Q:HOW TO REDUCE MOIRE PATTERNS FROM SCAN
R. Seckler
What's the trick in eliminating moire patterns in photo images from printed
materials like magazines or catalogs?
--
Robert Seckler
Stamp Asylum
http://www.stampasylum.com
Stephen Bohus
rs...@airmail.net (R. Seckler) writes:
> What's the trick in eliminating moire patterns in photo images from printed
> materials like magazines or catalogs?
First step: scan in your material at a much higher resolution than you will
need for your final image (typically a minimum of twice the width and height).
To minimize moire during scanning try to scan at a dpi which is evenly
divisible by the optical resolution of your scanner and scan at 100% scaling
(eg. if you have a 600x1200 scanner, scan at 600, 300, or 200 dpi, etc.,
in this case you wouldn't use an oddball value such as 137dpi or 231dpi since
it would increase moire from the scanner software's interpolation routines).
Next step, go under Gaussian Blur, and blur the image until you see the moire
pattern COMPLETELY disappear. For coated stock, I find values of 0.5 to 1.5
are usually adequate, and for scanning newsprint a value of 1.5 - 2.6 will
usually do. Every printed page is scanned differently, so just make sure that
you make the moire disappear. It's important not to use Gaussian blur more
than once (undo and use a higher blur value if you still see moire)
Final step, cut the image to size. Since the cut size of image is much
smaller than your scan (in terms of pixels), the image won't looked blurred.
Then do the steps you normally would in correcting the image. You can still
Unsharp Mask your image in the end, but you may not want to make it too
sharp because sometimes this can bring back some of the moire.
I tend to avoid using Despeckle, Dust & Scratches, and Median filters when
working with printed material.
Remember, if you are scanning in colour printed material, and if this
material is slightly out of register, then your final image will also be out
of register. Press operators are sometimes very annoyed at trying to
reproduce such photos. The moral of the story: nothing beats a good original.
- Stephen Bohus
c...@dgp.toronto.edu
Btw, we really do need a FAQ for questions such as this one.
Erik Johnson
On Tue, 09 Sep 1997 08:16:44 -0500, rs...@airmail.net (R. Seckler)
wrote:
>What's the trick in eliminating moire patterns in photo images from printed
>materials like magazines or catalogs?
I'm sure this would be in a photoshop faq. Scan at more than twice
the the resolution you want (but not an even multiplier larger, i.e.
not 2x or 3x or 4x...). Then guassian blur. Then reduce to the
resolution you want.
-Erik Johnson
er...@phidias.colorado.edu
http://phidias.colorado.edu/vgallery.html
Matthew Selleck
R. Seckler wrote:
> What's the trick in eliminating moire patterns in photo images from
> printed
> materials like magazines or catalogs?
>
> --
> Robert Seckler
> Stamp Asylum
> http://www.stampasylum.com
If you scan at a resolution 2.5 times higher than the screen ruling
of your printed matter you will lose most of the pattern - also before
you scan offset your original by about 2 deg when you place it in the
scanner
Matt
pen clark
Matthew Selleck wrote in article <34156204...@werple.net.au>...
> If you scan at a resolution 2.5 times higher than the screen ruling
>of your printed matter you will lose most of the pattern - also before
>you scan offset your original by about 2 deg when you place it in the
>scanner
>
>Matt
>
Also, if you're able to at scan time, reduce the focus (manually on a drum)
or use the drivers "descreen option". A gaussian blur can reduce moire
effects, but it comes at a loss of detial, Some moire's will never be
resolved, They reappear in the screening later.
Pen
Rusty Wright
Sometimes you may get these repeating diagonal bands of color running
across the picture, which are Moire patterns of a different flavor (I
think they're in just one or two of the color channels). What I do to
get rid of them is convert the image to Lab mode and then Gaussian
Blur the A and B channels. Do this blurring before you resize the
picture down.
Another advantage of Lab mode is that you can be a bit more aggressive
when using the Unsharp Mask filter if you use it only on the Lightness
channel. Do this sharpening after you've resized the picture down,
then convert the image back to RGB mode.
M...@writeme.com
I would almost never recomend using the sharpening and descreaning
software that comes with your scanner to fix the problem because in most
cases it is over simplifies the process by you clicking somthing like
newspaper quality or mag quality or photo quality and then it bases what
it does on that alone. With the desceening you may also loose image
clarity along with who knows what all else. In most cases you can do a
much better job in photo shop at removing the miore pattern. First try
using the despeckle filter. That works about 85% of the time right
there. If that dosn't do anything use your one (sigh) undo to reverse
that and then try a gaussian blur with a setting of one pixel. That will
do the trick most of the time when the despeckle won't. If that still
dosn't work just re-scan the image at about twice the size you want and
resize it once you are done working on it. The alterations you make to
it in editing will work towards hiding the miore and when you reduce the
file size it will more than likley loose the detail needed to see the
pattern to begin with. Hope this helps!
Eric
Safin Timur
This right way (without long explanation, just try it) for PhotoShop4.:
1) turn your paper or magazine at 15° angle (or 75° etc.). This
effectively could decrease moire up to twice;
2) never choice 'Sharp Photo ...' at your scanner program. Sharpening
would increase moire;
3) Select as much quality as you can (300 or 600 or greater dpi);
4) at PS4 apply small Filter|Blur|Gaussian blur (optional) if you scan
low quality pix with large moire dots;
5) apply Filter|Blur|SMART BLUR with radius: 1.2-1.8, threshold 12-25
and appropriate quality.
This operation effectively remove dots from large areas;
6) turn your image back at 15° or whatsoever angle;
7) resample image at requested size;
8) Apply Filter|Sharpen|Sharpen. Fade sharpening back at 15%
Isn't it magic?
Timur Safin
STATPROGRESS
Mike Russell
The July 97 issue of Computer Artist has a column by Dan Margulis on
minimizing moire when scanning.
There's a lot of detail in the article, but gist of it is to experiment
with scanning the material at different angles, and avoid scanning
parallel or perpendicular to the cyan, magenta, or black screens.
sha...@silcom.com
In article
<B26678EFFE34FBB5.F5BB33C0...@library-proxy.airnews.net>,
rs...@airmail.net (R. Seckler) wrote:
> What's the trick in eliminating moire patterns in photo images from printed
> materials like magazines or catalogs?
>
> --
> Robert Seckler
> Stamp Asylum
> http://www.stampasylum.com
Try scanning at a 45 degree turn. When you rotate it back up it gets rid
of some of the moire patterns.