Sky Replacement and Accurate Color Blending in Photoshop CS6
**UPDATE: Be sure to check out the video I made to go along with this tutorial, found at the bottom of this post.**
Some of the most powerful and visually aesthetic content in both landscape and architectural photography lies not in the foreground, but in the sky. A salient and impactful visual property, skies enhance and intensify temperature, colors, depth, mood, and feeling.
For better or worse, despite meticulous planning and untold hours of patience, Mother Nature makes her own plans. While most of us aren’t financially secure enough to persevere against prolonged inclement weather, the resources we do have can often save us time and money on location.
Sky replacement exists for those instances where you just so happen to have received the unfavorable luck of nature’s plain, unembellished circumstances. An example of this occurs frequently in my city, when at the moment of twilight the sky transitions from a royal blue to an unclassified version of yellow and black, filling the sky with light pollution and impairing the comprehensive aesthetic beauty of the image. Despite all of the meticulous prep time and planning, the framing, and the gorgeous foreground in front of me, without a brilliant sky, the image suffers, and – as a result – it loses significant visual interest.
The correction for this issue, like with most problems, is solved in post-production. Providing you have an alternative sky that is well suited for your foreground content, you can, with practice, make beautiful art out of what was once less than desirable photography.
The key to replacing sky content is first identifying how the light is interacting with the foreground. Special attention should be given to reflections, manmade materials such as concrete and artificial lights, nature – such as trees and grass, and all other content visible in the image. The intensity, direction, and color temperature of light is equally important.
Once you have identified a suitable sky to replace the original with, it’s time to begin your post-production workflow. Tip: A great source to look for royalty-free photographs is by navigating to Google’s Advanced Image Search Engine and selecting either the ‘Free to Use, Share, or Modify’ or the ‘Free to Use, Share, or Modify, even Commercially’ options, found under the Usage Rights category. Layer masks in Photoshop are essential tools when manipulating skies, as is the Magic Wand tool for selecting and eliminating the original sky.
The Post-Production Workflow
To begin, pull both of your images into Photoshop; the original and the sky replacement. To do this, I prefer exporting from Lightroom via ‘Library Module > Select Image > Right Click > Edit In > Adobe Photoshop’ (Figure 1).
Starting with the new sky image, select the entire image (Cmd+A on Mac, Ctrl+A on PC), copy it (Cmd/Ctrl+C), then paste it (Cmd/Ctrl+V) onto your original photo (Figure 2).
Using Free Transform (Cmd/Ctrl+T), hold the shift button as you stretch the sky image across your original, making every effort to align the horizons of both images (Figure 3).
To help with this, adjust the Layer Opacity of the new sky image as needed – around 40% should do the trick. Remember, too, that your new sky image doesn’t need to be the same dimensions as your original photo – you’re only masking out the sky, so modify your new sky image as needed, being careful not to ‘stretch’ or modify any clouds or other features that would otherwise make the sky look unnatural (Figure 4).
Once the new sky image is properly aligned, return the Layer Opacity to 100% and press Enter. Your new sky image layer should be on top of your original photo layer. The next step is to unlock your original photo layer by clicking Alt+double click on the padlock icon to unlock the layer. Then, move your sky replacement layer below your original photo layer (Figures 5A and 5B).
Now, it’s time to select the content you want to replace (the sky). Begin by selecting the Magic Wand tool, designate the option ‘add to selection’, set the Tolerance to 30, and begin selecting the sky you plan to replace (Figure 6). Importantly, any content within the marching ants selection will be replaced with the new sky.
This may become more difficult around the edges of buildings, or with any objects that project into the sky, such as trees. In these cases, I find it’s most helpful to reduce the Tolerance down to around 10 or so, zoom in on the image, and continue adding to your selection. Additionally, you can use the Color Range tool (Select > Color Range) with the eye droplet set to ‘+’. This tool is especially helpful for contiguous colors found throughout your image, such as an empty blue sky.
Once you have your selection, click ‘add a layer mask’. Your result will look terrible, as you’ve just cloned out your foreground instead of the sky (Figure 7).
To fix this, click Cmd+I to invert the layer mask. This should effectively replace the selection you made in your original image (Figure 8).
Take your editing one step further by zooming in on the image and checking the blend between the foreground and the sky. You want the transition to look natural, and this can be very difficult to do. To help, right click on your mask and choose ‘refine mask’. Begin by moving the ‘Radius’ slider under the Edge Detection category to help refine the blend of your replaced sky with the horizon line of your original image. Lastly, manipulate the sliders under the Adjust Edge category as needed to really authenticate the final blend result (Figures 9A and 9B). Tip: Be careful when modifying these sliders. I recommend zooming in on your image when making these adjustments, but be sure to zoom back out and check your work across the entire photo. Sometimes, moving these sliders may benefit you in one area of the image, but create harsh halos in other areas of the photo.
Taking Your Photos One Step Further
One very important technique in augmenting the ‘authentic relationship’ the viewer has with the image is by carefully blending colors from the sky with subject(s) in the foreground, as both color and light would in reality. One of the most effective ways to accomplish this is by creating a blank layer above the original image, changing the blending mode to ‘color’, then reducing the opacity to around 60%. Next, use a soft brush around 20% to ‘paint’ borrowed color from the replaced sky onto the foreground (Figure 10).
Finally, once you have a successful blend of your replaced sky with the original horizon, it’s time to go even further to authenticate your image. I highly recommend editing the sky through hue/saturation, color balance, photo filters, contrast and other edits to really express your creative vision (Figure 11). Each one of the previous edits will build on a new layer, so it’s easy to change as your editing process goes on.
Sky replacement requires a lot of time and attention, and is not a post-production method that should be hurried through. Much like in the field, due diligence, patience, planning, and execution will pay off in the end. However, if you can identify an alternative sky image with near identical light direction, color and intensity, you can and will make stunning backgrounds to enhance your intentioned foreground.