Elmar Eisemann

Flash photography enhancement via intrinsic relighting

We enhance photographs shot in dark environments by combining a picture taken with the available light and one taken with the flash. We preserve the ambiance of the original lighting and insert the sharpness from the flash image. We use the bilateral filter to decompose the images into detail and large scale. We reconstruct the image using the large scale of the available lighting and the detail of the flash. We detect and correct flash shadows. This combines the advantages of available illumination and flash photography.

Fast scene voxelization and applications

This paper presents a novel approach that uses graphics hardware to dynamically calculate a voxel-based representation of a scene. The voxelization is obtained on run-time in the order of milliseconds, even for complex and dynamic scenes containing more than 1,000,000 polygons. The voxelization is created and stored on the GPU avoiding unnecessary data transfer. The approach can handle both regular grids and locally optimized grids that better fit the scene geometry. The paper demonstrates applications to shadow calculation, refraction simultation and shadow volume culling/clamping.

Sample based visibility for soft shadows using alias-free shadow maps

This paper introduces an accurate real‐time soft shadow algorithm that uses sample based visibility. Initially, we present a GPU‐based alias‐free hard shadow map algorithm that typically requires only a single render pass from the light, in contrast to using depth peeling and one pass per layer. For closed objects, we also suppress the need for a bias. The method is extended to soft shadow sampling for an arbitrarily shaped area‐/volumetric light source using 128‐1024 light samples per screen pixel. The alias‐free shadow map guarantees that the visibility is accurately sampled per screen‐space pixel, even for arbitrarily shaped (e.g. non‐planar) surfaces or solid objects. Another contribution is a smooth coherent shading model to avoid common light leakage near shadow borders due to normal interpolation.

Visibility Sampling on GPU and Applications

In this paper, we show how recent GPUs can be used to very efficiently and conveniently sample the visibility between two surfaces, given a set of occluding triangles. We use bitwise arithmetics to evaluate, encode, and combine the samples blocked by each triangle. In particular, the number of operations is almost independent of the number of samples. Our method requires no CPU/GPU transfers, is fully implemented as geometric, vertex and fragment shaders, and thus does not impose to modify the way the geometry is sent to the graphics card. We finally present applications to soft shadows, and visibility analysis for level design.

Plausible Image Based Soft Shadows Using Occlusion Textures

This paper presents a novel image-based approach to render plausible soft shadows for complex dynamic scenes with rectangular light sources. The algorithms performance is mostly independent of the scene complexity and the sources size. Occluders and receivers do not need to be separated and no knowledge about the scene representation is required, making the method easy to use. The main idea is to approximate the occlusion in the scene with pre-filtered occlusion textures. The visibility of the light source at a point in space is estimated by accumulating the occlusion caused by each texture, using a novel formula based on probabilities

Clip Art Rendering of Smooth Isosurfaces

Clip art is a simplified illustration form consisting of layered filled polygons or closed curves used to convey 3D shape information in a 2D vector graphics format. This paper focuses on the problem of direct conversion of smooth surfaces, ranging from the free-form shapes of art and design to the mathematical structures of geometry and topology, into a clip art form suitable for illustration use in books, papers, and presentations. We show how to represent silhouette, shadow, gleam, and other surface feature curves as the intersection of implicit surfaces and derive equations for their efficient interrogation via particle chains. We further describe how to sort, orient, identify, and fill the closed regions that overlay to form clip art. We demonstrate the results with numerous renderings used to illustrate the paper itself.

Occlusion Textures for Plausible Soft Shadows

This paper presents a new approach to compute plausible soft shadows for complex dynamic scenes and rectangular light sources. We estimate the occlusion at each point of the scene using prefiltered occlusion textures, which dynamically approximate the scene geometry. The algorithm is fast and its performance independent of the lights size. Being image‐based, it is mostly independent of the scene complexity and type. No a priori information is needed, and there is no caster/receiver separation. This makes the method appealing and easy to use.

On Exact Error Bounds for View‐Dependent Simplification

In this article we present an analytical closed‐form expression to ensure exact error bounds for view‐dependent simplification which is of importance for several algorithms. The present work contains proofs and solutions for the general 2D case and particular 3D cases.