What dpi setting when scanning?

[psybear]

Hi.

When I use my Canon scanner I am offered several dpi settings to choose from, ranging from 75 up to 1200. I rarely scan at over 300 dpi and often use the 150 dpi setting for speediness.

However if I am scanning a 5 x 7 photo for editing in PS, I assume that I should be using a high (possibly the highest?) setting?

Any help appreciated - thanks.


PB

[UncleDoug]

Several schools of thought on this one...
The one I follow is "scan once, output many" meaning get the largest file you can get.
Shrinking down is not a problem, interpolating up is, as you "create" pixles when you do this.

Hope this helps.

-Doug

[Bodog]

It all depends on your final use of the scan. If you want to post on the web, 150 dpi should be more than enough, probably 72 would be better.. If you plan to edit the image and then print the image at the same size, then you want at least 300 dpi. If you plan to print the image larger, then up the resolution accordingly. A 5X7 scanned at 600 dpi will let you print a 10X14 at 300 dpi. Or as Doug sez scan at you max resolution and be prepared for anything. The only draw back to that is a 5X7 scanned at 1200 dpi may require a new hard drive to hold the file you get. :D

[psybear]

Thanks guys, very helpful.

[UncleDoug]

To give you some guidance....

5x7 @ 300 = 9mb
5x7 @ 1200 = 144mb

The scan @ 1200 may be too much but it follows my practice.

I own a digital imaging house/service bureau and for comparrison, when we scan a 35mm tranny on our Tango drum scanner at what I call full resolution, 5500spi, we get a file that is 109mb.

Hope this helps!

-Doug

[robertwgross]

When I scan film, I use the best resolution of my film scanner, 4000 lines per inch.

When I do a flatbed scan, I use the best resolution of my flatbed scanner ... short of where I get a warning about the high RAM or disk requirement.

I skipped a warning one time, and then I ended up with an 850MB image file. That is rough when one image file won't even fit onto a standard CDR.

---Bob Gross---