The Art of Sky Replacement in a Photograph

Photographer or Digital Artist

The Art of Sky Replacement

In my previous post, AI in Photography, we introduced the concepts of artificial intelligence and deep learning and their impact on photography. This is evident in both the camera technology and in post processing software. In this post, I would like to dive a bit deeper and have a look at one AI editing feature that’s being talked about a fair bit at the moment – Sky Replacement. The recent introduction to a simplified sky replacement in Photoshop and the launch of Luminar AI has made replacing a sky in your image far less complex and available for photographers of all skill levels. 

The concept of Sky Replacement is pretty straight forward; you replace a sky in a photograph with one that is more appealing or more dramatic. It may be because you won’t have the opportunity to revisit a location that presented you with a bland sky on the day you visited. 

AI: Making Life Easier

Up until now, replacing a sky in an image was a fairly complex process. You had to painstakingly select the sky in the image with a range of photoshop selection tools, mask the sky and then manually load the replacement sky on a seperate layer. A very time consuming process that was often beyond the skills or patience level of many photographers.

Enter the wonders of artificial intelligence and deep learning! Photo editing software now has the ability to ‘learn’ by analysing data from millions of images that have been loaded into it. As a result, it is now exceptionally skilled at performing complex sky masking without any input from the photographer. Making sky replacements as easy as a single click of the mouse. 

Not only does AI take control of the tedious task of masking and inserting your chosen sky into the image, it also assists in analysing additional changes that may be required to blend the sky into the rest of the image. This includes such things as the level of foreground exposure and colour tone, to name a few. 

So…Is This Cheating?

Sky replacement is a hot topic of debate in many on-line forums at the moment. There are plenty of opinions, on both sides, and like most on-line conversations, plenty of passion to be found. 

Replacing a sky in an image is not cheating, it’s compositing. Compositing is the art of combining multiple photos and manipulating them to create images that are only limited by your imagination. Therein lies your answer – Compositing is a form of digital art that goes beyond simply capturing an image with a camera – you are now creating an image. 

When you are presenting your composite, or digital art to others, you should present it as an image that you have created as opposed to an image that you have captured. It’s only cheating if you present the image as a photo that you have captured.

Compositing is form of digital art that allows you to truly unleash your creativity, which can only be limited by your imagination. The introduction of artificial intelligence based features such as sky replacement only makes your job as a digital artist easier. 

Just because you can – doesn’t mean you should! 

Just because a sky can be replaced using AI simply by selecting a different sky doesn’t mean your work is done. When done correctly an image with a sky replacement should leave the viewer believing that the scene is real. If your compositing efforts aren’t convincing the viewer will sense that something isn’t quite right. Even if they cant quite put their finger on it. 

Done well, you will create art that matches your creative vision. Pay attention to detail and your images will impress. Do it poorly and your images will come across like poorly shot instagram photos with bad filters. In the following image, the replacement sky that was used has the sun positioned behind the clouds on the horizon. When looking at the foreground, it is obvious that the sun was positioned low and behind the photographer when the image was taken. The sky and the shadows in the foreground image are mismatched, making the addition of the new sky obvious to even an untrained viewer. 

Bad Composite

Pay Attention to Detail

Here are some additional, basic details that you should pay attention to when performing sky replacements:

  • Light and Shadows – One of the more obvious things to look for in an image after you’ve done a sky replacement is whether the direction of light in the new sky matches the direction of the light and shadows in the rest of the image.  Pay close attention to the shadows in your image. It may be necessary to flip the replacement sky in order to match the direction of light in the rest of the image. You may even need to select a different sky if you cant quite get it right. 
  • Angle – Your replacement sky image should be taken at a similar angle and at a focal length that is as close to the main image as possible if you want the final image to be convincing. 
  • Colour – Matching the overall colour tone of the sky with the foreground image is another important factor when creating a composite with a replacement sky. Using a sky taken at sunset with a foreground image that was taken in the noon day sun will be more than obvious to the viewer. The AI software will use its neural network technology to make adjustments to exposure and colour tones to attempt to match your replacement sky. That doesn’t mean you shouldn’t keep a keen eye out for obvious mismatches in colour tones. 
  • Scale – Another obvious, but often overlooked aspect of great compositing is to ensure that the scale of all the subjects you wish to use in your image are taken at a similar scale or size. Unless of course if you are trying to purposely create an image where a mismatch in scale is required. 

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AI Sky Replacement Adjustments to the Rescue

Whether you’re using the Sky replacement capabilities in Photoshop, Luminar AI or another post processing software, there are additional, simple adjustments available to assist you in creating a convincing image. Let’s have a look at the Sky Adjustments available in Luminar AI. (Taken from the Luminar AI User Guide)Sky Adjustment

Orientation

  • Horizon Blending. This slider smooths the transition between the current horizon and the new horizon. Using a higher value often results in a more photo-realistic look.
  • Vertical Offset. You can freely position your new sky vertically and place it exactly where you want it in the scene. SkyAI will perfectly scale it to fit while keeping it aligned with the horizon.
  • Horizontal Offset. You can freely position the sky horizontally and place it exactly where you want it in the scene. SkyAI will perfectly scale it to fit while keeping it aligned with the horizon.
  • Rotation. You can rotate the new sky on the Z-axis for perfect alignment.
  • Flip. You can flip the new sky to change the direction of the sun.

Mask Refinement

  • Global. This slider affects how the texture is mixed into the scene. A higher value will increase the amount of new sky that is added. A lower value will remove sky adjustments that may be made in brighter areas of the subject. 
  • Close Gap. This slider fixes small details and holes that were not initially filled by the replacement sky. You may need to adjust this if the image has fine details such as trees or wires.
  • Fix Details. Takes care of small imperfections around the edges of your new sky.

Scene Relighting. 

The SkyAI tool relights the entire photo so the lighting and colours of the original image match the lighting and colours of the replacement sky. These sliders adjust the intensity of the relighting effect.

  • Relight Strength adjusts the exposure of the scene to match the new sky.
  • Relight Saturation adjusts the saturation of the relighting effect to realistically add the color from the new sky to the scene.
  • Relight Human controls relighting for any people in the scene, matching people to the new sky for a more realistic effect. Use this slider on environmental portraits and lifestyle photos to see the drastic difference!

Reflection

LuminarAI will automatically reflect the new sky in any body of water in the most realistic way. The new sky automatically conforms to the angle and depth of the scene to produce incredible results down to the smallest details.

  • Reflection Amount allows you to adjust the intensity of the reflection to your liking.

Sky Adjustment

  • Defocus. This slider defocuses the sky and is useful when a shallow focus is used with a foreground object.
  • Grain. Use this slider to match new skies to the grain in the original photo for a seamless, realistic effect.
  • Atmosphere Haze. Use this slider to add a soft haze to the sky. Haze is useful for matching a replacement sky to the original image, especially if there’s moisture in the sky or environmental pollutants.
  • Warmth. Use this slider to adjust the color temperature of the image.
  • Brightness. This slider darkens or lightens the new sky. It’s useful for matching the original scene.

Masking

If you’ve ever done any photo editing, you will probably be familiar with the idea of a mask. If not, a mask is what we call the area of the image that the edits we have made apply to. In our sky replacement example, everywhere that has the new sky is under the mask. Everywhere else is the original image.

The mask editing tools give you more fine-grained control over exactly where the replacement sky is. This can be useful for the occasional times when the AI doesn’t get it quite right.

There are three mask tools, a brush, a radial filter and a gradient filter.

  • Paint Mask. Using a Paint Mask is one of the easiest ways to mask an image. You can use brush strokes to add to or subtract from the mask.
  • Radial Mask. A Radial Mask offers a quick and easy way to mask an elliptical area of your photo.
  • Gradient Mask. The Gradient Mask is useful for creating a gradual blend.

If using the Paint Mask additional options appear. Adjust The Radius, Softness, and Opacity settings. Typically, Radius and Softness are good at the default values of 100.

Once you’ve added a mask, you can now add to or subtract from the masked area. Click on the mask controls (three-dot icon) next to the Mask Type drop-down menu to find the following controls:

  • Fill. This option covers your entire image with a mask. After using Fill, you can select Paint Mask and use the Erase mode to subtract from the mask.
  • Invert. This option inverts any mask you’ve created so that its opacity and transparency values are reversed.
  • Clear. This option removes your mask entirely. After clicking Clear, you can use the Paint Mask, Gradient Mask, or Radial Mask tools to add details back to the image.
  • Copy. This option copies the current mask to the clipboard. To use this copied mask, create a new mask using any tool and paste it into the new tool mask.
  • Paste. This option pastes the current mask stored on the clipboard for use on another tool mask.
  • Show Mask/Hide Mask. This option controls the visibility of the mask. Clicking Show Mask displays the mask as a red overlay. For greater precision, you may continue drawing your mask while this overlay is shown. Hide Mask removes the red overlay.
  • Masking just gives us more fine grained control over the end result, and can be very useful for particularly complex images.

Now that you have successfully blended a new sky into your image, you are free to explore the additional AI compositing tools Luminar AI offers such as Sky Augmentation, Atmosphere, Mood, Dramatic, just to name a few. 

Conclusion

There you have it, the art of sky replacement.   As the technology evolves, the photo editing tools we have at our disposal also evolves. We are offered easier, less complex ways of doing things. This allows more people of all levels of expertise to also evolve as artists without having to spend years learning complex skills.  This will allow more photographers, with the assistance of AI technologies, produce better images.

Whilst AI may provide the tools to make photo editing and compositing easier, the heart and soul of any image is your vision and your desire to bring that vision to life. 

 

Check out our recent review of Luminar AI Post Processing Software. Download a FREE 7-Day Trial of Luminar AI.

 

The Complete Pixel is a proud affiliate partner of Skylum and Topaz Labs.

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Brian Bird
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