Three-color image created from the emission (line+continuum) of three near-IR lines (red: Brγ2.167 μm, green: H₂1−0 S(1) 2.122 μm, blue: He i 2.059 μm). The three squares (I, II, and III) mark selected positions representing H ii region, ionization front, and PDR. A strip line with tick marks is also drawn perpendicular to the IF of M 17 SW. Offset at each tick mark is − 1, 0, + 2, + 4, + 6, + 8, + 10, + 12 in arcsec from northeast to southwest, respectively.