Post VFX: Pixel-by-pixel sampling from one area brushed over another — removes scratches, erases unwanted objects. Core tool in grading and compositing.
You know this from every post-production: a scratch runs through the original film, a light reflection sits exactly where it shouldn't, or a cable juts into the frame. Cloning is your first weapon against it — a pixel-for-pixel copy of a clean image area that you lay over the offending spot like with a brush. At its core, it's copy-paste with finesse: you sample a source (Hold Alt + Click in Photoshop, Nuke, After Effects) and then paint over it.
On set, you don't think about it. In editing and color correction, it becomes routine. The classic workflow: scratch or dust on the 35mm negative? Clone. An obtrusive person in the background you want to subtly remove? Clone. A boom shadow that exits the frame too late? Here too — clone. The tool works with Hardness, Opacity, and Brush Size — depending on how precisely or broadly you need to operate. For fine lines (scratches), you need a hard, small brush; for larger areas or organic regions (sky, water), it becomes softer and larger so that no patterns emerge.
The devil is in the details: if you always sample from the same point, a repeating texture emerges — the eye recognizes it immediately. Professionals vary their sample points, work with multiple sources, combine cloning with Healing Brushes (which intelligently blend textures), or use generative fill tools in modern systems. In Nuke, you do this via the Keyer and Clone nodes, in After Effects via the Clone Stamp or Content-Aware Fill — each system has its own pace and limitations.
A practical tip: Wasting time thinking about cloning during the shoot is a waste of time. But if your gaffer assures you the light won't get any better, or if the production designer has overlooked a mistake in the set — then you'll be glad you have this tool. Cloning isn't glamorous, but it's indispensable. It's the silent work that no one sees because it works too well.