Analysis of drawing characteristics for reproducing traditional hand-made stippling

Publication date: Available online 20 February 2019

Source: Computers & Graphics

Author(s): Domingo Martín, Germán Arroyo, Vicente del Sol, Celia Romo, Tobias Isenberg

Abstract

We contribute an in-depth analysis of the characteristics of traditional stippling and relate these to common practices in non-photorealistic stippling as well as to the abilities and limitations of existing printing and display technologies. Based on the properties of traditional stipple dots which depend on the used pens and paper types, we focus on a perceptual study of digital stippling that further informs our discussion and work toward an understanding of the requirements for the reproduction of hand-made stippling. To allow artists and illustrators to replicate the stippling process faithfully in the digital domain, we thus extract guidelines from the study results such as that the characteristics of real dots must be reproduced because they are perceived and that the results must be adjusted to the different properties of output devices.

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Full article: Analysis of drawing characteristics for reproducing traditional hand-made stippling

Interactive example-palettes for discrete element texture synthesis

Publication date: February 2019

Source: Computers & Graphics, Volume 78

Author(s): Timothy Davison, Faramarz Samavati, Christian Jacob

Abstract

Textures composed of individual discrete elements are found in everything from human-made glass-tilings to forests and tropical coral. We propose an interactive sketch-based system for synthesizing scenes consisting of many discrete element textures. We have implemented an example-palette, a design window where a user can use our sketch-based tools to create discrete element textures and then paint those textures into a scene or back into the example-palette to create new textures. Our interactive sketch-based tools use a new and fast region-growing algorithm that iteratively synthesizes new elements around previously synthesized elements. To support discrete element textures with different scales in the same output, we parameterize our region-growing algorithm on a per-element basis. Our method is capable of synthesizing structured and stochastic example discrete element textures. We explore applications of our system for building virtual worlds (such as for video games) and for sketch-based modeling.

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Full article: Interactive example-palettes for discrete element texture synthesis

An Efficient Method for Specular-enhanced BTF Compression

Publication date: Available online 30 June 2018
Source:Computers & Graphics
Author(s): Yong Hwi Kim, Junho Choi, Kwan Heng Lee
The Bidirectional Texture Function (BTF) has been used in the data-driven model to recover the reflectance of complex surfaces. The high-dimensionality of the BTF causes huge measurement data, but that needs to be compressed when real-time rendering is required. However, the distribution of BTF data is highly non-uniform due to non-lambertian reflections. Projecting the measured data onto a linear space constructed by a statistical analysis such as PCA results in low-quality of data compression. In this paper, we propose a computationally efficient and robust data compression method. Based on the assumption that there exist many overlapping measurements, we seek to find reflectance holes caused by the non-lambertian reflection with a series of linear algorithms. Before performing the standard compression, our method separates diffue reflections which can be well approximated with a linear model and compress them using a standard factorization. Specular components detected in the reflectance hole are separately stored using a sparse matrix representation to prevent the loss of the range of BTF data. Experimental results show that our method effectively improves the compression accuracy as well as the visual quality with a competitive computation time.

Full article: An Efficient Method for Specular-enhanced BTF Compression

Embodied VR environment facilitates motor imagery brain–computer interface training

Publication date: Available online 11 June 2018
Source:Computers & Graphics
Author(s): Filip Škola, Fotis Liarokapis
Motor imagery (MI) is the predominant control paradigm for brain–computer interfaces (BCIs). After sufficient training effort is invested, the accuracy of commands mediated by mental imagery of bodily movements grows to a satisfactory level. However, many issues with the MI-BCIs persist; e.g., low bit transfer rate, BCI illiteracy, sub-optimal training procedure. Especially the training process for the MI-BCIs requires improvements. Currently, the training has an inappropriate form, resulting in a high mental and temporal demand on the users (weeks of training are required for the control). This study aims at addressing the issues with the MI-BCI training. To support the learning process, an embodied training environment was created. Participants were placed into a virtual reality environment observed from a first-person view of a human-like avatar, and their rehearsal of MI actions was reflected by the corresponding movements performed by the avatar. Leveraging extension of the sense of ownership, agency, and self-location towards a non-body object (principles known from the rubber hand illusion) has already been proven to help in producing stronger EEG correlates of MI. These principles were used to facilitate the MI-BCI training process for the first time. Performance of 30 healthy participants after two sessions of training was measured using an on-line BCI scenario. The group trained using our embodied VR environment gained significantly higher accuracy for BCI actions (58.3%) than the control group trained with a standard MI-BCI training protocol (52.9%).

Full article: Embodied VR environment facilitates motor imagery brain–computer interface training

Real-time animation of human characters’ anatomy

Publication date: Available online 6 June 2018
Source:Computers & Graphics
Author(s): Aaron Sujar, Juan Jose Casafranca, Antoine Serrurier, Marcos Garcia
The animation of articulated characters is a central problem in the computer graphics field. Skeletal animation techniques define a workflow which has proven to be effective for boundary representations (B-Reps). This paper extends the classical skeletal animation pipeline to deal with characters internal tissues. In contrast to most common approaches, the proposed technique automates all the stages of this workflow. Well known skinning algorithms, such as Linear Blending Skinning, Dual Quaternion Skinning or Optimized Centers of Rotation were adapted to allow the use of our technique in applications where interactivity is required. The pipeline proposed in this paper can be used in many computer graphics systems such as games or educational applications to visualize and animate the internal anatomy of a virtual character at interactive rates.

Full article: Real-time animation of human characters’ anatomy

The Smart Pin: An effective tool for object manipulation in immersive virtual reality environments

Publication date: Available online 28 May 2018
Source:Computers & Graphics
Author(s): Fabio M. Caputo, Marco Emporio, Andrea Giachetti
In this paper, we present a novel method for object manipulation in immersive virtual environments. The proposed technique exploits a novel widget, called “Smart Pin”, to enable the user to select, translate, rotate and scale objects relying entirely on the positional tracking of a single hand. It is, therefore, suitable for several real-world applications where handheld devices are not available, the surrounding environmental conditions make orientation tracking hard, and the non-dominant hand may be involved in different tasks. We evaluated the method with users on two classical tasks such as detail search and docking, comparing it with a successful two-handed manipulation technique (Handlebar). The measured execution efficiency obtained with the two methods was similar, but most users preferred the Smart Pin for its gestural comfort and ease of use.

Full article: The Smart Pin: An effective tool for object manipulation in immersive virtual reality environments

Exploratory design of mechanical devices with motion constraints

Publication date: Available online 29 May 2018
Source:Computers & Graphics
Author(s): Robin Roussel, Marie-Paule Cani, Jean-Claude Léon, Niloy J. Mitra
Mechanical devices are ubiquitous in our daily lives, and the motion they are able to transmit is often a critical part of their function. While digital fabrication devices facilitate their realization, motion-driven mechanism design remains a challenging task. We take drawing machines as a case study in exploratory design. Devices such as the Spirograph can generate intricate patterns from an assembly of simple mechanical elements. Trying to control and customize these patterns, however, is particularly hard, especially when the number of parts increases. We propose a novel constrained exploration method that enables a user to easily explore feasible drawings by directly indicating pattern preferences at different levels of control. The user starts by selecting a target pattern with the help of construction lines and rough sketching, and then fine-tunes it by prescribing geometric features of interest directly on the drawing. The designed pattern can then be directly realized with an easy-to-fabricate drawing machine. The key technical challenge is to facilitate the exploration of the high dimensional configuration space of such fabricable machines. To this end, we propose a novel method that dynamically reparameterizes the local configuration space and allows the user to move continuously between pattern variations, while preserving user-specified feature constraints. We tested our framework on several examples, conducted a user study, and fabricated a sample of the designed examples.

Full article: Exploratory design of mechanical devices with motion constraints

A Delaunay triangulation based approach for cleaning rough sketches

Publication date: Available online 23 May 2018
Source:Computers & Graphics
Author(s): Amal Dev Parakkat, Uday Bondi Pundarikaksha, Ramanathan Muthuganapathy
Given a set of rough strokes drawn by an artist (either in pen-paper medium or in digital medium) in raster format, the objective is to group them meaningfully and represent the group with simple most appropriate curves. In this paper, a Delaunay triangulation based algorithm is proposed for grouping strokes. The grouping procedure is capable of identifying open curves and reconstructing broken strokes. The proposed algorithm is capable of helping the user in masking misinterpreted regions. We also introduce a shape aware skeleton smoothing procedure which best approximates the shape by taking input raster sketch as a reference to create final vector output. The user can also control the final output. The proposed algorithm combines the techniques in computational geometry as well as in image processing to utilize the power of both.

Full article: A Delaunay triangulation based approach for cleaning rough sketches

Rapidly contracting subdivision yields finite, effectively C2 surfaces

Publication date: Available online 23 May 2018
Source:Computers & Graphics
Author(s): Kȩstutis Karčiauskas, Jörg Peters
Tools of subdivision theory allow constructing surfaces that are effectively C 2 and have a good highlight line distribution also near irregularities where more or fewer than four quadrilateral patches meet. Here, effectively C 2 means that transitions that are only first-order smooth are confined to a tiny multi-sided cap. The cap can be chosen smaller than any refinement required for geometric modeling or computing on surfaces. The remainder of the surface parameterization is C 2. The resulting surface is of degree bi-5 and consists of three or fewer surface rings that are rapidly converging towards the tiny central cap.

Full article: Rapidly contracting subdivision yields finite, effectively C2 surfaces