SubBytes applies the AES S-box to every byte. The displayed state is recomputed from the input grid.
highlighted = computed this step
Why bytes are substituted
SubBytes replaces each byte through the standard AES S-box. The grid is recomputed cell by cell from the previous state.
S-box each byte
Read the SubBytes state
The recomputed state is 0xd42711aee0bf98f1b8b45de51e415230.
0xd42711aee0bf98f1b8b45de51e415230
Why this is nonlinear
The S-box is the nonlinear step in the round. Here it is only shown as exact byte substitution, not as a derivation of the S-box.
nonlinear byte substitution
Summary
SubBytes maps the starting grid to the pinned S-box output. NOTE: no-padding; no-side-channel; no-production; never-roll-your-own. Exact byte transforms of ONE AES round over GF(2^8); real AES with 128 runs 10 rounds with a key schedule inside a reviewed mode such as CBC or GCM.