Jasper van de Gronde
 room number: 491 (Bernoulliborg, building 5161)
 email: j.j.van.de.gronde rug.nl
Research interests
I am interested in all sorts of image processing topics, including compressed sensing, linear and morphological filters, and deep learning, with a special interest in applications on large/highdimensional and nonscalar data. Making proper use of vector or tensorvalued data, possibly as an intermediate step, also interests me greatly, as does the interplay between (mostly) linear approaches and morphological approaches. My PhD thesis was on morphological operators for tensor images, exploring shape and structure in movement and direction dependence. I defended my thesis on 30 June 2015, and am currently a postdoc.
Tensor images (or volumes) are just like ordinary images or volumes, except that at each point we have a vector or matrix (tensors are essentially a generalization of vectors and matrices). To visualize a tensor image with matrices at each position, we typically use "glyphs": for each position a small glyph is drawn whose shape represents the matrix (S). The glyph is often a unit sphere deformed in such a way that each vector v on the unit sphere is given the magnitude v.(S.v). Below you can interact with a live demonstration of this technique (requires a WebGL capable browser, I recommend Firefox, and possibly some patience):


In this case, the matrices describe stresses at atomic positions in a nanowire (courtesy of S.S.R. Saane, Micromechanics group, RuG). Blue shows positive values(/radii), while orange shows negative values. 
Demos
Apart from the rendering above, here is some more code you can try out both in the browser and using Node.js:
 Groupinvariant frames for colour morphology. This tries to make "false" colours much less objectionable by using group invariant frames (and thereby operators).
 Frames for Tensor Field Morphology. Uses rotationinvariant frames to apply morphological filters to structure tensors.
 Pathbased mathematical morphology on tensor fields. Path openings on general directed acyclic graphs derived from tensor fields.
 Efficient and Robust Path Openings using the ScaleInvariant Rank Operator. Generalized path openings on binary images and greyscale sequences.
There are also some demos that can only be run offline:
 Groupinvariant colour morphology based on frames. Similar to other previous demo concerning groupinvariant frames, but also has code for performing a simple classification task. (Python)
 Frames, the Loewner order and eigendecomposition for morphological operators on tensor fields. Demonstration of various methods for computing morphological filters on tensor fields. (Python)
 Fast Computation of Greyscale Path Openings. Novel algorithm for computing greyscale path openings on images. (C++)
 Tensorial Orientation Scores. Computes tensorial orientation scores. (Mathematica)
 Generalized Morphology using Sponges. Simple example of filtering anglevalued signals. (Mathematica)
Various projects not (necessarily) associated with a particular publication can be found on Github (also see the SciJS repository).
Further information and links
I maintain a bibliography of work done on both colour morphology and tensor morphology (note that I'm not too strict about what classifies as "colour" morphology). I try to subclassify (using tags) papers based on what kind of method they use. If you feel anything is missing or wrong, please let me know.
An interesting (informal) discussion of the problem of finding a total order for colours can be found here. Note that most of the approaches discussed there indeed correspond to actual algorithms that have been tried in mathematical morphology (and the overview is even fairly, although not entirely, complete). In particular, people have experimented with methods similar to the Hilbert curve approach (Chanussot1998), as well as the travelling salesman approach (Florez2005, Chevallier2014). But note that Chevallier has shown that any total order is necessarily discontinuous when computing joins and meets (this is part of the reason why much of my thesis is focussed on making partial orders more palatable).
Although I tend to talk about product orders and lexicographical orders, there are many more related concepts, as well as different terms for the same concepts. To clarify, I have made a short summary of different terms and in which context they are used.
Publications
Venustiano Soancatl Aguilar, Jasper J. van de Gronde, Claudine J. C. Lamoth, Natasha M. Maurits, and Jos B. T. M. Roerdink. Assessing Postural Control Performance during Exergaming based on Speed and Curvature of Body Movements. IEEE Transactions on Neural Systems and Rehabilitation Engineering, 1(26):171–180, 2018.  doi bib  
Chengtao Ji, Jasper J. van de Gronde, Natasha M. Maurits, and Jos B. T. M Roerdink. Visual Exploration of Dynamic Multichannel EEG Coherence Networks. Computer Graphics Forum, 2018. invited paper, accepted.  bib  
Venustiano Soancatl Aguilar, Jasper J. van de Gronde, Claudine J. C. Lamoth, Mike van Diest, Natasha M. Maurits, and Jos B. T. M. Roerdink. Visual Data Exploration for Balance Quantification in RealTime During Exergaming. PLOS ONE, 12(1):e0170906, January 2017.  doi url bib  
Chengtao Ji, Jasper J. van de Gronde, Natasha M. Maurits, and Jos B. T. M Roerdink. Visualizing and Exploring Dynamic Multichannel EEG Coherence Networks. In Eurographics Workshop on Visual Computing for Biology and Medicine. The Eurographics Association, 2017. Honorable Mention Award.  doi bib  
Jasper J. van de Gronde, André R. Offringa, and Jos B. T. M. Roerdink. Efficient and Robust Path Openings using the ScaleInvariant Rank Operator. Journal of Mathematical Imaging and Vision, 56(3):455–471, 2016.  doi url bib  
Jasper J. van de Gronde and Jos B. T. M. Roerdink. Generalized Morphology using Sponges. Mathematical Morphology  Theory and Applications, 1(1):18–41, 2016.  doi url bib  
Herman Schubert, Jasper J. van de Gronde, and Jos B. T. M. Roerdink. Efficient Computation of Greyscale Path Openings. Mathematical Morphology  Theory and Applications, 1(1):189–202, 2016.  doi url bib  
Chengtao Ji, Jasper J. and Maurits van de Gronde, and Jos B. T. M. Roerdink. Exploration of Complex Dynamic Structures in Multichannel EEG Coherence Networks via Information Visualization Techniques. In CCS 2016  Posters. 2016.  bib  
Chengtao Ji, Jasper J. and Maurits van de Gronde, and Jos B. T. M. Roerdink. Tracking and Visualizing Dynamic Structures in Multichannel EEG Coherence Networks. In EuroVis 2016  Posters. The Eurographics Association, pages 28–30, 2016.  doi url bib  
Venustiano Soancatl Aguilar, Jasper J. van de Gronde, Natasha M. Maurits, Claudine C. J. C. Lamoth, and Jos B. T. M. Roerdink. Curvature and Speed for Balance Quantification During Exergaming. In Proceedings of the 9th International Conference on Motion in Games. New York, NY, USA. ACM, pages 201–202, 2016.  doi url bib  
Venustiano Soancatl Aguilar, J. J. and Lamoth van de Gronde, N. M. Maurits, and Roerdink, Jos B. T. M.. Visual Data Exploration for Balance Quantification During Exergaming. In EuroVis 2016  Posters. Groningen. The Eurographics Association, pages 25–27, 2016.  doi url bib  
Jasper J. van de Gronde. Beyond Scalar Morphology. PhD thesis, University of Groningen, 2015.  url bib  
Jasper J. van de Gronde. Tensorial Orientation Scores. In Computer Analysis of Images and Patterns. Springer International Publishing, pages 783–794, 2015.  doi url bib  
Jasper J. van de Gronde and Jos B. T. M. Roerdink. Sponges for Generalized Morphology. In J\’on Atli Benediktsson, Jocelyn Chanussot, Laurent Najman, and Hugues Talbot, eds., Mathematical Morphology and Its Applications to Signal and Image Processing. Springer International Publishing, pages 351–362, 2015.  doi bib  
Jasper J. van de Gronde, Mikola Lysenko, and Jos B. T. M. Roerdink. PathBased Mathematical Morphology on Tensor Fields. In Ingrid Hotz and Thomas Schultz, eds., Visualization and Processing of Higher Order Descriptors for MultiValued Data. Springer International Publishing, pages 109–127, 2015.  doi url bib  
Jasper J. van de Gronde, Herman R. Schubert, and Jos B. T. M. Roerdink. Fast Computation of Greyscale Path Openings. In J\’on Atli Benediktsson, Jocelyn Chanussot, Laurent Najman, and Hugues Talbot, eds., Mathematical Morphology and Its Applications to Signal and Image Processing. Springer International Publishing, pages 621–632, 2015.  doi url bib  
Jasper J. van de Gronde and Jos B. T. M. Roerdink. Frames, the Loewner order and eigendecomposition for morphological operators on tensor fields. Pattern Recognition Letters, 47:40–49, 2014.  doi url bib  
Jasper J. van de Gronde and Jos B. T. M. Roerdink. GroupInvariant Colour Morphology Based on Frames. IEEE Transactions on Image Processing, 23(3):1276–1288, March 2014.  doi url bib  
Jasper J. van de Gronde and Jos B. T. M. Roerdink. Frames for Tensor Field Morphology. In Frank Nielsen and Frédéric Barbaresco, eds., Geometric Science of Information. Springer Berlin Heidelberg, pages 527–534, 2013.  doi url bib  
Jasper J. van de Gronde, Michael H. F. Wilkinson, and Jos B. T. M. Roerdink. Rotationinvariant morphological filtering of tensor fields using frames. In Poster session of the National ICT.OPEN (Eindhoven). November, November 2013.  pdf bib  
Jasper J. van de Gronde and Jos B. T. M. Roerdink. GroupInvariant Frames for Colour Morphology. In Cris L. Luengo Hendriks, Gunilla Borgefors, and Robin Strand, eds., Mathematical Morphology and Its Applications to Signal and Image Processing. Springer Berlin Heidelberg, pages 267–278, 2013.  doi url bib  
Jasper J. van de Gronde. Web Graphics for Science. In HTML5 Developer Conference. October, October 2013.  url bib  
Jasper J. van de Gronde and Jos B. T. M. Roerdink. GroupInvariant Frames for Colour Morphology. In ASCI.OPEN (Eindhoven). November, November 2013.  bib  
A. R. Offringa and J. J. van de Gronde and J. B. T. M. Roerdink. A morphological algorithm for improving radiofrequency interference detection. Astronomy & Astrophysics, 539(A95), March 2012.  doi bib  
Jasper J. van de Gronde, Michael H.F. Wilkinson, and Jos B.T.M. Roerdink. Making computers see tensors using mathematical morphology. In Poster session of the National ICT.OPEN (Rotterdam). October, October 2012.  pdf bib  
Jasper van de Gronde. A High Quality Solver for Diffusion Curves. Master’s thesis, University of Groningen, December 2010.  pdf url bib 