If you look at enough planetary nebulas you know they like to be random and avoid fitting comfortably into categories. One feature, however, seems rather common--a bright central core with sharply defined edges surrounded by another layer which is roughly half as bright and less sharply defined. Interesting, reticulated patterns can be seen in both layers and they are usually roughly elliptical in shape if not perfectly circular. IC 2448 is a typical example. It seems to lack FLIERs, however. (I only recently realized FLIERs is an acronym. Fliers as a rather simple noun seems to fit them even without the complexity of an acronym.)

Corners are discreetly missing data.

Red: hst_11122_03_wfpc2_f656n_pc_sci + hst_06119_49_wfpc2_f814w_pc_sci Green: hst_06119_49_wfpc2_f555w_pc_sci Blue: hst_08390_14_wfpc2_f502n_pc_sci