Secondary Color Correction Primer
Although primary color correction affects the entire raster, secondary color correction is limited to specific geographic regions—for example, vignettes or windows—or specific color vectors. Secondary color correction can also affect specific tonal regions, but these secondary regions are more specific than the shadows, midtones, and highlights that are used to qualify corrections in primary color correction.
As the tools have become more nonlinear, the distinctions between what is primary and what is secondary are beginning to blur. For the purposes of defining workflow, this distinction will probably never totally evaporate, but the boundaries between these two terms are more vague than they have ...