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Thread: Camera scanning: conservator's perspective

  1. #11
    Randy Moe's Avatar
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    Dec 2011

    Re: Camera scanning: conservator's perspective


    Thank you!

  2. #12
    Join Date
    Jan 2001

    Re: Camera scanning: conservator's perspective

    Quote Originally Posted by rdeloe View Post
    More pixels per grain clump is better, if your objective is to record grain clumps, so if you’re scanning a fine grained film (say 15 micron grain clumps), a resolution of 5,080 ppi will allow for 3 pixels per clump. At the other end, at 6,000 ppi, you’ll be able to cover each 25 micron grain clump with around 6 pixels. So yes, it seems that 6,000 ppi not only can preserve the grain structure of most black and white films, but do it with more useful detail.

    However, depending on the film and how much detail you want in recording the grain clumps, lower resolutions might do the trick too. From this perspective, it seems the people who came up with that FADGI 2016 standard of 4,000 ppi are happy having two pixels cover each 15 micron grain particle – because that only needs 3,387 ppi.
    No. You are correct about the fact that we're discussing grain clumps, but you are way underestimating the resolution required to accurately "describe" film grain. 6,000 ppi gets you in the ballpark for Tri-X. It is most definitely not sufficient to "preserve the grain structure of most black and white films".

    One important factor you're overlooking is the effects of discrete sampling of grainy originals. Because of that, increasing resolution can sometimes actually make a scan look worse before it starts to look better. This is where the concept of "aliasing" comes in. My point about grain aliasing was that the particular mix of ~4000 ppi and Tri-X grain is a "sour spot" where the interaction between the sampling frequency and the image structure of the film makes the scanned image look distinctly worse than the original - the grain is larger and uglier than it is in the negative. For some of us who consider the grain structure an important part of what gives Tri-X its personality, or whose conservation objectives include preserving all of those attributes that make a material contribution to the esthetic character of the film, a scan at that resolution more or less ruins it.

    At substantially lower resolutions the grain mushes out entirely. Users who are comfortable with that can sharpen the resulting scanned image and be happy. At substantially higher resolutions you get into the range where there's enough descriptive power to faithfully record the fine image structure. But the FADGI standard for films up to 4x5 is just wrong for a film like Tri-X, if the objective truly is faithful reproduction.

    4000 ppi is treated as something of a magic number because that's the highest resolution that's widely available in consumer-grade equipment at prices that many amateurs can afford. But the reality is that those of us whose budgets limit us to equipment of that caliber, yet who are hoping to mimic the character of our silver gelatin enlargements in our inkjet prints from film scans, basically can't have what we want. I include myself in that group, with regret.

    "Scanning" with digital cameras adds the further complication that the vast majority of such devices use sensors with Bayer or X-Trans color filter arrays, which force interpolation in raw conversion and which mean that the actual resolution recorded in the capture falls substantially short of what you'd suppose just by counting pixels. Live-view focusing limitations pose further challenges in achieving even that.

    Now it's plain that most folks who print from scans and who are using flatbeds, dedicated film scanners or digital cameras to capture their scans aren't trying to reproduce the fine image structure of their originals, and are comfortable with low-resolution scans that are sharpened to taste for purposes of printing. In some cases they recognize the aliased character of medium-resolution scanned grain from high-speed films, and they're OK with it. There's nothing wrong with any of that. The broader lesson I would draw here is simply that it's a mistake to try to figure out how much capture resolution is sufficient, just by counting scanner PPI or digital sensor pixels or even line pairs on a test target and then doing the arithmetic to see how that maps to prints at 300 or 360 or 720 ppi. Discrete sampling and color filter arrays do complicated things to image character and make simple arithmetic on nominal resolutions or pixel counts seriously misleading.

    Instead, you try the kinds of equipment that are available at a price you can afford, look at the resulting image character and decide what you're comfortable with and what kinds of tradeoffs of cost, practicality and convenience vs ultimate image character you're prepared to make. This is, in effect, what both you and Peter have done - each of you has arrived at solutions that work for your respective purposes by applying your experience, your judgment and your common sense to the actual results you've achieved with various types of scanning equipment.

    If you're responsible for teaching this stuff, stay away from the bogus arithmetic and concentrate on demonstrating how to optimally use the available equipment to acquire scans, how to process scans with skill and good judgment for printing at desired sizes, and how to evaluate the results relative to esthetic objectives, and all will be well.
    Last edited by Oren Grad; Yesterday at 21:03.

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