The main change to Luminar 4 is the addition of AI Sky Replacement which is designed to automatically mask out the sky (using machine learning) in your photos whilst ensuring that the tone and colours match the replaced sky, allowing for the replacement of a bland sky with another which better matches your artistic vision.
In terms of how it works, Skylum provided the following information;
AI Sky Replacement works by automatically detecting not only the sky, but also objects in a photograph’s scene. This helps make sure the photo ends up being as realistic as possible once you insert a new sky. It removes things like halos, artifacts and edges of transitions, problems that often were present in existing sky replacement techniques. AI Sky Replacement automatically adjusts the sky to fit the rest of your images — things like depth of field, tone, exposure and color — making it great for not only landscapes, but also portraits.
When working on an image, the AI Sky Replacement technology automatically creates a mask for the sky, taking a step that would oftentimes take minutes or even hours, and boiling it down to mere seconds with just the click of a mouse. But that’s not all it does — AI Sky Replacement also correctly selects the orientation of the sky so that it looks as realistic as possible.
Furthermore, when you select your sky of choice, you’ll see the rest of your photo change in terms of light and color. This makes sure that an image and sky match so they appear they were taken during the same conditions. Because of the toning that AI Sky Replacement does to an image, it looks as natural and smooth as possible.
An example of the sky replacement is shown below;
There are two packages available;
More information is also available here.