To speculate on these results a little: I'd say the performance in general with Libspng and Libpng is pretty similar. The apparent greater speed of Libspng in

To speculate on these results a little: I'd say the performance in general with Libspng and Libpng is pretty similar. The apparent greater speed of Libspng in the RelWithDebInfo build may be due to the use of the inline keyword, which libpng doesn't use. However once full program optimisation is enabled, and functions are inlined across translation units etc.., the code comes out pretty similar and hence has performance parity.