I Discovered A Secret About Photoshop's New Sky Replacement Feature

Updated: Oct 25, 2020

Photoshop tutorial by Craig Boehman.

With Adobe's Photoshop 22.0 release, I can't say I was all too thrilled with one of the features: sky replacement. Yes. I played around with it and took it on a test drive. I even wrote a little piece about it yesterday praising the usability of it.

See here: Adobe Launches Photoshop 22.0 - With Sky Replacement

But overall, it wasn't going to be a feature I'd be using a whole lot. My reasons aren't important for the sake of this piece, but allow me to wager a guess that Photoshop fads die hard deaths.

I kept thinking, however, about the new algorithm that made the sky replacement selection possible in the first place. Why was it so good at the job it did? To me, it appeared to be on par or even surpass the job of the also-recent 'Subject' selection tool, which does an excellent but not yet perfect job.

Which gave me an idea. Could I put this tool to work for me in another way entirely?

Earlier this year I took up fine art photography, a genre that can rely heavily on compositing. In my case, compositing was the backbone of my imagery. And to pull off these pieces, I almost always had to make a selection of my subject, cut it out, and then throw it onto a new canvas to be blended with other elements. As a people photographer, I usually had to make at least one selection of a person for every piece.

With compositing on my brain, another idea. Could sky replacement be used in compositing? The answer, it turns out, is a resounding yes.

My Experiment

What if I took a person I photographed against a plain background (negative space) and used the sky replacement took to make a selection? After all, what are skies but mostly negative space and clouds?

And that is exactly the experiment I performed with the below image.

To make things interesting, I would pit the sky replacement tool against the subject selection tool and compare the results. Then I'd count the steps necessary to cut out the subject and throw it onto a completely new background.

Here's the thing. I knew the sky replacement tool would win the fewer-steps contest. After all, the process is nearly automated as it is. I would only have to make the selection and then choose to upload my own "sky" as a background.

What I didn't know was which tool would do a better job. Or would they be too similar to notice a difference?

The Results

I ran both selections and used a pink background to test each tool against. I compare them both below. [Note: the main header image is the winner]

With all the foreshadowing, you may have rightly concluded that the new sky replacement tool won. And you would be correct. Here are the results.

Subject Selection:

I figured the Photoshop algorithm would treat the hair as clouds, albeit very complex clouds. But 'Select' subject did a reasonably good job still. Where it didn't do a fantastic job was naturally in the hair region, where strands are somewhat ragged and pieces near the bottom contain the tell-tale signs of a botched selection due to original background elements being present. I circled and drew arrows at the bottom pointing to these gray artifacts.

Sky Replacement:

Side-by-side, two things stand out to me. First, the sky replacement selection was superior in selecting hair strands and rendering them smoothly. The subject selection tool appears much more ragged.

Secondly, there are no artifacts from the previous background except perhaps a small bit buried deep in the hair, which my arrow is pointing at. It's entirely possible that this gray patch could be part of the pink gradient as well, which had lighter sections in the original image. Either way, the sky replacement tool is clearly the winner.

For more advanced users of Photoshop: I did not clean up either selection with the brush options. Both selections were implemented as they were.

Note: It's important to realize that the sky replacement tool is designed to find the horizon. So just because you may have a lot of negative space in an image, the selection will be hampered by any horizon and you won't get an entire subject selected. This method is best used without any horizontal lines whatsoever. For all else, use Subject select or any of the other methods available.


I can't and won't speak for everyone else out there, but for me, this new sky replacement tool is a boon for photo compositing. This just made my workflow for subjects with a lot of negative space much easier and a time-saver to boot.

Going forward, this means all I need to do is photograph my subject either against a plain background to get quick and easy selection results that are near-perfect. Not that this method is anything new for compositors, but the fact that hair is no longer a big issue is revolutionary in scope.

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