How To Use The Mixer Brush Tool and Frequency Separation in Photoshop

What is the mixer brush tool?

If you don’t already know how to use the mixer brush tool in photoshop, you are missing out on a hidden gem! When used in combination with frequency separation, the mixer brush is a powerful skin retouching tool that allows you to blend colour and tones in your image in a technique similar to working with wet paint on a canvas

For those photographers who love to create painterly style portraits, learning how to use the mixer brush effectively will help you transform elements of your portrait.

As with most tools in photoshop, you can apply this technique subtly or you can go for a full on painting effect. It depends on your artistic vision and what you want to ultimately achieve!

Where to find it

To access the mixer brush tool from your tool palette, click on the brush tool and hold the control key to expand the fly-out menu as shown below

What settings to choose

Think of the mixer brush tool as if it where an actual paint brush. This will help you to understand the different settings and which to apply. First select a large soft brush, then click on the drop down and select clean brush (image below) This effectively means that each time you brush a new stroke, your brush is ‘cleaned’ before applying the next stroke. I like to think of it like rinsing my paint brush in clean water before choosing another colour. With skin tones, even in a well lit image, there will be colour differences. For example in areas of highlight and shadow, darker tones underneath the eyes etc. So it’s important to clean your brush so that your not mixing different colour tones.

Adobe has provided a number of presets that vary in wetness, load, mix and flow. I tend to prefer to custom set these values but if i was choosing a preset my most used one is wet, light mix. Have a go at them all so that you can see the difference. As with learning any new technique in photoshop, it can take some time and practice to get it right! But once you do, you will love it!

How to use the mixer brush tool

To fully understand how the mixer brush works, let’s have a closer look at the each setting.

Wet controls the amount of paint that is picked up during each stroke of the brush. The lower this value, the less paint you are moving around. I tend to work at a lower value of <10%

Load controls how much paint the brush holds with each stroke. So imagine you are working with light water colour based paint when you set this value lower. Higher values could therefor be similar to loading your brush with a heavier oil paint. Just like with a normal paintbrush, the load runs out of paint as you paint with it.

Mix controls the ratio of the wet/load mix. But since i have set my brush to clean after each stroke, this value doesn’t really matter in this instance.

Flow works just the same here as with any brush. The value of flow controls the intensity of the brush. A lower flow value will apply the effect slower and more gradual than a higher flow value

Sample all layers when working with frequency separation. I am working on copy layers so I turn this option OFF so that the changes I am making only apply to that layer.

Frequency separation and the mixer brush tool

Frequency separation is a powerful skin editing technique that can smooth skin, minimise blemishes, reduce under eye circles and blend skin tones, without losing skin texture. And the mixer brush tool works so well with this technique!

But how does FS work?

In any image there are low frequencies and high frequencies. The low frequencies are skin tones and colours, while high frequencies are textures. The purpose then of frequency separation is to separate the high from the low so that you can work on each element individually. To smooth skin and even out colour and skin tones you can work on the low frequency layer without making any changes to the texture (high frequency) on the skin.

For the image below, my first step was to make small adjustments to my highlights and shadows in ACR. Then opening the image in Photoshop I used the healing brush tool to remove obvious blemishes and the patch tool to reduce under eye circles and areas of redness. Only when you have made these adjustments, should you begin with frequency separation.

When you begin, select the low frequency colour layer and apply the brush settings as shown above. Use a small brush and start to blend, being careful to move in the direction of the skin texture. Zoom in to see the direction of the area you are about to work on. I find using small circular brush strokes works best for me. This method can be a little time consuming, even more so when you are learning, but once you get the hang of it, the results are so worth it!