Combined PCM and PHOS double ratio $R_\gamma$ in the 0-20%, 20-40%, and 40-80% centrality classes compared with pQCD calculations for nucleon-nucleon collisions scaled by the number of binary collisions for the corresponding Pb-Pb centrality class. The dark blue curve is a calculation from Refs [51,52]. which uses the GRV photon fragmentation function [53]. The JETPHOX calculations were performed with two different parton distribution functions, CT10 [55] and EPS09 [56], and the BFG II fragmentation function [57].