Principal component analysis (PCA) has become a standard tool in spectromicroscopy and hyperspectral imaging to handle large spectral data sets and to decompose raw data into relevant and residual information. In particular in studies of complex compounds, PCA can be used to disentangle chemical information and thereby deepen the understanding of chemical and physical material properties. Surprisingly, in photoemission electron spectromicroscopy (PEEM), PCA is rarely used. This paper serves to demonstrate how powerful PCA can be to detect hidden chemical information in PEEM data. We demonstrate the capability of PCA in PEEM spectromicroscopy for the case of a thin film of a complex quaternary oxide, Pr0.5Ba0.5CoO3-delta (PBCO) which is a main contender catalyst material for electrocatalytic water splitting. Upon annealing in air, PBCO decomposes into different phases at the surface. Two of them become obvious from the raw PEEM images, but one is revealed only after PCA.