Plagued by Hotspots? Frequency Separation to the Rescue!
Glaring hot spots can be like the plague when it comes to shooting portraits. All too often the circumstances of the shoot don’t allow the luxury of time to reposition lights or apply makeup to resolve the problem. Crammed settings, and packed time frames get in the way, leaving us to have fix these issues via Photoshop. Fortunately Frequency Separation gives us a powerful tool for cleaning up those annoying hot spots!
By this point much has been written about Frequency Separation so I don’t want to delve too deeply into all the formulas, but I do want to focus in on how to deal with this specific situation in this article.
[Related Reading: Frequency Separation | What Is It Really And When Should You Use It?]
Let’s start here by taking a little closer look at the offending hot spot on the subject’s forehead.
As you can see the glare not only blasts out the tone and color, but we’ve lost the skin texture there too. Clearly we not only need to fill in the tone, we have to fix the lost texture as well.
You could try finding an area to use as a source for cloning in skin to fill in area, but in looking at this shot that looks like a very challenging task. In this case using a divide and conquer approach could make it a lot easier.
Setting Up The Frequency Separation Layers
Enter Frequency Separation! In short Frequency Separation (F/S) combines a blurred layer that has the tone and color information with a texture layer that has all the detail and texture information to let us take this ‘divide and conquer’ approach to solving a variety of problems.
(Do note, F/S can be a very powerful tool, but it should be used carefully as it can be too easy to go way too far giving you an oddly unnatural result. A light touch with this technique goes a long way.)
For those new to the technique, Frequency Separation takes a little time to set up, but once you’ve got the layers in place the work becomes much easier and you’ll find fixing difficult retouching challenges is a much simpler task.
To set up the Frequency Separation layers Merge all your existing layers into a copy, (Layer>Merge Visible), then make an additional copy of that layer so you have the two layers that will be the basis for the separation, (Layer>Duplicate Layer). Hint: make it easy to check your work by putting these layers into a Layer Group, then name this Layer Group “F/S”.
Next select the bottom layer in that group and name it “Low”. Then select the upper layer and name it “High”. Naming these layers will come in very handy a few steps later when you use Image>Apply Image to turn your ‘High” layer into the your texture/detail layer.
Use the Median Filter to Make the Low Layer
With the layers so named select the Low layer then go to Filter>Noise>Median to apply the blur that will leave you with the tone and color information you need to work with.
The advantage with using the Median filter over say Gaussian Blur is that the Median filter does a good job of preserving the important lines that define edges and other important information in your image. The ideal amount to apply in the Median filter depends on both the resolution of your image and the texture/detail you need to force onto the High layer. For this image I used a setting of “10”. The result looked like the image below.
Notice how the detail has been lost, but we can still see a clear definition between where his hairline, eyebrows, and eyes etc are.
Use Image>Apply Image to Make the High Layer
Next select the High layer then go to Image>Apply Image to bring up the dialogue that looks like this:
The Apply Image operation gives you a lot of power. For now we’re just going to look at the settings you need to use to make your texture/detail layer. The Source automatically chooses your current image. The “Layer” option should have your Low layer selected, the one you applied the Median Filter to. And the Blending option should have “Subtract” chosen and Scale and Offset should be set to 2 and 128 accordingly.
The result from using the Apply Image dialogue should be a layer that’s mostly 50% gray with light and dark areas that define the texture and details of your image. (If you’ve ever used the High Pass filter you’ll recognize the look.) Be sure to set the Blending mode for this layer to “Linear Light”. When used with the Linear Light Blending mode this layer combined with the Low layer from the previous step should look exactly like the image you started with. Turning the Layer Group for these layers on and off will let you double check to be sure you have the right result.
Fixing the Hot Spot
Now that we have the tone and color on the Low layer and the texture and detail on the High layer we’re about ready to fix the hotspot on the man’s forehead. One last note before we begin, I highly recommend making a copy of both the High and Low layers, clipping them to the original layers just to make it easy to fall back in case you need to restore a part of the layer after going too far. (Just be sure when you clip the copy of the High layer to the original one to set the Blending mode for the copy to Normal so you don’t double up the effect.)
Fixing the hotspot now involves 2 basic steps: 1) Using the Mixer Brush on the copy of the Low layer to bring in the missing tone and color, and 2) Working on the copy of the High layer to add in the missing skin texture.
Use the Mixer Brush to blend out the Hot Spot on the Low Layer
Using the Mixer Brush can make it easy to blend the colors and tones since this brush lets you pull in color and tone from a nearby area while blending in the result with the rest of the image. When working with the Mixer Brush I suggest using settings like the ones below:
The two parts circled on the left keep the brush clean. We want it to pick up a new sample each time we make a stroke with the brush, and letting it hold on to a previously sampled color will make it hard to get the results we’re looking for.
The Wet option in the middle of the options bar determines how much color the brush picks up when we begin a stroke. Start off using a setting around 20%, this will let you gradually build up the color in the area you’re working on.
And setting the Flow to around 10-20% will also help in giving you the control you need to work gradually while blending the results in with the surrounding area. Also notice “Sample All Layers” has been turned off. This lets us paint under the High layer without having to turn it off so we can see how our work is progressing.
As you get comfortable with the Mixer Brush you can try higher settings as needed, but these are pretty good starting points.
Using the Mixer Brush make several light strokes working from the outside in. As you work you’ll see the colors blending. Many times I find also using small circular strokes with the brush helps make a nice blend in the areas I need to work on. Since you’re working on a copy of the Low layer if you go too far, or feel a need to start over just make a new copy of the original Low layer and begin again.
Here is a look at the Before and After for the Low layer copy I worked on in fixing the hot spot for this image. On the right the hot spot on his forehead has been pretty well blended out.
Now that we have the color and tone where we need it we can see an improvement, but clearly we still to bring in the right texture. Below is a look at what the image looks like after blending out the hot spot on the Low layer copy.
Here is a closer look at the area in question, making it easier to see how the missing texture leaves us with an area of unnaturally smooth skin on his forehead.
Fill in the Missing Texture with the Healing Brush and the Rubber Stamp Tool
This brings us to our last step, fixing that missing texture. To do so select the copy of the High layer then use the Healing Brush and Rubber Stamp tool to sample and bring the texture from the surrounding area where needed. Working with both tools, while carefully looking at where you’re sampling from, will allow you to build up the texture while not winding up with any areas that are obviously copied from near by. Since the High layer uses the Linear Light Blending mode we need to be sure our Healing Brush and Rubber Stamp tool are set to sample “Current Layer”.
Here is a look at the High layer before and after working on it to bring in the missing skin texture.
With both the Low and High layers fixed we’ve filled in the blown out hot spot with the color, tone and texture that was missing in the original shot. And, while it took a little work to set up the Frequency Separation layers, doing so allowed us to fix what could be a challenging task pretty easily using the Mixer Brush along with the Healing Brush and Rubber Stamp tool.Here’s a close up look at our image with the hot spot nicely blended in.
Imagine having to fix this using more conventional techniques where you need to either paint while ‘stealing texture’ from other parts of the image or finding just the right areas to clone from while avoiding those telltale smudgy artifacts.