Frequency Separation is a retouching technique that is most often used in portrait touch up work. However, I find it to be useful for commercial product and still life photography too. For example, you may want to to fix a weird lightness difference on the side of an object that has a particular texture but want to maintain that special texture and, in that case, frequency separation makes lots of sense for our type of work.
The base principle is rather simple. The technique consists of separating the high frequency (sharp details, lines, texture) from the low frequency (colour) into two different layers, thus letting you retouch and edit any one individually and prevent the unaffected frequency from getting changed.
I have previously written an article on the five best tutorials on Frequency Separation out there and I would highly suggest you to go and read it in order to get a full grasp of the workings of the technique.
The actual task of setting up correctly the layers and messing with blend modes and dialog boxes can be daunting if you don’t remember everything perfectly. So, I have thought it would be of pertinence to share with you an action that takes care of all the boring and repetitive stuff and lets you get right to the meat and potato of the technique. It includes an action for 8-bit images as well as 16-bit variants.
What it does
Once you have commanded the action to run, it will duplicate the selected “BG” layer twice (yes, you need to make sure the layer you want the technique to be applied to is selected and that the layer name is exactly: BG (for Background). Failure to doing this will result in the action seriously not working.). Then, it will rename and group both layers for better organization and will apply a Gaussian Blur to the “Low Frequencies (colours)” layer. The suggested blur amount is variable for each image but 5px is a good general starting point and that’s where it’s at. Finally, the action will load the “Apply Image” dialog box to the “High Frequencies (sharp detail)” layer and set the Blending parameter to Subtract, Source to the “Low Frequencies (colours)” and Scale and Offset to 2 and 128, respectively. Then, its work is done.
The 16-bit version of the action is very similar to its brother but sets the “Apply Image” settings corresponding to that colour mode.That is, the Blending option is set to Add, Scale and Offset are at 2 and 0, respectively, and the Inverted checkbox is checked.
Just click on the download button and the actions will automatically download. After, a double-click will open the file and load it into your Photoshop.
So, here you go, another tool in your Photoshop toolbox! Have you used the Frequency Separation technique before for commercial and still life photos? Share with us your experience below!