Martin Pražák

London · 0751 431 8153 · name@email.com

R&D Supervisor at DNEG, with particular interest in crowd simulation and data-driven character animation. I have 7 years of experience in the VFX industry, and hold a PhD in computer science (specialised in data-driven character animation for crowd simulation).


Industry Talks

Taming the Swarm: Rippers on Pacific Rim Uprising

Martin Prazak, Damien Maupu, Mungo Pay
Muhittin Bilginer, Aleksandar Atanasov, Cristobal Infante Esquivel
Siggraph 2018 Talks

When constructing shots of non-human crowds that exhibit complex behaviors, the standard approach based on the well-established rules of boid simulation is likely to fall short when used for a group of characters with "intent". In Pacific Rim Uprising, Double Negative VFX tackled the challenge of producing a large crowd of highly articulated robotic creatures performing the complex and coordinated task of "assembling" a mega-Kaiju. This task required a number of innovative approaches to both crowd authoring and rendering, and close collaboration between the RnD and artists.

Artist-Driven Crowd Authoring Tools

Damien Maupu, Emanuele Goffredo, Nile Hylton, Mungo Pay, Martin Prazak
Siggraph 2017 Talks

While crowd simulation frameworks can be very powerful for virtual crowd generation, in a VFX context they can also be unwieldy due to their chaotic nature. Small changes on the inputs can produce markedly different results, which can be problematic when attempting to adhere to a director’s vision. Artist driven tools allow much more flexibility when constructing scenes, speed up turn-around time and can produce extremely dynamic crowd shots. To generate virtual crowds, Double Negative VFX (Dneg) has recently transitioned from an in-house standalone simulation-based solution to an artist-driven framework integrated into SideFX’s Houdini.

Flexible Pipeline for Crowd Production

Mungo Pay, Damien Maupu, Martin Prazak
Siggraph 2017 Talks

The complexity of crowd shots can vary greatly, from simple vignetting tasks that add life to an environment, to large and complex battle sequences involving thousands of characters. For this reason, a “one size fits all” crowd solution might not be optimal, both in terms of design and usability, but also allocation of crew. In this talk we present a suite of tools, developed across multiple platforms, each optimised for specific crowd tasks. These are underpinned by a data interchange library to allow for modification at any stage of the pipeline.

Data-driven Background Crowds in Exodus: Gods and Kings

Martin Prazak, Mungo Pay, Damien Maupu, Davide Vercelli, Ian Masters
Siggraph 2015 Talks

Large virtual worlds require large virtual crowds. One of the main themes of Exodus is a clash of ancient civilisations, represented via virtual background crowds in a large number of shots. To generate these crowds, we used an in-house crowd solution, whose development was aimed at background crowds for photorealistic scenes.

VFX crowds are subject to specific requirements, because they are used to enliven and extend crowd shots captured by a camera. Each shot consists of three layers – hero characters (usually real actors shot on set), crowd-anim (hand-animated) and procedural background crowds. To retain scene consistency, the background crowds must join seamlessly with other layers.


Research Publications

Locomotion for Crowd Animation

Martin Pražák
PhD Dissertation, Trinity College Dublin, May 2012

Real-time computer animation is an essential part of modern computer games and virtual reality applications. While rendering provides the main part of what can be described as “visual experience”, it is the movement of the characters that gives the final impression of realism. Unfortunately, realistic human animation has proven to be a very hard challenge.

Some fields of computer graphics have a compact and precise mathematical description of the underlying principles. Rendering, for example, has the rendering equation, and each realistic rendering technique provides its approximate solution. Due to its highly complex nature, character animation is not one of these fields. That is one of the reasons why even single character animation still provides significant research challenges. The challenges posed by a crowd simulator, required to populate a virtual world, are even larger. This is not only because of the large number of simultaneously displayed characters, which necessitate the use of level-of-detail approaches, but also the requirement of reactive behaviour, which can be provided only by a complex multi-level planning module.

In this thesis, we address the problem of human animation for crowds as a component of a crowd simulator.

Perceptual Evaluation of Footskate Cleanup

Martin Pražák, Ludovic Hoyet and Carol O’Sullivan
Proceedings of the 2011 ACM SIGGRAPH/Eurographics Symposium on Computer Animation, 287-294, 2011

When animating virtual humans for real-time applications such as games and virtual reality, animation systems often have to edit motions in order to be responsive. In many cases, contacts between the feet and the ground are not (or cannot be) properly enforced, resulting in a disturbing artifact know as footsliding or footskate. In this paper, we explore the perceptibility of this error and show that participants can perceive even very low levels of footsliding (<21mm in most conditions). We then explore the visual fidelity of animations where footskate has been cleaned up using two different methods. We found that corrected animations were always preferred to those with footsliding, irrespective of the extent of the correction required. We also determined that a simple approach of lengthening limbs was preferred to a more complex approach using IK fixes and trajectory smoothing.

Perceiving Human Motion Variety

Martin Pražák and Carol O’Sullivan
Applied Perception in Graphics and Visualisation, 2011

In order to simulate plausible groups or crowds of virtual characters, it is important to ensure that the individuals in a crowd do not look, move, behave or sound identical to each other. Such obvious `cloning’ can be disconcerting and reduce the engagement of the viewer with an animated movie, virtual environment or game. In this paper, we focus in particular on the problem of motion cloning, i.e., where the motion from one person is used to animate more than one virtual character model. Using our database of motions captured from 83 actors (45M and 38F), we present an experimental framework for evaluating human motion, which allows both the static (e.g., skeletal structure) and dynamic aspects (e.g., walking style) of an animation to be controlled. This framework enables the creation of crowd scenarios using captured human motions, thereby generating simulations similar to those found in commercial games and movies, while allowing full control over the parameters that affect the perceived variety of the individual motions in a crowd. We use the framework to perform an experiment on the perception of characteristic walking motions in a crowd, and conclude that the minimum number of individual motions needed for a crowd to look varied could be as low as three. While the focus of this paper was on the dynamic aspects of animation, our framework is general enough to be used to explore a much wider range of factors that affect the perception of characteristic human motion.

Moving Crowds: A Linear Animation System for Crowd Simulation

Martin Pražák, Ladislav Kavan, Rachel McDonnell, Simon Dobbyn and Carol O’Sullivan
O’Sullivan Poster Proceedings, ACM SIGGRAPH Symposium on Interactive 3D Graphics and Games, 2010

The animation of hundreds or even thousands of simultaneously displayed individuals is challenging because of the need for both motion variety and efficient runtime processing. We present a middle level-of-detail animation system optimised for handling large crowds which takes motion-capture data as input and automatically processes it to create a parametric model of human locomotion. The model is then used in a runtime system, driven by a linearised motion blending technique, which synthesises motions based on information from a motion-planning module. Compared to other animation methods, our technique provides significantly better runtime performance without compromising the visual quality of the result.

Perceptual Evaluation of Human Animation Timewarping

Martin Pražák, Rachel McDonnell and Carol O’Sullivan
ACM SIGGRAPH Asia 2010 Sketches, pages 30:1-30:2, 2010

Understanding the perception of humanoid character motion can provide insights that will enable realism, accuracy, computational cost and data storage space to be optimally balanced. In this sketch we describe a preliminary perceptual evaluation of human motion timewarping, a common editing method for motion capture data. During the experiment, participants were shown pairs of walking motion clips, both timewarped and at their original speed, and asked to identify the real animation. We found a statistically significant difference between speeding up and slowing down, which shows that displaying clips at higher speeds produces obvious artifacts, whereas even significant reductions in speed were perceptually acceptable.

Synchronized Real-time Multi-sensor Motion Capture System

Jonathan Ruttle, Michael Manzke, Martin Pražák and Rozenn Dahyot
SIGGRAPH Asia 2009 Sketches & Posters, pages 16-19, 2009

his work addresses the challenge of synchronizing multiple sources of visible and audible information from a variety of devices, while capturing human motion in realtime. Video and audio data will be used to augment and enrich a motion capture database that will be released to the research community. While other such augmented motion capture databases exist [Black and Sigal 2006], the goal of this work is to build on these previous works. Critical areas of improvement are in the synchronization between cameras and synchronization between devices. Adding an array of audio recording devices to the setup will greatly expand the research potential of the database, and the positioning of the cameras will be varied to give greater flexibility. The augmented database will facilitate the testing and validation of human pose estimation and motion tracking techniques, among other applications. This sketch briefly describes some of the interesting challenges faced in setting up the pipeline for capturing the synchronized data and the novel approaches proposed to solve them.

A Perception Based Metric for Comparing Human Locomotion

Martin Pražák, Rachel McDonnell, Ladislav Kavan and Carol O’Sullivan
Proceedings of the 9th Irish Workshop on Computer Graphics, pages 75-80, 2009

Metrics measuring differences between skeletal animation frames (poses) form the core of a large number of modern computer animation methods. A metric that accurately characterizes human motion perception could provide great advantages for these methods, by allowing the systems to focus exclusively on perceptually important aspects of the motion. In this paper we present a metric for human locomotion comparison, derived directly from the results of a perceptual experiment.

Towards a Perceptual Metric for Comparing Human Motion

rtin Pražák, Rachel McDonnell, Ladislav Kavan and Carol O’Sullivan
Poster Proceedings, ACM SIGGRAPH/Eurographics Symposium on Computer Animation, pages 13-14, 2008

Most of the commonly used approaches for editing human motion, such as motion graphs and motion blending, use some form of distance metric in order to compare character poses in keyframes. These metrics utilize a combination of three traditional methods – joint angular differences, dis- tances between points on an object and velocities of specified bodyparts. The presented method attempts to find a metric and its parameters (not limited to the usual Euclidean metric), which would match a dataset formed by a direct perceptual experiment as closely as possible. Previous meth- ods used peception for evaluation alone, but we use perception as the basis of our metric.

Rendering Fur Directly into Images

Tania Pouli, Martin Pražák, Pavel Zemcik, Diego Gutierrez and Erik Reinhard
Reinhard Computers and Graphics, 24(5):612-620, 2010

We demonstrate the feasibility of rendering fur directly into existing images, without the need to either painstakingly paint over all pixels, or to supply 3D geometry and lighting. We add fur to objects depicted in images by first estimating depth and lighting information and then re-rendering the resulting 2.5D geometry with fur. A brush-based interface is provided, allowing the user to control the positioning and appearance of fur, while all the interaction takes place in a 2D pipeline. The novelty of this approach lies in the fact that a complex, high-level image edit such as the addition of fur can yield perceptually plausible results, even in the presence of imperfect depth or lighting information.

Changing Object Appearance by Adding Fur

Martin Pražák, (supervisors – Erik Reinhard and Pavel Zemcik)
Masters Thesis, Brno University of Technology, 2008

The aim of this thesis is to demonstrate the feasibility of rendering fur directly into existing images without the need to either painstakingly paint over all pixels, or to supply 3D geometry and lighting. The fur is added to objects depicted on images by first recovering depth and lighting information, and then re-rendering the resulting 2.5D geometry with fur. The novelty of this approach lies in the fact that complex high-level image edits, such as the addition of fur, can successfully yield perceptually plausible results, even constrained by imperfect depth and lighting information. A relatively large set of techniques involved in this work includes HDR imaging, shape-from-shading techniques, research on shape and lighting perception in images and photorealistic rendering techniques. The main purpose of this thesis is to prove the concept of the described approach. The main implementation language was C++ with usage of wxWidgets, OpenGL and libTIFF libraries, rendering was realised in 3Delight, a Renderman-compatible renderer, with the help of a set of custom shaders written in Renderman shading language.

Open Source Projects

Possumwood

A graph-based sandbox

Possumwood is a graph-based procedural authoring tool, in concept not dissimilar to popular CG packages like Houdini, Blender or Maya. It is intended to serve as a sandbox for computer graphics algorithms and libraries, providing a user-friendly and coding-free UI for libraries that would otherwise be inaccessible for an average user.

Embree Viewer

A simple 3D viewer based on Embree

Embree viewer is a simple implementation of a progressive renderer, based on Intel's Embree raytracing kernels. Its UI is written in SDL2, and it supports Alembic and OBJ model file formats, with a simple JSON file to describe a scene.

Experience

R&D Supervisor, Creatures

DNEG, London

Supervising 4 teams of RnD developers, working on different aspects of representing creatures (human, realistic and sci-fi/fantasy) in the VFX pipeline.

Jul 2018 – Present

Lead R&D Developer, Crowd Tools

DNEG, London

Led a team of developers working on a comprehensive crowd tool set, which spans a large portion of pipeline and a variety of authoring and rendering software.

Jan 2015 – Jul 2018

R&D Developer, Crowd Simulation

DNEG, London

Worked as primary developer of a crowd framework, implemented from ground-up. Was responsible for architecture, design and development of the full system (C++ with Python integration and API, with a large number of both in-house and 3rd-party libraries).

Jan 2012 – Dec 2014

Animation Technology Intern

Walt Disney Animation Studios

Worked on a proof-of-concept dynamic registration of 3D models to 2D animations, implemented as an interactive plugin inside Maya viewport.

Jul 2011 – Sep 2011

Part-time Demonstrator and Occasional Lecturer

Trinity College Dublin, Ireland

  • Computer Animation (MSc. Interactive Entertainment, Motion Capture and Quaternion Algebra lectures, practical demonstrations)
  • Practical Project in Robotics (3rd year BSc. in Engineering)
  • C++ Programming (2nd year BSc. in Engineering)
  • C Programming (1st year BSc. in Engineering)
  • Mathematics (1st year BSc. in Science and Engineering)

2008 – 2011

Computer Graphics Programmer Intern

Aardman Animations

Worked on a feather generation and rendering system (Maya, Renderman, C++).

Jun 2007 – Jul 2007

Education

Trinity College Dublin

PhD, Computer Animation
Thesis topic: Locomotion for Crowd Animation
(supervised by Prof. Carol O'Sullivan, examiners: Dr. John Dingliana, Dr. Ronan Boulic)

  • researched data-driven character animation for real-time crowd simulation
  • gained practical experience with motion capture pipeline (Vicon)
  • acquired experience with crowd system development - simulation, animation, behaviour
PhD research projects and interests:
  • Natural Movers – a database of human motions (9000+ normalised motion capture clips from 83 actors performing a consistent set of actions)
  • Metropolis – developed a highly efficient animation system for a real-time crowd simulator
  • As Rigid As Possible shape manipulation applied to humanoid characters
  • Human Perception – investigation of the connection between human perception and character animation

2008 - 2012

Brno University of Technology, Faculty of Information Technology

Ing. (MSc. equiv), Department of Computer Graphics and Multimedia
Thesis topic: Image-based Material Editing: Changing Object Appearance by Adding Fur
(supervised by Doc. Dr. Ing. Pavel Zemčík and Dr. Erik Reinhard)

  • Graduated with Distinction (1st class honours equiv.), Dean's award for Master's Thesis
  • computer graphics course, with both taught and research elements
  • covered topics: image processing, procedural geometry, photorealistic rendering and Renderman shaders

2005 - 2008

University of Bristol

Exchange study under Socrates / Erasmus Programme, Department of Computer Science

  • one year exchange under Socrates / Erasmus programme
  • worked on master project under Dr Erik Reinhard's supervision

2006 - 2007

Brno University of Technology, Faculty of Information Technology

Bc. (BSc. equiv), Computer Science
Thesis topic: Tools for Polygonal Models' Symmetry Estimation
(supervised by Doc. Ing. Přemysl Kršek, PhD)

  • Graduated with Distinction (1st class honours, ranked 6th of 164 students).
  • developed a toolset for symmetry estimation of medical CT scans

2002 - 2005

Skills

  • excellent knowledge of object-oriented programming, template metaprogramming and application design in C++
  • extensive experience with common libraries (STL, OpenGL, Qt, Boost, OpenEXR, Alembic, WildMagic and more)
  • good knowledge of rendering domain-specific languages (GLSL, renderman, OSL)
  • practical experience with Autodesk Maya, Maya API and plugins programming
  • power user command of Unix/Linux systems and Windows
  • command of graphical applications in 2D and 3D (Maya, Clarisse, Houdini and others)