Scanning resolution advice, please

[Rupert49]

I've just got my first scanner (an Epson V500) up and running and I've been feeling my way around the various menus and options. I scanned a picture of a cat from a magazine page to assess for myself the resolution on my monitor (the magazine picture looked particularly sharp so I thought I might view fur and whiskers at hi-res to assess results).

I started with settings of 24-bit at 1,200 dpi but when I tried to open the resultant jpeg it said the file (24MB) was unopenable or might have been damaged or corrupted - why was this do you think?

I tried again at 720 dpi and the resulting scan was successful and looked pretty good to me (jpeg file size had reduced to 7.4MB in the process).

I've already discovered that scan times are dependent on the resolution setting, so when it comes to scanning old photographs for eventual digital aftercare, what would you suggest is the optimum resolution setting I might use to produce decent quality photographs from the jpegs generated by the scanner?

Another learning curve here I know, but I catch on pretty fast!
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Rupert

[Norman]

Generally I'd use the highest resolution your scanner supports, this will capture the maximum amount of data available. If scan times, disk space or processing power means this is problematic then calculate the print size you want and do the maths. If the original print size is 4" X 6" and you want to print it as a 8" X 12" then you need 2400px. X 3600px. if you print at 300ppi. So 3600px in a 6" length requires a scan resolution of 600ppi.

[Fen]

I don't scan any old photographs less than 600dpi

That's normally good enough for all for all restoration work.

[Rupert49]

Generally I'd use the highest resolution your scanner supports, this will capture the maximum amount of data available. If scan times, disk space or processing power means this is problematic then calculate the print size you want and do the maths. If the original print size is 4" X 6" and you want to print it as a 8" X 12" then you need 2400px. X 3600px. if you print at 300ppi. So 3600px in a 6" length requires a scan resolution of 600ppi.

Thanks Norman. As my scanner supports up to 128,000 dpi I guess I'm going to have to find a sensible middle ground - I dread to think how long a scan at that resolution would take! 600-720 dpi seems to be a suitable level judging by yours and Fen's responses.

Any idea why the jpeg file scanned at 1,200 dpi produced a '...appears to be damaged or corrupted' message and wouldn't open?
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Rupert

[Rupert49]

I don't scan any old photographs less than 600dpi

Thanks Fen, I'll follow your lead and see how things go
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Rupert

[Norman]

As my scanner supports up to 128,000 dpi I guess I'm going to have to find a sensible middle ground

That will be an output resolution. It's optical resolution is 6400. If you go higher than that then the results will be interpolated.

[Zou]

If scanning from prints/magazines I don't bother with more than 1200dpi as the resultant file sizes are much bigger than I personally would need. If scanning 35mm film, I go for 4800 as it is the best I can get from my scanner, but for 120 film 2400 is plenty, and for 5x4 1200 does the job (anything larger becomes ridiculously large when opened and layered in PS).

[Rupert49]

Cheers Zou, I appreciate your advice and guidance
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Rupert

[LargeFormat]

There is no point in scanning at a resolution that is higher than the information that can be resolved. The most that can be resolved on film is about 4000 dpi. That would be a top lens on fine grain film. On 4x5 that would give an inordinately large file (360MP or a 66" print at 300dpi)so, say 2400 dpi, scans will be likely to be enough and able to be handled by ones computer.

A print will generally be about 300dpi so scanning at, say, 600dpi would give plenty of lattitude. Magazines and other halftoned images would contain even less information.

Scanning at higher resolutions will not create information that isn't there.

[Rupert49]

A print will generally be about 300dpi so scanning at, say, 600dpi would give plenty of lattitude

I have yet to purchase a photo printer (I'm still weighing up the pros & cons - it's currently between Epson R800 or P50) so I am as yet unfamiliar with the resolution options when printing vs. those used when scanning, they would seem to be different things altogether. Is there a simple handy resource that might explain the various terminologies used when learning about scan resolution and print resolution?
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Rupert

[Roy5051]

Scanning and screen resolution is "pixels per inch" and printing resolution is "dots per inch". It is perfectly feasible to have a picture on your computer at 300 pixels per inch and print it at 4800 dots per inch. There is probably a lot more theory than this, but this keeps it simple, and has served me well for years.

[Rupert49]

Scanning and screen resolution is "pixels per inch" and printing resolution is "dots per inch". It is perfectly feasible to have a picture on your computer at 300 pixels per inch and print it at 4800 dots per inch. There is probably a lot more theory than this, but this keeps it simple, and has served me well for years.

Thanks for this simple aide memoire Roy; until I find out a bit more this would seem to be a pretty straightforward rule of thumb.
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Rupert

[pilliwinks]

A print will generally be about 300dpi so scanning at, say, 600dpi would give plenty of lattitude. Magazines and other halftoned images would contain even less information.

Scanning at higher resolutions will not create information that isn't there.

If I've done the calculation correctly, 300 dpi works out at about 5-6 lppm. At least some printing papers are capable of much higher figures than that, from what I've read. Ctein puts some at 10 times that figure.

The higher figures will depend on the paper surface; and it's perfectly possible that the degree of enlargement of the negative means that this figure can't be meaningfully realised. But in the case of contact prints from large negatives, it seems to me that scanning at 600 might lose some detail that is there.

I'm not saying that 600 isn't adequate; just that you can't necessarily adopt a one (scanning) size fits all.

[Roy5051]

I think Rupert49 was referring to scanning prints, not negatives. Scanning a print at 600 ppi gives adequate room for enlarging/cropping without losing too much detail. Scanning negatives is a different ball game. Most scanners with a negative-scanning function will scan at about 2400 ppi, which will give a file size of approx 25MB from 35mm film (2400 x 3600 pixels = 8437.5 pixels x 3 RGB = 25.31MB) giving a print size of 12"x 8" and 300ppi - adequate for A4 prints.

[pilliwinks]

I was also referring to prints - hence my remark about the resolution of printing papers. My point was that in some cases, 600 would lose details. Anyone care to comment on if the Nyquist limit comes into play here, and we need 1200 to get 600 actual?

[Roy5051]

Printing a 600 ppi picture is unnecessary, even magazines only ask for 300 ppi to get magazine quality pictures. In fact, pictures of lower than 300 ppi can easily be printed to give adequate detail at normal viewing distances. There is too much supposed "science" being bandied about about detail in printing - I must admit to not knowing what Nyquist is (I bow to your greater knowledge), only that I have printed many pictures over the past ten years, using a MAXIMUM ppi of 300, and printing at 2400-4800 dots per inch on the printer. This gives good detail from normal viewing distances.

[Roy5051]

As an addendum, we are getting into the muddle of "pixels per inch" and "dots per inch" AGAIN!

Pictures on your computer have a resolution measured in "pixels per inch". Pictures printed on paper have the resolution that the printer can output in "dots per inch". As I have said many times before, it is quite feasible to print a picture with a screen resolution of 300 pixels per inch at 4800 dots per inch on a printer.

[pilliwinks]

Printing a 600 ppi picture is unnecessary, even magazines only ask for 300 ppi to get magazine quality pictures. In fact, pictures of lower than 300 ppi can easily be printed to give adequate detail at normal viewing distances.

Sorry - you lost me here. I thought that the point under discussion was scanning prints, and I admit that I assumed that darkroom prints were meant. Here the resolution is in excess of prints produced at 300dpi on an inkjet printer. Or can be in some cases .

I don't see where the "printing at 600 dpi is unnecessary" comes in to this.

[Roy5051]

Sorry, I must have misread your post. I agree that darkroom photographs probably have more detail than 300ppi, but in my experience it is almost impossible to convert all that detail into a digital file, even using a higher scanning resolution, on a normal flatbed scanner. Also, the file sizes would become unwieldy; and printing them out again on an inkjet would not necessarily retain all that detail. I do not know why this is, but it is probably something to do with the way an inkjet printer works. In normal circumstances, if you scan at 600dpi, there is enough latitude to enable a similar size print to be made after manipulation/cropping with adequate detail.

[Rupert49]

Good grief! I seem to have stirred up a bit of a technology hornet's nest here, although I'm grabbing the wisdom laden pearls as they apply, so thanks to everyone for getting involved in this discussion.

To recap, I have a V500 flatbed scanner, no printer as yet (R800 and P50 under serious consideration .. any views anyone?) and I shall mostly be scanning darkroom prints. However, depending on the scan quality of 35mm negatives, I may do some of those as well, although I don't think I'll be embarking on a total digital archiving exercise (I can't afford a CoolScan, neither do I think it's necessary - I have the negatives after all, and that's what we in this digital age are most precious about).

Just to throw in a flanker to the dpi/ppi discussion .. how does a printer's droplet size affect the final print quality? Most printer technical specifications proudly proclaim the virtues of a 1.5 picolitre droplet size, so to an uninitiate like myself it would seem to make sense to go for a printer with the smallest droplet specification, among the numerous other considerations of course.
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Rupert