[filmscanners] Re: over resolving scans

["Arthur Entlich" <artistic-1@shaw.ca>]

Hi Stan,

I suppose I could, but I'm much more a 'big picture' guy.  I'm sure
there are others on this list who live for these details and can provide
you with all the fine details, but I'd have to look them up.

What's most important IMHO, is that there is an understanding of what
happens when a random sized and positioned set of grain or dye clouds
are represented through a fixed matrix or even sized sensors.

Regardless of the size of grain, or the sensor, etc, in strict numerical
terms, the principal is the same.  You are, of course, correct that
sizes are important, but it is still the concept that I want to get
across here.  The places where the errors really mount up, both in terms
of color and size "expansion" due to taking curves and making them into
squares, is at the edges of transitions of grain or dye clouds with
others, or with an empty background of film base.

   The smaller the sensors relative to the average grain/dye cloud size,
the more accurately the size of the grain will be portrayed, and the
more accurately the edge will be defined in terms of size, luminosity
and color.  Larger sensors increase the percentage of pixels which
introduce errors (artifacts), and once they have been unsharp masked,
the problems are further amplified.

Again, this is why I keep on suggesting people consider 4000 dpi
scanners over 2700-2900, if they can afford them.  As I have also stated
before, it isn't just the file size that matters, it is the quality and
the accuracy of the data in that file.

It is one of the reasons I suggest the Canon FS4000 for people on
restricted budgets.  For people who have more to spend, the SS4000 and
SS4000+ are even better.  Everyone here knows the reasons I do not
recommend the Nikon LS-4000, so I won't repeat them.


Art


snsok@swbell.net wrote:

> Art,
>
> Can you expound on this a bit more in more concrete terms. Let's use the
> specific examples of a 4000 dpi scanner and a fine grained film like Velvia.
>
> A 4000 dpi scan would mean that each pixel is thus 6 microns long. What is
> the size of the grain in film such as Velvia? Isn't the grain much smaller
> than that?
>
> Stan
>
> -----Original Message-----
> From: filmscanners_owner@halftone.co.uk
> [mailto:filmscanners_owner@halftone.co.uk]On Behalf Of Arthur Entlich
> Sent: Friday, October 11, 2002 4:16 AM
> To: snsok@swbell.net
> Subject: [filmscanners] Re: over resolving scans
>
>
> In part, you answered our own question.
>
> Scanning resolution isn't just about the necessary input size of a file
> to produce a print.
>
> I think a lot of people do not fully understand some of the dynamics
> behind capturing a set of random sized and placed dots (grain, or dye
> clouds) within a non-random set of squares, and therefore the whole
> discussion on grain aliasing gets lost.
>
> Keep in mind that any one pixel can only be one color and luminosity,
> and is always square (or rectangular).  Now, what happens when you have
> to translate a irregular piece of grain, or overlapped dye clouds in the
> case of color film, into that square regular format?
>
> Let's take an example of a black and white film grain the size of the
> pixel, but round.  Assuming it was perfectly centered in that pixel (or
> CCD sensor) it will be translated into a square element of a certain
> luminosity, slightly lower that the actual grain, since some of the
> lighter area surround that circular grain will influence the final
> luminosity of the pixel.  Already, that grain is enlarged, because the
> "round" grain is now filled out into a square, and the luminosity is
> also no longer correct.
>
> Now, let's expand that grain to 2 times the size of the pixel element.
>
> Draw a grid 3 units by 3 units, or nine squares, like a tic-tac-toe
> board with the perimeter lined as well.  Now, draw a circle centered in
> the nine squares, which has a two square diameter.  You should now have
> nine squares with a circle pretty much bisecting the outer eight
> squares.  Now, imagine that each square can only be one luminosity,
> representing the amount of the square which is included in the circle.
>
> The middle square, (Whoopie Goldberg or Bert Renolds, depending on when
> you last tuned in Hollywood Squares ;-)) is fully covered by the circle,
> so it is 100% gray, or black.  The middle top and side squares would be
> about 50% gray since they are covered about that much by the circle, and
> the four corner squares would be about 25% gray to represent the amount
> of the circle that within those squares.
>
> Two things have occurred.  One, the circular grain is now enlarged to a
> 3 x 3 square, and secondly, it is represented by 3 different gray
> levels, 100% (black), 50% gray, and 25% gray.
>
> As the number of squares required to represent a "grain" increase, the
> less "errors" occur and the closer the digital representation becomes to
> actually representing the shape and size of the grain, and also the
> greater number of squares that are of the correct luminosity.
>
> The way more squares are required to represent a grain is a function of
> the size of the grain and the size of each pixel (or the scanning
> resolution).  Therefore, the finer the grain is, the finer the scanner
> resolution required to represent that grain, but even larger grained
> films will show less errors of size and luminosity with a higher
> resolution scanner.
>
> Now, imagine what happens when you have irregularly shaped grain, and
> overlapping grain or colored dye clouds that make up color film.
>
> You want very many squares to make up one small clump of dye clouds, so
> that although each square or pixel can only be one color and luminosity,
> it will nearly represent what the film is showing at that location.
>
> The reason the drum scanner provided cleaner, less "grainy" scans that
> could handle more USM, is simply because they used a lot more "squares"
> (I'm not sure drum scanners use square "pixels", either), but because
> less grain aliasing occurred, leading to much finer, more accurate
> digital information, meaning much less artifacts when USB was applied.
>
> I have been trying to tell people for a long time that there are more
> advantages to be found in a 4000 dpi scanner than that they can make
> larger prints, and the reason is because the more component pixels that
> make up any one element of the film image, the more accurate in shape
> and luminosity the digital representation will be relative to that
> original image, and the less gritty the scan will become when USM is
> used to restore the sharpness.
>
> And this has nothing to do with no stinkin' dynamic range ;-)
>
> Art
>
>
>


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