Optimal settings to scan from 35mm slides

[dtokez]

Hi all

We have lots of 35mm slides to scan and have purchased a Epson V330 scanner. I have done some tests at 600 DPI and they look OK, but the filesizes are quite large.

What is the optimal DPI to scan at to not loose any quality, but obviously not to be overkill and have unnecessary large file sizes? Also what about JPEG compression?

Many thanks

 

[PMN]

Unless you're pulling the image apart in editing you don't need to worry about JPEG compression.

600dpi seems very much on the small side to me personally though, on such a machine 2400 would be my 'go to' resolution for 35mm!

 

[TheGreatSoprendo]

600dpi does seem a bit low.

It's horses for courses...what's the purpose of the scans? If just viewing on screen, sharing online, or printing at 6x4 then a file size around 1800x1200 will suffice. Given that the short side of a 35mm frame is about 1 inch, you therefore need a dpi of 1200 to achieve that (I think that makes sense, someone will be along to correct me if not). For anything bigger then you'll need more. 2400 is pretty close to optimum in terms of quality on this kind of scanner, though obviously that increases file sizes and the time required to scan.

 

[s162216]

You have to balance it against what gives a large enough file size (600 is way too low), but also take into account what your equipment can do. Most flatbeds don't resolve detail higher than about 1800 to 2300 dpi even at their highest settings (this simply because of the laws of physics, the sensor may be able to resolve 6400 dpi etc, but other optics in the scanning path reduce this) so scanning at a higer dpi doesn't actually gain any extra detail and just bloats the file with needless information. Therefore I would scan at a maximum of 2400 dpi.

 

[dtokez]

Thanks guys

They are just for viewing on the PC and keeping safe at the moment, but some will more than likely be printed off and maybe even blown up so if possible I would like to preserve all the quality that I can. I was worried about having massive file sizes with no worthy data in them as you say Samuel.

I will do some test runs at 2400 later

 

[Woodsy]

Most flatbeds don't resolve detail higher than about 1800 to 2300 dpi even at their highest settings (this simply because of the laws of physics, the sensor may be able to resolve 6400 dpi etc, but other optics in the scanning path reduce this) so scanning at a higer dpi doesn't actually gain any extra detail and just bloats the file with needless information. Therefore I would scan at a maximum of 2400 dpi.

Exactly this.

 

[ChrisR]

If 600 dpi is giving you file sizes too big then I guess you're saving TIFFs? For many purposes, JPEGs are enough, and that gets the file sizes down... lots!

When I scan my slides, I use 1200 dpi if it's a fairly rubbish shot, but worth scanning "for the record" as it were (ie sets the scene for what was happening at that time). Then 1800 dpi or 2400 dpi for "better to good" shots (by my own standards, of course) for PC/web use, and 3600 dpi for anything I like so much I might want to print at larger sizes than A4 (a whole 2 shots, so far!). Most of the 3600 dpi scans are in fact re-scans, as it takes ages for me to settle on a shot (from the past) that I really like. But 2400 dpi gets you a really nice A4 or 10*8" print.

 

[s162216]

If 600 dpi is giving you file sizes too big then I guess you're saving TIFFs? For many purposes, JPEGs are enough, and that gets the file sizes down... lots!

When I scan my slides, I use 1200 dpi if it's a fairly rubbish shot, but worth scanning "for the record" as it were (ie sets the scene for what was happening at that time). Then 1800 dpi or 2400 dpi for "better to good" shots (by my own standards, of course) for PC/web use, and 3600 dpi for anything I like so much I might want to print at larger sizes than A4 (a whole 2 shots, so far!). Most of the 3600 dpi scans are in fact re-scans, as it takes ages for me to settle on a shot (from the past) that I really like. But 2400 dpi gets you a really nice A4 or 10*8" print.

Even a TIFF at 600 dpi should not be too big, as at that resolution the file will only be approximately 864 x 567 which is only the same as approximately half a megapixel. Assuming a 24 bit file (so 3 bytes per pixel, or 6 bytes if at 48 bits) then the TIFF in theory should only be about 1.5 mb.

@dtokez are you sure that your scanning at 600 dpi, and not outputting at 600 dpi (which will make no difference to the file size)? What are the approx dimensions of the scans your getting as it sounds to me like your scanning at a much higher resolution if your getting massive files (a 24 bit TIFF file from my Reflecta dedicated 35mm film scanner is about 48 mb when scanning at 3600 dpi for instance).