Photometric isolation parameters. a) Calculated isolation parameters (local number density η_k,p and tidal strength Q_Kar,p) for similar-size neighbour galaxies using the photometric data. Symbols and colours in the legend correspond to the number of neighbours that violate the CIG isolation criteria. b) Comparison between isolation parameters (local number density η_k,p and tidal strength Q_Kar,p) for the CIG and the comparison samples using photometric data. Pairs (KPG) are depicted by violet plus signs, triplets (KTG) by blue triangles, compact groups (HCG) by green rectangles, and Abell clusters (ACO) by red diamonds. The mean values of each sample are indicated following the same colour code.