Scanning slides - 4000, 2000 or 1200 DPI?
July 31, 2012 4:03 PM   Subscribe

Scanning slides - 4000, 2000 or 1200 DPI?

I'm going to use a company in Dublin to scan about 2,000 old slides dating from the 1960s to the 1990s. Prices per slide are €0.70 for 4,000 DPI, €0.55 for 2,000 DPI and €0.45 for 1,200 DPI, meaning quite a difference in cost overall.

I'll probably print out a few of the pictures in 'normal' sizes (i.e. not A4 or anything like that), and otherwise view them on a computer screen. Is the DPI resolution going to make much difference? Are there other numbers I should be paying more attention to?

Bonus question for anyone who has done this before - do those prices look reasonable to you?

Thanks!
posted by StephenF to Computers & Internet (7 answers total) 4 users marked this as a favorite
 
300dpi is a good resolution for printing a photo. Assuming a "normal" size maxes out at 5x7, you need an image of 1500px x 2100px to print it at 300dpi. A 35mm slide is approximately 1"x1.4". A 2000dpi scan would give you 2000px x 2800px, which is plenty for that size of print.

However, there are other considerations. For one thing, I believe it's dangerous to make assumptions about your future use of photos, especially if they are truly significant (historical, sentimental, etc.). Having the highest possible quality scan of them can be a good thing. It might be worth spending a bit more now to get the highest resolution scan, and then if you need it, you have it. If anything ever happens to the physical slides, you'd still have a best-possible digital representation of the photos.

On the other hand, depending on the quality of the slides, above a certain dpi, you're not going to be gaining any actual image data.
posted by primethyme at 4:14 PM on July 31, 2012 [1 favorite]


Absent a compelling reason to scan at a low resolution, I would scan at the maximum (i.e. native) resolution of your film scanner.

What would be the point of scanning at 1200dpi, only to decide later on that you want to make a bigger enlargement and have to go back and rescan? That's a pain.

You may find older resources online advising you to scan at a lower resolution. 10 or 15 years ago, people used to scan at low resolutions and then go back and rescan at higher ones, because storage was expensive. Many people considered it an acceptable tradeoff to only scan at 1200 dpi or lower, because that was okay for most uses, and then they'd just go back and pull the slide out of the box and rescan it if they wanted a higher dpi version. The storage vs. time tradeoff just worked out that way. But that's really not the case anymore, and unless you have an Imacon or some other drum scanner, you're not going to create files that even a moderately-priced home PC has trouble working with. So scan away at whatever your scanner can do.

The only reason I can think of to not use the highest resolution on your scanner is if takes a really long time -- some scanners take exponentially (or at least something-greater-than-linear) more time when you increase the resolution. I don't think this is really an issue with modern USB 2.0 or FireWire scanners, but it was an issue with some old SCSI-1 or USB 1.0 ones (and don't get me started about parallel port ones!).

It's true that depending on the kind of film you're scanning, you can be scanning at a resolution that's higher than the film grain, above which you are arguably not pulling additional information off of the slide. However, I personally think that "being able to zoom in and see film grain" is a good goal or standard when scanning, not something you should avoid or undershoot. And if you're scanning slide film with a tight grain, like Velvia, even a 4000dpi scan may not get you down to grain.

The real problem when you are scanning film is making sure that you're capturing the full dynamic range from the film. Many inexpensive scanners don't have a Dmax that's sufficient to get even common consumer films, especially slide films. So even if you scan at 4000+ dpi, be sure to save the slides and store them properly -- you may want to rescan them later with better equipment depending on application.
posted by Kadin2048 at 5:17 PM on July 31, 2012 [1 favorite]


These are 35mm slides, right? That is a lot of money. If you have the time, that figure would justify going to fleabay and getting a nice Nikon Coolscan slide scanner (I got mine for $A500), and diy - then resell the scanner. This would give good results on slide film, but you should expect a pro lab to do a good job too (you have had them do a few samples, including some 'problem' slides,haven't you?).

I am in the higher resolution camp generally, but here I would suggest a sorting process to grade the slides by whatever criteria suits, into basically one group which is highly likely to require high res scans, and the rest. Going back to do a smaller number of re-scans will probably cost less than doing all as high res initially, but you will have a better idea than us of the numbers involved - after that the math is simple.

In my case I was only interested in the slides with people in them, and I simply did not scan the rest - but I still have them if I need to go back and do some more.
posted by GeeEmm at 7:06 PM on July 31, 2012


Kadin2048:
Absent a compelling reason to scan at a low resolution, I would scan at the maximum (i.e. native) resolution of your film scanner.

What would be the point of scanning at 1200dpi, only to decide later on that you want to make a bigger enlargement and have to go back and rescan? That's a pain.
I could not disagree more. For example, the Canoscan 8800F claims to scan at 4800x9600 dpi (and claims it can interpolate detail up to 19,200x19200!!) but scans by the Canoscan 8800F only have an effective resolution of about 1600 dpi.

For comparison, my Coolscan 5000 is claimed by Nikon to scan at 4000 dpi. The Coolscan 5000 has an effective resolution of 4900x3650 dpi. Clearly, a whole lot close to what's being claimed.

Don't crank up the resolution (which cranks up the time and storage requirements [and thus the backup requirements]) in your scanner software if it's not going to give you the result you think you're going to get.

There must be a reason that used Coolscan 5000s are going for $2000 on eBay when used Canonscan 8800s can be found for under $100.

Don't scan at the maximum resolution of the scanner, scan at its highest effective resolution. Anything beyond that needlessly inflates the file size. This means you need to see if you're going to get 4000 dpi of detail. You might get 2500 dpi of detail at the 4000 dpi setting and you might get 1300 dpi of detail at the 2000 dpi setting.
The real problem when you are scanning film is making sure that you're capturing the full dynamic range from the film. Many inexpensive scanners don't have a Dmax that's sufficient to get even common consumer films, especially slide films. So even if you scan at 4000+ dpi, be sure to save the slides and store them properly -- you may want to rescan them later with better equipment depending on application.
Here I could not agree more. This is another reason that dedicated transparency scanners (e.g., Coolscans) cost more than flatbeds with a transparency adapter.

Also, Digital ICE will clean things up in a super automated way. (Danger, does not work with silver-based B&W [read: virtually all B&W negatives] and most scanners' Digital ICE won't work on Kodachrome. Color neg and you're in the clear.)

Now that talking shop about the DIY method is out of the way, it looks like Scan Cafe might be cheaper at €0.18 per 3000 dpi scan if you get their value kit, slightly more (but less than your prices) if you don't.
posted by Brian Puccio at 7:29 PM on July 31, 2012


I apologize for being slightly off-topic, but I have a Canon 8800F scanner that I bought for scanning flat copy. It works great for that, and is very fast too.

It is absolute junk for any kind of film scanning; so bad that I'm amazed the company even advertises that specific capability.

That all aside, I am always a big advocate of having film scanned at the highest possible resolution, whether I do it or whether it's done by a third party. You never know what a future use for the images might be.
posted by imjustsaying at 3:48 AM on August 1, 2012


It depends on the slide film used. A Kodachrome that is clean can benefit from a higher resolution than say a blurry Ektachrome that has been pushed. I've had some B&W slides that used grainy film and is not worth scanning above 1800dpi.
posted by JJ86 at 10:39 AM on August 1, 2012


I should clarify that my comments really pertained to dedicated film or slide scanners, not flatbed scanners with transparency adapters. I assume the company in Dublin is going to use a real film scanner, and that its resolution options (4000, 2000, 1200) are real, uninterpolated resolutions and that they're within the limits of their equipment.

In general, I totally agree that you don't want to use some bogus "interpolated" or "non-native" resolution, and that if your scanner offers resolutions that are in excess of the actual resolving power of its optics, that's pretty useless too. (Though it's been my experience that most decent film scanners don't do this; e.g. a 4000dpi Nikon will generally be able to resolve something at least close to 4000 dpi. And I've used older Minolta scanners where the sensors really were the limiting factor, and didn't approach the optical resolving limit. With flatbed scanners or anything consumer-grade, you're probably on your own though.)

If you are going to DIY, I'd get a dedicated film scanner rather than trying to kludge something up using a flatbed and transparency adapter. And I'd toss the software that comes with the scanner and use either Silverfast or, better yet, VueScan. It's a great product and worth every penny, IMO.
posted by Kadin2048 at 11:16 AM on August 1, 2012


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