Visualization by proxy: A novel framework for deferred interaction with volume data

visualize multiple layers of a 3D object (shown in (b)) in multiple orientations. We can also inexpensively simulate complex lighting models such as proxy-based ambient occlusion, while retaining the spatial relationships between semi-transparent layers. This is done without accessing 3D volume data. (c) Accumulated attenuation proxy images allow us to explore data sets in transfer function space and to apply depth-aware enhancement, which highlights shape and alleviates depth ambiguities, often found in static images. (d) We can combine accumulated attenuation proxy images (shown in (c)), with depth proxy images (below) to support lighting effects. (g) Multi-perspective accumulated attenuation proxy images allow us to visualize a volumetric object in multiple orientations. Abstract—Interactivity is key to exploration of volume data. Interactivity may be hindered due to many factors, e.g. large data size, high resolution or complexity of a data set, or an expensive rendering algorithm. We present a novel framework for visualizing volume data that enables interactive exploration using proxy images, without accessing the original 3D data. Data exploration using direct volume rendering requires multiple (often redundant) accesses to possibly large amounts of data. The notion of visualization by proxy relies on the ability to defer operations traditionally used for exploring 3D data to a more suitable intermediate representation for interaction- proxy images. Such operations include view changes, transfer function exploration, and relighting. While previous work has addressed specific interaction needs, we provide a complete solution that enables real-time interaction with large data sets and has low hardware and storage requirements. Index Terms—Volume visualization, deferred interaction, image-based rendering, volume distortion camera.