The Black Generation Method Based On Maximized Printing Gamut

In the process of color image reproduction,the traditional Neugebauer equation is limited by the equation itself.If only the tristimulus values are used to solve the dot area ratio of the four channels of CMYK,there will be many solutions.Therefore,how to choose the best black value is of great significance to color printing.In this type of method,gray balance algorithm and algorithm based on color gamut range division are typical.These two methods need to artificially set the black replacement rate during calculation;and the value of the best black plate replacement rate can only be set by experience,which greatly reduces the efficiency of the model.However,in this thesis’ s printing black generation method based on color gamut maximization,there is no need to set the black replacement rate,and the calculated black value is the best black value.At the same time,in the process of generating the gamut boundary lookup table,by adding black ink at the boundary of the gamut,the gamut after color separation calculation can also be maximized.In this thesis,the gamut space of the printer is regarded as a cube,and it is divided into six tetrahedrons,then the gaumt center black generation lookup table and the gamut boundary black generation lookup table are constructed.Each tetrahedron contains a gaumt center black generation lookup table and two boundary black generation lookup tables.For the color points to be calculated for color separation,first calculate the c,m,and y values according to the Neugebauer Equations,and then find the corresponding tetrahedron according to the size relationship between c,m,and y.Use min(c,m,y)as the index to calculate the CMYK value of the corresponding point on the lookup table,finally perform linear interpolation on the obtained CMYK value to obtain the final CMYK value.In order to make the color separation results more accurate,an optimization algorithm is used to optimize the results.In order to test the effect of color separation calculation in this thesis,three evaluation experiments are designed: model accuracy evaluation experiment,gamut space evaluation experiment,and image reproduction effect experiment.The experimental results show that: in the model accuracy evaluation experiment,the average color difference,maximum color difference,color difference fluctuation coefficient and other parameters calculated by this thesis are better than the professional color management software i1 Profiler.In the color gamut space evaluation experiment,after using the model in this thesis for color separation calculation,the distribution of color points is the same as before the color separation calculation,and it can also maximize the color gamut after color separation calculation changes.In the image reproduction effect evaluation experiment,the color-separated image using the method of this subject is close to i1 Profiler software,and is better than the gray balance algorithm.The innovation of this thesis is reflected in two aspects.(1)In the process of generating the gamut boundary black generation lookup table,a series of new gamut vertices are obtained by continuously adding black ink in the gamut boundary.By connecting these vertices,a new gamut boundary line is obtained,which significantly expands the gamut space after color separation calculation compared with the gamut boundary line generated by the traditional method.At the same time,when determining the black plate value,there is no need to set the black replacement rate,which greatly improves the efficiency and accuracy of color separation calculation.(2)In order to solve the problem of CMYK value contradiction at the lowest point of lightness in the color gamut,this thesis adopts a double-threshold processing method.When designing color blocks and calculating the look-up table,thresholds are set separately,thus ensuring at the lowest point of lightness,C,M,and Y take the same value as CMYmax.