Over a century of research has shown the importance of image context for colour perception. Image regions that are physically identical -- filled with the same paint, or with the same RGB values -- may nonetheless appear different due to their surrounding regions.

I will present two studies on the importance of image context on visual perception. In the first study, I will talk about the perception of glow, i.e., what makes an object appear to emit light. We found that whether an object appears to glow can depend on the 3D interpretation of its shape.

In the second study, I will talk about the perception of lightness, i.e., the appearance of how light or dark a surface is. We adapted the reverse correlation method, a technique for characterizing receptive fields, to determine the task-specific "perceptual receptive fields" of human observers in our experiment. We also implemented four computational models of lightness, and found that the models' "receptive fields" were not even qualitatively similar to those of human observers, indicating that none of the models did not explain human lightness perception.

Artists throughout the centuries may have developed much intuition on how colour should be depicted, but a complete scientific understanding of perceived colour remains elusive. Indeed, these studies show that even something as simple as determining whether a surface is black or white may not be so straightforward.