All feature maps of one feature are combined into a conspicuity map yielding one map for each feature: , , . The bottom-up saliency map is finally determined by fusing the conspicuity maps:
The exclusivity weighting is a very important strategy since it enables the increase of the impact of relevant maps. Otherwise, a region peaking out in a single feature would be lost in the bulk of maps and no pop-out would be possible. In our context, important maps are those that have few highly salient peaks. For weighting maps according to the number of peaks, each map is divided by the square root of the number of local maxima that exceed a threshold : Furthermore, the maps are normalized after summation relative to the largest value within the summed maps. This yields advantages over the normalization relative to a fixed value (details in ).