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Subject: Re: You say you want a resolution ... Well-l-l, you know ...
From: Paul Constantin <[log in to unmask]>
Reply-To:Discussion of Type and Typographic Design <[log in to unmask]>
Date:Fri, 19 May 2000 10:32:30 +0300
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> You folks realize, of course, that for all your knowledge and expertise,
> y'all left me utterly confused!<g>
>

I am not so surprised about your confusion. It happens often to less technical
people to make the confusion between dpi and lpi and anything related to them.

Lpi is reffering at the halftone's step. Offset printing runs usually with
halftones between 65-100 lpi for newspapers, 131-175 for magazine, ads, etc.,
and over 200 lpi (even 300-400 lpi) only for x-treme high quality dry printing.
The laser printers are running basically at 65 lpi (for 300 dpi models), 75-80
lpi (for 600 dpi models) and 85-105 lpi (for 1200 dpi models).

The values above do not apply to inkjet printers. The inkjet printers (even
high resolution models)  don't quite have the capability to place equal and
controlled sized dots at a specific point (due to mechanical and paper/ink
relation resons), so the halftones generated by them are very coarse (usually
not more than 60 lpi). But they are using with better results diffusion dither
alghoritms (they are better suited for this technology) which allow you to work
for your images with lower resolutions, without losing detail (for small prints
at 1440 dpi inkjet printer, 150-200 dpi for your images are more than enough.
For wide-printers even 75 dpi for your images suits you).

Unfortunatelly, dpi has two different meanings:

1. As related to the resolution of a physical imaging device (laser printer,
imagesetter, etc) and represents the number of equal sized monochrome dots per
inch.

2. As related to the resolution of a bitmap it represents the number of square
dots (pixels), each having a different colour level.

More details you will found in pre-press related literature. Also you may found
in 1998 Publish collection an article clarifying this topic (sorry I'm not
having at hand the exact issue).

To resume, for your 300 dpi printer, work your images at 150 dpi and you'll get
the best results.

Luck,
Paul

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