Ultimate Guide to Photo, Film & Slide Scanning Resolutions
Memories 2 Digital • September 27, 2019Photo Scanning Slide Scanning
One of the most important decisions when scanning photographic media is choosing the resolution. There's many factors that go into choosing the best resolution, so we've broken them down to help you decide what's best for you.
Scanning resolutions are generally quoted in DPI or Dots Per Inch, and range from as low as 100dpi to upwards of 16000dpi. Beware of cheap scanners (especially cheap slide/negative scanners), as they often misrepresent the DPI, or use interpolation to boost the resolution.
There's a lot of resources out there on the optimal resolution for scanning photos, as often they recommended using the highest optical resolution supported by your scanner. This will result in the highest quality scans, but it doesn't take into account the time it takes to scan each photograph.
|Scanning times for a 6x4" print on the Epson v800
What scan resolution should I use for reprinting photos?
If you are just scanning a few precious photos for the purposes of re-printing or archiving it makes sense to use the highest optical DPI available. To find the highest optical resolution, check out the section on interpolated resolutions below.
What scan resolution should I use for digitising my collection?
For those digitising their entire photo collection, it quickly becomes obvious that scanning at the highest resolution isn't feasible. For example, on the Epson v800 a scan at 4800dpi takes almost 15 times as long as one at 600dpi
In our experience, 600dpi is the best resolution as it provides a balance of high image quality while still keeping the scan times reasonable.
A 600dpi scan can be reprinted to roughly double the size of the original print without loss of quality and comes in at about 10mb for a compressed JPG, or about 40 for an uncompressed TIFF.
If you're planning to enlarge specific photos, or for particularly special photos consider scanning them at high resolutions, saving you from having to re-scan them down the track.
Scanning Slides and Negatives
What scan resolution should I use for reprinting slides & negatives?
Just scanning a few slides so you can get them re-printed? We'd recommend a resolution of 3000dpi to 4800dpi.
Scanning at a resolution this high will take considerably longer than a scan at say, 2400dpi but will produce a image suitable for much larger re-prints. The other disadvantage of such high resolutions is each scan will produce a massive image, around 100MB for an uncompressed TIFF or around 30MB for a compressed JPG.
I'm digitising my slide and negative collection, what resolution should I use?
For those scanning a large quantity of slides or negatives, the extra time required to scan at high resolutions begins to add up quickly, so the resolution you pick depends on how much time you are willing to dedicate to the project.
|Scanning times for a 35mm slide on the Epson v800
We'd recommend scanning at 2400dpi, as it provides the best time vs quality balance in our option. If you are running short on time, 1200dpi scans will be fine for sharing online & viewing on your computer, but any prints will come out sub-par.
It's also worth keeping in mind that higher resolutions won't always produce better scans. If you push the scan resolution too high, it will start to introduce noise and grain into the output image, especially for photos that weren't perfectly focuses or exposed originally. Have a go and experiment with the resolutions that your scanner offers, and remember that every scanner is different.
Should I use Digital ICE / Infrared Dust Removal?
If you have a higher end scanner, it will probably have ICE, or infrared dust/scratch removal.
When you enable ICE on your scanner, it will perform two separate scans, once with the standard sensor (to produce the RGB image) and then again with an infrared (IR) senor. The IR sensor is able to detect the location of dust, scratches and other physical imperfections, and the ICE algorithms will attempt to correct and mask them from the final image.
If your slides have been well stored & cared for, you probably don't need ICE. Generally, it will be a lot faster to use compressed or canned air to clean the slide prior to scanning.
For degraded slides, ICE will work wonders but comes at the cost of considerably longer scans. In our testing, scanning with ICE enabled takes about 3 times as long as a standard scan.
It's also worth keeping in mind that digital ICE doesn't work on some types of negatives & slides (for example, kodachrome slides which contain silver that reflects the IR light).
Some scanners also offer software dust removal, which is much faster as it doesn't require an extra IR scan, but won't produce results as good (and sometimes will mistake parts of the image as dust, when they are are in fact part of the actual photo).
Should you use Digital or Interpolated resolutions?
Make sure to check the specifications of the scanner you are using, and limit the resolutions of your scans to the highest “optical” resolution it supports.
Interpolated resolutions work by faking the missing pixels above the optical resolution, similar to how digital zoom works on your smartphone or camera. The scans produced by interpolated resolutions are often worse than those produced by the lower optical resolutions.
The box or specification sheet of your scanner will generally list both of these separately. For example, the Epson v800 has an optical resolution of 6,400x9,600 dpi, but a digital/interpolated resolution of up to 12800dpi. Make a note of your scanners highest optical resolution and keep below it for the best quality scans.