Question About Film Scanning Resolution

I recently purchased a film scanner (Pacific Image PF3650Pro3) which has a
maximum "Optical Resolution" of 3600 ppi.

When I scan at that resolution I end up with image files whose property
sheets say that they are 5148 x 3420. I would like to know how it is that I
appear to be getting higher resolution than the scanner is capable of
delivering.

Is my film scanner creating scans equal to 17.6 MP (5148 x 3420)????

I thought that my images would be 3600 x 2400, based on a 3:2 aspect ratio.
So how am I getting 50% more ppi than that?

If someone could help me understand these numbers I'd appreciate it.

 

You're gonna hate yourself when I say this, Norman... ;-)

Resolution is at pixels per *inch*. You're scanning something that is
36 x 24mm, or (roughly) 1.4 x 1 inches

So, using the file measurements you gave above, your actual scanning
area measured 1.43 x 0.95 inches, or 36.32 x 24.13mm. Which is just fine.


- Al.

 

Great! Thanks for clarifying that for me.

Now, about the 17 MP, am I getting images that are approximately equivalent
to what a 17MP digital camera would produce? Frankly, I don't see any
margin of superiority over digital, but this could be because I'm scanning
negatives from 20 years ago. I've seen articles claiming that a film scan
is equivalent to 20, 25 even 35MP digital, but I can't see anything so great
when I view my digital scans at, say, 300% zoom on screen.

 

Hi.
First of all, Your scan is a second generation image but a digital
image is a first generation image. Every time You reproduce the image
the quality suffers, this is inevitable. There are also other things,
You need a good lens and good technique to use all the quality of a good
slide film. Scanning will not improve on image quality, on the contrary.
Also not all scanners are equal. Scanner resolution may be high but
image quality may be something else. Scanner lens and light are
important, also how You scan. Scanning programs are not equal, You may
get much better results with program B.
After all that, I have a Nikon Coolscan V ED I am very, very happy
with. See, for example
http://shutterbug.com/equipmentreviews/scanners_printers/0504sb_nikons/
35 mm scan versus digital first generation image.. hmm. The amount of
information 35 mm slide includes might be about 20 MP or 15 MP or 10 MP.
But final image quality is something else. You might wish to visit
http://www.clarkvision.com/imagedetail/scandetail.html or
http://www.clarkvision.com/imagedetail/film.vs.6mpxl.digital.html .
Clark says, among other things: "Digital 9.8 Mpixels, monochrome:
Intensity detail similar to or slightly better than 35mm film detail.
Color detail still lacking film." And "Digital 17 Mpixels, monochrome:
The intensity detail is now clearly better than the 35mm film, but the
color detail is just beginning to be comparable."

Väinö Louekari

 

Digital camera images are pretty much an entirely different thing,
and usually appear sharper. This is because camera pixels are unaffected by
any neighboring pixel (usually), and thus can have sharper contrast
differences between them. This is what we see as sharpness and resolution.
Futher, the camera software often does some interpolation to produce the
finished product.

Film, on the other hand, produces a chemical response through three
or more overlapping layers of emulsion. And they respond in a linear manner
- rather than "on" or "off", there is progression of exposure. It's a bit
like the light that a flashlight throws: The beam may be brightest right in
the focused center, but there's still some residual light that drops off
outside of that. So film emulsion has a progression of change to all
details, and the goal is to keep this progression as rapid or narrow as
possible, producing a higher level of contrast and what we perceive as
"sharpness."

At high magnification, digital looks better, true enough. This is
great if you really need to see the individual pixels. Now, I don't know
about you, but I can't say that's ever done anything for my photos - people
generally want to see the subject and how it's portrayed, not what it looks
like through a microscope ;-)

And if you want to do some post-scan software tweaks to alter the
contrast closer to a digital file, go for it. But otherwise I would suggest
not worrying about it too much and concentrate instead on the photo itself
- composition, lighting, timing, and so on. Don't get suckered in by the
pursuit of statistics and specifications - those don't make the image. I'm
speaking a bit of heresy in this day and age, but then, I like to live
dangerously ;-)

By the way, viewing the image at 300% won't really tell you much -
anything above 100% doesn't reveal the detail any better, and all you're
doing is telling the computer to make one pixel go across multiple dots of
your monitor. It does have its uses when doing touchups, since you can
translate your mouse movements into smaller and finer increments of the
image, but that's about it.

Hope this helps. Good luck!


- Al.

 

Because a 35mm film frame is not 1" wide.

A 35mm frame is 36mm x 24mm, or 1.42" x 0.94", and there's typically a
bit of overscan to account for frames that are slightly misaligned.

At 3600 dpi, 1.42" x 0.94" yields 5112x3384 pixels.

Whether or not there's actually 16Mpx of visual information there to
capture depends on the film, lens, and processing.

 

Digital camera noise is in one axis: color
Film noise is in three axis': color, x and y.

To get high res from film, the original image has to be from high
quality, sharp glass, perfectly focused, at the sharpest aperture, high
shutter speed, perfectly isolated camera, mirror lockup, in high
contrast lighting (preferably flash) with a sharp, highly detailed
subject. Better yet, hold the shutter open with a cable release in a
perfectly dark room and expose with flash only, then let the shutter close.

Only deliberate efforts to bring all of these elements together at one
time will get you that resolution at scan time.

Alan.

 

So what is your theory as to why you have to go through all of that
with film when with digital you can just snap the photo?

My 350D has a pixel pitch of 3954 ppi, almost exactly what a 4000 ppi
film scanner has. So pretty much we can compare directly a shot from
my camera with a scan of film, I will get a cropped view due to the
smaller image but the center part of the image we are comparing apples
to apples.

So this was shot in poor light at 1/250 second with a $70 lens hand
held.
http://www.pbase.com/konascott/image/68928171/original

And yet that has more detail then any 4000 ppi scan from film I have
ever seen.

Scott

 

Ah, but only 38% of the area of a 35 mm frame.

We agree of course -- per unit area, silicon makes
a much better sensor than film.


rafe b
www.terrapinphoto.com

 

And the point I was making was that with a DSLR I don't have to do
all of the rather extreme measures that Alan outlined as been needed to
get a good sharp image on film. I can just hold my camera by hand and
use a cheap lens and still get an image that is sharper then film can
for the same area. Sure I have less of the frame covered with my
sensor but that should not matter when talking about hand holding the
camera or how good the lens is.

Scott

 

It is not quite that simple. With a bad lens you get a low-quality image
to begin with. Capturing it digitally does not improve it. Good film or
good digital can handle more than a bad lens can deliver.

Väinö Louekari

 

But then I did not say I used a bad lens, I said it used a cheap lens.
Canons 50mm 1.8 may only cost $70 but it is pretty darn sharp none the
less.

Scott

 

What you have seen is a tiny proportion what's been shot and an even
tinier proportion of what's been shot at the limits of resolution.

 

Of course it does. Look up edgfe sharpness.

 

Well in area it is about 39%. But so what, are you saying that you only
need to do all the things you outlined to get the full frame sharp?
that if you hand held the shot and used a slower shutter speed and did
not use a strobe that the center of the film shot would be sharp but
not the edges?

Scott

 

And, I neglected to add, that all of those steps are cumulative in terms
of results. Each step resulting in yet finer detail.

Poor light? What are you talking about? ISO 200 f/9 for 1/250 is just
1.3 stops from sunny-16. That would make it, probably, a mid day shot
with high, not very thick cloud cover or lots of low cumulus and open
sky with the sun hidden. At that the highlights look washed out, so
that 1/3 stop was probably not needed ... more like EV 14.

1/250s with a 50mm lens is hardly setting up a tough handheld shot. And
for that matter, even reduced as shown does not look particularly sharp.

 

No. See my other post. And what I meant is the there are a lot of
exceptionally sharp film images that have been made. You haven't seen
many of them.

 

It was diffuse light, which tends to make things look dull.

This is not a reduced image, that is a 100% crop would should be
compared to a 4000 ppi scan.

Sure 1/250 with a 50mm lens is not hard, that is the whole point. You
gave a list of requirments for getting a sharp film image that was
pretty exterme, like locking up the mirror and using a strobe if
posible.

So let's see your 100% crop when you have done everything right and see
how it compares.

Scott

 

Well since this thread is about the sharpness of a scanned film image
it should be easy for you to show me a link to one of these images.
Again I am looking for an image that is sharp when viewing at the pixel
level at 4000 ppi.

Scott

 

But certainly not "poor" light. Difuse light is quality light and in
this case sufficiently bright.

No, I listed the chain to maximize detail. Each step leads to greater
and greater detail.

Of course that's how you get full detail on film at a level that an 8
Mpix sensor cannot.

Sure. I probably have several. But I'm not exercizing this mutt for
that purpose alone. Next time I have the right film in the Maxxum 9 and
I have the studio setup, I'll shoot frames just for this purpose.