Post-crop vignette
Vignette (post) · Nabewerking
A deliberately darkened edge around a photo, added in post-processing to draw attention to the centre.
A subtle vignette (−10 to −20 in Lightroom) guides the eye toward the subject without being noticeable. Too much vignetting gives a dated, heavy-handed look. In Lightroom find it under Effects; the option applies after cropping.