圆明亮琢型立方氧化锆在环形光源下的亮度测量研究

运用钻石光学效果观察仪采集合成立方氧化锆（CZ）样品的光学效果的实测图样，采用中国地质大学（武汉）珠宝学院石斌博士研发的宝石切工仿真分析系统模拟样品的光学效果仿真图样及可视亮度。通过量化程序统计样品实测图样的亮度值，以及仿真图样的亮度值。研究在入射角度为7．12°-12．58°的环形光源下，样品的实测亮度与主要切工参数的关系；对比仿真图样与实测图样的异同；分析样品可视亮度与仿真图样的统计亮度值的变化趋势，发现样品仿真图样的统计亮度值与模拟的可视亮度变化趋势基本一致；对称性较好样品的仿真图样与实测图样较一致；亭角38．5°-41．5°，冠角27°-39°之间一些特定组合的样品具有较高的亮度。结果表明，通过采集、分析图样测量圆明亮琢型宝石实际亮度的方法是准确可行的；对称性或某些参数的细微变化都可能引起样品亮度很大的变化；亮度较高样品的亭角、冠角满足加和规律，即亭角减小必须与需锫增加相静会．才鲐呈拥掂高的毒序

Study on Measuring Brilliance of Round Brilliant Cut Cubic Zirconia under Ring Light

In this paper, the instrument for observing the illumination effects in diamond, in- vented by Professor Yuan Xinqiang,is used to capture the actual image pattern of 48 round brilliant cut cubic zirconia（CZ） under the incident light with angle of 7.12 degree to 12.58 degree. The cutting parameter of samples is diverse from each other. Table width ranges from 57% to 63% and crown angle ranges from 25 degree to 42 degree, with pavilion angle changing from 36 degree to 42 degree. The actual image pattern is a real colour bitmap file, and the pixel is comprise of red, green and blue. The quantification procedure transforms RGB colour space to YUV colour space. The Y component determines the brightness of the colour and refers to luminance or luma, which ranges from 0 to 255 in digital formats. Accu- mulating Y value of all pixels of the actual image pattern and the summation are regarded as the brilliance of the sample. Then the brightness value is normalized and the contour map is done with crown angle as the X-axis and pavilion angle as Y-axis and brightness values as Z-axis. Brightness values of several samples are relatively high and they can be easily found in the map. The crown angle ranges from 27 degree to 39 degree, and pavilion angle ranges from 38.5 degree to 41.5 degree. However, not all the samples in the scope own the high brightness value. The change of brightness values over cutting parameters is discontinuous uneven. Sometimes, the brightness values vary considerably, even their cutting parameters of the samples are very similar. While sometimes the brightness values are similar, but their cutting parameters are quite different. The computer 3D modeling system created by Shibin is used to simulate the Viewable Brightness Return （VBR） and virtual image pattern of the round brilliant cut CZ. Contrasting the similarities and differences between virtual image pat- terns and actual image patterns, we can find that virtual image patterns and actual image pat- terns of 36 samples are generally consistent, as symmetrical characteristic of these samples is good and cutting parameter is exact. However, examining the image patterns carefully, there are still some differences in details. Obviously, the virtual image patterns are perfect, and the actual image patterns have some irregular bright and dark regions. The phenomenon is possible because of the complicated path of the light, which goes through the CZ samples. The light may deviate from the ideal light path while the cutting parameter, the symmetrical characteristic or the internal characteristics vary. The virtual image patterns and actual im- age patterns of the other 12 samples are different and some even show opposite patterns. Their symmetrical characteristics are had, such as bigger than 12 % ovality, culet significant- ly deviating from the center, uneven thickness of girdle. In a conclusion, symmetrical char- acteristic has a great influence on the actual illumination effects of the samples, which should not be neglected. Calculating the brightness values of the virtual image patterns, comparing and analyzing the brightness values and the simulative VBR, the authors find variation tend- encies of the VBR and the brightness values are similar. It is proved that the method used to deal with the image pattern is accurate and reasonable. The results show that the symmetri- cal characteristics or subtle differences of some parameters may lead to big changes of bril- liance to a certain range. The reverse change of crown angle and pavilion angle can produce a similar good brilliance. The method of measuring the appearance to evaluate the illumination effects of round brilliant diamond is viable.