What resolution to scan at?

[Philippe Debeerst]

Hallo,

Perhaps this item might have been discussed over here, but I could not find the right answer in the postings, or my English isn't just good enough to understand the comments...

So, I have a Epson V750 with the fluid mount accessory, of which I am very well satisfied. The scanning software is SilverFast v6.6.2r5 on a Mac Pro OSX 10.6.8 platform.
Right now I am mainly scanning B&W negs coming out my Linhof Technorama 617 II, a wonderful camera BTW.
I set the scanning scale at 350% what gives me an output format of +/- 61 cm long at 360 dpi and files of about 50MB in 16 bit gray. While pushing the ctrl key (MAC), the resolution is shown as 1600 dpi, I suppose that is the resolution as would it be set at 100%, right?
The format of 61 cm long and 21 cm high suites me perfectly, these photo's will never be printed larger (why should they?).
Now my question: everywhere I reed about scanning at 4200 dpi (= at 100% ?) and higher, does this means than the final scale compared to 360 dpi will be far more than twice the scale of 350% cm, I am working on now, which would be about 900% scale (at 360 dpi) then?
If so, what's the purpose of scanning at these high resolutions, if not for larger reproduction scales (unwanted) and hard to handle large file sizes?

I have a feeling that I must be overlooking something somewhere...

Anyway, thanks for the replies!

[Kirk Gittings]

The scanner is really not capable of real optical resolution gains above 2400 SPI (my tests on mine don't support that high of a real optical res.). So I wouldn't bother scanning above that for resolution improvement. There is some slight evidence that scanning at the higher resolution and then downsampling can give you better shadow noise. This can be preset in Vuescan but I don't remember how.

[Doug Fisher]

I would scan at 3200 ppi just in case you have an example of the V7xx that is able to exceed 2400 ppi. Some are capable of exceeding 2400 by a modest amount. It sounds like you might be unclear in regard to scanning ppi (dpi) and output dpi. My quick answer is to scan at original size and 3200 ppi, but for a better understanding of why, I would suggest working through the excellent free tutorials at Wayne Fulton's www.scantips.com website. His tutorials help clear up this confusing topic.

Doug
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www.BetterScanning.com

[paulr]

There is some slight evidence that scanning at the higher resolution and then downsampling can give you better shadow noise. This can be preset in Vuescan but I don't remember how.

It's actually a well established phenomenon. If you don't mind the extra time it takes to do a scan, oversampling will give you better results as far as noise, which can have an impact on useable resolution and on the sharpenability of the final file.

My 4880 has a sampling frequency of 4800 dpi, and a useable optical resolution (established by my own very unscientific tests) of around 2200 dpi. So I scan at 4800 and have Vuescan downsample to 2400. This avoids odd interpolations ... the software is basically taking the actual pixels produced by the ccd and averaging each block of four into an image pixel. I end up with a small amount of excess file size, but I know there aren't going to be any interpolation artifacts.

I like letting Vuescan deal with the downsampling, because it's automated in the background. I don't have to fuss around with oversized files in photoshop.

[lbenac]

The scanner is really not capable of real optical resolution gains above 2400 SPI (my tests on mine don't support that high of a real optical res.). So I wouldn't bother scanning above that for resolution improvement. There is some slight evidence that scanning at the higher resolution and then downsampling can give you better shadow noise. This can be preset in Vuescan but I don't remember how.

I scan 4x5 at 3200 dpi and do not downsample just because of the time it takes.
On MF I scan at 6400 dpi (first tab in Vuescan) and downsample to 3200 dpi (Output tab reduction factor of 2)

Cheers,

Luc