Computer Graphics

Computer Graphics is about digital models for threedimensional geometric objects as well as images. These shapes and images may represent approximations of the real world or could be synthetic, i.e., exist only in the computer. Goals of computer graphics research are the generation of plausible and informative images, and computation with reasonable resources, i.e. in a short amount of time with little storage requirements. The models and algorithms for this task combine knowledge from different areas of mathematics and computer science.

Optimal Discrete Slicing

Slicing is the procedure necessary to prepare a shape for layered manufacturing. There are degrees of freedom in this process, such as the starting point of the slicing sequence and the thickness of each slice. The choice of these parameters influences the manufacturing process and its result: the number of slices significantly affects the time needed for manufacturing, while their thickness affects the error. Assuming a discrete setting, we measure the error as the number of voxels that are incorrectly assigned due to slicing. We provide an algorithm that generates, for a given set of available slice heights and a shape, a slicing that is provably optimal. By optimal we mean that the algorithm generates sequences with minimal error for any possible number of slices. The algorithm is fast and flexible, it can accommodate a user driven importance modulation of the error function and allows the interactive exploration of the desired quality/time tradeoff.
We can demonstrate the practical importance of our optimization on several 3D-printed results.

The technical background is described in a paper that now appeared in ACM TOG.

UIST 2016: Changing the Appearance of Physical Interfaces Through Controlled Transparency


We present physical interfaces that change their appearance through controlled transparency. These transparency-controlled physical interfaces are well suited for applications where communication through optical appearance is sufficient, such as ambient display scenarios. They transition between perceived shapes within milliseconds, require no mechanically moving parts and consume little energy. We build 3D physical interfaces with individually controllable parts by laser cutting and folding a single sheet of transparency-controlled material. We explore the benefits of transparency-controlled physical interfaces by characterizing their design space and showcase four physical prototypes.

Please see our project page for more details.

Our work was featured on Fast Company Co.Design, Vice Motherboard and Futurism.

CG&A Special Issue: Measuring Visual Salience of 3D Printed Objects


We investigate human viewing behavior on physical realizations of 3D objects. Using an eye tracker with scene camera and fiducial markers we are able to gather fixations on the surface of the presented stimuli. This data is used to validate assumptions regarding visual saliency so far only experimentally analyzed using flat stimuli. We provide a way to compare fixation sequences from different subjects as well as a model for generating test sequences of fixations unrelated to the stimuli. This way we can show that human observers agree in their fixations for the same object under similar viewing conditions – as expected based on similar results for flat stimuli. We also develop a simple procedure to validate computational models for visual saliency of 3D objects and use it to show that popular models of mesh salience based on the center surround patterns fail to predict fixations.

Please see our project page for more details.

NPAR 2015: The Markov Pen – Online Synthesis of Freehand Drawing Styles


Learning expressive curve styles from example is crucial for interactive or computer-based narrative illustrations. We propose a method for online synthesis of free-hand drawing styles along arbitrary base paths by means of an autoregressive Markov Model. Choice on further curve progression is made while drawing, by sampling from a series of previously learned feature distributions subject to local curvature. The algorithm requires no user adjustable parameters other than one short example style. It may be used as a custom “random brush” designer in any task that requires rapid placement of a large number of detail-rich shapes that are tedious to create manually.


See the project page for more details.

Eurographics 2015: Approximating Free-form Geometry with Height Fields for Manufacturing


We consider the problem of manufacturing free-form geometry with classical manufacturing techniques, such as mold casting or 3-axis milling. We determine a set of constraints that are necessary for manufacturability and then decompose and, if necessary, deform the shape to satisfy the constraints per segment. We show that many objects can be generated from a small number of (mold-)pieces if some deformation is acceptable. We provide examples of actual molds and the resulting manufactured objects.

See the project page for more details.

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Panono one of the 36 coolest gadgets of 2014

Panono-Panoramic-Ball-Camera-5Panono’s panoramic camera, originally developed as a thesis work by CG alumnus Jonas Pfeil is now in it’s second revision and has been selected one of the 36 coolest gadgets in 2014 by CNN.

Eurographics Outstanding Technical Contributions Award


Prof. Alexa receives the Outstanding Technical Contributions Award of Eurographics. The award is “given each year to an individual in computer graphics to highlight some outstanding technical achievement.”

The award has been presented at the yearly main conference of Eurographics, which took place in Strasbourg, France this year.

Andy Nealen’s Osmos on The Simpsons!

Screen Shot 2014-04-15 at 9.51.34 AM

Prominently featured in an episode of The Simpson was CG alumnus Andy Nealen’s game, Osmos: Milhouse had his iPad stolen on “The Simpsons.” When he finds it in Bart’s possession and begins to confront him, he is entranced by “the music of this bubble game.”

Panono at TV Total


Jonas Pfeil, alumnus of the CG group, is turning his thesis work into a product: panono – a panoramic ball camera. Right now they are running a crowd-funding campaign on indiegogo and he appeared at TV Total, a popular late night talk show.