Individual variations in an average colour

The forty facades photographed in the rue des Anglais is a concrete example of what can be obtained by means of this method. A palette of colours which, when quantified, can be redistributed to as many points in the HSL colorimetric space. “In summary, we collected 2000 “individuals” in eighteen different neighbourhoods which were spread throughout this large cylinder and this allowed us to already observe certain trends. The distribution in a commercial zone, for example, was very different to that of the rue des Anglais yielding a palette that tended towards grey. In the case of workers’ apartment blocks, we observed a dominant reddish-brown”.

By means of this sample characterizing each of the 2,000 facades by a single colour, the study had already taken a first step, using this number-based approach, to determining the colour of towns. Each point had a value which made it possible to characterize these eighteen neighbourhoods divided into four urban zones and to already identify some trends. The second stage required the use of statistical tools to assemble these 2,000 individuals divided into samples (neighbourhoods) based on common characteristics. “In simple terms, it involved the arbitrary creation of four large colorimetric types. A concept which belongs to another very extensive heritage in architecture, the typology that attempts to classify buildings by category. Once again, typology is historically based on shape, whereas we applied these methodologies to colour”.

Four generic, synthetic colours should therefore describe the main trends observed in the different neighbourhoods of the city of Liege. “In order to achieve this, we therefore regrouped the 2,000 points present in space in four sets, using a partitioning algorithm, while taking account of their spatial proximity in the cylinder. We then attributed to each of these sets, a point in the centre of all the individuals of a group, called a centroid, which corresponds to HSL colorimetric coordinates, a generic colour, a type for a set of facades sharing similarities in terms of colour”.