Soft Light is a gentler Overlay where pure black or white inputs do not produce pure black or white outputs

Soft Light is closely related to Overlay but has a key difference: applying pure black or white as the blend layer does NOT result in pure black or white in the output (unlike Hard Light, which does). The result depends on the base layer value. Multiple formula variants exist (Photoshop, Pegtop, W3C/Cairo) that give the same result for pure black, pure neutral grey, and pure white blend values, but differ in how they interpolate between these points. Soft Light is commonly used for gentle contrast enhancement and ‘light painting’ effects without the harshness of Hard Light.

Examples

Soft Light at 50% grey blend: no change to base (like Overlay). At light grey blend: subtle brightening. At dark grey blend: subtle darkening. Never goes to pure black or white even at extremes.

Assessment

Compare Soft Light and Hard Light: what is the key behavioral difference when the blend layer is pure white? Why would a photographer choose Soft Light over Hard Light for a subtle contrast enhancement?