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Conquering Moire from the Pentax K-5 IIs

12-05-2012 · By PF Staff in Photographic Resources
Conquering Moire from the Pentax K-5 IIs

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.

Pentax K-5 IIs

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:

Click to view a larger version of this photo

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. 

Selection tools

We use the latter and obtain the following selection:

Cactus 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:

Refining selection area

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.

Selective Color Adjustment

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:

Hue/Satudation Adjustment

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.

Removing Moire by De-Saturating

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):

Roof Moire

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:

blur tool

Then select a suitable brush size:

Blur brush size

Now brush over the areas with moiré, thereby reducing it. If you combine this with de-saturation, it can be quite effective!

blur tool comparison

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.

PF Staff's avatar
About the author: Various writers regularly contribute articles to the Pentax Forums homepage blog. More recent articles are published under each author's forum username. We hope you enjoy our guides and news coverage!

Tags: moire, pentax k-5 IIs, post-processing, eliminating moire, moire removal, photoshop, camera raw

More Posts in Photographic Resources | More Posts by PF Staff

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manishved [Delete] Dec 6th, 2012 10:25AM

Great article - I will try out these fixes....

harmonica2 [Delete] Dec 5th, 2012 10:03PM

Great article. For those of us used to dealing with issues like purple fringing, this seems like no big deal. @KFrog: Aperture 3 has a moire tool. In Aperture 2, it's called "Chroma Blur".

desertscape [Delete] Dec 5th, 2012 6:18PM

For shots that are known for Moire problems, switch to film. It's handy to use both digital and film bodies.

zosxavius [Delete] Dec 5th, 2012 5:45PM

I take a lot of pictures of man made objects (buildings, cityscapes, etc) as well as landscapes. To honest I don't see the benefit here. I'm usually stopped down to f8-f11 for extended DOF and to hit the sweet spots of the lenses I use where the frame evens out. At these apertures the resolution benefit is already decreased. Even the excellent 15mm ltd is best above 5.6. I get moire with AA filters as it is. The k-7 and k-5 I have both seem to have weakened filters. The k-7 possibly more so, as its output at the pixel level looks just ever so slightly sharper. However the k-5 files seem to sharpen up better than the k-7s in post, so it evens out ultimately and is a minor difference. The k-5 does have noticeably better resolution as well. I think its a toss up. I'll probably get a k-5 IIs next, but for someone like me, this probably won't be a huge deal. I'm already generating files that are nearing the resolution of the 5dmk2 and better in IQ IMO. How about a filterless K-1000D based on the sony 24MP FF sensor in the D600 pentax?? Are you listening? Or just go whole hog and do the 36MP D800 sensor?? OH PLEASE!!!! We can dream can't we? :)

regor [Delete] Dec 5th, 2012 3:51PM

Well, this has me wish even more that Pentax next AA-Filterless cameras will not use the Bayer's pattern (like the Fuji Xe1), hence avoiding moiré altogether ! Seems to me a simple solution(though a bit more complex to process).

jrpower10 [Delete] Dec 5th, 2012 3:02PM

So this helps me understand moire a bit better, I think. Am I interpreting this correct when I say that moire is basically a color error and always shows as a false color pattern? Or did I miss it?

KFrog [Delete] Dec 5th, 2012 10:58AM

I don't think there is a morie tool in Aperture 2, which I still using. Doubt there is one in 3 either.

Tanzer [Delete] Dec 5th, 2012 10:39AM

Great article. I didn't realize that moire could be so easily induced when photographing natural objects; I thought this was almost exclusively seen on man-made objects. This makes a stronger case for having an AA filters in general, than I had originally thought. I wonder what other natural objects are prone to moire besides saguaros?

br.davidson [Delete] Dec 5th, 2012 9:55AM

Saguaros are moire machines! Even on my K-7 I got tons of moire while shooting cactus landscapes with the DA35 macro. Easy enough to correct with the moire brush in Lightroom 4, just a bit tedious if there are lots of cacti that exhibit the problem.

NewTake [Delete] Dec 5th, 2012 7:33AM

Also note that Lightroom 4 has a moire brush as well.