Henrik Lieng

I am an associate professor at HiOA working on computer graphics and imaging. This webpage presents an overview of my research activities. For a list of my publications, see my Google Scholar page.

Traditionally, HiOA has been a teaching institution producing students tailored towards the local industry. However, the institution is shifting its focus towards basic research and is in the process of becoming a research university. My primary role as a member of this institution is to produce high-quality research in the fields of graphics and imaging.

In 2014, I graduated with a PhD from the University of Cambridge, Fitzwilliam College. My PhD research, supervised by Neil Dodgson at the Computer Laboratory Rainbow Group, investigated novel techniques with applications to design and art.

In the academic year of 2014/2015, I took a leave from research to teach computer engineering courses at Bergen University College and in 2011, I graduated with a MSc in graphics, imaging, and vision from University College London. My MSc project, supervised by Jan Kautz, resulted in a Eurographics 2012 paper on multi-perspective imaging.

Research overview


Our work on arbitrary-manifold gradient meshes has been accepted to Computer Graphics Forum! Read our article here (early view).

2D colour gradients in vector graphics (2013-2015)

ninja sonic smiley girl girl flower
flower blue blue

Vector graphics provides a powerful suite of artistic tools to define scalable 2D graphics. It is employed heavily in graphics design, where crisp image quality at any resolution is essential. Vector graphics is also becoming increasingly popular on the web because images are frequently scaled to fit any given viewing device. However, current vector graphics primitives, employed in formats like SVG, do not handle complex variations in the colour function very well. From interviews with professional artists and designers, pixel-based tools, such as Adobe Photoshop, are preferred over vector-based tools when the design requires more sophisticated variations in colour than what the standard linear gradient tool can handle. This reluctance to employ vector graphics has spurred many graphics researchers, including myself, to investigate whether more powerful, yet flexible, vector primitives can increase the attractiveness of vector graphics for graphic design.

The shading curve primitive, proposed in a 2015 CGF article, represents a light-weight primitive for defining smooth 2D colour gradients from curves. This primitive was inspired by traditional drawing techniques for achieving chiaroscuro. To achieve such effects in vector graphics, we argue that explicit control over the colour gradient is needed. We believe we achieve such control via our so-called 'shading profiles', which are curves representing the colour gradient perpendicular from a given geometric curve. For more details, have a look at our project webpage and our Eurographics 2016 presentation (PDF or PPTX).

The gradient mesh tool is the current tool employed by professional vector designers for defining 2D colour gradients. The mesh is topologically restricted to rectangular meshes, because it employs Ferguson patches as its underlying interpolation method. We argue that this restriction heavily hinders the flexibility of the tool, an argument not too different from supporters of subdivision surfaces in 3D design. Using subdivision surfaces, we were able to define an interpolation method that supports arbitrary topology of the gradient mesh. See our CGF article for more details.

An alternative primitive that has received a lot of attention in the research community is the diffusion curve primitive. In my PhD dissertation, supervised by Neil Dodgson and co-supervised by Jiri Kosinka, then at Cambridge, I argue for a superset primitive with support for both diffusion curves and gradient meshes. A brief overview of this idea was presented at MMCS9 (an international conference on curves and surfaces: PDF and PPTX). To achieve such a primitive, several problems must be dealt with. One of them is to provide fast random-access interpolation of diffusion-curve constraints. A solution to this problem is to perform GPU 2D ray tracing. I have expanded the solution space of this approach to support for diffusion points and local colour gradient constraints. This work was presented in a poster at SIGGRAPH 2016 (abstract and poster pdf).

Artistically-inspired imaging (2011-2012)

multiperspective mountain toys flower

Artistically-inspired imaging within my research field has been going on since the early 1990s. First, great techniques have been perfected over the centuries to achieve perceptually-related effects (e.g. impressionism) and photorealism. A common theme in computer graphics is to automate these techniques so that they can be employed in filters and tools. Second, looking at the development of art in the past centuries, we see a huge range of different types of visualisations. To algorithmically produce these visualisations has turned out to be challenging - solutions to these visualisation problems can be seen in applications like Photoshop, 3ds Max, and mobile apps for image and video editing.

Neo-impressionist paintings are filled with vivid colours and strong contrasts. The most prominent artist during this period, Georges Seurat, used a beautiful blend of colours and an innovative contrast-enhancement technique, based on the psychophysical 'mach band' illusion, to achieve the impressive neo-impressionist look. It can be experienced, for instance, at the National Gallery in London where the masterpiece 'Bathers at Asnières' is on display. With collaborators Tania Pouli and Erik Reinhard, then at the Max Planck Institute for Informatics, we aimed to emulate the contrast-enhancement technique of Seurat. Our method, which does not produce the visible halo-artefacts often created by previous methods, is presented in a Computers and Graphics article.

The British painter Clive Head takes an interesting approach to depicting a particular scene: he gathers visual information of the scene from different viewpoints and sources, like photographs and sketches. The goal is never to faithfully reproduce the scene, but rather to depict an alternative, perhaps a more interesting, scene or reality. Thus, he takes information from multiple viewpoints and includes this information into a single painting. Inspired by Head's approach, aided by my collaborators Jan Kautz and James Tompkin, then at UCL, I made a framework for making multi-perspective images and videos. The framework, using computer vision techniques, requires much less setup compared with previous methods. For more information, check out our project webpage.

Abstract art (2012)

dots randomness kitchen

My supervisor at Cambridge, Neil Dodgson, is particularly interested in abstract art and has previously contributed to the field of computational aesthetics. I was challenged to improve on recent work on multi-class blue noise sampling, which can be used to produce coloured dot paintings, similar to Damien Hirst's spot paintings. The previous work used a random-dart sampling procedure, which is computationally expensive. In the discrete setting, where you only need to sample the colour dimension, and not the geometry dimension, this seemed like an overkill. My method, presented at the computational aesthetics 2012 conference, outperforms this previous method in the discrete setting by orders of magnitude. See our project page for more details.