Can multiple scans increase resolution?

[wombat2go]

Here are some numbers I am putting together for scanning 6x7 C41 with a PrimeFilm120 Pro
Scanner:
optical res = 3200 dpi >> Nyquist Pitch = 16 micrometre or 63 cycles/mm

Film:
Dye clouds are stochastic in range 1.5 to 10 um
The data sheet for Extar 100 give MTF of about 50 cycles/mm

Lens:
The MTF of a typical older manually focussed 6x7 camera/lens is in range 30 cycles/mm. 33 micrometre

I think (just opinion) that one issue is aliasing with the die cloud because the scanner Ny is in amongst the dye cloud range. When I scan 35mm C41 iso 800 I sometimes have unpleasant "graininess" but I think that is not directly visible dye clouds, it is artifacts of aliasing.
I do not see this effect so far on properly exposed Fuji or Kodak of iso 400, 160, 100

I think moving the image and taking multiple scans in some cases will be effective in reducing scanner artifacts ( film curve etc) but of course it can't improve the mtf of the film or the camera system.

As to moving the image by a pixel pitch, firstly that is difficult or impossible at the amateur level with a store bought scanner. Secondly,image alignment software works on the image data so should not be necessary provided the scanner Ny is sufficiently above the other components.

[Greg Miller]

My thinking is--based on nothing!--that you are combining two sharp images, with the final image being the same size as the uncombined version. And wouldn't being pixels vs film matter in this case?

Darin

I think there are flaws in the technique that was provided in the link. Here are the Photoshop steps that they describe (along with my comments):


Import all photos as stack of layers
Resize image to 4x resolution (200% width/height) (GM: introduces interpolation)
Auto-align layers (GM: introduces more interpolation; and auto-align uses warp so the interpolation will vary for any given area)
Average layers ((GM: Averaging interpolated pixels)

There's a lot of interpolation going on, so any actual increased resolution may appear OK, but is basically/potentially an improvement in up-res interpolation (would need to compare to a product like Genuine Fractals) and isn't technically very factual. Looking at their samples, I see increase in contrast and detail, but the detail is mostly exaggerating digital sensor artifacts. I don't see that as a positive, and I have to wonder how real any improvement is at actual real world viewing size.

[BetterSense]

So Bettersense, you are saying that the new Olympus E-M5 I I is a scam?

I have no idea. I know nothing about it or about digital photography period.

[paulr]

I played with photoacute for a few minutes. In my one attempt, using images made on a tripod with various long exposures (intended for exposure blending) it gave more resolution, but also a more processed look ... like too much noise filtering. It would take a lot more experimenting to come to a real conclusion, but so far it seems like more work than it's worth.

I'm glad someone's doing something with the idea though. Maybe we'll see a bigger variety of products like this someday.

[mdarnton]

I have no idea. I know nothing about it or about digital photography period.

Well, you certainly had a lot to say about it until I asked this question! :-)

[mdarnton]

I have no idea. I know nothing about it or about digital photography period.

Well, you certainly did until I asked this question! :-)

[paulr]

Here are some numbers I am putting together for scanning 6x7 C41 with a PrimeFilm120 Pro
Scanner:
optical res = 3200 dpi >> Nyquist Pitch = 16 micrometre or 63 cycles/mm

Film:
Dye clouds are stochastic in range 1.5 to 10 um
The data sheet for Extar 100 give MTF of about 50 cycles/mm

Lens:
The MTF of a typical older manually focussed 6x7 camera/lens is in range 30 cycles/mm. 33 micrometre

Not sure what any of these numbers mean. Do you mean MTF/50 at those resolutions? Or some other percent?

It's very difficult to come up with ideal scanning resolutions based on numbers and theory. Because the noise performance of film ultimately determines the highest useful sampling frequency. There's a limit to how much MTF you can recover through sharpening when the MTF drops close to the noise floor.

Most of the high resolution film scans I've looked at are oversampled by at least a factor of two or three. This is useful for reducing noise that's introduced in the scanning process (generally not much), but it does nothing to recover more actual image information. The result is that a lot of these 300 megapixel scans are functionally about as good as 30 or 40 megapixel scans.

[BetterSense]

Well, you certainly had a lot to say about it until I asked this question! :-)

I only know theory and practice of sampling data; I do not know about commercial/consumer tools currently available or how they work or how well they work in a given application.

One of the reasons I do not do more digital imaging is that I feel digital imaging is really advancing through creation of new tools, rather than anything done by those wielding the tools. This is similar to the way invention of new instruments is what really drives electronic music; the progress of imaging technology, more so than the people holding the cameras, is what drives digital imaging. The electronic musicians who are quite more involved in the creation of new instruments and techniques are rightly seen as the pioneers and creative core, while there are many others with ProTools on their laptops who are happy to take what's available and use it to essentially imitate that which they don't have the skill to do for real. Photography on the other hand does not even seem to have a group analogous to the first, except perhaps the developers of imagemagick and CHDK. Most real tool-creation happens behind closed doors at Adobe and Nikon et.al., and not shared in the community, and this in turn is a result of the industrial-industrial - age thinking that regards programmers as engineers rather than as artists.

[polyglot]

Yes you can, using superresolution. It requires that you deliberately and physically jitter the position of the film in the scanner between exposures and then combine them digitally. It specifically requires
that you do not align the film pixel-perfect for every exposure because you're trying to extract sub-pixel information; if the film were perfectly aligned and therewere no noise, you'd get no additional information in each scan.

You won't get more information than what is on the film though, so this is only valuable when scanning super-fine (Tech Pan etc) films on a low-res scanner. I believe PhotoAcute uses superresolution.

You can also use superresolution by taking multiple shots of the scene (multiple sheets of film). Easier to just use finer film though

VueScan multiple-scan does not do this but is a means of obtaining additional dynamic range and reduced scan noise.

[Darin Boville]

Well, I'm getting mixed results. I'm using a cheap office scanner and scanning book pages for the test. The processed scan looked a little soft but the unprocessed scan exhibited significant artifacts at 100%. (Looked like jpeg artifacts though I was saving to TIFF.) Those artifacts were gone in the processed version. Not clear if I was seeing any more resolution but the artifact reduction was significant. (I've never seen these artifacts on my Epson 700, fyi, so this may not be relevant to most people here.)

Will have to play with this more...

--Darin