Abstract: Direct volume rendering (DVR) is an effective method for volumetric data visualization, while it usually needs a transfer function that assigns different optical properties such as color and opacity to the voxels.However, to find a good transfer function is time consuming, since it generally requires the considerable expertise of the user.In this paper, we present feature-based opacity modulation for DVR.We obtain the feature of voxels from the ray profile of DVR, and these features are represented as different layers of sampling points.The opacity of these sampling points will be associated with the number of features of the ray.In order to achieve maximum visibility of the farthest sampling points, we modify the traditional ray integral for DVR.Our demonstration shows that our approach does not require the complicated transfer function, and it can produce more features in the final rendered image than previous methods.