Photoshop contains a lot of hidden gems. One of them is certainly the “Content-Aware Scale” (CAS) tool. This feature is perfect for expanding the sky or background, scaling the image to fit a specific form factor for sharing online or printing, or even shrinking the image (such as to turn a regular image into a panoramic format).
CAS offers two incredible advantages over simply enlarging or shrinking your image. First, it is an intelligent tool that does a pretty good job on its own of preserving the most important detail rather than blindly changing the size of everything. Second, and this is where things get really powerful, it lets you directly specify which areas to protect and which can be stretched or compressed. In this tutorial, you’ll see just how powerful it can be, learn the basic workflow to use it, and some advanced techniques for pushing it to the limits.
Note that I push the second demo image to the extreme by converting a lanscape image to a square crop. This can be useful for posting to a platform like Instagram. But regardless of whether you would personally change this image in this way, the key lesson is that you can substantially enlarge your sky with the right workflow when needed.
The general CAS workflow is:
- Create a selection of the area you wish to protect. A rectangular marquee works very well. Alternatively, you may wish to use Quick Select on the sky and then invert to target the foreground. Don’t worry about being pixel perfect with the selection, you just need a reasonable target to get good results.
- Save the selection as a channel via the Channels Panel or Select / Save Selection. It helps to rename the channel here to find later it in the steps below.
- Deselect via <ctrl/cmd>-D. If you leave the selection active, you only transform the selected area and won’t get good results.
- If you are enlarging the image, expand the canvas with the crop tool (<C>). Leave the “content-aware” box unchecked in the crop tool. If you are trying to hit a target aspect ratio, enter value in the crop box and you’ll be able to use it to both visually crop in one dimension while expand to fill the other.
- If your target layer is locked (including background layer), click the lock icon to unlock the layer.
- Go to Edit / Content-Aware Scale.
- Change the “Protect” dropdown from “none” to your saved selection.
- <shift>-click and drag to scale the image without being constrained to the original proportions. Watch out for artifacts with significant resizing, especially in the main subject or areas you cannot easily clone.
- You may wish to compare setting “protect” to none or try a few different selections to see which produces the best result, especially when you are first learning the tool or working with complicated images.
- Click the check mark when you are finished.
- Delete your saved selection by dragging it to the trashcan in the Channels Panel. Keeping it increases the saved file size.
- If you were not able to stretch as far as you needed. You have several options:
- Use the double-stretching technique below to repair artifacts that show up with large stretches.
- Use Content-Aware Crop to expand further at this point (without adding artifacts to your existing work).**
- OR, use a little Content-Aware Crop BEFORE you use CAS. In this workflow, you expand the canvas a little (within the limits of what the cropping tool does well) and then expand it further using CAS. This is a great approach that often works best by making the most of two great tools.
- Use the spot healing brush, regular healing brush, or clone stamp. This works well when there are just a few artifacts or they are mostly in simple areas like clouds.
- Use a Edit / Transform or Image / Image Size to finish expanding. This will affect the entire image, but you’re working from a better starting point than using these tools directly on the original image.
** You can of course increase the sky using just the content-aware crop tool without CAS. This has the advantage of simplicity as you don’t have to create a channel. It also avoids any stretching of the original image and only fills in the expanded canvas. It’s a great tool for slight expansions or for images where you absolutely want to avoid stretching or distortion. However, it can create strange artifacts and CAS often excels for more significant expansions. CAS can also be used for shrinking/compressing the image as well. Ultimately, they are both great tools and using them together is often an ideal way to get the best results.
If you push CAS too far, you are going to run into artifacts. If you run into more significant artifacts, you can use some creative blending to things work in order to achieve greater enlargement. As shown in the tutorial above, the following double-stretching technique is a great workflow to push the limits with CAS:
- Duplicate your original layer and then use the CAS workflow above on one of the layers. You’ll use the other layer for the rest of the steps below to create a stretched version without artifacts in your subject.
- Put the unstretched layer on top, change it to “difference” blend mode, and use <ctrl/cmd>-T to transform it. As with the CAS tool, hold <shift> to resize without constraint. The goal here is to stretch this copy until it covers the edge where the subject meets the sky (and the difference blend mode will help you easily assess the alignment). The transform tool will not create artifacts, so this is your clean copy and you just need to blend it into the CAS version now.
- When it is aligned, accept the changes and switch back to “normal” blend mode.
- Add a white layer mask to your cleanly transformed layer.
- If you want to protect the subject when blending, create a selection of the sky and contract/feather it.
- Now paint black on that layer mask to hide the clean sky. This will reveal the CAS sky and eliminate any edges shown between the two.
- If you have any artifacts in the CAS sky, you should be able to easily fix them with the spot healing tool.