By Chris Malinao
Frequency separation has been around ever since Photoshop came along and it has become a favorite of photographers as a classic retouching method. We are revisiting frequency separation because it is an excellent tool. It preserves details while enhancing the overall appearance of a photo.
Frequency separation is a method of retouching a photo by separating the high frequency pixel information from the low frequency pixel information; we make edits to them separately. Pixel data are placed in two layers, one to take care of details (the high frequency) and the other to blur and take care of color (the low frequency).
Before you can apply frequency separation in Photoshop, make sure to remove the obvious blemishes first such as pimples or dirt because they could show up in both the low and high frequency layers.
By doing frequency separation, we clean up and enhance a photo while still preserving details or texture. Pores are visible but cleaned, wrinkles and eyebags are mitigated but not totally obliterated, making the image look more realistic but pleasant. Some retouchers proudly call this “high-end retouching” and accordingly charge good money for it.
Let’s do it:
- Open photo, then hit CTRL+J twice to make two copies of the image.
- Name the top layer HighFreq_Texture (for detail) and the middle layer LowFreq_Blur (for tone and color).
- Click on the eye icon of the top layer to temporarily hide it and make the middle layer active and go to Filter > Blur > Gaussian Blur.
- Drag the slider until it blurs the skin just enough to hide most of the pores and blotchiness and click OK.
- Make the top layer active and go to Image > Apply Image. Enter the following – Source Layer: LowFreq_Blur, Blending: Subtract, Scale: 2, Offset: 128. Click OK.
- You will be seeing a grey image at this point. Change blend mode to Linear Light and your photo will look exactly like the original (while the thumbnail in the layers panel is still grey). At this point, we have subtracted the low frequency pixel information from the high frequency layer and eliminated high frequency pixel information from the low frequency layer. We have separated the frequencies —thus, we have frequency separation. But if we combine both high and low frequency layers at this time, we see the original image; we haven’t done anything yet.
- Make the middle (Blur) layer active. Zoom in on forehead. With the Lasso tool, draw a selection on the forehead and feather the selection. To know how much feathering to apply, go to Select > Refine Edge, then drag the Feather slider to blur the edges just enough. Take note of the feather value in pixels, remember it, then Cancel.
(In Photoshop 2019 and 2020, go to Select > Hold down Shift key and click on Select and Mask to bring up the old Refine Edge dialog box.)
- At the top Feather field, type in that pixel value. Deselect and draw another Lasso selection on the forehead and go to Filter > Blur > Gaussian Blur. Slide the blue slider until the blotchiness disappears. Texture remains because it’s on a different layer. Click OK and deselect it. If you see some imperfections in the texture, we’ll deal with it shortly. Right now, we’re just removing blotchiness and overall inconsistency.
- Draw another selection on one cheek and make sure you don’t get too close to the eyes, nose, and hair. Press CTRL+F (or Alt+CTRL+F, depending on PS version) to apply the last Gaussian Blur. Do the same with other areas of the face and neck to remove blotchiness.
If there are still significant blemishes to be removed, work on the details with the high frequency (texture) layer by flattening the image (CTRL +Shift + Alt + E) and using the clone tool or healing brush tool. Alternatively, you may also patch, heal, and polish irregularities on the low frequency layer. The Mixer Brush Tool may be used on the low frequency layer instead of the repeated lasso selections and Gaussian blurs in many areas.
There are variations to the frequency separation method, and the photographer who is serious about retouching should learn and develop his own style of doing this. The main idea is to separate details from color—the high and low frequencies —and edit each layer separately, and the aim is to come up with a pleasant and more natural looking image that improves color and tone while preserving texture and details.
If you do frequency separation on a regular basis, you may want to save the steps to create the separate layers as a Photoshop action so you can re-use it. The photographer who aims for high-end retouching will find this method very useful, it will serve him well to master frequency separation. It is a classic retouching tool in Adobe Photoshop.
[Chris Malinao teaches digital post-processing methods such as the Lightroom workflow software and Photoshop editing software to photography students at the FPPF (Federation of Philippine Photographers Foundation). The FPPF is a non-profit organization that offers year-round workshops in Comprehensive Digital Photography, Advanced Photography, Wedding Photography, Strobist Lighting, Food Photography, Photoshop, Lightroom, and other specialty photography workshops. For details of FPPF workshops, please visit www.photoworldmanila.com.]