Colour, Texture and 3D Shape Interactions in Real-World Surface Perception
EPSRC Project EP/D068738/1

PI: Anya Hurlbert

PDRA: Yazhu Ling

PhD student: Milena Vurro

Natural surfaces tend to be nonuniform in both chromaticity and luminance. Often, the chromatic texture of a natural object is distinctive and diagnostic – think of the pocked yellow surface of a lemon, instantly identifiable as such.  This feature of natural surfaces is not captured by traditional studies of colour perception, which typically employ stimuli of uniform colour and brightness. In this EPSRC-funded project, we explore the consequences of surface ‘polychromaticity’** for colour discrimination, colour constancy, memory colour, and material appearance.

**Term coined by (Beeckmans, Philosophical Psychology, 2004)

Natural surface colour (tri-stimulus) image database

For our experiments and analyses, we required accurate and digitally manipulable representations of surface colour distributions of objects. We obtained these by imaging a series of objects, both natural and man-made, under several types of controlled artificial daylight illumination, using a tri-stimulus-calibrated camera system.  These objects include fruits, vegetables, foliage, and textiles. Sample thumbnails appear below, together with links to the associated datafile containing tristimulus values at each pixel.

For access to the full database, please contact anya.hurlbert@ncl.ac.uk.

carrot_banana CIE XYZ imagefile

leaves CIELab imagefile

matlab code for reading XYZ imagefile

matlab code for reading CIELab imagefile

Colour constancy from surface polychromaticity

The distribution of within-surface cone contrasts for a given object forms a distinct signature in three-dimensional cone-contrast space, which transforms predictably under changes in illumination. For many natural surfaces, the distribution is an elongated cluster whose vector direction in cone-contrast space remains roughly constant under illumination changes, provided the contrasts are calculated with respect to the illumination whitepoint. This feature provides a surface descriptor which remains stable under adaptation to the illumination, thereby potentially mediating colour constancy.

For more information, see Y Ling, M Vurro, A C Hurlbert (2008), “Surface chromaticity distributions of natural objects under changing illumination”, Proceedings of
the 4th European Conference on Colour in Graphics, Imaging and Vision (CGIV), 263-267. pdf

Page still under construction .....