Re: [Gimp-user] Fw: scan-mirrage-effect-Problem with postcard

[Ofnuts via gimp-user-list]

If the moiré isn't the same when you do several scans (after moving the
card a bit), then you can eliminate the moiré by making several scans
and averaging them after making them overlap exactly.

To average images you can stack them and set the opacity to 100/N where
N is the order of the layer in the stack starting from the bottom: 100%
at the bottom, then 50%, then 33%, 25%, 20%, 17%... There is also a
average filter in the GMIC plugin (but the median filter it contains may
be even better).


On 11/05/2021 02:56, Rick Strong wrote:

I didn't see my reply show up on the Gimp user list.
RS
-Original Message- From: Rick Strong
Sent: Monday, May 10, 2021 11:33 AM
To: Tim (from Hamburg) ; gimp-user-list@gnome.org
Subject: Re: [Gimp-user] scan-mirrage-effect-Problem with postcard

Well, it's not moiré from the glass.

It seems to be a scanning artefact introduced by the scanner. But you
say it
doesn't happen with scans of images on plain or matte paper.
try putting a black card over the postcard before you lower the lid. Also
check your scanner settings.

If that doesn't work, you could try photographing the glossy postcard
with a
camera. With some fridge magnets you could stick it vertically to the
side
of something metallic in good light, like your refrigerator or your car.
Then crop out or clone out the magnets from the photograph.

Rick S.
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Re: [Gimp-user] Fw: scan-mirrage-effect-Problem with postcard

[Liam R E Quin]

On Tue, 2021-05-11 at 03:02 -0400, Gene Heskett wrote:
> > 
> > Did you look at the image?
> 
> No, I just got interested in the thread 

If you find the xcf file in the archives your comments may be very
useful. Right now you are guessing, albeit at some length :)

In the meantime it's probably a case of investigating  the options
provided by the scanner driver - without knowing the details of the
exact scanner model and operating system it's impossible to know for
sure.

Liam


-- 
Liam Quin - web slave for https://www.fromoldbooks.org/
Click here to have the slave rewarded with custard.

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Re: [Gimp-user] Fw: scan-mirrage-effect-Problem with postcard

[Gene Heskett]

On Monday 10 May 2021 23:55:17 Liam R E Quin wrote:

> On Mon, 2021-05-10 at 23:22 -0400, Gene Heskett wrote:
> > The moire pattern is without a doubt, from scanning a litho print
> > which
> > is microscopic patterns of different size colored dots that mix in
> > the
> > eye to make the color. 
>
> Did you look at the image?

No, I just got interested in the thread as it seemed to be going on for a 
longer time than most, and the fact that I've shared chemical darkroom 
space with a print shop so I am somewhat familiar with the tech that 
probably printed that postcard.

Whats the date/time of the post containing the image?

And, most importantly, is that image raw, uncompressed staight out of the 
scanners cable, very unlikely, or has it been passed thru a compression 
utility, in the latter case all bets are off. Simply put, any scan good 
enough to publish out of my scanner will be jpegged or png'd because the 
raw scan is going to be half a gigabyte or more, and will be compressed 
to under 300k base64'd for transport over the net. gimp is very good at 
that, but it is not without lots of artifacts to the trained eye.

> Although there's evidence of dot screen 
> atrefacts, that'snot what is being referred to.  In addition, the
> stripes change direction on the second scan, suggesting they are not
> coming from the actual postcard.

in that event, I'd blame that on sloppiness of the scanners head 
transport linkage. A .1mm inconsistency of square would change a moire 
pattern, a lot. or moving the card on the glass by replacing it on the 
glass for the 2nd scan. Even if the lid is not raised, the scanner could 
easily displace the second scan enough just from temperature effects to 
change the pattern. Unsynchronized data clocking would also see to that. 
In fact combining multiple scans with a 32 or 64 bit addition, and 
decimating it back to 16 or even 8 bit depth by throwing away the lsbits 
might well be the cure because it would cancel the moire pattern by 
averaging the sums. But thats not practical to do on a large scale with 
todays computers, but when we get 256 bit cpu's and terabytes of fast 
ram it will be routine.

Astronomers with access to supercomputers do that stacking and 
synchronizing of images all the time to Hubbles images to get the 
amazing pix we get out of it. That scope is a time machine, looking back 
in time as much as 13.8 billion years. To a time when the universe was 
new, maybe 200,000 years after the big bang. We can't see any further 
back because it was opaque before then. It had to cool a while before 
light became uncoupled and could escape to begin its journey to Hubbles 
single photon detectors.

Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis
Genes Web page 
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Re: [Gimp-user] Fw: scan-mirrage-effect-Problem with postcard

[Liam R E Quin]

On Mon, 2021-05-10 at 23:22 -0400, Gene Heskett wrote:
> 
> The moire pattern is without a doubt, from scanning a litho print
> which 
> is microscopic patterns of different size colored dots that mix in
> the 
> eye to make the color. 

Did you look at the image? Although there's evidence of dot screen
atrefacts, that'snot what is being referred to.  In addition, the
stripes change direction on the second scan, suggesting they are not 
coming from the actual postcard.



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Re: [Gimp-user] Fw: scan-mirrage-effect-Problem with postcard

[Bradley S. Rosen]

Unsubscribe

Brad

On Mon, May 10, 2021, 10:23 PM Gene Heskett  wrote:

> On Monday 10 May 2021 20:56:27 Rick Strong wrote:
>
> > I didn't see my reply show up on the Gimp user list.
> > RS
> > -Original Message-
> > From: Rick Strong
> > Sent: Monday, May 10, 2021 11:33 AM
> > To: Tim (from Hamburg) ; gimp-user-list@gnome.org
> > Subject: Re: [Gimp-user] scan-mirrage-effect-Problem with postcard
> >
> > Well, it's not moiré from the glass.
> >
> > It seems to be a scanning artefact introduced by the scanner. But you
> > say it doesn't happen with scans of images on plain or matte paper.
> > try putting a black card over the postcard before you lower the lid.
> > Also check your scanner settings.
> >
> > If that doesn't work, you could try photographing the glossy postcard
> > with a camera. With some fridge magnets you could stick it vertically
> > to the side of something metallic in good light, like your
> > refrigerator or your car. Then crop out or clone out the magnets from
> > the photograph.
> >
> > Rick S.
>
> The moire pattern is without a doubt, from scanning a litho print which
> is microscopic patterns of different size colored dots that mix in the
> eye to make the color. If the scanner or camera lens is sharp enough and
> the autofocus accurate enough, it can be quite a problem. you may be
> able to reduce or eliminaate it with what ever is in the toolbox to
> reduce the unwanted sharpness, which should blend the dot pattern away
> if done in the right amount and size of the blend. Ideally, the size of
> the blend should match the size of the dot pattern but tolerances in
> paper positioning as the printer lays each ink color may make this
> difficult to balance without adversly effecting the overall sharpness.
>
> Be aware that copyright info may be hidden, invisible to the eye in this
> dot pattern.  And it is considered valid proof of a violation.
> > ___
> > gimp-user-list mailing list
> > List address:gimp-user-list@gnome.org
> > List membership:
> > https://mail.gnome.org/mailman/listinfo/gimp-user-list List archives:
> >  https://mail.gnome.org/archives/gimp-user-list
>
>
> Cheers, Gene Heskett
> --
> "There are four boxes to be used in defense of liberty:
>  soap, ballot, jury, and ammo. Please use in that order."
> -Ed Howdershelt (Author)
> If we desire respect for the law, we must first make the law respectable.
>  - Louis D. Brandeis
> Genes Web page 
> ___
> gimp-user-list mailing list
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>
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Re: [Gimp-user] Fw: scan-mirrage-effect-Problem with postcard

[Gene Heskett]

On Monday 10 May 2021 20:56:27 Rick Strong wrote:

> I didn't see my reply show up on the Gimp user list.
> RS
> -Original Message-
> From: Rick Strong
> Sent: Monday, May 10, 2021 11:33 AM
> To: Tim (from Hamburg) ; gimp-user-list@gnome.org
> Subject: Re: [Gimp-user] scan-mirrage-effect-Problem with postcard
>
> Well, it's not moiré from the glass.
>
> It seems to be a scanning artefact introduced by the scanner. But you
> say it doesn't happen with scans of images on plain or matte paper.
> try putting a black card over the postcard before you lower the lid.
> Also check your scanner settings.
>
> If that doesn't work, you could try photographing the glossy postcard
> with a camera. With some fridge magnets you could stick it vertically
> to the side of something metallic in good light, like your
> refrigerator or your car. Then crop out or clone out the magnets from
> the photograph.
>
> Rick S.

The moire pattern is without a doubt, from scanning a litho print which 
is microscopic patterns of different size colored dots that mix in the 
eye to make the color. If the scanner or camera lens is sharp enough and 
the autofocus accurate enough, it can be quite a problem. you may be 
able to reduce or eliminaate it with what ever is in the toolbox to 
reduce the unwanted sharpness, which should blend the dot pattern away 
if done in the right amount and size of the blend. Ideally, the size of 
the blend should match the size of the dot pattern but tolerances in 
paper positioning as the printer lays each ink color may make this 
difficult to balance without adversly effecting the overall sharpness.

Be aware that copyright info may be hidden, invisible to the eye in this 
dot pattern.  And it is considered valid proof of a violation.
> ___
> gimp-user-list mailing list
> List address:gimp-user-list@gnome.org
> List membership:
> https://mail.gnome.org/mailman/listinfo/gimp-user-list List archives: 
>  https://mail.gnome.org/archives/gimp-user-list


Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis
Genes Web page 
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