It is consistent, but there is no discussion of what how to decide what resolution to use. All the discussion provides is figures for maximum actual resolution obtainable from various different scanners. That is actually two different subjects...
selmslie wrote:
Based on my own observations of extensive use of a V750 scanner I have found that it is optically limited to about 2400 DPI. That's great for medium and large format film and prints but it generates an image of under 8 MP from a 35mm slide or negative. That's enugh to produce an 8x10 print at 300 DPI. Doubling the scanner resolution setting quadruples the megapixels and file size but does not produce a visible improvement in resolution.
On the other hand, a dedicated film scanner is likely to produce a genuine improvement in resolution based on a higher optical resolution. I use a Nikon Coolscan 9000 for 35mm and medium format that generates a legitimate resolution of 4000 DPI, over 21 MP for 35mm and about 70 MP for 6x6. There are other dedicated film scanners that can produce resolutions of 3200 DPI (nearly 14 MP) as well as some expensive scanners that will scan film at 6000 (48 MP) or 7000 DPI (65 MP) or more.
Nevertheless, the best film I can get my hands on is still good for only about 21 MP from a 35mm negative.
br Based on my own observations of extensive use ... (
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All of which is to say, that as suggested in previous articles the ideal scan rate to produce 8x10 prints from a 35mm slide would be a minimum of 4800 DPI. It is, granted, a good point to add that any given scanner many not actually be able to produce an image with 4800 DPI resolution despite settings for even higher resolution. The question then becomes one of does it actually make any difference, and if so what does it take to benefit from setting a higher scan rate?
The cited article helps only with listings of the maximum actual resolution, but doesn't provide any discussion of the topic past that. A specific discussion about what resolution to use can be found in a
PDF document from Plustek, which also references another document from the Federal Agencies Digitization Guidelines Initiative Still Image Working Group. Plustek recommends, "Going by these specifications, it means that you should scan at a minimum of 3600 dpi on a Plustek
OpticFilm 35mm scanner."
Note that both Plustek and the previously cited article mention SilverFast scanning software. Not on that specific page cited, but elsewhere on that site there is more information about what SilverFast software does to produce better scans. But there unfortunately is not a generic discussion of what else can be done to optimize scanning for different purposes.
Regardless of which scanning software is used, scanning at better than 4800 DPI produces files that can be post processed for the best results for any given purpose. That is true primarily because the maximum resolution of 35mm film can reasonably be assumed at about 2400 DPI. The resulting output file from the scanner may or may not actually be able to produce resolution equal to 4800 DPI, but for a 1x1-1/2 inch scan area it will produce a 4800x7200 pixel image that can be used, at 240 PPI or more for printing at 20x30 or smaller without re-sampling to a larger pixel dimension. Obviously it will need to be re-sampled to a smaller pixel dimension for sizes like 8x10. That is where the benefit from oversampling with the scanner comes in. Ideally one would not use an Adobe software, all of which use Bicubic Sharper, for re-sampling. Nor should it be left to the print driver, which might even be worse. Something like the tools from ImageMagick package, where a wide range of different filters are available, is optimal. For most images using a Lanczos filter or a RobidouxSharp filter would be acceptable.
There is a lot more to getting the ultimate scan from an image than is easily found even with Google. Some of it is obvious, some is not. Obvious: a slide copier mounted on a Nikon D800 or D810 camera will produce a better image file than virtually any scanner for the same price. The 7360x4928 pixel file is essentially a 4928 DPI scan.