How to Remove Shadows With Frequency Separation

If you want to lift your retouching skills to the next level, you should familiarize yourself with frequency separation and how it can aid you in various photo editing tasks. One of those can come up in cityscape and architecture photography. Especially during blue hour and nighttime, you can get unwanted shadows in your photos. In this article, I explain how to remove those with frequency separation.

The photo in the before and after comparison might look familiar to you. I've recently published an article about how to improve blue hour photos by introducing a vignette in the sky. I also had to deal with a shadow in this photo created by one of the street lights behind me. This shadow unbalanced the composition, and a first attempt to hide it by introducing a vignette into the foreground failed miserably, as I explain in the feature video.

A better way to handle it is to remove the shadow completely through clever retouching. One way to do so is by using curves and luminosity masks to brighten up just the shadow areas. The problem is that this technique will also lighten up some of the structures that should remain dark, if you're not careful. Multiple adjustments targeting different tonal ranges can help, but I prefer another approach.

Frequency Separation to Remove Shadows

In a recent article, I shared one use of frequency separation. I used it to remove footprints from sand in a desert photo. The principle is the same for retouching shadows. First, separate the fine details from the details you want to retouch. The shadow in my example has a blurry look to it. It resides at a low frequency. The fine structures of the cobbles in the street, on the other hand, sit at a high frequency.

Whenever you use frequency separation in your editing, the first task is to isolate the details you want to retouch from the ones you want to leave intact. The steps to create the frequency separation layers are the same as in my article about editing the desert photo:

1. Create a merged copy of your edit by holding down Ctrl/Cmd + Alt + Shift + E and renaming it to "low".

2. Copy this layer and rename the copy to "high".

3. Select the low layer and go to Filter - Blur - Gaussian Blur... . Use a radius large enough to blur the details you want to separate from the shadow. This blurred layer should still show the shadow but not the structures hiding in the shadow.

4. With the high layer selected, go to Image - Apply Image... and dial in the following settings: Make the low layer the source; activate the Invert checkbox; set Blending to Add, Opacity to 100%, Scale to 2, and Offset to 0. These settings work only for 16-Bit images. For 8-Bit photos, uncheck the Invert box, set Blending to Subtract, and insert an Offset of 128. The Scale remains at 2.

5. Set the blend mode of the high layer to Linear Light.

In the feature video, I show how to use a combination of cloning, dodge and burn, and a color layer to eliminate the shadow and some lens flares introduced by the city lights. I also talk about the mistake I made with the vignette in my first attempt to hide the shadow.

Cloning

To apply cloning in a non-destructive manner, create a new layer above the low-frequency layer and use the Clone Stamp Tool set to sample Current & Below to remove the shadow. By holding down Alt you can sample details from an adjacent area by clicking on it. Then release the Alt key and paint over the shadow area. You can hide the high-frequency layer while performing this task.

Typically, the low-frequency layer will still contain structures and contours. Try to align the sampled details with those you are retouching before starting to paint. You don't have to be 100% perfect with the alignment as I show in the feature video. The blurry layer you are working on is quite forgiving. You also don't have to paint with 100%. Using low opacities of 50% or less and building up the effect might help you to arrive at the optimal result.

Dodge and Burn

Create a Soft Light layer above the low-frequency layer and use it to brighten the shadow by painting with a soft, white brush at low opacity. With a black brush, darken areas around the shadow to get a smoother transition. It helps to combine this technique with the cloning layer.

An alternative to a dodge-and-burn layer is Curve adjustment layers, which you can use to brighten and darken certain areas. And if you want to be super precise, use luminosity masks to target only the shadow.

Fixing Colors

A layer set to the blend mode Color can be helpful when you have color shifts caused by the shadow or by lens flares in your photo. Sample a color with the Eyedropper Tool from a clean area and draw over the shadow or lens flare inside the color layer. It removes any color shifts in those areas. Combine this technique with cloning and dodge and burn for optimal results.

Conclusion

As you can see, the right combination of post-processing techniques in Photoshop can help you fix a lot of problems. But if possible, try to avoid such flaws while in the field. In my case, there wasn't a position to set up my camera where I could have avoided the shadow without compromising the composition. But in many cases, moving the camera can already solve the problem.

You might also be wondering what to do with the high-frequency layer. When retouching shadows or footprints, there is no need to work on the fine details. All adjustments usually focus on the low frequencies of the photo. But there are situations where you'll want to target the higher frequencies. An example of that is the removal of chromatic aberrations and color fringes.

And there are certainly more ways to use frequency separation. Let us hear of your favorite use case in the comments below.