Getting moire pattern in scans

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Lordhutt
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Getting moire pattern in scans

Post by Lordhutt »

Trying to scan some album art. Getting a moire pattern... is this something that I can solve during the scan or will I have to edit?
I would assume this should be able to be handled by the scanner...
I am using an Epson V550
leepenny
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Re: Getting moire pattern in scans

Post by leepenny »

I use mostly photoshop but most filters are used in gimp as well - you will always get moire from scans - its what you do to the image once you have the scan that is important.
First off try to scan at the highest DPI (dots per inch) possible - giving you a large image.
Open the image in your program of choice and use a combination of gaussian blur (a low amount - it will vary depending on resolution of image), surface blur (google for an equivalent filter in gimp) - again a lower amount - and also making sure you set your black and white levels correctly will help reduce moire.
You could also use in photoshop the reduce noise filter and/or the dust and scratches filter but am not sure of the equivalent in gimp
After finding what combination works best (it will vary from scan to scan) - resize your image to fit the template (make sure you correct any dust marks or blemishes before resizing) - have a look at how it looks - you may need to go over the process a couple of times to perfect it.
After you are happy with the decrease in moire you should (possibly) sharpen the image slightly - if necessary and finalize your brightness/saturation and vibrance .
It may take a few attempts but a combination of any of the above filters will reduce moire significantly (works best for larger images though)
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akovia
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Re: Getting moire pattern in scans

Post by akovia »

Lordhutt wrote:Trying to scan some album art. Getting a moire pattern... is this something that I can solve during the scan or will I have to edit?
I would assume this should be able to be handled by the scanner...
I am using an Epson V550

First off, look in your scanning software for a descreening filter. This is used exclusively for the problem you are experiencing. Regardless, there is a descreen filter for gimp and it works great. I made a video a while back to show its use and need to track it down. I'm out of town right now so not sure what I can do using my phone.

Will post again with more details.
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akovia
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Re: Getting moire pattern in scans

Post by akovia »

OK,
Here's the link to the video.
https://www.dropbox.com/s/73f579550174m ... leanup.mkv

Did a quick Google search for Epson descreen and saw that they indeed have it in their software.

The gimp plugin can be found here. http://registry.gimp.org/node/24411
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schimi2k
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Re: Getting moire pattern in scans

Post by schimi2k »

a little old tip that sometimes work - try to rotate the cd a bit... try some scans with various rotations 8-)
Lordhutt
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Re: Getting moire pattern in scans

Post by Lordhutt »

Yep in the Epson settings... but I had no idea what it was for until now. You are the Man, akovia!!
100 times better.
Thank you.

BTW, schimi2k... its for folder art but thanks anyway :)
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schimi2k
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Re: Getting moire pattern in scans

Post by schimi2k »

you can rotate all of things a bit to reduce moire fx of course ;)
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Re: Getting moire pattern in scans

Post by ZincRider »

Here's a video that shows how to descreen a printed image using any fourier transformation plugin:


I'm getting mixed results with this method. Sometimes it works really well, other times it leaves moire patterns in some spots and creates artifacts.
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akovia
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Re: Getting moire pattern in scans

Post by akovia »

There are many types of moire patterns that respond differently to this technique. If the pattern is really symmetric then you will tend to get very good results, but that isn't always the case.

I always start with the descreen filter for gimp first with some sane defaults that that give very good results for most images before manually going into G'MIC. It really is a trial and error process unless you get very lucky. This page is a pretty good resource for understanding the G'MIC tool and asking questions. I especially like the ability to use this tool to add an invisible watermark to your images. ;)

I planned to do a descreening tutorial for those not familiar with it at some point. I will cover both tools when I do, but first I need to find some good images to work with.

For anyone interested, I modified the script from the plugin registry to make the despeckle option actually work so you can turn it on or off. Otherwise it's always on no mater what you choose in the filter options. I also changed the defaults to something that gives me more consistent results. Make sure to download the required FFT plugin if you do use this as noted on the descreen filter link above.
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Re: Getting moire pattern in scans

Post by ZincRider »

I really need to get the descreen filter to work. sure would make my life easier. :)

Some of the results I've been getting so far are really spectacular, check this one out:
descreen.png
descreen.png (239.68 KiB) Viewed 15172 times
Unfortunately the same image has very strong artifacts:
artifacts.png
artifacts.png (949.15 KiB) Viewed 15172 times
Sometimes I got the best results by not blacking out all the stars in the transformed image..
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