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Thread: side by side comparison... large print digital back VS 4x5 color film

  1. #51

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    Re: side by side comparison... large print digital back VS 4x5 color film

    Quote Originally Posted by willwilson View Post
    It sounds like there are many parallels to digital audio at work here, but with some optical twists. In essence we are talking about the fundamentals of digital sampling. In the digital audio world an anti aliasing-filter cuts out the garbage that is out of the range of the sampling frequency. This reduces noise that would be introduced by audio signals above the sampling frequency. It seems the aperture of a scanner serves the same purpose, at least it appears so from the scans Lenny posted a link to.
    I think this is a good analogy, only small distinction is an anti-alias filter prevents higher frequency signals from folding into the sampled data and masquerading as an in band signal. If we sample at 20K samples / sec we must cut off all frequencies above 10KHz to prevent them from aliasing down into the in-band signals. That is, a 12KHz tone would end up being sampled as a 2KHz tone if not for the anti-alias filter. I am sure this is what you meant by the above, I simply am amplifying to it.



    Quote Originally Posted by willwilson View Post
    Are drum scanners oversampling up to the mechanical limits of the machine (38,000 samples for every 1/16,000th of an inch)? Where the aperture is determining the frequency of oversampling by controlling the physical size of the sample area?

    Doesn't the scanner have to be scanning every grain more than once or it would not be able to decipher individual grains. At a minimum, you must be taking samples at twice the frequency/size of the smallest grain you would like to render accurately, correct?
    To continue the anti-alias filter concept, I suspect the camera lenses we are using act as such a filter. The really high frequency components that would cause alias problems are stopped by our camera lenses. At the scanner one can push the aperture down and down into the single micron range but the film (at least commercial film and not 'spy' film) has nothing more to give up other than the grain or grain clumps (or whatever the term). This is my theory on the subject feel free to take it with a grain of silver.

    Quote Originally Posted by willwilson View Post
    Wouldn't a higher bit depth substantial increase the accuracy of scanning? 8-bits is only 256 possibilities. That is not very many in the digital sampling world. 16-bit is 65,536 possibilities. Shouldn't scanning at a higher bit depth lower the noise within the sample, as well?
    It should, that is the signal to noise ratio (SNR), should improve as bit depth increases otherwise the added bits are totally meaningless. PMT's do have some noise associated with their operation. The interested student is encouraged to check the Hamamatsu site for some interesting reading on PMTs. Including photon counting with PMTs.

    Best,

    Tim

  2. #52
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    Re: side by side comparison... large print digital back VS 4x5 color film

    Quote Originally Posted by Tim Povlick View Post
    Actually a Stochastic process can be completely deterministic.
    A stochastic process can be completely random. But if a process is deterministic, it is by definition not stochastic. It's been many years and my old statistics books were sold off years ago. But I don't remember any definition of stochastic that didn't include some level of randomness.

    That said I suspect that eventually a stochastic process could give the same result as a deterministic process if that's what you mean.

    Quote Originally Posted by Tim Povlick View Post
    I think our biggest challenge is getting the silver exposed to interesting subjects and developed correctly (at least for me).
    Well there's something we can certainly agree on without reservations! We're discussing the technical minutia of the easy part of photography here. The hard part is finding and capturing the interesting subjects. I've been working one scene for at least six years now. I never can seem to show up when everything is ready for a photograph. That scene is beginning to bug me -- it's caused too many sheets of film to hit the trash can. Sigh...

    Scanning a poor photograph can't make it a good photograph no matter how high the scan quality is.

    Bruce Watson

  3. #53

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    Re: side by side comparison... large print digital back VS 4x5 color film

    FWIW...The result of a stochastic process in all but trivial cases is a random variable(s). Thus, it is not deterministic. However the parameters of the resulting random variable(s) can be deterministic. For example, the expected value of the stochastic process can be deterministic (but it can also be a random variable itself).

  4. #54

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    Re: side by side comparison... large print digital back VS 4x5 color film

    A comment on the original topic... Based on Tim Vitale's article (which is worth reading) the approximate digital resolution of 4x5 Tmax 100 would be 9,700x12,200 pixels if your lens could resolve 70lpm. That's 118mp. This would equate to a 30"x40" print at 300dpi. Lenny, how do you get 320mp off of 4x5?

    I would like to see a valid large print (30x40+) comparison as well; maybe 5DII, Phase One P65, and Top quality Drum Scanned 4x5 Tmax 100 and Velvia.
    Will Wilson
    www.willwilson.com

  5. #55

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    Re: side by side comparison... large print digital back VS 4x5 color film

    You can get (roughly) a 320 mp file from 4X5 by scanning at 4000 spi.

    How much of that is useful pixels is debatable. My experience is that there is no gain from scanning at more than the effective resolution of the camera/lens/film system. Scanning at 4000 spi suggests that the scanned material has the equivalent of about 80 lines per millimeter of information. 80 llines per mm on 4X5 may possible in certain specific conditions, but in most practical situations one is very lucky to get as much as 50 lines per mm on film, which is about 2400 spi. That gives a file of about 115 mp, which IMO is about as many effective mp one can get from 4X5 format.

    Sandy King

    Quote Originally Posted by willwilson View Post
    A comment on the original topic... Based on Tim Vitale's article (which is worth reading) the approximate digital resolution of 4x5 Tmax 100 would be 9,700x12,200 pixels if your lens could resolve 70lpm. That's 118mp. This would equate to a 30"x40" print at 300dpi. Lenny, how do you get 320mp off of 4x5?

    I would like to see a valid large print (30x40+) comparison as well; maybe 5DII, Phase One P65, and Top quality Drum Scanned 4x5 Tmax 100 and Velvia.

  6. #56

    Re: side by side comparison... large print digital back VS 4x5 color film

    Yes, this is a very misunderstood topic. Scanning for more resolution than the camera/film system can deliver is proving dubious with experience. Beyond that it gets back to grain representation. Then how is that definition delivered? In the case of a drum, despite common thinking, it's the aperture not file size. Up to a point of course.
    Then, to get to a big print, how one gets to the printer native ppi is the real question. More physical sampling from the scanner, higher than that native for the chosen aperture? Rezing in editing software? Letting the print driver or RIP do it?
    Lot's of interesting stuff here-
    http://www.ddisoftware.com/qimage/quality/
    I've drawn no conclusions from that yet, but a few tests show the presentation is viable.

    Tyler
    http://www.custom-digital.com/

  7. #57

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    Re: side by side comparison... large print digital back VS 4x5 color film

    Quote Originally Posted by sanking View Post
    You can get (roughly) a 320 mp file from 4X5 by scanning at 4000 spi.
    How much of that is useful pixels is debatable. My experience is that there is no gain from scanning at more than the effective resolution of the camera/lens/film system. Scanning at 4000 spi suggests that the scanned material has the equivalent of about 80 lines per millimeter of information. 80 llines per mm on 4X5 may possible in certain specific conditions, but in most practical situations one is very lucky to get as much as 50 lines per mm on film, which is about 2400 spi. That gives a file of about 115 mp, which IMO is about as many effective mp one can get from 4X5 format.
    Sandy King
    Sandy,
    I think useful pixels is certainly debatable. However, my experience doesn't match your conclusions. I think the difference may be in the scanner, or more specifically, PMT's vs CCD's. However, if you are correct, then an Epson 750 at 2400 would yield the same file as a top drum scanner (or even a Cezanne). I just don't see this to be the case. Every time I look at a scan from these animals, they don't match up.

    Maybe I am wrong. Do you have a test negative that you use to determine this? I would be happy to scan it here at different resolutions and put it to the test.

    That said, I am reminded that I am always frustrated by these tests. Resolution is one thing. Sensitivity, pixel by pixel, is quite another.

    And just in case you are wondering I'm not trying to piss you off - I sincerely would love to know the answer...

    Lenny
    EigerStudios
    Museum Quality Drum Scanning and Printing

  8. #58

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    Re: side by side comparison... large print digital back VS 4x5 color film

    "However, if you are correct, then an Epson 750 at 2400 would yield the same file as a top drum scanner (or even a Cezanne). I just don't see this to be the case. Every time I look at a scan from these animals, they don't match up."

    Lenny,

    Absolutely not. I am not saying that at all, and indeed am surprised at your confusion. I think we agree that some scanners deliver more real, effective resolution than others. Drum scanners, if calibrated, should deliver close to 100% of stated optical resolution. My EverSmart Pro delivers close to 95% of stated optical resolution. Most consumer flatbed scanners, Epson 4990, Epson V750, etc. deliver only about 40% of stated optical resolution. You can test this by scanning a high resolution target: you may have a pixel count of 4800 spi, but the effective resolution would be only about 40% of this, say about 40 lp/mm.

    It is not a question of PMT versus CCD technology in the least. It is simply a question of understanding the fact that all pixels are not equal in terms of their detail/resolution. The concept of a "useful" pixel is only debatble if one has no understanding of what "useful" is.

    Sandy King



    Quote Originally Posted by Lenny Eiger View Post
    Sandy,
    I think useful pixels is certainly debatable. However, my experience doesn't match your conclusions. I think the difference may be in the scanner, or more specifically, PMT's vs CCD's. However, if you are correct, then an Epson 750 at 2400 would yield the same file as a top drum scanner (or even a Cezanne). I just don't see this to be the case. Every time I look at a scan from these animals, they don't match up.

    Maybe I am wrong. Do you have a test negative that you use to determine this? I would be happy to scan it here at different resolutions and put it to the test.

    That said, I am reminded that I am always frustrated by these tests. Resolution is one thing. Sensitivity, pixel by pixel, is quite another.

    And just in case you are wondering I'm not trying to piss you off - I sincerely would love to know the answer...

    Lenny

  9. #59
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    Re: side by side comparison... large print digital back VS 4x5 color film

    Quote Originally Posted by sanking View Post
    You can get (roughly) a 320 mp file from 4X5 by scanning at 4000 spi.

    How much of that is useful pixels is debatable. My experience is that there is no gain from scanning at more than the effective resolution of the camera/lens/film system. Scanning at 4000 spi suggests that the scanned material has the equivalent of about 80 lines per millimeter of information. 80 llines per mm on 4X5 may possible in certain specific conditions, but in most practical situations one is very lucky to get as much as 50 lines per mm on film, which is about 2400 spi. That gives a file of about 115 mp, which IMO is about as many effective mp one can get from 4X5 format.
    My experience suggests that there is a little to be gained from scanning at more than effective resolution of the camera/lens/film/processing system. If, that is, you are printing somewhat bigger.

    For example, if you want to make that 50 x 40 inch print from 5x4 film. You could scan at full file size. Or, you could scan at effective resolution which would give you say a 40 x 32 inch print, and then uprez to 50 x 40 inches.

    The little bit to be gained here is the elimination of the uprez step. Because every step that requires some shuffling of pixels to some extent looses some information.

    Now is that little bit of gain visible in the final print? YMMV. On the other hand, once you've got the film on the scanner, why not? Again, YMMV.

    Bruce Watson

  10. #60

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    Re: side by side comparison... large print digital back VS 4x5 color film

    Anyone care to comment on how the a sampling frequency of between 2600 and 4000 ppi can be the wrong match for the grain structure of specific films? I've run up against grain aliasing/moire with color print films like NC and Portra which seems to amplify the appearance of their grain structure. Wouldn't this make a strong case for sampling at higher ppi--even if there were no gain in line pair or edge resolution to be found?

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