Figure 1.

(A) Optical scan of a painting as an example of a non-biological sample and (B) the results of spatially-aware sparse clustering with C = 15 clusters. The discovered sub-regions often match up with the known colors used in the painting, but also shows regions that could not be accurately distinguished, such as the gray donkey in the lower right. (C) The mean mass spectrum of the cluster corresponding to the red houses with the 27 structurally-important ions selected via regularization for s = 0.2 marked in red and (D) the ion image for one such peak at m/z 419.