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RE: filmscanners: What causes this and is there any easy solution ?



>I thought I had covered this with some sort of statement like "even when
>viewed quite close-up", but I must have rephrased this and removed it
before
>I posted the message.

You did in your original message; but everything is relative.  Some films
and scenes display the grain more prominently than others as you have noted
and are obvious even at further distances; while others display grain less
prominently even at quite close distances.  However, the grain is none the
less still there in all cases.  You recent test seems to bear not only this
point out; but the tests from what I can tell given the comparative
information you provided  are inconclusive on my point that the screen
texture masks the grain structure more so than a smooth surface under the
same conditions would for the same original.

>My sketchy understanding of digital signal processing tells me that you
>require 2x (a few experts insist 4x is better[just], but for the rest of
>this post I'm going to use 2x).... I think the 300dpi used in the best
printers
comes from the human eye being unable to see more than 150dpi so you need
2x150 or 300dpi to achieve the desired result.

I am not sure that they are speaking of sampling when it comes to scanning
as much as they are speaking about the role of line screens and how they are
to be taken into account when scanning for a halftone output like an offset
press or a laser printer.  These are less of a factor with respect to inkjet
printers and direct digital-to-photographic print processes. The 300 dpi
figure comes only in part from the workings of the human eye (which can see
the difference between 150 dpi and 300 or more dpi but begins to see les and
less of a difference between line screens of 150 and greater) and more from
the fact that this tended to be the physical limits of most desktop laser
printers ( which is now no longer true).  Current laser printers will
optimally work with 300 dpi X 2 or 600 dpi with the best laser printers even
accepting twice that.  Inkjet printers are a different story unless one is
using a RIP; they do not generate halftone patterns per se and use
stochastic dithering.  For them the 200 dpi to 350 dpi range is optimum and
has nothing to do with accounting for line screens (e.g., 1.5 or 2.0
factors).

I think you need to keep clear and distinct the differences between scanned
in resolutions measured in ppi, display resolutions measured in pixels width
time pixels length, and output resolutions measured in dpi.  You also should
keep in mind the difference between the different hard copy outputs and how
they define dpi for their outputs.

>Scanning at best optical resolution will always produce the best possible
>result. When you scan an image you are digitizing it and to get an accurate
>result you need 2x the dpi to have an accurate representation.

This is questionable for two reasons.  First, the statement turns on what
one takes "best" to mean; and secondly, the 2x notion only has validity if
one is talking about halftones.  Even there, the 2x  line screen factor has
little to do with accuracy of representation or rendering as much as it has
with the fineness or subtleness of the halftone process' ability to appear
as a continuous tone to the human eye.  The finer the line screen the more
the halftone appears as a continuous tone and the higher the resolution scan
required to account for the screening process.  Once again if you are
printing with an inkjet, this line screen factor has no real bearing.

>This is true for poor quality original images that will only print 7x10.
But
>you can only achieve the same or better result by resampling down.

Technically what I suggested may be resampling down; but I am unsure of how
you are using the resampling terms as differentiated from the notions of
optical resolutions.  My suggestion was not to resample upward or downward
in the sense of interpolation but to reduce the optical resolution of the
scan from the scanner's maximum optical resolution of 4000 dpi to an optical
resolution of less than 4000 dpi.  This does not involve any interpolation;
it is a reduction in the optical resolution of the scan.

>Scanning at a point where you see no grain means you are invariably giving
away image
>detail too and the grain will still be there but the human eye won't pick
it
>up because the pattern has gone.

True; but what I suggested was a compromise between the elimination of the
appearance of grain and the lose of image detail.  It is up to you to
determine where the sweet spot lies.  If you use blurring to eliminate the
appearance of grain, you will also be giving away image detail.  There is no
way to eliminate the appearance of grain totally and maintain every bit of
image detail - at least not in this imperfect world.

> I realised that the quality of the Epson 1270 digicam prints were much
better
>than the vast majority of the prints I had done in Labs. Even some of the
so
>called hand prints.

I think that this is more a byproduct of the operators than a product of the
process.  You are also comparing apples and oranges.  Do you have your
digicam images processes and printed in a photographic lab?  The question is
how do your traditional negative or slide based prints made on the Epson
1270 compare with those made at a good traditional photographic lab.

>So I figured 3Mp(bodged 8bit) v 20Mp (12bit) , no
>problem.

??? I do not understand what you are trying to say.

>I also saw the output from a digital Fuji Pictrography 4000 - hell
>these are significantly better than the 1270 and better than any print I
can
>remember seeing.

They can be quite good.  They are digitally based prints on traditional
photo papers which are wet processed.  They are not inkjet prints and print
at higher resolutions than inkjet printers.  However, since neither prints
from film directly, it does not permit any comparison between the quality of
digital source versus analog source (or film based) printing.  Your use of
the term "print" in the above statement is rather ambiguous.  It could refer
to any variety of types of hard copy outputs from traditional negative based
photographic prints to traditional photographic Ilfochrome prints to desktop
color laser prints to inkjet prints to dye sublimation prints to Lightjet
laser prints to offset prints to lithographic prints and so on.

>Yes. But I think slide film has traditionally had less grain. Don't know
why
>or maybe I've just been using the wrong brands.

But practically it makes little difference which has less grain; what is
relevant is which displays more obviously.  I contend that even if the slide
film did have less grain its higher contrast would result in scans that made
the appearance of whatever grain existed more obvious than would be the case
for negative film even with more grain but less contrast.

>The grain was not totally removed by the resize and so scaling up whether
>with GF or PS the output will still contain parts of the grain.

We may not be communicating with each other.   Yes the grain will still be
there; the object, I thought was not to remove the grain structure but to
make it less obvious.  I suggested that resizing and resampling in GF so as
to use its technological features would reduce the obviousness of the grain
not remove it totally; I also suggested that GF because of its technological
features would do this where the Photoshop method of resizing and resampling
would not.


>GF works takes ages but works much better than PS with 3x+ magnification
>below this the benefits become more and more marginal so certainly below 2x
>I would argue are not worth the effort (or the money) and felt it wouldn't
>have made a significant difference in my test. Once I have downsized below
>2000 dpi I am starting to throw away detail and I don't want to do that
>either. GF cannot recover detail that has been lost so I would prefer to
>filter the grain out. If the image is very grainy then I realise that I
will
>have to compromise the final potential size - as you would if you printed
>the image normally.

Yes GF is slow.  I do not see how magnification enters into the picture at
all or for that matter how you are using the term or in reference to what -
image size, file size, image resolution. Actually, you hare confusing the
hell out of me.  I am not sure if we are referring to 35mm negatives and
slides, enlarged photographic prints, digicam files, or what.  Even if
magnification was relevant and if you are referring to sizing by the term,
you would be magnifying a 35mm negative or slide greater than 3X to get a
standard 3.5x5 inch print size; it would only be possibly in the case of
enlarged photographic prints or maybe digicam files that you would have
magnifications of less than 3X.

Secondly, I think you are under a misconception about how GF works.  It is
not a traditional interpolation procedure similar to Photoshop's resampling
modes; nor is it a conventional compression program like JPEG or TIF LWZ
compression routines.  Using the lossless mode of GF, one does not really
throw away any information like traditional compression schemes; instead it
translates the bitmapped pixels into vector-like mathematical formulas using
wavelet and fractal technologies.  These
formulas can then be rendered in different sizes and resolutions without
loss of detail or image informational data or without creating or inventing
new informational image data as is the case in standard interpolation
methods.  If you use standard interpolation methods to downsample the
resolution an image or standard compression techniques to downsize the file,
you will lose information; and that information cannot be recovered by GF as
you say.  However, if you do these things strictly within GF and using its
Lossless mode, you will not lose that information.  As for your preference
to use a filter to minimize grain, how is that any different than what you
have suggested GF would do and rejected it because of.  The use of a filter
to minimize grain will result in the loss of other image detail which will
not be recoverable.

>Wouldn't use GF STN has it may have no future as you point out.

Of course that is possible; but it is also possible for any file format
including JPEG and TIF with LWZ compression.  The probabilities of this
happening if lower for JPEG and TIF; but it is becoming less probable for
.STN as time goes on and GF becomes bundled with more and more hardware like
printers, digital camera, and scanners.


-----Original Message-----
From: owner-filmscanners@halftone.co.uk
[mailto:owner-filmscanners@halftone.co.uk]On Behalf Of Steve Greenbank
Sent: Saturday, May 12, 2001 11:28 PM
To: filmscanners@halftone.co.uk
Subject: Re: filmscanners: What causes this and is there any easy
solution ?




....SNIP...




 




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