Realistic Sky Replacement Using Luminar 4

If there is one tool in Luminar 4 that really makes the software stand out from the crowd, it is the Artificial Intelligence (AI) Sky Replacement tool. The software algorithms not only do an astounding job of identifying sky portions in your image. But it also:

  • Relights the scene to balance out the colours across the rest of the image.
  • Removes any halos that you tend to get around hard edges when replacing skies.
  • Removes chromatic aberrations and artefacts around softer edges like trees and grass.

Sky Replacement in Luminar is very easy!

To achieve the same results Adobe Photoshop (at time of writing); you need to have several tools in your photo editing arsenal. All of which I would categorise as being intermediate to advanced photo processing techniques. Luminar though makes the job achievable regardless of your image post-processing skill level. However, there are still some basic rules that you need to follow, as well as some simple techniques to use; in order for a sky replacement to be believable.

Image Quality

Make sure that the new sky image is at least the same quality (pixel resolution) as your foreground image. If you are using the built-in Skylum skies, or the market place ones on their website; then this is not one to worry about. However, it’s worth keeping in mind if you are importing custom sky images.

Lighting Direction

When you replace a sky using Luminar, pay attention to that the replacement sky lighting is in the same direction. This seems such an obvious thing to say right? But you will be surprised how many photographers, even professionals miss these sort of details. If you cant find a sky with the light in the right direction, then at a minimum, choose a sky image where the lighting direction is more ambivalent. What you don’t want, is for example shadows on your foreground on the left-hand side of the image, and the sun shining in the background also, on the left-hand side of the image. The result would look just wrong!

Image Style & Context

With so many skies available to you at the press of a button, it’s easy to get a little carried away; and overlay a Caribbean sunset over your favourite picture of the Lake District in the UK. Nobody is going to be fooled by this for one minute. Take a look at the example below, looks great? Well no, the Northern Lights only happen in the far reaches of the Northern Hemisphere; and not over the City of London.

After - Not Good!
After - Not Good!
After - Not Good!

Ok, so I used an extreme example here to make a point! But the principle behind the example is to keep your sky replacement in context & in the same style as your foreground image. So let’s say you have a picture of a plain blue sky, and you wanted to add interest with clouds. Select a sky of very similar tone/hue to replace it, and not an extreme sunset. Luminar will do its best to harmonise the colours between the two images regardless, but the human eye is sure to spot inconsistencies, so keep things sympathetic.

Here is another example using my long exposure photo of a sunset over Tower Bridge in London. I actually like the original, as whilst there are no clouds in the sky, the length of exposure has allowed stars to shine through and adds interest. Anyhow, the sunset I used to replace the sky is of a similar style to the original sky. Also, the lighting is in the correct direction, the result is much more natural than my extreme example above.


AI Sky Replacement in Luminar: How-To

Ok, so we have now covered some of the things to look out for in your sky replacements, let’s quickly cover how to replace the sky in your image to demonstrate how easy the process really is. With your image opened in Luminar, click on the “Creative Tab Icon” in the right-hand menu bar (see figure below). The Creative Tab Icon is the one which looks like an artboard. From here you are presented a number of options, select “AI Sky Replacement”, and the tool pops up in a new window.

AI Sky Replacement Menu
AI Sky Replacement Menu

The very top option brings up a menu with all the skies installed within your Luminar library, you also notice that you get the ability to import your own from within the menu. Select the sky you want, and Luminar does the rest for you. I did say the process was easy!

Get Creative with Luminar Sky Replacement

As alluded to in the introduction, the AI Sky Replacement software algorithms do a pretty good job of identifying the sky in your original image, replacing it, and then harmonising the merged images. A lot of people will probably stop right there. However, If you want to take your image to the next level, then the other options in the AI Replacement tool are worth a look. These are:

Horizon Blending:

Smooths the transition between the current horizon and the new one.

Horizon Position: 

Allows you to fine-tune the alignment the horizon of the original photo with the new sky’s horizon.

Relight Scene: 

Luminar automatically relights the merged photo to harmonise the colours between the foreground and background. This slider allows you to manually adjust the intensity of the relighting effect.

Sky Global: 

The AI Sky Replacement could more correctly be described as a blend between the original and new sky. This slider allows you to manually control the intensity of the blend.

Close Gaps:

This slider allows you to manually fix any small details or holes that Luminar has not fixed automatically. It is particularly useful in small details such as leaves on trees.

Sky Local: 

This slider allows you to manually control how the clouds in the original image are replaced.

Sky Defocus:  

This slider is particularly useful if for example the background in your original image was blurred, and you want to mimic the same amount of blur to better harmonise your image.

Flip Sky

As its name suggests, this option flips the new sky texture in the horizontal plane. This is another option which is particularly useful if you need to match the direction of light in the merged images.

Atmospheric Haze:  

This slider adds a soft haze to the sky and is another useful option for harmonization with the original image.

Sky Temperature:

This slider increases or decreases the temperature of the new sky, and again is useful for harmonization.

Sky Exposure: 

This option controls the exposure for the new sky.

Taking Luminar Sky Replacement to the next level!

If you want to take things to the next level again, then there are a couple more tools in the Creative Tab that are worth looking at, they are Film Grain and Fog. See figure below.

Luminar: Film Grain & Fog
Luminar: Film Grain & Fog

Both of these options have similar effects as they essentially add small particles of random noise, accordingly they should be used very sparingly. However, a little bit goes a long way to further harmonise your merged image.

I hope that this article on Sky Replacement in Luminar was useful. Please also check out our series of Learn Photography guides.

Here are some other Luminar articles that may be of interest to you:

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