Archived posting to the Leica Users Group, 1997/12/01

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Subject: Re: [Leica] Re: Digital storage/ Printer dots
From: Alex Hurst <>
Date: Mon, 1 Dec 1997 09:23:46 +0000

Tom wrote:
>>Keep these numbers in mind:
>>600 DPI printer: 85 line screen (LPI)
>>720 DPI printer: 100 line screen (LPI)
>>1400 DPI printer: 150 line screen (LPI)
>>Now, you need an image file that has a PPI of about double your target LPI.
>>(You can often get by with 1.5x.) So, a 600 DPI printer needs a 170 DPI
>>file. A 1400 DPI printer, like the Epson Photo needs a 300 PPI file.

And Nick replied:

>The Stylus Photo, I believe, is 720 X 720. The Stylus 800 is 1440 X 720.
>For printers like the 800 should we use the higher resolution, the lower,
>or in-between, when figuring possible LPI?
>Please understand I am not taking issue with Tom. Just a footnote.
My understanding of the relationship between pixels per inch and dots per
inch is that you'll get better printing quality if the number of pixels per
inch is EXACTLY divisible into the number of dots per inch selected on the

This prevents the printer software fudging the image because it can't print
an exact number of dots to represent a pixel.

So for instance, on the Epson Stylus Photo (very good printer, BTW) at 720
dpi, output in ppi could be (amongst other numbers):

72, 80, 90, 120, 144, 180, 360, 720.

Forget where I read this, but it makes sense to me and certainly seems to
be borne out by the results.

Am I right? If not, would someone more experienced with digital imaging
please enlighten me.



Alex Hurst
Cork Florists
19 Winthrop St, Cork
Republic of Ireland
Tel: +353 21 270 907
Fax: +353 21 271 248
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