So you got that new Pentax K-5 IIs and despite what you had hoped for, you get visible moiré in one or more of your photos. Don't despair, because it can easily be avoided or, if needed, fixed through post processing.
In case you'd like to learn more about what moiré is, or haven't heard the term before, read this page of our K-5 IIs review.
When we tested the IIs for the review, we noticed that moiré was particularly common in photos of Saguaro cacti when shot from a moderate distance. The fine ridges and the repeating patterns created by their needles are to blame. In the scene below, all of the highlighted areas contain moiré:
Here's a 100% crop showing the false color and rainbow effect that it causes:
Before we get into how to remove moiré let's talk about how to completely avoid it in the first place.
Avoiding moiré is actually quite easy: just stop your the lens down to F11 or more whenever you suspect that moiré could be an issue in your scene. What happens here is that lens diffraction kicks in and it blurs the image, resulting in an image just like the one you'd get from an ordinary camera with a low-pass filter (AA filer), like the K-5 II, K-5, K-30, K-01, K-r, etc.
When you stop down to F11, effective resolution decreases and you will not benefit from the increased resolution potential of the K-5 IIs.
At F5.6, you do get moiré in the K-5 IIs shot, but there's also more detail in the entire photo:
But let's say you didn't foresee that your scene would be susceptible to moiré: then your only option would be to fix up the images that you brought home. The good news is that it's actually quite easy to do so!
Fixing RAW files
If you use Adobe Photoshop then the best way to remove moiré is to shoot RAW and use the moiré removal tool found in Adobe Camera Raw (ACR). You get to the tool from the horizontal tool bar at the top of the window. Click on the local adjustment brush:
This brings up a panel on the right-hand side of your window with sliders for various tools:
You only want to use the moiré tool so slide it out to around 20, which is a good starting point (refer to arrow 1 above). You will see a circle representing the brush - use the size and feather sliders (2 above) to make the brush match (or be smaller than) the area with moiré, and then paint over the area. If the effect is too strong (too much blur) then start over using a smaller value for moiré reduction (we used 18).
Fixing JPG files
Fortunately, Adobe Camera Raw can also open JPG files, so follow the same steps as above to fix up your JPEGs if you have access to ACR.
Fixing Photos Manually
So you don't have Photoshop or Adobe Camera Raw. You're not totally out of luck, but you'll have to experiment a bit to find the method that works best for your photos. What works best on one image may not work well on another. There are also other programs out there (just as DxO's photo tools) that have built-in moiré removal- if you'd like a cheaper alternative to Photoshop, why not ask in our post-processing forum?
Moiré can produce two different types of artifacts: false color and noise patterns. The former can generally be corrected through de-saturation. If you get noise patterns, de-saturation may get the job done, but it might also help to apply a blur to the entire region, which is what the low-pass filter in most digital cameras does to begin with.
Removing False Color
To get rid of false color, you first have to select the affected area. You can use the magic wand, lasso, rectangular marquee, or quick selection tool.
We use the latter and obtain the following selection:
It's then a good idea to smooth out the edges so that your adjustments blend in with the rest of the photo. To do this, click on the "refine edge" button at the top of the screen. Use the sliders in the dialog box to adjust the selection:
When you're done, click on the OK button. We're now ready to start de-saturating! The first thing to do is to use the Selective Color tool (found in the Image > Adjustments menu, or in the sidebar) to reduce the intensity of the false red color. This is done by selecting "reds" in the dropdown and reducing the presence of magenta. You can experiment with other channels as you see fit.
Next, you can try reducing the overall saturation of the selected area. Open the Hue/Saturation tool, found in the same menu. We made the following adjustments:
Here's what we ended up getting. You'll notice that the colors in the cactus are a bit off, but this can be corrected through finer tuning through the selective color tool.
You may need to do more work along the way if your subject has a less repetitive appearance or more varied color. If there are also repetitive patterns in your photo, this technique will probably not eliminate them (the top photo has been de-saturated):
Using the Blur tool from the toolbar
The blur tool can be used to remove moiré, but you may end up having to sacrifice a lot of detail in the process. To blur part of a photo in Photoshop, select the blur tool from the tool bar:
Then select a suitable brush size:
Now brush over the areas with moiré, thereby reducing it. If you combine this with de-saturation, it can be quite effective!
The Clone Tool
A third solution could also be the clone tool, which is found in just about all advanced photo editors. In our example it wouldn't be hard to find a cactus arm without moiré and simply clone it over to the areas with false color.
Have you come up with any techniques that do a good job of removing moiré? Share them below!
All images were shot at ISO 100 with the SMC Pentax-FA 77mm F1.8 Limited lens.