Color–color diagrams of the NEP-Wide NIR sources matching with optical data. a) (N2 − N3) vs. (N3 − N4) color and b) (N2 − N3) vs. (N2 − N4) color. Dark dots represent all of the sources having optical counterparts and red dots represent the “star-like” sources defined as having the criteria of stellarity  >0.8 and r′ < 19. The histograms in both the right and lower panels show the number of sources per 0.2 mag bin.