'Merge divide' is a technique that is commonly used in the world of compositing. In technical terms, it is called 'Image Frequency Separation'.

It enables you to restore fine details or reuse them in other places while keeping the same shading and lighting of the targeted area.
There is a node for it in Nuke called 'Laplacian'. It is frequently used when removing elements from a shot and de-aging or aging actors, but also for sharpening out-of-focus shots and lighting changes.

In this video, you will learn how to use image frequency separation through a brief overview demonstrating how to remove a mole from a face.

The tutorial includes another use-case example showing you how to remove more complex elements, such as a road sign.

Follow along by downloading the Nuke script in the course files tab.

Here are the links to the images used if you want to purchase them:
https://www.istockphoto.com/photo/senior-man-portrait-gm1394669704-450064939?clarity=false
https://www.pexels.com/video/passenger-bus-making-a-stop-on-designated-bus-stops-2950082/