scanning calibration

[cliveh]

Can someone tell me what resolution I should scan a 6cm X 6cm colour transparency to print at 300dpi at 38cm X 38cm and/or 50cm X 50cm?

 

[gmikol]

Clive, I think you will find the DPUG community always willing to help, but it's important that you exercise a bit of critical thinking of your own, in my opinion.

I will gladly explain to you how to figure this out in 24 hours from now, provided you post explaining how you would try to figure it out first.

I'm a firm believer in the saying, "It's better to teach a man to fish than to give a man a fish."

--Greg

 

[cliveh]

I appreciate the philosophy, but I don't know how to figure it out, which is why I am asking the question.

 

[pschwart]

Google is your friend -- there are plenty of online resources for this kind of stuff. Try: Scanning Basics 101 - All about digital images

I appreciate the philosophy, but I don't know how to figure it out, which is why I am asking the question.

 

[gmikol]

Not gonna get a chance to reply tomorrow, so here it is:

First off, it helps to think in terms of "pixels per inch" (ppi), and not "dots per inch".

38 cm / 2.54 = 14.96 inches

14.96 inches * 300 pixels per inch (output) = 4488 pixels of image data

Since a 6x6 frame is really about 56mm x 56mm, then:

56mm / 25.4 = 2.20 inches

4488 pixels / 2.20 inches = 2040 pixels per inch.

In order to get maximum image quality for your 38cm x 38cm print, you should try to scan your 6x6 frames at a resolution equal to or greater than 2040 ppi.

A similar calculation can be done for your 50cm print, yielding a scan resolution of approximately 2680 ppi.

Now, for cases in which the viewing distance is greater than approximately arm's length, the 300 ppi requirement can be relaxed somewhat. A 50cm x 50cm print may appear acceptably sharp from 6 feet viewing distance even when printed at 200 ppi output resolution, for example. But that's a topic for some other time.

--Greg

 

[cliveh]

Thanks Greg, much appreciated.