How can I remove a Moire Pattern

D
Posted By
dweinin
Jan 15, 2007
Views
867
Replies
3
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Closed
Hi Everyone-

I have an image with a guy in a pin stripped suit. I didn’t notice the moire pattern until I printed it and the pattern is much more visible. So I went back and looked at the original image. Sure enough there it is plain as day in the digital file. Can I do anything with photoshop to remove the pattern? What can I do to avoid something like this in the future.

The image was origianlly captured with a Nikon D70 SLR. It’s a 6 megapixel camera. I wasn’t using the RAW format. I was using JPG. Which probably doesn’t help.

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C
chrisjbirchall
Jan 15, 2007
Check out this movie tutorial: <http://av.adobe.com/russellbrown/GoAwaySM.mov> at <http://www.russellbrown.com>

And yes RAW would be better as would working in 16 bit.
I
ImageSkill
Jan 15, 2007
wrote:
Hi Everyone-

I have an image with a guy in a pin stripped suit. I didn’t notice the moire pattern until I printed it and the pattern is much more visible. So I went back and looked at the original image. Sure enough there it is plain as day in the digital file. Can I do anything with photoshop to remove the pattern? What can I do to avoid something like this in the future.

The image was origianlly captured with a Nikon D70 SLR. It’s a 6 megapixel camera. I wasn’t using the RAW format. I was using JPG. Which probably doesn’t help.

Try to use the following (I do nor remember where I saw it, may be on http://retouchpro.com/)

– Duplicate the background layer;
– On this duplicate layer apply the High-pass filter at radius (3.8) – Apply a Gaussian blur to this at radius (0.9)
– Invert the layer;
– Set blending to Linear Light;
– Set opacity at 50%;
– Mask to show only where you want to take out the Moire.

Dmitry
———————————————————— ——- ImageSkill – Software for digital image processing
http://www.imageskill.com
GH
Gernot_Hoffmann
Jan 15, 2007
dweinin,

Moiré cannot be removed from images, generally.
But no rule without exception:
‘Dan Margulis’ describes in his book about
‘Photoshop Lab’ a case where the image could be
cleaned up.

Moiré happens if the image, as projected onto
the CCD area, contains more details than 1/3
cycles per pixel.
In other words: a cycle is sampled by less than
3 pixels (not a magic number, but reasonable).
A cycle is a pair line+gap.

This tells us how to avoid Moiré (for the rare
cases where it might happen otherwise):
a) a little blur: patterns should be out of focus.
b) a rather large aperture number, e.g. f/16
for lens f/4..f/32. This causes blur because
of diffraction. A larger aperture number,
e.g. f/16 instead of f/4, produces a larger
depth of field, but the image is generally more
blurred.

Numbers are results of tests for Nikon D100 with
zoom lens 28mm..80mm, actually 50mm. Mainly the
threshold, where diffraction starts to blur the
image visibly, depends on the actual objective
(guess: halfways between f-stop-min and f-stop-max).

Best regards –Gernot Hoffmann

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