Detail Enhancement in Volume Rendering* Wenli CAT, Tianzhou CHEN, and Jiaoying SF11 State Key Lab of CAD&CG, Zhejiang University Hangzhou, Zhejiang 3 10027, China ABSTRACT Aiming at detail enhancement in volume rendering, a new volume illumination model, called Composed Scattering Model (CSM), is presented. In order to enhance different details in data, scattering intensity is decomposed into volume scattering intensity and surface scattering intensity, and composed with boundary detection operators. CSM can generate images containing more details than current volume rendering models. This model has been applied to the direct volume rendering of 3D data sets obtained by CT and MRT. The resultant iMages show not only rich details but also clear boundary surfaces. CSM is demonstrated as an accurate volume rendering model suited for detail enhancement in volume data set. Key Words: volume rendering, volume illumination model, ray casting algorithm 1. INTRODUCTION Currently, the displaying of 3D data sets, especially 3D scalar data sets including CT and MIRI, is the main research direction in scientific visualization. The methods include contour extraction or reconstruction [1, 2, 3J, voxel-based rendering under surface illumination model [4, 5], and direct volume rendering under volume illumination model [6, 7, 8, 9, 141. Due to its high fidelity, direct volume rendering attracts more research attentions and becomes the most highlight research direction in scientific visualization. In direct volume rendering, the widely used volume illumination models include source attenuation model [121, varying density emitters model [8] and classification and mixture model [7]. The results under these models are proved to be lack of details. Aiming at the accurately volume rendering, Krueger [14] proposed a model according to the transfer equation [13]. He employed the Monte Carlo random simulation method to compute the intensity. His method is very time- consuming and his attention lies on the general theory base, did not reach to the volume illumination model from the point of view of showing the data features, especially on the details in the data sets. In order to enhance the details in volume data, we put forward a new volume illumination model, called Composed Scattering Model (CSM), also based on the transfer equation but with different aims. The goal of CSM is to supply a measure to approximate the details in volume. The early works on direct volume rendering are the rendering of random medium, especially on gas object, such as cloud, fog, mist, vapor, etc. Blinn[1OJ, Kajiya[6], Max[1 1] and Sakas[9] studies the attenuation of rays crossing through the random medium. Their researches resulted in a series of random medium illumination models and rendering algorithms aiming at blur boundaries like cloud and fog. CSM are based on the source attenuation model and aiming at clear details compared with the blur details in radium mediums like fog and smoke. In CSM, the details we enhanced are the details in volume and the details in boundary surface. The rendering result should show the strength and position of the details. In order to reflect these two kinds of detail information in volume, the scattering intensity are decomposed into volume scattering intensity and surface scattering intensity. The detail of the volume data is preserved in the volume scattering intensity and the detail of boundary surface is preserved in the surface scattering intensity. The value of segmentation is used to represent the strength of these details. The image segmentation operator is direct integrated into the composition of scattering intensity as the weights. We called it composed scattering model (CSM). CSM takes the segmentation and illumination intensity calculation as two coherent processes. Therefore, * This research was supported by the special grant from NSTC of China, the grant (No.69303008) from NNSF of China, and the grant (No.692053) from NNSF of Zhejiang Province. O-8194-2015-8/96/$6.OO SPIE Vol. 2644/267