中文摘要：

运用钻石光学效果观测仪采集钻石样品在环形光线下的图像,运用HSI（色调、饱和度、亮度）颜色 模型转换技术,将图像由RGB颜色模型转换到HSI颜色模型进行处理,计算钻石的火彩值.对比分析钻石 图像中彩色的分布特征和火彩值,彩色分布较多的钻石样品,火彩值也较高,火彩值与肉眼感知结果基本一致,说明定量分析钻石火彩的方法准确可行.对比分析钻石的火彩值与冠角、亭角之间的关系,结果显示托尔 夫斯基提出的理想切工的钻石呈现出较高的火彩,彼此佐证;钻石的火彩值与亭角或者冠角之间并非简单的 线性函数关系,说明定量分析钻石火彩的必要性.

英文摘要：

The main illumination effects are brilliance, fire, and scintillation. In this paper, we took photographs of some diamond samples in the light source with different incident an-gles in order to evaluate the fire of round brilliant cut diamond. The light source was com-posed of LED light arranged in six circle, with incident angles at 14. 5°, 18. 5°,21. 5°,25. 5°, 28. 5° and 32. 5°. The photographs by software programmed were BMP bitmap files. The software could capture the RGB colour model of each spot in the image, and converse the RGB colour space into HSI （Hue,Saturation, Intensity） colour space. Until the value of saturation is more than 25%, and the value of intensity is more than 20%, the pixel point can be regarded as fire, which add up intensity of all pixel points. The fire value is equal to the sum of intensity divided by the number of the pixel points related to the diameter of the diamond. The result showed that the accuracy and stability of system were enhanced by av-eraging the values of tests.There are 48 diamond samples with table 56 %± 1 % , star facet 53 % ± 5 % , lower girdle facet 76%±6 %,girdle 3%±0. 5%,the crown angle range from 27° to 40° and the pavilion angle range from 38° to 43°. The fire value of 48 diamond samples are 2. 0 -12. 0. Observingthe images of diamond by naked eye, the fire value was quite higher when the colour area in the image is more, the test results were consistent with the feeling of people. The fire value is irregular between the fire and crown angle or pavilion angle of round brilliant cut diamond. The ideal cut diamond （suggested by Tolkowsky M） really can present good fire.In conclusion, the method to evaluate the fire in round brilliant cut diamond is exact. The diamonds with pavilion angle at 40° or 41° and the crown angle at 35° or 39° can display better fire. The relationships among the fire, crown anglei and pavilion angle are nonlinear, it is necessary to evaluate the