Replacing the sky in an image
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Other Raw Converterson: January 20, 2020 at 5:01 am
I recently purchased Sklyum’s Luminar 4.1 whose signature advance is an automatic sky replacement facility that they claim is controlled by ‘artificial intelligence’ — by which I assume they mean methods informed by machine learning. It finds sky backgrounds and replaces them with an alternate sky image using blending techniques that intentionally ‘leak’ into the foreground to ‘relight’ the scene. It often works flawlessly when you use the Skylum sky-replacement images — especially where there’s a clear horizon — but, as I found, much less often when I used my own sky images.
I’m certainly not averse to improving dull images ‘artificially’. Photography is artifice in my view. Still, the artifice must carry conviction: that was where I found a problem.
The Skylum marketing showed the replacement blend worked surprising well. I found that was ‘sort of’ borne out in use. The big problem for me was to stop the replacement sky leaking too much into the rest of the scene. I found the new sky would often muddy or stain the foreground near the horizon. I tried using the available Luminar masking tools to reduce this leakage, but failed. Luminar has limited local selection tools (brush, gradient) that respond slowly and unpredictably on my (fully spec’d 2019 iMac) and no edge-aware selections. I found it horribly difficult to mask our or erase the ‘sky-replacement filter’ in the foreground. When I (sort of) succeeded, the time it took made the effort just too expensive to justify the results.
I tried several Photoshop sky replacement techniques recently while I was considering the Luminar purchase. None was more successful than Luminar and each was time-consuming. None of them (using ‘blend-if’, or channels or gaussian blurs to clear up ‘leaks’ into the middle- or foreground) was uniformly useful. I believe it is possible to make convincing sky replacements in PS. But, for my images anyway, I found it takes too much effort and time-consuming attention to minuscule details. Worse, the end result of ecstasies of fiddling often failed to convince (me at least) for reasons that were subtle but unmissable.
Finally, I’ve reached the conclusion that if an image needs sky-replacement to make it more interesting then it’s very likely due to poor technique on my part. Either I made the wrong image OR I made the image wrongly. In the majority of cases I could have made a much more successful image simply by bracketing my exposure. In some cases, the RAW file contains sufficient information for me to ‘rescue’ the image or improve it if I process carefully in Lightroom. In other cases, I simply framed the image badly or was not close enough to my subject.
By the way: I apologize for being the only member to break the silence in this part of the Forum. I really have no agenda in doing so.
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