Fleming, Breidt & Bülthoff Supplementary Images The following slides contain a number of example photographs to show how the claims in the main submission generalize to other everyday scenes and objects. We provide examples of glossy objects that appear glossy even though they have non- or negatively skewed histograms, and a variety of matte surfaces that have positively skewed histograms. Some of the images were taken under carefully controlled lighting conditions, others were spontaneous. Some of the images have been processed slightly, mainly to sharpen the image or correct the colour balance. Luminance histograms were calculated using a mask to select only those pixels belonging to the object. We believe these examples are important as they show that although histogram skewness may be a useful measurement, it does not circumvent the inherent ambiguities between lighting, shading and texture that the visual system typically faces.

Glossy surfaces with negative skew The following images show glossy objects that present negatively skewed histograms to the observer. Despite this, the broad highlights conform correctly to the shapes of the objects and lead to a clear impression of gloss.

Glossy surfaces with negative skew Histogram of object

Glossy surfaces with negative skew

Histogram of object

Glossy surfaces with negative skew Histogram of object The peak at the dark end comes from the spine of the book

Glossy surfaces with negative skew Histogram of object

The following images show examples of non-glossy objects that present positively skewed histograms to the observer. Factors other than gloss, such as grazing illumination, spotlights, texture patterns or shading patterns due to 3D shape can lead to positively skewed intensity statistics. This means that taken in isolation, positive skew is an ambiguous cue to glossiness. In order to infer that a surface is glossy, the brain must somehow measure consistency between its estimates of 3D shape, illumination and reflectance. Matte surfaces with positive skew

Histogram These are rough surface patches similar to those used by Motoyoshi and colleagues

Matte surfaces with positive skew Histogram Crumpled matte card illuminated from the side.

Matte surfaces with positive skew Histogram The white spots lead to positive skew in the histogram but are not interpreted as highlights.

Matte surfaces with positive skew