Can multiple scans increase resolution?

[Lenny Eiger]

A scanner does not take a picture of the image that's really small. These samples are not images. They are numbers, generally an RGB value.

If the sample size matches the size of a grain clump (no scanner can see actual grains) then it can convert the clump to a representative number, and write that to a file.

If you do this again, and nothing moves, or is ever so slightly out of alignment, then you should get the same number. If you don't, then how does one know if the first number was correct, or the second one? Should they be averaged?

I could see a system that maps the whole image, clump by clump, and keeps this in a database, then samples it over and over, and then does an average. That might work, but none of the scanning software is that sophisticated. I could see a system that would deliberately map each grain clump, sample the center of it, then each of the edges, etc. and create multiple samples per clump, increasing the pixel count by 4 or 6. this would increase resolution, maybe.

Drum scanners do best when the clump size and the sample size match. If they are out of alignment they sample the same clump twice, its off-kilter and two values are written that are very close, and you get grain anti-aliasing, which looks like pixel partial overlap, or grainy, whatever you want to call it. One also has to remember that the grain clumps are not all the same size, that maybe 70 or with luck and development with good developers (not D-76 or other solvent type developers, or highly over-active like Rodinal), 80 per cent of the grains are the same size. That means 20% will have improper samples no matter what you do.

No matter how many times you scan, all you will be able to do is average the values. Averaging usually doesn't increase resolution, quite the reverse. Including averaging with stacking.

I don't think this has any way of succeeding. Scan samples aren't pixels. They are numbers.

Lenny

[fishbulb]

Hi Lenny, recognizing that you know a lot about scanning, what are you thoughts on why it appears to work (increasing resolution with multiple scans) at least in these two examples?

http://photo.net/film-and-processing-forum/00b6OH (upper left vs. upper right in this image)
http://www.rangefinderforum.com/foru...d.php?t=130731 (this image vs. this image)

[paulr]

Lenny, the reason it can work is that optics degrade an image by spreading (blurring) points and lines. A binary pattern degrades into a sinusoidal function that transitions from pure white to pure black over a distance that could be many pixels, or less than one.

In either, moving the the target sub-pixel distances will change the recorded value of that pixel location. The direction of motion can be extrapolated, and this information can be used to reconstruct that spread function on a sub-pixel scale. It's a kind of virtual oversampling.



(from Wikipedia) Both features extend over 3 pixels but in different amounts, enabling them to be localized with precision superior to pixel dimension.

[Lenny Eiger]

Lenny, the reason it can work is that optics degrade an image by spreading (blurring) points and lines. A binary pattern degrades into a sinusoidal function that transitions from pure white to pure black over a distance that could be many pixels, or less than one.

In either, moving the the target sub-pixel distances will change the recorded value of that pixel location. The direction of motion can be extrapolated, and this information can be used to reconstruct that spread function on a sub-pixel scale. It's a kind of virtual oversampling.



(from Wikipedia) Both features extend over 3 pixels but in different amounts, enabling them to be localized with precision superior to pixel dimension.

I have a cold, and am having trouble putting two related words together, so excuse me if I don't follow exactly, or can't communicate what I think I see.

Looking at the graph, I can see that if you average the squares to the left and the right of A you might move it to be B. However, a scanner can not do All of the pixel of B with the edges. You are correct that the Area inside the square the B inhabits will record darker, but you won't get the edge effect. I suppose its another way of sharpening... and Photoshop can do some pretty amazing things. So I suppose some of it is possible... but its hard to believe you would get much and you might get a lot of false positives...

The main point I was trying to make is that its a number, not a pixel, that a scanner generates. It's a point on the drum (or flatbed glass), and not a part of an image. I suppose if you moved a grain clump to the center, as in B, you might get a better reading. But then you are moving it... Ayyyy, my head hurts...

Lenny

[BetterSense]

Lenny,

It's ok if you don't understand it. In some cases it is not intuitive. But your assertions that it cannot work are tiring, even aside from your meaningless comments about numbers not being pixels.

The mathematics of sampling signals are quite mature and oversampling, noise-shaping, filtering, and reconstruction algorithms that do what you say is impossible are in operation in millions of consumer devices and telecommunications technologies all over the world. Did you know that almost all CD players reproduce the 16 bit-depth PCM signal using a 1-bit DAC?

Taking many samples and averaging them can filter out noise, which can have a positive impact on reproduction, but nobody is arguing that it increases resolution. There are many other techniques to increase resolution beyond the "native" resolution of any of the components of the system though. In theory, one should be able to achieve almost arbitrarily high resolution and bit depth from e.g. a consumer flatbed scanner. The limiting factor is more likely to be noise and even that can be dealt with to some extent. Indeed, what's remarkable about high-quality scanners is not that they provide high-quality results, but that they do so quickly. Given that images on film do not move, and thus the only bandwidth constraint in scanning is the patience of the operator, these techniques should be exploited more.

[Kirk Gittings]

Taking many samples and averaging them can filter out noise, which can have a positive impact on reproduction, but nobody is arguing that it increases resolution. There are many other techniques to increase resolution beyond the "native" resolution of any of the components of the system though. In theory, one should be able to achieve almost arbitrarily high resolution and bit depth from e.g. a consumer flatbed scanner. The limiting factor is more likely to be noise and even that can be dealt with to some extent. Indeed, what's remarkable about high-quality scanners is not that they provide high-quality results, but that they do so quickly. Given that images on film do not move, and thus the only bandwidth constraint in scanning is the patience of the operator, these techniques should be exploited more.

Curious what your opinion is of what they are doing with PhotoAcute: http://www.photoacute.com/

[BetterSense]

Curious what your opinion is of what they are doing with PhotoAcute: http://www.photoacute.com/

It is impossible to say for sure since I imagine they are not publishing their algorithms, but multiple images can be combined in an oversample-y way with simple pixel math. How well it works depends on a number of boundary conditions. In a commercial product they probably expend more effort on checking those conditions and alignment etc.

[Lenny Eiger]

Lenny,
It's ok if you don't understand it. In some cases it is not intuitive. But your assertions that it cannot work are tiring, even aside from your meaningless comments about numbers not being pixels.

Why do the conversations here always have to turn into some sort of personal vendetta? Why do you have a need to tell someone their comments are meaningless? Get a life...

As to the issue at hand, I'm still listening. If this stuff was easy, I'm sure Adobe (and every digital camera manufacturer) would have done this years ago. We all would be happy for everything to have better resolution. I can see some part of it... just not all of it. I'm not stupid, and if the explanation was clear enough I could understand fully...

Lenny

[djdister]

So what everyone is talking about, I presume, is getting better resolution than the nominal max resolution of a given film scanner, right? No one is saying you can get better resolution in a digital file than what the film is capable of resolving, are they?

[Kirk Gittings]

Why do the conversations here always have to turn into some sort of personal vendetta? Why do you have a need to tell someone their comments are meaningless? Get a life...

They don't always but yes they do too often for sure. Part of it, I am convinced, has to do with anonymous posters and lack of consequences, but that is not always true either as evidenced by the many anonymous people here who are civil. Even when not anonymous there is a tendency to be more acidic than if one were physically standing in front of the person. I have been guilty of this myself and am trying to think before I write-ie "how would I phrase this if I were face to face with this person"........always a sobering thought.