Skylum’s Luminar 4 software will feature sky replacement based on machine learning. The software identifies the sky and replaces it, adjusting the overall lighting of the scene. The examples shown so far suggest it works well on examples where the sky is easy to detect because of being much brighter than the foreground, or containing only certain blue hues typical of skies.
That isn’t necessarily a problem as those are also the examples that need sky replacement the most. For an example, see below.
The software will provide several alternative renderings according to “moods”. These roughly correspond to different times of day and different weather situations:
Skylum Luminar is primarily software for converting RAW images (I don’t recall exactly, but it may work on JPEGs and TIFFs, too).
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Update: There are now two videos showing this, a teaser one and a bit of a “how-to” (although for an as yet unavailable product).