Digital photography used to quantify the greening of north-facing walls along Broad Street in central Oxford, UK

Abstract

The outdoor integrated digital photography and image processing (O-IDIP) method was used in this study to quantify the appearance of greening due to algal cover and moss build-up on historical buildings situated in central Oxford, UK. A photographic survey was taken along north-facing building facades on Broad Street in the winter of 2010. The main objective of this study employing digital photography was to quantify surface greening of historical buildings using O-IDIP. Images were taken with a high-resolution digital camera (Nikon Coolpix S4) close-up ca. 1 m from building facades at various locations along this street. Calibration was based on an X-Rite ColorChecker included in photographs. Images were processed in Adobe Photoshop in order to acquire quantitative information about the spectral colouration of each photograph. Lab Color provided mean (as well as median) and standard deviation values, including the green-red (a) channel of chromatic colour, and numbers were employed to quantitatively assess the greening of walls. The O-IDIP method was able to numerically capture changes in wall colouration predominantly due to the accumulation of algae and mosses.