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Re: Question about scanner resolution

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Posted by Laura Rajsic-Lanier on January 04, 1997 at 23:17:58:

In Reply to: Question about scanner resolution posted by Bobby R. on January 04, 1997 at 17:54:02:

: Everything Iv'e read suggests a formula of 1.5-2X the line screen or lpi. of the output device for scan resolution.

First, you need to know what you're going to do with the image(s) you scan in. If you're scanning in for a Web page, you can safely use 72 dpi. It will work for most monitors. If you start getting more dpi than that, you have additional information in your image that will not be displayed on screen. You'll be wasting bandwidth.

If you're scanning in for printing, it gets more complicated. The 1.5 to 2 times the size is correct. Grab a newspaper or magazine and look really closely at the photos. You'll see rows of little dots. The rows of dots are in lines per inch (lpi). Newspapers use about 85 lpi. Instant printers with lesser quality presses can handle 60-90 lpi. The commercial printer I used to work for always had screens put out at 150 lpi. We did one job at 200 lpi and it looked fantastic.

As you can see, the more lpi, the more you need an exact dot. Newsprint is a cheaper paper and the ink spreads, hence less dots.

Well, now, for the formula. If you want to do work for a newspaper - 85 lpi x 2 = 170 dpi. Commerical printer - 150 lpi x 2 = 300 dpi.

All of the above has been for photos and items with screens. If you're working with logos where you are trying to get the exact image on your computer, you need to scan it in as high as possible so you don't get jaggies on it. Usually, you need to scan those about 800 - 900 dpi if you can. If not, blow it up on a copier, scan that it and reduce it to get the dpi you need. You'll need to do more cleaning up, but you'll have a truer representation of the logo.

I hope I'm not confusing you more than you were. ;)

There's a Scanning FAQ somewhere on the Web, except I can't remember where it is. I'll see if I can find it and get back to you!

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: : Everything Iv'e read suggests a formula of 1.5-2X the line screen or lpi. of the output device for scan resolution. : First, you need to know what you're going to do with the image(s) you scan in. If you're scanning in for a Web page, you can safely use 72 dpi. It will work for most monitors. If you start getting more dpi than that, you have additional information in your image that will not be displayed on screen. You'll be wasting bandwidth. : If you're scanning in for printing, it gets more complicated. The 1.5 to 2 times the size is correct. Grab a newspaper or magazine and look really closely at the photos. You'll see rows of little dots. The rows of dots are in lines per inch (lpi). Newspapers use about 85 lpi. Instant printers with lesser quality presses can handle 60-90 lpi. The commercial printer I used to work for always had screens put out at 150 lpi. We did one job at 200 lpi and it looked fantastic. : As you can see, the more lpi, the more you need an exact dot. Newsprint is a cheaper paper and the ink spreads, hence less dots. : Well, now, for the formula. If you want to do work for a newspaper - 85 lpi x 2 = 170 dpi. Commerical printer - 150 lpi x 2 = 300 dpi. : All of the above has been for photos and items with screens. If you're working with logos where you are trying to get the exact image on your computer, you need to scan it in as high as possible so you don't get jaggies on it. Usually, you need to scan those about 800 - 900 dpi if you can. If not, blow it up on a copier, scan that it and reduce it to get the dpi you need. You'll need to do more cleaning up, but you'll have a truer representation of the logo. : I hope I'm not confusing you more than you were. ;) : There's a Scanning FAQ somewhere on the Web, except I can't remember where it is. I'll see if I can find it and get back to you!

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