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03-12-2009, 01:03 AM   #1
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moiré

I have bee reviewing some photos that I have taken with the FA77, brilliant lens...but there's a catch. and it is moiré. does anyone here know of any techniques for removing or reducing it?

the first image is the worst... 100% crop, no sharpening applied in either image.


Last edited by Digitalis; 06-20-2009 at 06:51 AM.
03-12-2009, 06:29 AM   #2
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That is actually called aliasing. The only cure I've found is to not shoot things with a small repeating pattern.
BTW, it has nothing to do with the lens.
03-12-2009, 06:49 AM   #3
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let me guess...you're using a K10D? :-)

it has a weaker vertical AA filter...you get better sharpness than other DSLRs that use the same sensor as a result. It's a tradeoff...
03-12-2009, 07:33 AM   #4
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QuoteOriginally posted by kenyee Quote
let me guess...you're using a K10D? :-)

it has a weaker vertical AA filter...you get better sharpness than other DSLRs that use the same sensor as a result. It's a tradeoff...

yes I am, one of the reasons I chose the K10 was because of the weak AA filter. Medium format backs don't have the either.

yes I know it's aliasing. some Fashion photographers use medium format Digital Backs for a lot of their work, and I recall wedding photographers having problems with it as well. I was asking if anyone knew how to deal with it.

the only solution I can come up with it off the top of my head, is to deliberately shoot at f/16 or higher and using diffraction to enhance the AA filter's blurring of detail. that shot was at f/4 perhaps I could go the other way around and use f/2.

03-12-2009, 07:35 AM   #5
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Reduce colour noise in your favourite raw-developer, that might hide the problem.
03-12-2009, 08:00 AM   #6
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QuoteOriginally posted by Gimbal Quote
Reduce colour noise in your favourite raw-developer, that might hide the problem.
looks like I'll have to run a copy through Capture one 4 - that software is designed to work with medium format backs. I know it has some powerful aliasing suppression filters available...no offence Adobe, but Lightroom II still has some way to go.
03-12-2009, 08:27 AM   #7
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QuoteOriginally posted by Wheatfield Quote
That is actually called aliasing. The only cure I've found is to not shoot things with a small repeating pattern.
BTW, it has nothing to do with the lens.
Ah, but to quote wikipedia on aliasing
QuoteQuote:
An example of spatial aliasing is the Moiré pattern one can observe in a poorly pixelized image of a brick wall. Techniques that avoid such poor pixelizations are called anti-aliasing.
03-13-2009, 04:10 AM   #8
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In the case of the shed shot, the colour banding on the corrugated iron can be adjusted in Photoshop via IMAGE>ADJUSTMENT>REPLACE COLOUR. (Sorry, I don't use LIGHTBOX or any other PP program, so someone else can advise if this tool is available in other apps)

Basically, select the section of the image you want to adjust with the eyedropper tool, then move the HUE, SATURATION and LIGHTNESS sliders until the colour of the bands matches the rest of the iron. This allows all parts of the image with the same colour to change simultaneously. Adjust the tolerance-level slider to ensure other colours aren't affected.

This is fiddly and has various levels of success depending on the image, but when it works, it's brilliant.


Last edited by marcdsgn; 03-13-2009 at 04:21 AM.
03-13-2009, 04:43 AM   #9
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The Pro Sean Reid prefer to spot correct moire (locally) than to give up visual information across the frame in all his pictures. He would prefer that Canon and Nikon decided to offer non-AA-filtered versions of their higher-end DSLRs.
I’m no PP guru, but I guess you can just do what DSLRs with stronger AA-filters do; apply a mild blur to the areas.

http://www.reidreviews.com

The images you show are 100 % crop, I’m sure it would be little problem in regular size enlargement prints.


Edit:
I read that one possibility in general :
"...Photoshop does give this advantage if you're an advanced user or wizard. You can mask off the sky, and hit it with a smart blur or Gaussian blur."

Last edited by Jonson PL; 03-13-2009 at 05:22 AM.
03-13-2009, 08:24 AM   #10
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I wonder if an application of the following software would help?

PTLens
03-13-2009, 09:03 AM   #11
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I have a Kodak SLR/c Professional (15 MP full frame with a Canon mount). It has no anti-aliasing filter and moiré can be a serious problem. With very few exceptions the full version of the RAW developer Sikypix 3 removes it all in seconds.

I know that a version of Silkypix is supplied with Pentax cameras nowadays and you have presumably tried this, but I wonder if the full version is better in this respect - hopefully someone else can inform you. I have never tried the Pentax version.
Tony
03-13-2009, 09:12 AM   #12
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QuoteOriginally posted by Digitalis Quote
I have bee reviewing some photos that I have taken with the FA77, brilliant lens...but there's a catch. and it is moiré. does anyone here know of any techniques for removing or reducing it?

the first image is the worst... 100% crop, no sharpening applied in either image.
In your favorite editing software:

Make a new layer.

Apply a gaussian blur to the entire image. Pick the amount of blur that just makes the moire disappear.

Use the erase tool or any similar tool with a very soft edge to paint through the layer to the background in the areas where there is no moire.

Flatten layers.

Sharpen to taste.

Alternately you could make a layer mask first and then blur the un-masked areas, and then flatten and sharpen.

This seems to work well for me.

Ray
03-13-2009, 09:21 AM   #13
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I was able to reduce but not eliminate the pattern in the first image greatly by using the moire pattern removal in PSP X2.

A raw image might be better for fixing this,

It's funny though, I have never noticed this in the 11000 shots I have taken with my K10D.
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03-13-2009, 09:33 AM   #14
graphicgr8s
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I've also noticed this effect on tv programs. Norm Abrams wears those plaid shirts and there's always a moire in them when it's straight up and down or left and right. Has to do with the alignment with the sensor. An easy way out is to shoot at an angle leaving enough room for cropping then just crop it straight. The pattern doesn't line up with the sensor and therefore the problem doesn't occur in the first place. This isn't a problem unique to digital however. Anything printed with multiple screens (color work mostly and also grayscale when rescreening) on a printing press, if the screen angles are not right will exhibit this.
03-13-2009, 11:07 AM   #15
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Moiré or aliasing is the only artifact that can't be removed by computer algorithms.

This is due to the fact that the rule of Nyquist Theorem as been broken and and that a high spacial frequency have been under-sampled. To avoid such pattern, a low-pass filter is implemented also called anti-aliasing filter.

Its effect is basically to reduce edge sharpness of the image hitting the sensor (or blur the image)

The K20D has a much stronger aa-filter than the K10D that the reason why image don't look that much sharper on the 14Mpx of the K20D, but you can feel much more secure with tiny details like fabrics (when shooting portraits)

Another lesson to know that pixel count and sharpness don't make everything on image quality.

Regards,
Guillaume
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