Study On 3D Printed Object Color Difference Evaluation

With the continuous development and innovation of 3D imaging technology and 3D printing technology,3D image acquisition equipment can not only capture and simulate 3D images of objects,but also accurately measure the shape,structure,volume and texture of the measured object.Combined with 3D printing technology,it can realize fast,simple and cheap industrial manufacturing.In order to build a bridge between the users of 3D printed products and the 3D printing process,and to ensure the color fidelity of 3D printed products,this article will be based on the color measurement and color difference evaluation experience and results of flat objects accumulated by color science researchers in the early stage.In view of the lack of experience and methods of 3D object color difference evaluation in 3D printing intelligent manufacturing,an objective evaluation method of 3D object color difference is discussed,and provides experimental data for the establishment of visual perception 3D object surface color difference evaluation standards.The main research work and innovative points of this thesis are as follows:(1)A total of 150 3D sample pairs around 5 CIE color centers(gray,red,yellow,green,blue)and two shapes(spherical and flat)were prepared by a Mcor Iris 3D paper-based printer.Among them,spherical sample and flat sample each account for 75 pairs,the average color difference is 10.3 and 6.7 CIELAB color difference units,respectively,and the sample diameter is 4cm.Before printing,the polynomial regression method was used to characterize the color printer color characteristics to obtain the color RGB of the 3D printed samples.The entire printing process takes about three and a half months.(2)In order to study the correlation between two illumination light sources,diffuse lighting and spotlight,and the shape of the sample,with the visual perception of the color difference on the surface of the 3D object,10 observers were organized to participate in the psychophysics experiment of color difference evaluation,and the data of visual perception color difference was collected and used.The evaluation methods such as STRESS and color discrimination ellipse,as well as mathematical statistics,chromaticity ellipse fitting,Monte Carlo ellipse comparison and other methods were used to systematically analyze this experimental data set and the data sets collected in other previous experiments.The analysis results show that the size of the color difference affects the human eye's perception of the color difference,and it has a greater impact on the color difference than the sample shape and the illumination source.Comparing the ellipses of the experimental data set,it is found that the ellipses of the spherical samples have better correlation than the ellipses of the flat samples.(3)Based on the experimental data set,the prediction performance of 10 classic color difference formulas including CIELAB,CIEDE2000,CIE94,CMC,DIN99d,CAM02-SCD,CAM02-LCD,CAM02-UCS,OSA,OSA?GP?Eu were tested.The test results show that for large color differences,the performance of all the tested color difference formulas in predicting the color difference of 3D objects are very close.Among them,the CAM02-LCD color difference formula used to evaluate large color differences performs best,and the CMC formula performs worst.In this paper,the lightness parameter factor(k_L)was used to optimize the color difference formula,and the optimization effect was not large,which indicates that the existing color difference formula is more accurate in predicting 3D objects.