Remember, aliasing is when two or more different input signals appear identical
at the output of a sampled system. This only happens when the input signal
exceeds
the Nyquist limit of the sampled system.
I've just twigged that you and others are only thinking in the frequency domain,
Basically, I'm trying to say that scanner softness has many causes but the
inherent reason is not related to aliasing at all. It is the from low pass
filtering due to the individual CCD cell.
Fundamental disagreement about the 'not related' bit here. How are filter
characteristics
Tony Sleep [EMAIL PROTECTED] wrote:
I'm not going to try and explain this properly without graphics, as (heck,
is that the
time) I have work to do, and it will be instantly obvious what the problem
is from a
web page I am working on.
Speaking of web pages, I just modified my scanning page,
- Original Message -
From: "Tony Sleep" [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Sent: Monday, December 04, 2000 11:45 PM
Subject: Re: Re[3]: filmscanners: Film Scanners and what they see.
The visible effect of aliasing is increased "apparent
grain" in the ima
- Original Message -
From: "Tony Sleep" [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Sent: Tuesday, December 05, 2000 6:28 AM
Subject: Re: Re[3]: filmscanners: Film Scanners and what they see.
1) Defocus the input signal.
2) Optically filter the input signal.
Those are
Craig W. Shier [EMAIL PROTECTED] wrote:
physically implementable scanner. If the sample areas
are sufficiently samll. i.e. if they do not overlap,
there will be no reduction in sharpness for a
sufficiently high resolution scan. For example, if
your lens resolves 50 lppm, a 2540 dpi scan
Filtering is not aliasing.
Agreed. But ...
Furthermore, aliasing doesn't occur in the
continuous domain. And that is where the effect I described occurs.
It's a physical fact of CCD's, the mismatch between sub-Nyquist target detail and
pixel
size. The Nyquist limit is the filter, and
Bottom line. Fuzziness of a scan is caused by two
things, a) sampling error and b) correlation.
Thanks for all that. It seems to confirm the etymological origins of WW3 :)
Regards
Tony Sleep
http://www.halftone.co.uk - Online portfolio exhibit; + film scanner info
comparisons
Byron am I right in
understanding that you're saying aliasing does *not* cause scanner image
softness. On the other hand you *aren't* saying that the enhancing of
apparent grain caused by the interference between scanner resolution and
film grain (dye cloud patterns) - is something other
Craig, I like your explanation, but it doesn't take into account the
interference between the grain (or dye cloud patterns) in the film and the
scan resolution, which seems to be the main source of pain in film scanning.
When the grain is taken into account, it's the relationship between the
- Original Message -
From: "Rob Geraghty" [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Sent: Monday, December 04, 2000 3:57 AM
Subject: Re: Re[3]: filmscanners: Film Scanners and what they see.
bjs [EMAIL PROTECTED] wrote:
One can design a scanner that doesn't hav
Craig wrote:
Good point. I haven't heard the interference you
refer to called aliasing (although apparently it has
been done)and I've not heard a really good technical
explanation of this effect.
Pete (photoscientia) has a good explanation on his web site. I first saw
this kind of aliasing
Austin Franklin [EMAIL PROTECTED] wrote:
Interesting! Is aliasing THE reason why scanning loses some sharpness.
What do you think aliasing is? I am curious what you base your claim
above
on, and I do not believe it is a correct statement.
In my experience with the LS30, aliasing doesn't
on 3/12/00 2:08 am, bjs at [EMAIL PROTECTED] wrote:
The most fundamental reason that scanners lose sharpness is because they are
area samplers rather than point samplers. This is a physical necessity due
to the finite size of each CCD cell. The resulting area integration of
each sample
Uh no, it is not aliasing. Not even in the slightest. The physical cell
simply acts as low pass filter due to its size and geometry. Mathematically it
is the 2 dimensional convolution of the cell's structure with an idealised
point sampler. NONE of this causes ANY aliasing to occur but
Both phenomena depend on the use of a grid. But while aliasing
is exemplified by forcing a pixel to be all one color (a binary
sort if thing), the low pass effect has to do with diffraction
That is *colour* aliasing, which is a special case of aliasing in general (luminance).
You don't need
Here's a terse version from Kodak's dictionary of digital imaging terms -
"Aliasing
An effect caused by...
Be careful here. Aliasing may be the effect that is caused by...but that
does not make that the definition of aliasing. Sorry to sound so obtuse
here, but
- Original Message -
From: "Tony Sleep" [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Sent: Sunday, December 03, 2000 10:15 AM
Subject: Re: Re[3]: filmscanners: Film Scanners and what they see.
Uh no, it is not aliasing. Not even in the slightest. The physical cell
simply a
Tony is right here but just so we all understand each
other:
There are two valid uses of the term aliasing I have
come across in my experience in signal processing and
human machine interface development which are
technically correct in context but mean very different
things.
The signal
- Original Message -
From: "Tony Sleep" [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Sent: Friday, December 01, 2000 5:16 PM
Subject: Re: Re[3]: filmscanners: Film Scanners and what they see.
Interesting! Is aliasing THE reason why scanning loses some sharpness. Or
are th
- Original Message -
From: "Tony Sleep" [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Sent: Friday, December 01, 2000 5:16 PM
Subject: Re: Re[3]: filmscanners: Film Scanners and what they see.
Interesting! Is aliasing THE reason why scanning loses some sharpness. Or
are th
The most fundamental reason that scanners lose sharpness is because they are
area samplers rather than point samplers. This is a physical necessity due to
the finite size of each CCD cell. The resulting area integration of each
sample forms a physical low pass filter which softens the
- Original Message -
From: "Tony Sleep" [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Sent: Saturday, December 02, 2000 6:16 PM
Subject: Re: Re[3]: filmscanners: Film Scanners and what they see.
The most fundamental reason that scanners lose sharpness is because they
are
are
Interesting! Is aliasing THE reason why scanning loses some sharpness.
What do you think aliasing is? I am curious what you base your claim above on, and I
do not believe it is a correct statement.
Weird - I just received truncated messages from the list (they're empty).
Any ideas, Tony?
Unfortunately not, though I have noticed them as well:(
Run as it is now, via a remote listserver, I have no more insight than anyone else
except for a few admin commands I have to send by email. I
: Film Scanners and what they see.
Weird - I just received truncated messages from the list (they're empty).
Any ideas, Tony?
-- Original Message --
Rob Geraghty [EMAIL PROTECTED]
http://wordweb.com
And with what I have I should be
able to get the LS-30 to produce a scan that is in focus.
A couple of points. First that scanning loses some sharpness due to aliasing, and you
should expect to apply a small amount of unsharp masking to retrieve crispness.
However
if you are doing this
- Original Message -
From: "Tony Sleep" [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Sent: Wednesday, November 29, 2000 12:25 PM
Subject: Re[3]: filmscanners: Film Scanners and what they see.
And with what I have I should be
able to get the LS-30 to produce a scan that i
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