Moiré interference patterns

First time I've come across this effect. Scanning a calendar, I get
gross 'interference patterns'. Understand they're more correctly
called Moiré patterns. I'm disappointed that my Epson Perfection (!)
2480 doesn't seem to have any setting to remove them at source.
(Gather some scanners have a 'de-screening' facility to do this.)

What is best way to handle this please? Is it a matter of scanning at
say 600 dpi and then using an image editor to reduce the size?

--
Terry, West Sussex, UK

On Wed, 30 Nov 2005 17:33:10 +0000, Terry Pinnell wrote:

First time I've come across this effect. Scanning a calendar, I get
gross 'interference patterns'. Understand they're more correctly
called Moiré patterns. I'm disappointed that my Epson Perfection (!)
2480 doesn't seem to have any setting to remove them at source.
(Gather some scanners have a 'de-screening' facility to do this.)

What is best way to handle this please? Is it a matter of scanning at
say 600 dpi and then using an image editor to reduce the size?

Terry,

filters exist that take the mathematical approach to remove
moiré patterns entirely. The last time I encountered such a
filter was when I still used a program called Picture Publisher
by Micrografx. This program had an excellent moiré filter which
used clever mathematics to obtain a precise model of the moiré
pattern and deducted it perfectly without losing any visible
sharpness.

Unfortunately I haven't seen anything like it ever since, and I
had to drop Picture Publisher because of its excessive number of
defects.

The moiré filter in Paint Shop Pro is a joke in comparison. It
is only a soft filter that essentially doesn't remove the moiré
at all, it just reduces it along with any other high frequencies
by applying a low pass filter, making the whole picture soft.

I would also like to know a third-party tool that does what
Picture Publisher did.

Hans-Georg

--
No mail, please.

Terry Pinnell wrote:
First time I've come across this effect. Scanning a calendar, I get
gross 'interference patterns'. Understand they're more correctly
called Moiré patterns. I'm disappointed that my Epson Perfection (!)
2480 doesn't seem to have any setting to remove them at source.
(Gather some scanners have a 'de-screening' facility to do this.)

What is best way to handle this please? Is it a matter of scanning at
say 600 dpi and then using an image editor to reduce the size?

Turning the picture at a slight angle when scanning can reduce the problem.

calendar scanning should not get moiré pattern. I think it should be the
screen dots pattern which can be removed by de-screen in your Epson scanner
advance setting menu.

"Terry Pinnell" wrote in message
...
First time I've come across this effect. Scanning a calendar, I get
gross 'interference patterns'. Understand they're more correctly
called Moiré patterns. I'm disappointed that my Epson Perfection (!)
2480 doesn't seem to have any setting to remove them at source.
(Gather some scanners have a 'de-screening' facility to do this.)

What is best way to handle this please? Is it a matter of scanning at
say 600 dpi and then using an image editor to reduce the size?

--
Terry, West Sussex, UK

"kctan" wrote:

calendar scanning should not get moiré pattern. I think it should be the
screen dots pattern which can be removed by de-screen in your Epson scanner
advance setting menu.

Is there such a feature? If so, as I said, so far I haven't found it.
Could you tell me exactly where it is please?

See also my other replies, re apparent difference between viewers.

BTW, why do you say "Calendar scanning should not get moiré pattern"?

--
Terry, West Sussex, UK

In article ,
says...


First time I've come across this effect. Scanning a calendar, I get
gross 'interference patterns'. Understand they're more correctly
called Moiré patterns. I'm disappointed that my Epson Perfection (!)
2480 doesn't seem to have any setting to remove them at source.
(Gather some scanners have a 'de-screening' facility to do this.)

What is best way to handle this please? Is it a matter of scanning at
say 600 dpi and then using an image editor to reduce the size?


Yes. Scan images in printed material at least at 300 dpi, and at 600
dpi if you can stand it (if the image is small enough it is bearable).
Moire is digital aliasing, caused by scanning resolution insufficient
to resolve the detail. The dots are the detail, and the dots are
typically (often) 150 dpi, which therefore theoretically requires at
least 300 dpi to resolve them (Nyquist). 600 dpi is better.

There are other workarounds, but the best solution is to increase the
scanning resolution, and then resample it to any smaller desired size.

--
Wayne
http://www.scantips.com "A few scanning tips"

Hans-Georg Michna wrote:

On Wed, 30 Nov 2005 17:33:10 +0000, Terry Pinnell wrote:

First time I've come across this effect. Scanning a calendar, I get
gross 'interference patterns'. Understand they're more correctly
called Moiré patterns. I'm disappointed that my Epson Perfection (!)
2480 doesn't seem to have any setting to remove them at source.
(Gather some scanners have a 'de-screening' facility to do this.)

What is best way to handle this please? Is it a matter of scanning at
say 600 dpi and then using an image editor to reduce the size?

Terry,

filters exist that take the mathematical approach to remove
moiré patterns entirely. The last time I encountered such a
filter was when I still used a program called Picture Publisher
by Micrografx. This program had an excellent moiré filter which
used clever mathematics to obtain a precise model of the moiré
pattern and deducted it perfectly without losing any visible
sharpness.

Unfortunately I haven't seen anything like it ever since, and I
had to drop Picture Publisher because of its excessive number of
defects.

The moiré filter in Paint Shop Pro is a joke in comparison. It
is only a soft filter that essentially doesn't remove the moiré
at all, it just reduces it along with any other high frequencies
by applying a low pass filter, making the whole picture soft.

I would also like to know a third-party tool that does what
Picture Publisher did.

Thanks Hans-Georg.

Since my post, I've discovered something very puzzling. By default, I
was viewing the finished JPG scan in IrfanView. That showed the bad
patterns. And they remained with various DPI changes in Epson Scan
(300, 400, 600, 150, 96). But I happened to open one in PaintShop Pro
8 (in order to see what filters I might use), and the patterns were
gone! This is with both programs filling the screen with the image to
about the same size.

I also found something else that I haven't figured out. Those first
scans were done by opening Epson Scan direct and using its
Professional Mode. But just now I instead tried opening Smart Panel
and then selecting Scan & Save. That doesn't present any options, it
just appears to scan using Fully Auto mode (and takes a fair while,
presumably because it's scanning the entire area, because there's no
Preview allowing cropping). But the resulting JPG was not patterned!

Any help getting my mind around these would be appreciated please.

--
Terry, West Sussex, UK

Marvin wrote:

Terry Pinnell wrote:
First time I've come across this effect. Scanning a calendar, I get
gross 'interference patterns'. Understand they're more correctly
called Moiré patterns. I'm disappointed that my Epson Perfection (!)
2480 doesn't seem to have any setting to remove them at source.
(Gather some scanners have a 'de-screening' facility to do this.)

What is best way to handle this please? Is it a matter of scanning at
say 600 dpi and then using an image editor to reduce the size?

Turning the picture at a slight angle when scanning can reduce the problem.

Thanks, I'll experiment with that when I get these other puzzles
sorted!

--
Terry, West Sussex, UK

Wayne wrote:

In article ,
says...

What is best way to handle this please? Is it a matter of scanning at
say 600 dpi and then using an image editor to reduce the size?


Yes. Scan images in printed material at least at 300 dpi, and at 600
dpi if you can stand it (if the image is small enough it is bearable).
Moire is digital aliasing, caused by scanning resolution insufficient
to resolve the detail. The dots are the detail, and the dots are
typically (often) 150 dpi, which therefore theoretically requires at
least 300 dpi to resolve them (Nyquist). 600 dpi is better.

There are other workarounds, but the best solution is to increase the
scanning resolution, and then resample it to any smaller desired size.

Thanks Wayne. Just tried one (a photo of about 5" x 8") at 600 dpi
then halved its size in IrfanView and it did indeed make a big
improvement. But please see my reply to Hans-Georg. I'm now confused
as to whether this patterning is *real*, or just a flaw in my usually
excellent IrfanView.

Here are a couple of screen shots showing the comparison. Both scans
were at 240 dpi. I then used Print Scrn to capture both and paste as a
new image in PSP 8. As you see, the view in IrfanView shows the
patterns, but PSP 8 does not (or vet much diminished).

http://www.terrypin.dial.pipex.com/I...-IrfanView.jpg
http://www.terrypin.dial.pipex.com/I...hot240-PSP.jpg

--
Terry, West Sussex, UK

In article ,
says...

Thanks Wayne. Just tried one (a photo of about 5" x 8") at 600 dpi
then halved its size in IrfanView and it did indeed make a big
improvement. But please see my reply to Hans-Georg. I'm now confused
as to whether this patterning is *real*, or just a flaw in my usually
excellent IrfanView.

Here are a couple of screen shots showing the comparison. Both scans
were at 240 dpi. I then used Print Scrn to capture both and paste as a
new image in PSP 8. As you see, the view in IrfanView shows the
patterns, but PSP 8 does not (or vet much diminished).

http://www.terrypin.dial.pipex.com/I...-IrfanView.jpg
http://www.terrypin.dial.pipex.com/I...hot240-PSP.jpg


You always want to judge images ONLY at 100% actual size on the monitor
screen (even if you must scroll around on it). If you scanned at 600 dpi,
it is a huge image, but I think you will see that pattern is false and not
actually present in the image when you view it at 100% actual size.
(IrfanView menu View - Actual Size).

Viewing programs only do a quick and dirty (nearest neighbor) resample to
make large images smaller to fit the screen window (fast and immediate,
but relatively poor quality), and it is not unusual to see moire effects
on the video screen, from even real photos, but especially from the dot
patterns in scanned printed images. Photo editors do this in different
ways, some a little better than others, but none are the same result as
actually viewing the actual real pixels, which are seen only when at 100%
actual size.

If this smaller size is what you want to view on the screen, then use the
resample menu to make a smaller copy that is the right size for viewing.
That resample menu is slower, not quite immediate, but wont create that
false pattern, because it uses better (slower) resampling methods.

--
Wayne
http://www.scantips.com "A few scanning tips"