combined color gamut to the total pixel number of the image.
5. The split-type modeling method for multicolor halftone equipment facing to the copied object according to claim 1, wherein in step 7, the number Q of pixels is more than 100 and less than Q and less than 200, the point W in the space of the combined ink volume of the four-color model is defined as the point where the dimension of the ink volume takes on the value of 50, and the solution of the average color difference C should be calculated by using a CIEDE2000 color difference formula and using a D50/2 chromaticity condition.
6. A split modeling system of a multicolor halftone device facing a copied object is characterized by comprising the following modules:
the device enumeration splitting module is used for splitting the multicolor halftone device into M four-color models in an enumeration form, wherein each model contains black ink;
the ink amount limiting module is used for preparing a T-level Neugebert ladder ruler on the basis of a four-color model in the equipment enumeration splitting module, eliminating an ink amount overrun sample by a visual observation method and finishing equipment ink amount limiting on the basis;
the color measuring module is used for measuring the color information of samples of a Neugebauer ladder ruler in the ink amount limiting module by using color measuring equipment and removing the color data of corresponding ink amount overrun samples;
the color gamut volume calculation module is used for enumerating the color gamut volumes of the four-color models in the splitting module by utilizing a convex hull algorithm calculation device on the basis of the color data measured by the color measurement module;
the gamut coverage rate calculation module is used for calculating the gamut volume of the four-color model combination with the number of N by an enumeration method on the basis of the gamut volume calculation module, wherein N =1,2,3,4; then, aiming at any image to be copied, judging the color gamut coverage rate G of the color gamut corresponding to each four-color model combination to the image to be copied by using a color gamut judgment method;
the four-color combination initial selection module determines the four-color model combination according to the principle that the color gamut coverage rate G of the four-color model combination in the color gamut coverage rate calculation module is maximized;
the four-color combination final selection module is used for determining that the four-color combination initial selection module is the optimal split if only one group of model combinations in the four-color combination initial selection module meets the conditions; if a plurality of groups of combinations in the four-color combination initial selection module meet the requirements at the same time, firstly resampling the image to be copied to reduce the number of pixels to Q, then calculating the average color difference C between the Q pixel points and the color value corresponding to the midpoint W in the ink volume space of the N four-color models selected by the four-color combination initial selection module, and selecting the final four-color model combination according to the minimization of the average color difference C to finish splitting and modeling.
7. The replication-object-oriented multi-color halftone apparatus split modeling system of claim 6, wherein the Neegber step number T in the ink volume limiting module should be greater than 20.
8. The split modeling system for multicolor halftone equipment for replicated objects according to claim 6, wherein the color information measured in the color measurement module is spectral reflectance information or chrominance information.
9. The split modeling system for multicolor half tone apparatus for copy object as claimed in claim 6, wherein the number of models N should be tried from small to large when the gamut coverage G is calculated in the gamut coverage calculation module, and if N = N opt If < 4, G =100%, then N > N need not be tried opt And combining the situations, wherein the solution of the color gamut coverage rate G adopts an inhull algorithm, and the value of the inhull algorithm is equal to the ratio of the number of pixels of the image to be copied in the four-color model combined color gamut to the total number of pixels of the image.
10. The split modeling system for multicolor halftone equipment facing to the copied object according to claim 6, wherein the number Q of pixels in the four-color combined final selection module is 100 < Q < 200, the point W in the ink volume space of the four-color model is defined as the point where each dimension of the ink volume takes on the value of 50, and the solution of the average color difference C in the four-color combined final selection module should be calculated by using the CIEDE2000 color difference formula and using the D50/2 chromaticity condition.
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