AI Sky Replacement in Luminar

Lately, I’ve been using the AI Sky Replacement tool inside Skylum’s Luminar 4.

The idea behind it is to make a scene more engaging by enhancing the sky. It cleverly replaces an uninteresting sky for another of your choosing. Anyone whose done this manually in Photoshop knows it’s a tedious chore to get right.

An image of a harbor entrance light before sky replacement.
The same image after using Luminar’s AI Sky Replacement (click for full size)

Luminar provides several dozen sky images with the tool; all you have to do is try one out. If you don’t like it, try another and keep experimenting until you find one you like.  

In some scenarios, if it doesn’t recognize a sky in your image, the tool becomes disabled. For instance, if you take a picture of your foot, AI Sky Replacement is disabled. But if there is the sky in your image, it works more often than not. I’ve tried cases where I thought it wouldn’t work, and it does.

Here’s an example where Luminar correctly identified the sky through an arch. This surprised me as I thought the software would get confused, but the AI proved me wrong. The photo is of an Instagramer at the Abbey of Montserrat in Catalonia.

Also, there are sliders you can use to tweak the results, but it does the job with or without the sliders. As someone who spends a lot of time looking at details in images, it’s pretty good. 

I won’t go into the arguments of what’s real and what’s fake. I create a lot of images, and I always manipulate them one way or another. I consider photographs straight out of the camera raw material. It is with this resource that I apply post-processing techniques to get the look and tell the story I have in my mind. In that vein, I have no compunction about using software (AI or not) to edit photos. 

Over the years, I’ve taken many thousands of digital images that now sit in a Lightroom library. Less than one percent ever qualify for public consumption. Compositionally, most are just plain bad, but in a few cases, it’s because the sky is too flat.

I’ve started looking at some of these “reject” images with new eyes and asking myself, what if? What if it had a different sky and, perhaps, different lighting? Before I go on, let’s pause here because it’s the second part of this question that I find the most interesting. 

Not only does it (as the name suggests) replace the sky, but it intelligently relights the scene to match the light from the new sky.

Here’s a surreal image of a mountain lake in Oregon after adding a long exposure of the Florida sky? The lighting of the scene below the sky is a result of the AI software.

Think about that for a moment. If your scene was taken in midday, but the sky you’ve chosen as a replacement is from sunset, merely replacing one sky for another might create an unbelievable, if not odd, lighting contrast. As humans, we recognize subtle changes in light, even if we are not always aware of it. But combine a sunset sky with a noontime landscape, and we get a feeling that something is not quite right. 

This is where the AI shines through. Skylums’s software agent works at relighting the non-sky elements with subtle tones of the sky that you selected. If Luminar simply replaced the sky, that would be a cool thing indeed, but Skylum is building upon years of AI experience. They’ve created a machine that combines the expertise of masking (sky replacement) with the techniques of expert toning. That is, given a scene, figure out how to achieve a believable lighting scheme. Of course, the idea of “believability” is subjective, and it depends on your individual preferences. All things considered, it does a pretty good job in a fraction of the time that you could do manually. There are infinite combinations of skies and landscapes, and each result is entirely unique. You could make the argument that it’s not perfect, but then, what or who is? The goal of AI is not perfection, rather accomplishment of things that formerly, only humans could do. In that regard, it’s as good or better and way faster than most humans. 

While we’re on the subject of AI, I just finished Stuart Russell’s book, Human Compatible, Artificial Intelligence and the problem of control.

In it, he explains just how far and fast AI is advancing. Stuart draws the curtain back on the future of our civilization once AI is fully realized. And from the sounds of it, we are much closer to that than most of us wish to believe. I recommend picking it up if you are the least bit interested in what the future holds. 

Skylum’s Luminar is a fascinating tool, and it’s a little uncanny how well of a job it does. But as I’ve come to learn from Russell’s book, this is just the tip of the iceberg, everything is moving in this direction, and we’d all better get used to it. Children born today will never know a world without AI. Any doubts you may have are quickly dispelled the next time you look at your smartphone or ask Google a question. 

So back to the photos, I’ve included some examples of both extreme and subtle applications. In the most extreme case here, the lighting of the ENTIRE scene is changed from daylight to night, as determined by my selection of one of Luminar’s out-of-the-box night skies. I added some additional elements like the light in the lighthouse and some extra toning. But the majority of the scene lighting is done by AI. 

This is how the Oregon coastal scene appears straight out of the camera.
Here, the same image is toned automatically to match the starry sky. (Click for full resolution).

By now, I’ve used it in a lot of different scenarios, some extreme like the previous example, but more often, I use it in subtle ways. Examples of this are where I’m just adding a little bit of texture to a picture where the sky is only a minor background component, not necessarily to be noticed. Here are some examples of that. 

An example of the subtle use of sky replacement on a minor background component of an image
Another example of sky replacement as a minor element to an image.

There’s a lot to like with the combination of replacement and toning, but there’s one more thing that seals it, at least for me. Luminar supplies about thirty skies, from sunrise to the Milkyway galaxy, and everything in-between. So they basically give you enough of a selection for most situations. They also provide addition sky packs from accomplished photographers that you can purchase as plug-ins. But to be frank, I would prefer to use my own skies. And the one feature clinches the deal for me is that Luminar allows you to use your own skies. 

As it happens, I take way too many pictures of the sky. Whenever I’m out shooting landscapes, and I see beautiful clouds, I can’t help but take a picture. By itself, an image of the sky is not that interesting; pretty maybe, but as far as being a complete composition, generally not. 

It’s always been in the back of my mind that one day I’d do something with these images, and that time has come. All those skies I’ve collected can now be used in Luminar AI Sky Replacement. 

I’ve started selecting a few and preparing them for use in the tool. I have morning, daylight, sunrises, and sunsets. I don’t have many night skies, so, for the time being, I’m using nights supplied by Luminar, and truth be told, those are the most fun to try out.

Playing with Luminar’s night skies are perhaps the most fun of all. Here is the silhouette of Mt Tibidabo from Barcelona with one of the out-of-the-box skies supplied by Luminar.

But I’m more of a sunrise and sunset person, so that’s most of what I have. Here’s a snapshot of the ones I’ve prepared so far. 

A snapshot of some of the skies I’ve prepared to be used inside Luminar. Most are from Florida where I live and others are from around the globe.

With my old skies now ready, I’m going back over my archives and revisiting images. Luminar’s AI Sky Replacement is breathing new life into my library. Photos that would never make the cut are being reconsidered with some pleasant results. Anyway, if you’re into post-processing, give it a try. As for me, it’s become a permanent part of my kit. And, like it or not, this is a taste of the future, even as it is upon us now. 

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