If you have been retouching for a while, you must’ve at least heard about the Split Frequencies, or the Frequency Separation technique. It is a method that is used widely in portrait retouching, and there are multiple videos and articles on the subject. To save myself and yourself some time, I’ll skip the theory part and we’ll go straight to the
If you tried that and still don’t get how it is done in theory, don’t worry much, as it’s not necessary to use the technique. At least I am using a microwave without a clear grasp on how microwaves actually work except that I know they somehow heat liquids inside my food. And I still get my food heated. So anyone can use the frequency separation method, but unlike a microwave which can be used efficiently straight away, you have to practice to get the hang of it.
A method with a bad reputation
I know that this method has a controversial reputation and it is the cause of many heated arguments all over the internet. While some retouchers absolutely love it and try to use it as much as possible (with horrifying results), others are not satisfied with the pictures they get and they prefer traditional Dodge & Burn techniques when working with human skin and portraits. As for the product image photo editing, there is little space for controversy. It’s either you are able to use the frequency separation method skillfully and do it fast, or you just ruin your images with it. What I want to underline is that the Frequency Separation is a working method. There's no argument about whether it works or not because that's out of the question, it's proven to work. So when people claim it doesn't work they mostly mean that they can't apply it properly. In
So, the whole idea of the frequency separation method is that you split your image into two separate images, one of which contains all the fine details, while the other has everything but details – volume, color, light, and shadows. When you combine both images, you get the original image. Now, why do we need to use this technique? In product image editing we often have to deal with wrinkled materials. Some of the wrinkles and folds look nice, but some, especially those caused by accidental folding and lack of ironing, have to be removed. Traditional wrinkles and other defects removing in Photoshop is basically stamping or healing, which is actually replacing the faulty texture with some other texture, taken from a nearby spot or created with the Photoshop content-aware algorithm. And if you have to remove a few dirty patches, hairs or a bit of dust, you don’t need anything else. But when we work with wrinkles, they tend to be quite large, and we often find that stamping is not very efficient. Even if you can find a patch of good texture big enough to be a stamping source, stamping it over a big surface leads to spots and patchy looking texture, because light and dark areas do not match. This is not appropriate when you retouch, be it for the
There’s also this problem when you retouch tricky materials like suede that was not properly prepared for the shooting. Sometimes the whole surface looks patchy and there’s no such a place that you can use as a clone source. So if you want to fix something like that and use the Clone Stamp for that, you’ll see that it just doesn’t work. The result will look messy and unnatural. The split frequency method deals with situations like this and doesn’t require much effort.
How to make it work
To me it already sounds like a great thing, so let’s learn how to use it so that you can see how necessary it can be in catalogue retouching. The deal is that if the objects and clothes you work with had been properly prepared in the first place, you wouldn’t even need the split frequency method. But the world is not perfect, and being able to use it might and will save you a lot of time.
Let’s start with the technical part, that is what exactly you need to do in Photoshop to do the frequency separation. First of all, you have to go to the Actions panel, create a new action and record it. Because we’re not going to do this manually, as there’s absolutely no reason to. If you search online, you’ll find tons of complicated actions that use many layers, adjustment layers, groups of layers, but as I said before, we try to keep things as simple as possible in catalogue retouching. Our action will be very simple.
First of all, we’ll make two copies of the background layer by pressing Ctrl-J two times. Then we’ll apply the High Pass Filter, which can be found in the “Other” submenu of the Filters menu. It doesn’t have a shortcut as it’s not used often. You can set any Radius, but my experience says the most common value in catalogue retouching is 4. It covers most of the textures we usually work with, but please, have in mind that this is not a constant value, it has to be set depending on the task at hand. In most cases when people claimed that frequency separation didn’t work was when they couldn’t set the Radius correctly. But 4 is a good number to start with. Now apply the Filter and click on this small box here next to the High Pass command we’ve just recorded to toggle the dialog mode on. Every time you run the action, it will bring the High Pass panel so that you can input an appropriate Radius value. Then go to the Image/Adjustments and click on the Brightness/Contrast command. It’s also a very rare thing to use in catalogue retouching, and it doesn’t require a shortcut. Check the “Use legacy” checkbox and set the Contrast to – (minus) 50. Great! Now set the blending mode of the current layer to the Linear light and we’re done, at least with this particular layer. Now switch to Layer 1 by pressing Alt – [. This equals to the “Select backward layer command”, and this is better than just clicking on the layer, because if you click on the layer, the action records the fact that you clicked on a layer with a particular name. So if you try to run the action on something other than the Background layer, it won't work. So we'll only be using the Forward layer and Backward layer commands because of that. Then access the Gaussian Blur from the Blur submenu of the Filter menu and set the Radius to 4, just as the High Pass filter. And don’t forget to click on this small box here next to the Gaussian Blur command we’ve just recorded to toggle the dialog mode on. Then, as the Mixer Brush is the most commonly used tool when we do frequency splitting in catalogue retouching, it’s also reasonable to record a “Select Mixer Brush” command as the final step of the action.
Now it’s necessary to check if everything went well. The best way to check is too look at the image you are working with at 100% scale, run the action, then go back in History to the step just before the action. And then click on the last step to go back again. If your image look any different after running the action, something went wrong, as it should be the same. Maybe you’ve forgotten to check the “Use legacy” checkbox in Brightness/Contrast panel, or maybe it’s a wrong blending mode for the High Pass layer. Or maybe you’ve used two different numbers in the High Pass filter and in the Gaussian Blur. Make sure the action doesn’t change the image at all, otherwise you won’t be able to work with it.
Before we switch to the method itself, let’s record another action on the base of the previous one. For some people it’s more convenient to use the High Pass filter first, as it’s easier for them to predict the result of splitting when looking at the High Pass preview. But for others, I don’t know why, as I am not one of them, it’s easier to work with the Gaussian Blur filter first. Remember, that only the first used filter matters, as you’re going to input exactly the same number, or Radius, the second time. And this number has to be the same both times, otherwise the image won’t be the same after splitting.
To make another action, you have to
Now let’s talk about why we did all that and how it works. But I want to add one thing because if you know the method well you are probably aware that there’s a way to record a frequency separation action without the necessity to enter the same radius twice. To split an image, you need to pick a radius in pixels, that will determine what will be recognized as the fine details, or the high frequency, and what will go to the low frequency. To do so quickly, most people prefer the Apply Image approach. At least if you download actions from the internet, you’ll most probably find that they use the Apply Image command there (as well as many layers and even groups). If you do it that way, you have to input just one radius instead of two – one for either the High Pass filter or for the Gaussian Blur depending on what you prefer. This is just great, but unfortunately, all the actions like that have a huge flaw, that makes them unusable in
In product image retouching, we often have to isolate images, that is put them on a white background instead of their original background. The process of splitting based on inverting and applying is not as flawless as it seems on portraits. Try to use an action like this on an isolated image and you’ll get a halo. It is barely visible, but it’s there. If you access the Levels and move the left slider to the far right, you’ll see it. The width of the halo depends on the radius you used. Use a big number like 20 and the halo will be enormous. You might say: “So what, it’s barely visible, no one will ever find it’s there”, but the problem is that it will affect the image alignment if it’s trim based, especially if we’re working with invisible mannequins, and this is not the right way how you should think about your images in catalogue retouching. All images produced for one project, be it a single shooting or a huge online-store, should be the same no matter how many retouchers worked with them and which actions they used.
The objects on the image above were both isolated. Then I used a frequency separation action, but the upper object was with the two-steps approach that I've described, and the bottom was split with the Apply Image method. They might look the same, but if you adjust the Levels to turn everything but the white background black, you'll see a halo around the bottom object. This halo is 6 pixels wide – the same value that was used as the Radius while splitting. It's hardly visible without adjustments, but it will not let you align the image with any Trim-based actions, and it will get worse if you decide to split one more time. With all these facts in mind, I'd rather stay away from this method.
Of course, you can still use the Apply
Bear in mind, that when you're using the method that I've described in the video, you apply the changes to the whole image. And despite the fact that the image after splitting looks just like before, the method is still a bit destructive. If you use it on an image with a natural gray background, run the action a couple of times and then make the image darker with the Levels, you'll see it. There will be a bit more noise on the background. It's not a big deal in product image retouching, but I've had to warn you anyway. The method is not harmless, use it in moderation.
Removing wrinkles with frequency splitting
If everything goes well with preparation and shooting, you won’t even need frequency separation, as the Healing Brush and the Clone Stamp Tool are quite efficient in most cases. Don’t
The tricky part in frequency separation is picking the appropriate radius. It’s as simple as that – pick a proper number and your image will look great after just a couple of minutes of retouching. Pick
I’ve got several images with different texture that we can practice on. Remember, when you split the image in two, there are two layers that you can work with. Retouching on the
After a bit of effort, the skirt looks better, but there’s this weird recurring motif, some patchiness that can be spotted if you examine it for a while. It doesn’t look too bad though. But I was only able to do this with the Clone Stamp only because this big piece of nice texture existed. What if it didn’t? And what if the skirt was not totally beige, what if one side was colored, what if it was green? So let’s make this harder for ourselves.
Have a look at this. The skirt is creased all over, and one of its sides is green. Can you use the Clone Stamp to fix it? I don’t think so. At least not in a few minutes. First of all, we don’t have a big spot of nice texture to use, and secondly, you can’t stamp green over beige and vice versa. But with the frequency separation, it’s not a problem at all! Because when the texture is separated from the color, you can stamp green over beige, and you don’t need any big spots of nice texture to work.
To start retouching, we need to separate frequencies first. I’ll run the action we’ve recorded a while ago, the one where the High Pass filter goes first. Remember when I said 4 was the most common radius in
Whatever radius I pick now, I have to duplicate the number in the next window. This is very important, otherwise, the whole image will look different after separation, and it’s not supposed to. As I said, some people prefer picking their Radii while looking at the blurred image. As for me, I can’t really do that, but I’ll at least show how it’s done so that you can decide for yourself. I’ll go back to square one and start again, but this time I’ll run the other action, the one that uses the Gaussian Blur filter first. This time I have to decide what shouldn’t be in the
Finally, we can start retouching. Now let’s have a look at the two layers that we have apart from the Background layer. The layer on top is gray, and if I hide two layers below you’ll be able to see that it has nothing but some texture on a gray surface. But combined together with the layer below it seems to be the same as the background layer. The layer below looks kind of blurry because it’s basically the Background layer with the Gaussian Blur filter applied. So what should we do to fix the skirt?
To remove wrinkles, I need to work on the low frequency layer, the blurry one. Because if you think about what a crease actually is on an image like this, you’ll realize it’s just a combination of dark and light spots on an even surface. How can I remove spots like this from a surface? I can fill it with some solid color using a brush, or I can just smudge it, mixing dark and light to get something in between. Both methods are good. The normal Brush works faster than the Mixer Brush Tool, but it requires some smart opacity changing in the process. It’s also very easy to overdo an image with a normal Brush, so beware.
Let’s start with the beige side. I’ll pick a color from a good piece of texture and use a soft Brush with 50% opacity to draw over the wrinkles. I have to make the tip smaller as I get close to the green surface, as I don’t want to make it beige. It would look unnatural and weird if I covered the whole skirt with even surface, so don’t overdo it, leave a few tone transitions. But what about the texture? You do realize, that if you tried something like this in normal mode, you will just cover the whole thing with nothing but a solid color, don’t you? Well, not in the frequency separation mode. If you look at the skirt at 100% scale, you'll see that the texture is left untouched because while I was dragging the brush over the image it was contained in a separate layer.
To retouch the other side, the green one, I’ll use the Mixer Brush. Don’t forget about the settings! It only works well if you set it up right. We don’t really want it to mix paint from the canvas with any other colors, so to prevent this either set the brush to “clean after each stroke” by pressing the button with the same name, or by setting it Load and Mix to 100%. Then, set Wet and Flow to something about 20%. Now I’ll start mixing with the Mixer Brush. I do with the same movements as if I’m trying to rub it with a finger to smudge the paint. The direction is important! Don’t mix green onto beige and vice versa.
When I set the Mixer Brush the way I did, I made sure that when I mix, I mix just then colors that are already in the image. The mixer brush can be used in a different way, as you can set it to mix some color from the foreground swatch in. But this requires some twiddling with the settings, as the ratio of mixing can be set to anything from 0% to 100%. This is why I prefer to leave it as it is, and if I need any other color, I just switch to the normal Brush. But it’s up to you how exactly you like to use these brushes and what settings you apply. There’s no such thing as the best way to do things here.
Okay, after just a minute or even less the mixing is done. But there are still some small wrinkles, that cannot be painted over, as they are a part of the texture layer. Let’s proceed to the other layer and see how you can work with the texture when in frequency separation mode.
Switch to the top layer, the gray one. You can use the Clone Stamp, the Spot Healing Brush and the regular Healing Brush Tool while in here. If you prefer the Clone Stamp, make sure it’s set to the “Current Layer”, otherwise it won’t work as desired. It’s better if the brush tip is hard, as it gives a better result. Now I’ll get a good sample from somewhere nearby, and pay attention to this: I don’t have to care about the color of the sample, just the texture. I can get a sample from the beige side of the skirt and use it on the green side, and it will work. I can pick a sample from a darker area and use it on the lighter area, and it will work.
You might notice that some small wrinkles stay in place, but don’t worry: what cannot be removed on the high frequency layer, is just not there, it’s on the low frequency layer. If you’re unsure what’s where, you can try hiding some of the layers so that you can see clearly what each layer contains. Some people even prefer working this way: stamping on a gray layer and mixing and painting on a blurry layer. But I prefer seeing the final result, as it prevents over-retouching, which happens a lot with the frequency separation. Remember, that when you remove wrinkles like this, you break the initial shadows and highlights, and if the object is not flat like this skirt, it will look unnatural. The texture contained in the high frequency layer is not the real thing, it’s just a resemblance of the real thing. Make it stand out and it will look unnatural. Before you finish, make sure to check the before-and-after results by merging the two layers and comparing them to the background layer. You can then remove some of the effect by erasing the top layer with the Eraser Tool, just keep opacity low, 10 or 20 percent. Also, don’t try to make it look perfect while it’s still a hi-res image. It’s more reasonable to finish retouching the image after resizing while looking at it at 100% scale for the best comprehension of the texture.
Let’s try another image, something more difficult. Like this suede shoe. Suede is one of the trickiest materials for us retouchers, especially if it’s black. But I have a separate chapter dedicated to black suede, and for now, a blue sample will be enough.
What’s the problem here? Before doing anything, it’s really necessary to ask yourself this question. Is everything’s fine? Maybe you don’t need to do anything at all. Well, not in this case. Most online stores I know don't care much about their suede. You can see a lot of shoes just like on the image above when you browse. But the client I worked for in this case was very specific, as the shoes were quite expensive. In fact, prior to shooting, all the suede had to be brushed in one direction first, so it wouldn’t look spotted. And because of some problem, maybe because there was no brush or someone has forgotten to do their job, I got this image. So I’ll show you how to retouch a suede shoe like this one if you really have to.
We will do the frequency separation, but not straight away. Before doing it, I’d better remove the big white scratches on the surface. Because if I separate the frequencies, big spots like this will go into both layers, and I’ll have to remove them twice. So to save myself time, I’ll remove the most definite blemishes with the Healing Brush Tool. I’ll also remove the tiny white spots on the surface, they are actually pieces of paper from the shoe box. I can do it later, but it doesn’t matter, I have the right tool for the task at hand active at the moment, so why not.
Now it’s time to do the separation. Remember to switch to 100% scale before running the action, otherwise, it won’t be possible to evaluate if the Radius is right. In this case, 4 is good, as well as 5 or 6. I’ll pick 4. And 4 goes into the Gaussian Blur filter as well. If you’re not sure about the radius, just give it a quick smudge or paint over with the normal Brush to see if the texture looks decent. If not, go back in history and repeat.
As the area I’m going to work with is blue, and I don’t want to mess with the black leather rim and other black parts of the shoe, it’s worth selecting the blue area in the low frequency layer. Now, what’s so tricky about this shoe? The deal is, that if I just grab a normal brush, pick a color and paint over it will look flat. Because I removed the volume as well as the wrinkles. Remember, that the low frequency layer contains all the color and volume of the image. Mess it up and it will look flat and unnatural. So what can we do in this case? Use different colors, lower the opacity of the brush and watch what you’re doing, be careful and accurate.
You can also use the Mixer Brush and do the same thing, but don’t forget, that selection will not save you from mixing black over blue if you try, so the direction of the strokes is important, too. See this dark spot in the middle of the shoe? That’s what we need to preserve if we don’t want it to look as flat as a flatfish. And don’t overdo it, or it will look unnatural. If you notice that the selection was a bit off and you’ve painted over the black parts of the shoe, it’s easy to fix it with the History Brush. Our goal here is to preserve the suede texture while making it look smooth, not spotted. Make sure you check the before-and-after to see that it still looks like a real shoe. In this case, we don’t even need to work on the
The frequency separation technique allows you to do things that would be impossible otherwise. On this image, the client wanted me to remove the dark outline of the jeans from under the sweater so that it would not seem transparent. Doing it with the Clone Stamp would be crazy hard if possible at all. But with the split frequencies, it's a piece of cake. I'll just run the action and use Radius 8. Then I'll just smudge the jeans with the Mixer Brush and the sweater will lose its transparency in mere seconds. Might as well do the same on the bra outline.
Some people that try to use split frequencies without giving much thought to the stage of radius picking fail to get decent results and blame the method instead of themselves. This t-shirt is severely creased, so it would be only natural if I use the frequencies separating action on the image. But look, Radius is everything. This particular texture is larger than it seems. If use a small Radius, like 4, and try to smudge the wrinkles with the Mixer Brush, you will see a weird texture appear. This is hard evidence that tells you that the Radius is wrong. But try a bigger Radius, like 12, and you'll see the difference. Now the result looks much better.
This is the freedom given to us by the frequency separation method. If you know any other way how to fix images like this, and fast, I’d love to know that for sure. But if you still think that the frequency separation technique is too complicated, well think twice, as this is something really worth learning. It saved me and my team a lot of hours, that otherwise would be wasted on precise clone stamping.
You can download the images for practice purposes from the gallery above. Each thumbnail is linked to the respective hi-res image, just click on the thumbnails you need to open them in a separate window. You can right-click and "Save link as…" to download images without having to open them first.
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