About me

avatarWelcome to my portfolio site, a showcase of my scientific work and photography. I’m originally from The Netherlands but currently living and working in Japan as a Research Associate at NTT Communication Science Laboratories. Here I study the perception of shape and materials using psychophysics, statistical modelling, computer graphics and machine learning. Next to work I also have great interest in photography. Mostly while traveling I find time to pick up my camera as you might see in the photography section.

I have a background in computer science and a bit of computer/electrical engineering. During my bachelor and master studies I picked courses that were mostly HCI (human computer interaction) oriented. For my doctorate I studied the perception of liquids. Now I’m driven to understand the efficiency of our sensory systems and how to exploit this to create experiences beyond the capabilities of our regular senses.

If you have more specific questions please don’t hesitate to contact me at mail [at] janjaap [dot] info.

Research: Liquids

Fluids and other deformable materials have highly mutable shapes, which are influenced by both intrinsic properties (e.g. viscosity, velocity) and extrinsic forces (e.g. gravity, object interactions). During my PhD in Professor Roland Fleming’s lab at Gießen University I studied the perception of liquids and how we are able to estimate their properties consistently across a wide range of contexts.

Research

In my research I try to map the perceptual space and cues we use to perceive liquids. We find that especially mid-level shape/motion cues (e.g. spiralling, ripples, spread) are very informative of liquid properties and allow us to extract context invariant information. It is hard to physically measure concepts such as blobbiness or folding in a way that is scale and orientation invariant across 3D shapes. Therefore, we use neural networks to perceive viscosity in images and especially focus on networks that make similar estimation errors as human observers. By studying the learned properties of the networks we hope to gain insights on new image-based cues we use to achieve viscosity constancy. The larger goal is to achieve better generalisation in computer vision.

The Stimuli

I invested much time to set up a technical pipeline to generate stable, precise and realistic liquid stimuli. I used a particle simulation program RealFlow made for the VFX industry to simulate liquids. The computational costs of these stimuli are quite high. I wrote specific scripts to distribute the calculations over various systems and clusters. Millions of images were generated showing liquids with different viscosities and optical appearances interacting in different scenes. In 2018 I became a certified RealFlow Xpert.
RF_certified-xpert-logo-2018

Research: Gloss

For my Master studies at Leiden University in The Netherlands I did a graduation project on gloss perception. The actual research was done in the Perceptual Intelligence Lab at Delft University of Technology where Sylvia Pont and Maarten Wijntjes were my external supervisors.

Research

We investigated the influence of the spatial structure of the illumination on gloss perception. The inspiration came from various art works like the paintings of Vermeer, where much simpler highlight shapes are used compared to real world situations. We performed three experiments of which two took place using digital photographs on a computer monitor and one with the real spheres in a light box. The results show that more complex highlight shapes were perceived to produce a less glossy appearance than simple highlight shapes such as a disk or square. These results demonstrate that the complexity of a highlight shape’s spatial structure alone is not the main criterion for an increase perceived glossiness.

The Stimuli

A diffuse light box in combination with differently shaped masks was used to produce a set of 6 simple and more complex highlight shapes. In the box we placed spherical stimuli that were painted in 6 degrees of glossiness. This resulted in a stimulus set of 6 highlight shapes and 6 gloss levels. Observers were asked to rate glossiness looking at the real scene in the light box, but we also performed experiments with photographs of the stimuli. The figure below shows a subset of the stimuli. The masks where chosen to represent common shapes used in studio photography and paintings, like the disk, square, and window shape. Other shapes were chosen to see how shape complexity influences the perceived glossiness.

stimuli selectie

Publications

Papers

2018 Jan Jaap R. van Assen, Pascal Barla, Roland W. Fleming (2018). Visual Features in the Perception of Liquids. Current Biology, 28(3), 452-458, doi: 10.1016/j.cub.2017.12.037. [PDF]

2017 Filipp Schmidt, Vivian C. Paulun, Jan Jaap R. van Assen, Roland W. Fleming (2017). Inferring the stiffness of unfamiliar objects from optical, shape, and motion cues. Journal of Vision, 17(3):18, 1–17, doi: 10.1167/17.3.18. [PDF]

2017 Vivian C. Paulun, Filipp Schmidt, Jan Jaap R. van Assen, Roland W. Fleming (2017). Shape, motion, and optical cues to stiffness of elastic objects. Journal of Vision, 17(1):20, 1–22, doi: 10.1167/17.1.20. [PDF]

2016 Jan Jaap R. van Assen, Roland W. Fleming (2016). Influence of optical material properties on the perception of liquids. Journal of Vision, 16(15):12, 1–20, doi: 10.1167/16.15.12. [PDF]

2016 Jan Jaap R. van Assen, Maarten W. A. Wijntjes, & Sylvia C. Pont (2016). Highlight shapes and perception of gloss for real and photographed objects. Journal of Vision, 16(6):6, 1–14, doi: 10.1167/16.6.6. [PDF]

Talks

2017 Jan Jaap R. van Assen, Pascal Barla and Roland W. Fleming. Shape features underlying the perception of liquids. Computational and Mathematical Models in Vision (MODVIS) Annual Meeting 2017.

2016 Jan Jaap R. van Assen, Pascal Barla and Roland W. Fleming. Identifying shape features underlying liquid perception. European Conference on Visual Perception (ECVP) Annual Meeting 2016.

2016 Jan Jaap R. van Assen, Pascal Barla and Roland W. Fleming. Cues Underlying Liquid Constancy. Visual Sciences Society (VSS) Annual Meeting 2016.

2015 Jan Jaap R. van Assen and Roland W. Fleming. The influence of optical material appearance on the perception of liquids and their properties. Visual Sciences Society (VSS) Annual Meeting 2015.

Awards

2015 Elsevier/Vision Research Travel Award

2013 ECVP 2013 Travel Grant Award

Photography

Below you will find a selection of my more recent work. Recently I switched to shooting medium-format film with a Mamiya 7 leaving my digital camera mostly at home. I still need to get used to developing and scanning negatives but I hope to add more photos soon. More photos can be found on my 500px page.