局部特征加强的体绘制算法

摘要

最大强度差值累积结合了直接体绘制和最大强度值投影的优势,但其在累积过程中会遗漏一些局部特征.为了绘制体数据中局部特征信息,提出一种局部特征加强的直接体绘制方法.通过查找采样光线上特征边界点来确定局部最大强度的区域,利用局部差值累积的方法加强特征区域的绘制；为了提高特征分界点的查找精度,引入移动最小二乘法来平滑采样光线上的标量值,并利用用户自定义的阈值函数来控制特征的绘制；在绘制过程中,采用特征分析的表面光照模型增强绘制特征的三维立体感,引入深度信息对局部特征累积算法进行优化,并引入了Tone衰减方法使累积颜色值处于正常显示范围.实验结果表明,文中方法可在不需要传输函数的前提下绘制体数据中的特征信息.%Maximum intensity difference accumulation combines the advantage of direct volume rendering and maximum intensity projection, but other features with local maximum intensity are not displayed in the final rendering image with this approach. In this paper, we present a novel feature enhanced accumulation approach to enhance features with local maximum intensity in the ray profile. Moving least squares is employed to smooth each ray profile and obtain the significant features with transition points. A local minimum-point searching method is adopted to analyze the features of the ray profile. In the rendering stage, a local intensity difference accumulation is proposed to improved integral composition of color and opacity. Also a feature analysis based surface shading is introduced to improve the spatial cues of features. Finally, Tone-reduction is employed to solve the problem that the accumulated color of the final image is beyond the luminance limitation, and preserve the original local contrast. Our approach highlight the features without complex transfer function. The experiments demonstrate the high quality rendering results of several datasets, especially from medical field.