This is the personal webpage of Jeroen Granzier
webpage of Jeroen Granzier

My research:

Below (and on other pages of this webiste) you can read about the specifics of each research topic I find interesting.

 

The role of eye movements in color perception:

I am interested in the influence of eye movements on color perception. For example, does it matter which color an observer looked at previously for determining the color of a surface of interest? The research that I did shows that this is indeed the case. The initial research that I did was in collaboration with Eli Brenner (see: http://personal.fbw.vu.nl/ebrenner/) and Jeroen Smeets (see:http://personal.fbw.vu.nl/jsmeets/). 

Recently I investigated the role of eye movements in the chromatic induction (simulatneous color contrast) and color constancy. This research was done in collaboration with Matteo Toscani (see: http://www.allpsych.uni-giessen.de/toscani/) and Karl Gegenfurtner (see: http://www.allpsych.uni-giessen.de/karl/). Remarkably we know very little about how what we look at influences how we perceive colors.

Below you can see an example of a stimulus that we used for studying the effects of eye movements on color constancy. Observers see a virtual scene containing a checkerboard and spheres under one illuminant in scene A and a similar scene (scene B) under a different illuminant place at the opposite site of a computer monitor. The task for observers is to match the color of one colored square in the checkerboard of scene A to the color of another square in scene B (color constancy). We investigated whether the variability in color constancy within observers and between observers can be predicted by where obserbvers were looking within the image (i.e. highlihts, local color contrast etc.).   

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Perceiving the difference between emitted light (monitor) and reflected light (real surfaces)

Color vision scientists use more and more computer monitors to study color perception. One of the questions that I am interested in is whether human observers perceive the colors presented on a computer monitor in the same way as when identical colors are presented as real surfaces. My work shows that there are important diferences in how we perceive colors when presented on a computer monitor compared to when presented as real surface (see picture below).

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Question: is the surface depicted in the middle of the photo a real piece of paper or a color presented on a computer monitor?

 

Observers show large differences in color perception when a color is shown as a piece of paper comparted to when an identical color s shown on a computer screen (see image below).

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The effects of different materials on color perception:

The Real-world typically consist of objects made of different materials. Our natural environment consists of a multitude of materials and they potentially contribute to estimating the illuminant and supporting a stable appearance of objects. Different material properties like surface roughness and gloss can potentially provide us with cues about the illumination to stabilize our color percept, and of course, the ultimate goal of color perception research is to understand how we perceive the colors of the objects that surround us. These are 3-dimensional and made of different materials (like fur, stone, glass, metal, etc.). This is the question we want to address here: how does the color of an object interact with its material properties (like gloss and roughness) under changes in the chromaticity of the illumination?  There are few previous studies on this topic.

This work is done in collaboration with Romain Vergne (see: http://romain.vergne.free.fr/blog/).

My work shows that how we perceive colors depend on the material properties of the object itself.

 

perceiving rough surfaces

 

 

Perceiving object colors under changes in illumination and backgrounds:

Under normal circumstances, the color sof objects don't change much under changes in both background and the illumination. However, there are circumstances for which we predict that our mind (or brain) might be fooled when estimating the color of an object. For example, photo cameras are mostly fooled when the illumination is strongly shifted towards a certain color (for example during sunset) or when the color of the background is biased (see examples below). However, my research shows that even for scenes which are biased towards certain colors, the mind is not influenced by this bias when estimating surface colors. A remarkable accomplishment!

 

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Perceiving colors in 'the real world':

Mostly colors are studied in the laboratory under very artificial conditions. My reserach involves how we perceive colors in 'the real world'. Under daily circumstances, we are not fooled by differences in changes in background color or under changes in illumination (eg., when the illumination changes from daylight to artifcial tungsten light to filtered light); see examples below.  

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