Slide Scanning: Part 2—Deciding on the resolution
The Epson Perfection V600 Photo scanner allows for an optical resolution up to 6,400 dpi and a colour bit-depth of 24 or 48. A quick test scan at the 6,400 resolution with a bit depth of 48 produces a non-compressed TIFF file of around 260MB. This is a huge file. If I assume that I am going to end up scanning 3,000 slides then that would result in around 800GB of file space being required just for the initial scan.
If I assume that I am going to then do at least one fix-up editing pass for each slide scanned and that the fix up edit will be at least half the size of the initial scan, then that will add up to an additional 400GB of space.
This means that, assuming 3,000 slides scanned, I will need 1.2TB of space if I scan at 6,400 dpi.
The following picture shows a 6,400 dpi slide scan reduced down to 2000 pixels wide.
Click to enlarge
Additionally, scanning at 6,400 dpi mean each scan pass of four slides will take close to 12 minutes.
Because of these results I decided to see what the outcomes are if I scan at 3,200 dpi with a bit depth of 48. At this resolution the raw scan of a slide is 61MB, making it pretty much a quarter of the size of the 6,400 dpi scan.
But! What are the downsides of this reduction in scanning resolution?
Scanning at 6,400 dpi I could comfortably produce a 20 x 30" poster/print at 240 dpi print resolution. Scanning at 3,200 I would be struggling to do a decent 16 x 20" print—unless I dropped the print resolution down to around 200 dpi.
On the upside, scanning at 3,200 dpi only takes about one minute a slide, compared to about three minutes a slide at 6,400 dpi.
The following picture shows a 3,200 dpi slide scan reduced down to 2000 pixels wide.
Click to englare
Don’t worry about exposure, sharpness (unsharpening), and colour. I haven’t got to those bits yet. That is all coming up in future posts.