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Bidarahalli, Suman; Kuijper, Arjan [1. Gutachten]; Brunton, Alan [2. Gutachten]

A Distributed 3D Print Driver

2017

Darmstadt, TU, Master Thesis, 2017

Determining material arrangements to control high-resolution multi-material 3D printers for reproducing shape and visual attributes of a 3D model (e.g. spatially-varying color, translucency and gloss) requires large computational effort. Today's resolution and print tray sizes allow prints with more than 1012 voxels each filled with one of the available printing materials (today up to 7 materials can be combined in a single print). Cuttlefish, a 3D printing pipeline, processes the input in a serial fashion leading to increased computation time for higher number of models. Distributed computing is one way of achieving better performance for large computations. Through this master thesis, we have developed a distributed version of the cuttlefish printer driver in which the computational task is distributed amongst multiple nodes in the cluster and the resulting partial output is merged to generate the full slices. The architecture supports streaming, which is required to rapidly start the print before the full computation is finished, as cuttlefish processes the input in small parts and generates chunk-wise output. Finally, the comparison of the performance achieved by the distributed vs the non-distributed cuttlefish version is established to get a better understanding of the advantages and the challenges of distributed computing.

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Reinhard, Johann; Kuijper, Arjan [1. Gutachten]; Brunton, Alan [2. Gutachten]

Discrete Medial Axis Transform and Applications for 3D Printing

2017

Darmstadt, TU, Bachelor Thesis, 2017

3D printing is becoming a more commonly used manufacturing process, both for industrial and consumer use, with ever increasing capabilities and areas of application. These opportunities also introduce higher expectations on the quality of the resulting prints, generally in terms of the resulting shape and appearance of the object, but also rigidness and structural integrity. Detecting characteristics in a model that are a source of errors opens up possible approaches to mitigate or eliminate these errors before printing it. One such characteristic are thin structures that can lead to missing or deformed shapes, changes in the appearance of full color prints or fragile structures that break during post-processing steps. The aim of this work is to detect thin structures using the discrete medial axis, representing the centers of a shape. In order to compute the discrete medial axis a discrete medial axis transform based on image processing techniques is implemented in the Cuttlefish 3D printer driver. The result for different models are assessed and possible correlations of the medial axis and thin structures evaluated. Possible applications of the medial axis or filtered medial axis are proposed and discussed.

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Shehu, Aurela; Brunton, Alan; Wuhrer, Stefanie; Wand, Michael

Characterization of Partial Intrinsic Symmetries

2015

Computer Vision - ECCV 2014 Workshops. Proceedings Part IV

European Conference on Computer Vision (ECCV) <13, 2014, Zurich, Switzerland>

We present a mathematical framework and algorithm for characterizing and extracting partial intrinsic symmetries of surfaces, which is a fundamental building block for many modern geometry processing algorithms. Our goal is to compute all "significant" symmetry information of the shape, which we define as r-symmetries, i.e., we report all isometric self-maps within subsets of the shape that contain at least an intrinsic circle or radius r. By specifying r, the user has direct control over the scale at which symmetry should be detected. Unlike previous techniques, we do not rely on feature points, voting or probabilistic schemes. Rather than that, we bound computational efforts by splitting our algorithm into two phases. The first detects infinitesimal r-symmetries directly using a local differential analysis, and the second performs direct matching for the remaining discrete symmetries. We show that our algorithm can successfully characterize and extract intrinsic symmetries from a number of example shapes.

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Arikan, Can Ates; Brunton, Alan; Tanksale, Tejas Madan; Urban, Philipp

Color-Managed 3D-Printing with highly Translucent Printing Materials

2015

Measuring, Modeling, and Reproducing Material Appearance 2015

Measuring, Modeling, and Reproducing Material Appearance (MMRMA) <2, 2015, San Francisco, CA, USA>

Many 3D printing applications require the reproduction of an object's color in addition to its shape. One 3D printing technology, called multi-jetting (or poly-jetting), allows full color 3D reproductions by arranging multiple colored materials (UV curing photo-polymers) on a droplet level in a single object. One property of such printing materials is their high translucency posing new challenges for characterizing such 3D printers to create ICC proles. In this paper, we will first describe the whole color-managed 3D printing workflow and will then focus on measuring the colors of highly translucent printing materials. We will show that measurements made by spectrophotometers used in the graphic arts industry are systematically biased towards lower reflection. We will then propose a trichromatic camera-based approach for measuring such colors. Error rates obtained in comparison with spectroradiometric measurements for the same viewing conditions are within the interinstrument-variability of hand-held spectrophotometers used in graphic arts.

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Brunton, Alan; Arikan, Can Ates; Urban, Philipp

Pushing the Limits of 3D Color Printing: Error Diffusion with Translucent Materials

2015

ACM Transactions on Graphics

Accurate color reproduction is important in many applications of 3D printing, from design prototypes to 3D color copies or portraits. Although full color is available via other technologies, multi-jet printers have greater potential for graphical 3D printing, in terms of reproducing complex appearance properties. However, to date these printers cannot produce full color, and doing so poses substantial technical challenges, from the shear amount of data to the translucency of the available color materials. In this article, we propose an error diffusion halftoning approach to achieve full color with multi-jet printers, which operates on multiple isosurfaces or layers within the object. We propose a novel traversal algorithm for voxel surfaces, which allows the transfer of existing error diffusion algorithms from 2D printing. The resulting prints faithfully reproduce colors, color gradients and fine-scale details.

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Wuhrer, Stefanie; Pishchulin, Leonid; Brunton, Alan; Shu, Chang; Lang, Jochen

Estimation of Human Body Shape and Posture Under Clothing

2014

Computer Vision and Image Understanding

Estimating the body shape and posture of a dressed human subject in motion represented as a sequence of (possibly incomplete) 3D meshes is important for virtual change rooms and security. To solve this problem, statistical shape spaces encoding human body shape and posture variations are commonly used to constrain the search space for the shape estimate. In this work, we propose a novel method that uses a posture-invariant shape space to model body shape variation combined with a skeleton-based deformation to model posture variation. Our method can estimate the body shape and posture of both static scans and motion sequences of human body scans with clothing that fits relatively closely to the body. In case of motion sequences, our method takes advantage of motion cues to solve for a single body shape estimate along with a sequence of posture estimates. We apply our approach to both static scans and motion sequences and demonstrate that using our method, higher fitting accuracy is achieved than when using a variant of the popular SCAPE model [2, 18] as statistical model.

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Brunton, Alan; Bolkart, Timo; Wuhrer, Stefanie

Multilinear Wavelets: A Statistical Shape Space for Human Faces

2014

Computer Vision - ECCV 2014. Proceedings Part I

European Conference on Computer Vision (ECCV) <13, 2014, Zurich, Switzerland>

We present a statistical model for 3D human faces in varying expression, which decomposes the surface of the face using a wavelet transform, and learns many localized, decorrelated multilinear models on the resulting coefficients. Using this model we are able to reconstruct faces from noisy and occluded 3D face scans, and facial motion sequences. Accurate reconstruction of face shape is important for applications such as tele-presence and gaming. The localized and multi-scale nature of our model allows for recovery of fine-scale detail while retaining robustness to severe noise and occlusion, and is computationally efficient and scalable. We validate these properties experimentally on challenging data in the form of static scans and motion sequences. We show that in comparison to a global multilinear model, our model better preserves fine detail and is computationally faster, while in comparison to a localized PCA model, our model better handles variation in expression, is faster, and allows us to fix identity parameters for a given subject.

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Brunton, Alan; Salazar, Augusto; Bolkart, Timo; Wuhrer, Stefanie

Review of Statistical Shape Spaces for 3D Data with Comparative Analysis for Human Faces

2014

Computer Vision and Image Understanding

With systems for acquiring 3D surface data being evermore commonplace, it has become important to reliably extract specific shapes from the acquired data. In the presence of noise and occlusions, this can be done through the use of statistical shape models, which are learned from databases of clean examples of the shape in question. In this paper, we review, analyze and compare different statistical models: from those that analyze the variation in geometry globally to those that analyze the variation in geometry locally. We first review how different types of models have been used in the literature, then proceed to define the models and analyze them theoretically, in terms of both their statistical and computational aspects. We then perform extensive experimental comparison on the task of model fitting, and give intuition about which type of model is better for a few applications. Due to the wide availability of databases of high-quality data, we use the human face as the specific shape we wish to extract from corrupted data.