Colour Variations Within Light Fields: Interreflections and Colour Effects

The human visual system incorporates knowledge about local chromatic and lightness effects of interreflections (Bloj et al., Nature, 1999). Here, we study basic principles behind chromatic effects of interreflections using computational modelling and photometric measurements. The colour of interreflections varies as a function of the number of bounces they went through. Using a computational model, we found that those colour variations can show brightness, saturation, and even hue shifts. Using a chromatic Mach Card, a concave folded card with both sides made of the same colour, we demonstrated those three types of colour effects empirically. Finally, we tested the effects of such coloured interreflections on light fields in three-dimensional spaces. Via cubic spectral illuminance measurements in both computer simulations and full mock up room settings under different furnishing scenarios, we measure the chromatic variations of first-order properties of light fields. The types of chromatic variations were found to depend systematically on furnishing colour, lighting, and geometry, as predicted, and also vary systematically within the light field and thus throughout the space. We will next compare the physical light fields with visual light fields (including chromatic properties) and test perceived material colours for (combinations of) the three types of effects.