goethe-universität frankfurt - professur graphische ... · surface reconstruction and artistic...

Surface reconstruction and artistic rendering of small paleontological specimensSebastian Schäfer, Carsten Heep

Goethe-Universität Frankfurt

Acknowledgement: We thank Dr. Thomas Lehmann and Dr. Krister Smith from Senckenberg Research Institute and Natural History Museum Frankfurt for their expert opinions and support.

Outline1. Reconstruction

Record imagestack

Create heightmap

Create mesh and

total-focus-texture

2. Rendering

Render G-Buffers

Create Outlines

Render artistic style:

Realistic

Gooch-Shading

Hatching

Stippling

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AbstractAn important domain of paleontological research is the creation of hand-drawn artistic images of small fossil specimens. In this paper we discuss the process of writing an adequate tool to semiautomatically create the desired images and export a reconstructed 3D-model. First we reconstruct the three-dimensional surface entirely on the GPU from a series of images. Then we render the virtual specimen with Non-Photorealistic-Rendering algorithms that are adapted to recreate the impression of manually drawn images. These algorithms are parameterized with respect to the requirements of a user from a paleontological background.

Reconstruction

The first step is to reconstruct the 3D-surface of the fossil. We concentrated our study on small paleontological specimens that have a diameter of a few millimeters. From a specimen we create an imagestack using a motorfocus microscope.

A method called Shape From Focus [2] generates a heightmap by using energy to identify focused pixels. We implemented the original algorithm on the GPU and extended it by an energy-threshold [3] to filter out low energy pixels. The holes are filled with a two-step algorithm on the GPU as it was described in [1]. Compared to a CPU-based implementation we achieve a maximum speed-up factor of 30.

Artistic RenderingWe render the final image using a deferred rendering system:

Depth- and Normalmap usefull for Outlines Albedomap based on total-focus-texture Illuminationmap based on a modified lambertian illumination

Scientific drawings are usually drawn from five perspectives: dorsal, lateral left, lateral right, anterior and posterior which we realized as presets for the camera position. Light source and camera can be positioned around the object on a hemisphere using polar coordinates.

Currently there are three artistic renderstyles implemented: Gooch-Shading to visualize surface & structure [5] Hatching for an artistic illustration [4] Stippling for a scientific illustration

The user can choose to add an outline which is created from Depth- and Normalmap.

We implemented hatching and stippling as screen-space algorithms. Both rely on textures that are generated in a preprocess step. While the hatching-textures are manually drawn the stippling-texture is automatically generated. The points are randomly placed on the texture plane until it is filled. For every point the iteration it was placed is encoded in its RGB-Value. Depending on the value stored in the Illuminationmap the number of stippling points

shown in an area can be varied so that darker image parts have more stippling points. The final image is filtered with an adaptive blur for more pleasing results.

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References:[1] HEEP & SCHÄFER, 2010:

3d-oberflächen-rekonstruktion und plastisches rendern [...][2] NAYAR & NAKAGAWA, 1994:

Shape from focus[3] SCHÄFER & NAGL, 2010:

3d surface reconstruction of arbitrary (image) layer[4] PRAUN, HOPPE, WEPP & FINKELSTEIN, 2001:

Real-time Hatching[5] GOOCH, GOOCH, SHIRLEY & COHEN, 1998:

A non-photorealistic lighting model for automatic technicalillustration

First erase noisy areas via threshhold, then fill them up in two steps

1. Step 2. Step

NPAR: Non-photorealistic Animation and Rendering - 2011 - Vancouver/Canada

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