These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 1.51 s (backtrack: 0/20).

[ebuild     U  ] media-libs/libpng-1.6.58:0/16::gentoo [1.6.55:0/16::gentoo] USE="apng -static-libs -test" CPU_FLAGS_X86="sse" 1056 KiB

Total: 1 package (1 upgrade), Size of downloads: 1056 KiB