Denoising and feature extraction for an SDSS LRG. The absorption lines from left to right are CaII (H and K), G-band, MgI and NaI. G-band absorption is not strictly an absorption line, but rather an aggregate absorption feature due to the presence of multiple lines arising from metals (mainly iron) in the numerous G-type stars present in the galaxy population. Also not to be confused with the SDSS photometric filter g-band.