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What colours are our towns?

Continued research at LEMA

Luan Nguyen therefore began his thesis at LEMA, which had already suggested tools for characterizing buildings and urban planning. These tools would enable him to adapt his approach to an already existing quantitative framework. Up to that point it had always been a question not of colours but of forms. This meant that LEMA was able to call upon important expertise which, in particular, made it possible to objectively characterize the formal impact of the annexes to the courthouse in Liege on their environment.

Another determining legacy was the characterization by the Wallonia government of ten types of urban areas based on the shape of buildings. The research of Luan Nguyen focuses on four specific urban areas:  historic centre, periurban housing districts, working-class neighbourhoods and commercial zones. The categories grouped together eighteen representative fragments of the Liege urban area, a sample on which the young researcher decided to apply his methodology. “The reason behind the differentiation of these neighbourhoods was to make it possible to determine the dominant colours for each area and to create a representative sample for the city of Liege”.

From prospecting to the establishment of a single colour

In the first instance, some 2,000 photos of buildings were taken by students in standardized conditions. “The light and therefore the colour observed are not the same at midday or towards the end of the afternoon”, continues the researcher. “Another example, if a building is exposed to the direct light of the sun while one part of the wall remains shaded, its bricks will reveal two main colours that are different from each other”. The photographs were all taken in the spring, at midday, beneath a covered sky, with the systematic presence of the same neutral grey chart for a consistent white balance. The same camera was used for all the photographs and was calibrated to the same aperture and exposure settings etc. The colours of the 2,000 buildings could then be assessed having been taken under uniform conditions.

“We needed to decide what we wanted to study in these photos. Made up of stone, wood, roofing and panelling, a facade presents various materials of different colours. We were developing a global approach which would combine all these elements. But we first focussed on the brick which was the principal material and therefore the dominant colour. A second stage of the procedure consisted of cropping the rest of the photo from this principal material. We then used an algorithm to rebalance the colour of the brick based on our white balance. We finally had a dominant colour for a building”. This colour fragment was then characterized by means of a graphic tool in the HSL chromatic system (Hue, Saturation, Luminosity, which characterizes a colour according to its hue, saturation and luminosity).

Etapes caracterisation
“The HSL system offers three parameters which are very intuitive for characterizing a colour”, explains Luan Nguyen. “We could have kept the RGB system, but the coordinates, ranging from 0 to 255, do not make it possible to identify a colour. If somebody says, for example, that a colour is at 127 in the red, 62 in the green and 201 in blue, this means nothing to anyone”.  On the other hand, in the HSL system, the hue is expressed in a circle with degrees as a unit of measurement. Knowing that 0° corresponds to red and this then migrates towards yellow, green, blue, indigo etc., we can rapidly imagine the hue of a colour when we are given its corresponding degree. Saturation determines the purity of the colour and is expressed in percentages. Once again, a colour with a level of saturation close to 100% can be easily imagined as very pure Conversely, a colour with a saturation level of 10% will tend towards greyish pastel colours. While maintaining the hue and saturation level, if we see a point at 15° with a 90% saturation level, we can assume that the colour is saturated red. Luminosity, then, makes it possible to position the colour between black and white. Therefore, any colour can be represented by a point located in a cylinder, in a 3D space space based on polar coordinates. This can be done according to the degrees in the circle and their relative positions with regard to the centre in terms of saturation and based on how high or low they are in the cylinder in accordance with the light.

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