Scanning Advice: DPI and Color Depth?

[vicwang]

This isn't so much a tech support question as it is an invitation for general advice. I have a co-worker who is interested in scanning several old 8x10 photographs into his PC, both to print on his inkjet printer and for archival purposes. Basically he wants to find out what are the best settings to scan photographs at without losing quality to the naked eye? His scanner supports up to 1200 DPI and 48-bit color, both of which I would assume are overkill for such a purpose (in other words, I would think something like 600 DPI at 32-bit color would suffice).

Another bit to consider is that his system is a P4 with a measly 128 megs of RDRAM, in the form of two 64-meg RIMMS. Once he determines what are the optimal settings to scan at, he will basically use that info to determine what RAM upgrades he will need, if any.

Any suggestions would be much appreciated!

 

[cchan]

When you say

<< His scanner supports up to 1200 DPI and 48-bit color >>

you better read the specs carefully. If a scanner &quot;supports&quot; 1200 DPI but only has an optical resolution of say 600 DPI will interpolate the missing pixels. The resulting file might not be as sharp as if it were done in 600 DPI.

On the same note, many scanners support obscenely high colour depths but output a much lower one. Anyhow, if your friend plans to touch up the photos on his computer before he prints them, he can't see 48-bit colour on his screen.

As a benchmark, a 4x6 photo scanned at 600 dpi 24-bit colour usually results in a file ~25-30MB. Scanning at 1200x600 would double that and 1200x1200 would quadruple that, all at 24-bit colour.

 

[vicwang]

Thanks for the tip. So would you recommend 24-bit color as a good baseline, regardless of the DPI?

 

[dullard]

As far as I know, people can't really tell any difference once you go past 600 DPI. Your friend probably could get away with 300 DPI without too much quality loss. Also people can't see much more than 16-bit color. Note: some graphics cards have color banding at 16-bit but that is due to the card and not to your eyes.

I'd start at 300 DPI and 16-bit. If the results aren't quite as good as expected, bump them to 600 DPI and 24-bit.

 

[Ladi]

Note that most home/office printers can't do much above 300 dpi reliably and that 300 dpi is a commonly requested resolution at print shops....It will also give you leeway if you need to resize or edit the image.

Also, it's worth creating 72 dpi versions of the pictures for thumbnail and browsing purposes...72 is as high as a monitor will display and will print decently well on most printers, as long as the image is not resized.

As far as color depth, most scanners will have presets for photos/black&amp;white/line art/etc. I'd pick the photo preset, bump up the resolution to 300 and see how the results look...Chances are, they'll be pretty close to what you want.

Another caveat is to make sure your monitor is at least somewhat color sync'd. Adobe software (like Photoshop) generally comes with a gamma correction tool to adjust color balance and contrast. You can also use an image with *known* colors (ie, fill an image with pure green, red, blue, black, and white) to do some adjusting.

~Ladi

 

[NelsonMuntz]

IMO, I think 600 dpi and 24 bit would be more than sufficient for archival purposes and less than that would be okay for printing. If it was me, I would scan them in at 600 dpi and 24 bit print them out at lower resolutions (whatever looked good) and then burn them all to a CD to get them off the hard drive and backed up.