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Advanced moire reducing methods

There are some advanced methods that allow you to get rid of different kinds of moire. Most of them catch moire patterns with a High Pass filter and then suppress them, just like in Frequency Separation. One of the methods requires you to change the image mode to Lab and do some tricks there. I do realize that explaining each method is going to take a lot of time, and those of you who don't really get the mathematical idea behind all these processes might not be able to thoroughly understand the whole thing. I doubt I would be able to explain it properly in less than an hour or so, and this is exactly why I won't be doing much explanation.

I hope you already got the moire reduction action set from the shop, but if not, here it is. It has 5 actions altogether. The first one is the "stage_size" – a simple action we already discussed.

There are also 4 advanced actions which we will soon try on different kind of moire and I will explain how these actions work. And those who like to get to the bottom of the technical processes can also do their own research. There's a lot of information online, but what most of the free tutorials miss is repeatability. It means that the methods described work on the image or images used in the tutorial, but when you try to use the same methods on other images they don't work.

It happens because every kind of moire pattern is unique. Some of them are easy to remove while others are a pain, but there's no single method that is able to suppress every kind of moire. That's the deal. So I tried to describe all the methods I know so that the probability that one of them will work will be as high as possible. I'm not talking about the preview moire, which doesn't exist, or the interpolation moire, that happens because you or a camera reduced an image in size and failed to do so properly. It's about the real moire, colored or monochrome, that occurs in original, even raw images. But before you try to run any actions, make sure you can't get rid of moire with simpler methods, like coloring it. Because most of the time it will work well enough and you won't need anything else. But coloring is not such an easy thing, so let me say a few words about the process.

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This skirt is totally covered in moire. When you try to color it with the Brush in Color mode, you might have a hard time picking the right color sample. So when you pick a sample and color with it, you see the overall appearance change. It happens because there's a whole bunch of colors out there and what you need to pick is some average color, but what you actually are picking is some point sample. To deal with that matter, you can access the Eyedropper Tool and change its settings to something average, like 11 by 11 pixels. After that, when you pick a sample, it will be an average color, which is exactly what you need. But don't forget to change it back to something less average, like 3 by 3 pixels, because it might make your life tough in some circumstances. This setting affects not just the Eyedropper Tool, it gets also automatically transferred to your Magic Wand settings, and for this tool, it matters a lot. The more average the area of selection, the more you will select in one click. So you'd better stick to one value there, either Point Sample or 3 by 3 pixels, but definitely not more than that.

There's another way how to get an average color of a surface. Select an area with the Rectangular Marquee tool and then go to the Filter menu, Blur submenu and click on the Average command. It will fill your selection with some average color, and you can use it to pick a sample and then just press Ctrl-Z to undo the last step and bring the texture back.

Sometimes colorizing won't work. It will remove color stains from an image, but the pattern will stay there. This is the right time to start using more sophisticated methods.

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Channel Mixer action

This is my favorite method so far, as in most cases it's possible to preserve the texture and tone of the original image while eliminating moire completely. I stumbled upon it when I was googling moire removal methods, and it was originally posted by Alexander Milovsky. I don't use it verbatim though, as it seemed to require some simplifications to be applicable to our fast-paced process.

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First of all, if you did anything with the brush to color the moire, undo it. Because what you did might have made it worse. I'll check the RGB channels of the colorized image by clicking on them in the Channels tab or just pressing Ctrl-3, Ctrl-4 and Ctrl-5 on my keyboard – there's a moire pattern in each channel. But undo the colorizing work and check again: you'll see that the Green channel is actually clear. When one of the channels doesn't not have any signs of moire, this is good news. You can use one of the best moire removal methods, which is based on channel mixing. Your task is to get a black and white image that is devoid of moire. This image is later used together with the High Pass filter to suppress moire and give you a perfectly clear image. Run the “Channel_mixer” action from the “Moire Killing” set. You'll get the Channel Mixer window that offers you to use 100% of the Green channel, as it's the channel that usually has less moire than the rest of them. Look at the black and white image preview – if it's clear, press OK. Otherwise you can do some mixing by moving the sliders, but in this case it will bring more moire, so 100% of the Green channel is perfect. After pressing OK you'll get the High Pass filter preview. It doesn't work like your regular High Pass filter, it's more a Moire Suppressing filter now. It is only possible because of some smart settings and a clear black and white image. Increase the radius until moire disappears from the image and press ok.

The action leaves you with a gray layer above your original image. It is completely masked, so if you want to reveal the layer, you have to work with the Eraser. Use it on all the areas covered in moire and you will see it disappear. It works like a miracle, but I assure you, this is pure math. If you can get a black and white image with no moire, you can subtract it from the original, catching moire separately and suppressing it with no problem at all.

In case the green channel contains some moire, too, you won't be able to work with this action as easily as before. But it's still manageable. You'll just have to play around with the sliders until you get a more or less acceptable result. Even in this case, when the moire pattern is just horrible, you can make it significantly better with channel mixing. Let me show you how. I'll zoom in to 100% scale and run the action. In the Channel Mixer dialogue window, set the blue channel to about 40, the red to – 80 something, and the green one to about 70. Now the pattern is not as visible as before, but the texture doesn't look so perfect. Press Enter to apply the changes, and use a pretty big radius for the High Pass prompt, like 30. Now I won't be wasting time on erasing all the necessary spots to reveal the effect, I'll just load a selection from an alpha-channel and you'll see it straight away. Just remember that if you don't want the seams and buttons to be ruined, you'll have to do some masking. This is how it looks at 100%, and this is how it looks after resizing. Not perfect, but not bad either, at least better than it was originally, and when moire is that serious, this kind of result is definitely a success.

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No matter how powerful, the Channel Mixer doesn't do any magic. There are certain cases when it won't work at all. For instance, if one of the channels is clipped, that is, if there are some blown out pixels – either in the shadows or in the highlights, you won't be able to mix anything properly. It usually happens in two cases: when you have a heavy shadow clipping, which shouldn't actually happen if you work with good images and if you know what you're doing when you work in Camera Raw. It also happens with really bright and saturated colors like red or fuchsia, when the red channel gets clipped because colors like that don't really want to fit in the narrow RGB color model.

So, if you can use the Channel Mixing method for good, use it, as it is the only method that allows you to remove moire without altering the texture or tone of the image. The rest of the methods are not so perfect. But if you click through the RGB channels and you see that they all are tainted with moire, you won't probably be able to use the method with such a great result, but it's still worth trying.

Pay attention to the fact that the High Pass acts like a blurring filter for the color spots. It might not be able to remove them completely, and in this case, you'll have to colorize the rest with the brush in Color mode after wiping through the mask. I only added it to save time on manual coloring, because most moire removing tutorials require you to mask the affected area one way or another. But as we normally try to avoid manual masking as much as possible, it's reasonable to try and use the High Pass first. If the moire waves are not too large, and the rest of the texture is single-colored, the result might be good enough as it is. Just remember that it will blur all the color spots in the image, not just moire, so watch it where you erase the mask, or it will cause weird effects on the image.

Hue method

The hue method is so similar to the Channel Mixer, that it doesn't require much explanation. Just run the action and adjust the sliders in the Hue/Saturation panel – Hue first, Saturation next if you can't make moire disappear with just that. What you need to achieve is a black and white image devoid of ripples. Then the moire pattern gets knocked out with the High Pass filter and you have to reveal the clean pattern with an Eraser. That's it. Personally, I prefer the Channel Mixer method, as I'm usually able to achieve the result faster. But since the method exists and is valid, why not tell you about it and include it in the action pack as well?

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In the video, it seems really quick, but the most tedious part is twiddling with the Hue/Saturation settings. Sometimes it requires a lot of twiddling, so beware. No magic in Photoshop.

Lab mode moire suppression

I'm not a huge fan of the Lab color space and I don't really find this method very useful, but if you google moire removal you'll see that a lot of people offer it as a solution. Problem is, I couldn't find any images this method worked best on. If it worked at all, Channel Mixing method got me a better result on the same image. The Lab method doesn't remove moire as efficiently, and sometimes when it does, it also changes the tones and colors of the image. But still, if it's widely used by many people, you should at least get familiar with it. The fact that I couldn't find images it worked on perfectly doesn't mean the method was faulty. It might work great on your images.

I believe that the original author of this method is Dan Margulis. If you work in retouching, you must have at least heard about him. The idea is very similar to Channel Mixing, but you work with Lab channels instead of RGB. Why Lab? There are also three channels there, which are Lightness, A and B channels, but unlike RGB channels, A and B contain color information and Lightness channel contains luminance information. Lab is not an abbreviation for “laboratory”, it's an abbreviation for the three channels, which are Lightness, A, and B, you see.

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Let's try this on the skirt that is completely covered in colored moire. To change the image mode to Lab, go to the Image menu, then Mode submenu and choose Lab Color there. Now when you go to the Channels panel, you'll be able to see these three new channels there. You can click on them to see what's inside of each. Here is the Lightness channel, which is clear. The A channel contains moire as well as the B channel. These conditions are perfect. If there was moire in the Lightness channel, things would get much more complicated. But relax for now, as you can just blur each of the color channels, remove moire and get away with it.

Let's do it. Click on the A channel and access the Gaussian Blur filter. Increase the Radius until you see no moire, like, until 12 and press OK. Repeat the process In the B channel – here it might take a bit more, like 17. Now when you switch to the composite image and make all the channels visible you'll see that the image is no longer covered in moire. Congratulations!

But do tell me, why did we have to go to some other color mode and spend time on picking Radii twice when we could have just colored the image instead? Or used the Channel Mixing method, which would work wonderfully, as the Green channel is completely clear, you wouldn't even have to do any actual mixing.

Let's see if it's possible to deal with monochrome moire in Lab mode. What if it actually can remove it, unlike colorizing and the Channel Mixing method. Let's try some other image. Before we even start doing anything, I want to remind you that this particular image has a clear green channel, and it can be Channel-mixed in no time. But let's do it in Lab mode. Run the “Lab” action from the moire killing set. The Apply Image window that just popped up will offer you to apply the inverted B channel to the Lightness channel in the Hard Light blending mode with 60% opacity. The method is not limited with this choice – you can try applying the A channel, you can tick the Inverted check box or leave it empty, you can change the Blending mode to Soft Light or even Overlay and you can also play with the Opacity setting. Hard Light, inverted B channel and 60% Opacity is the combination of settings that seems to work for me, more often than any other settings. What you are trying to achieve is the same thing as with the Channel Mixer – get a black and white image with no moire. I was not able to do so in this case. The best result I could get was this, with Opacity 20. After applying it, you'll get a Gaussian Blur prompt twice, where you should increase the Radius until the pattern goes away. After that, you'll get a masked layer. By erasing the mask you'll reveal the results. Colored moire is dealt with, but there are still some monochrome stains left there. The action requires a lot of tweaking on your side, and you see that even after trying all the possible combination, you might not be able to remove monochrome moire.

Let's also check it on this image. As you know already, there's moire in every channel. When I run the Lab action, it doesn't really work well, as the Lightness channel is seriously damaged with the moire pattern. Hard light at 100% seems to work, but not too well. Forget about blurring for now, let's just see what the Apply Image command did. When I reveal the result with the Eraser, you can see that the tone of the jacket has changed rather drastically. This is not cool, it means that you'll have to apply a Curve to the upper layer to make it look the same. But I don't really think it's worth the time, because moire is still there in the image.

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Even if you manage to reduce the visibility of the moire pattern by carefully adjusting the Apply Image settings and then apply lots of blur to both A and B channels, and then use a correcting curve to fix the tone shift, the result might still be far from perfect.

If you deal with a single-colored piece of material, you don't have to be shy when blurring channels, as it doesn't actually make the image any worse. We normally try to keep it as low as possible, but here you can go sky high without any problems. However, if you have quite a bunch of colored spots, they will be blurred, the bigger the Blur radius, the more.

You can play around with this action and I hope you'll find it useful. I do realize I might just not get something about it. When I analyzed the images from the online tutorials that used this method successfully, I found out that this whole Lab idea worked. I just didn't have much success with it when trying to use the method on my own images. But as the Lab method is proved to work in the numerous tutorials online, I've included this action in my moire killing set. Personally, I find it unreliable and slow, and in catalogue retouching, it's not something that is used often. But there are not so many methods that don't alter the texture of your items, and this fact alone makes this action worth trying. The rest of the methods is much more destructive than that.

Split frequencies method

Another valid method for removing monochrome moire is based on the principles of split frequencies. What you have to do it push the moire pattern out of your image, into a separate layer, and then blur it. Before you do anything, make sure you colorize the moire pattern if you need, because this method doesn't really help you with colored moire. It deals with the dreaded monochrome moire, something that you can't easily remove from an image – because it's contaminating every possible channel. I don't quite remember, but I first came across this method when reading on of Alexander Milovsky's articles on the matter.

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This image is a bad case of camera-induced interpolation moire, the kind of moire that is easier to prevent than to suppress. All the channels are equally tainted, be it RGB or Lab mode. What can we do if reshooting is not an option? Well, in case we can't really get a decent black and white image from any of the channels existing, we will deal with the moire in another way. I hope you remember how the Frequency Separation technique works because this is exactly what we will be using. A moire pattern is repetitive, which means it can be caught with the High Pass filter as a frequency. And if we manage to catch it, we can suppress it. I'll resize the image first so that you see the final texture straight away, but it doesn't really matter.

Run the “Split_frequencies” action from the moire killing pack. You'll get the Gaussian Blur prompt first, where you need to pick a Radius so that all the moire stripes disappear. In this case, 4 seems to be it. Then it's time for you to decide which Radius in the High Pass filter will be used to form the high frequency or the texture that will stay in the final image. Increase it until you get moire stripes appear and then decrease just a bit. If you let moire in this layer, you won't be able to suppress it later. Well, that's it.

What you have now is a layer with a mask that hides it. When you use the Eraser on the mask, it will remove the moire leaving a texture that you've managed to capture in the high frequency. Now this is not something that looks perfect, is it? There you have all the flaws of a faulty frequency separation – a funky texture that comes through, an unnatural overall look. But this is how it works. What would I do if I had to give it a quick finish – I would just click on the gray layer to switch to it and add some noise on top of that with the Add Noise filter. Lots of noise, like 2.5. Now it looks much better.

You might ask: “Why didn't we just add some blur and noise, why do the splitting at all?”. The deal is that blurring doesn't work so well without splitting. I'll copy the final image to a new document and then just go back in History to right after the Image Size step. I'll copy this image to a new layer and blur it with the Gaussian Blur, Radius 4, just like before. Then I'll create a Layer Mask and fill it with black so that all the blurry effect is hidden. Then I'll wipe through the mask with the eraser to reveal it, and when that's done, I'll switch to the Layer and add the same amount of Noise to it, which is 2.5. Now I'll flatten the image and copy it to compare with our previous result. Doesn't look the same, right? So, frequency separation is essential in moire suppression, just remember that it does affect texture. Don't get all discouraged with the results yet, if the texture is right – you'll be able to remove moire without much problem. I just didn't want to show you any miracles, like some tutorials do – by carefully selecting the images. This method doesn't always work well, make sure you remember that and keep watching.

This image is covered in monochrome moire which cannot be removed by colorizing. I painted it green already and that didn't help. Let's try the “Split_frequencies” action. I'll use 16 in the Gaussian Blur prompt and 3 in the High Pass. Now all I have to do is use the Eraser to reveal the results. And moire fades away, it's as easy as that! It worked so fine because the moire stripes were bigger than the dress texture and we managed to push all the moire out without affecting it. This is a much better result than before – which means that it really depends on images whether the method will work or not. Your task here is to set the Radii for both filters right, which is not so hard if you understand what exactly has to be done.

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If you want a more subtle approach than just wiping away the whole frequency, you can use the regular frequencies splitting action to do the same thing. Run it and pick the right Radius to preserve the texture of the item, and then just use the Mixer Brush to smudge the moire pattern on the low frequency layer. It's basically the same thing because this is exactly the same method.

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.

Next: True moire

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