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Re: [CSS21] Issue 149 - px vs. pt

From: Brad Kemper <brad.kemper@gmail.com>
Date: Tue, 29 Jun 2010 10:48:15 -0700
Message-Id: <E2465A25-05BF-465F-B6FA-9E647A72273F@gmail.com>
Cc: fantasai <fantasai.lists@inkedblade.net>, "www-style@w3.org" <www-style@w3.org>
To: David Singer <singer@apple.com>
On Jun 29, 2010, at 9:56 AM, David Singer <singer@apple.com> wrote:

> The problem comes when you have a device with say 300dpi.  If you want 96 px/in, and CSS pixels are an integer number of device pixels, then you have to pick 3:1 for that ratio, which results in a CSS inch being 288 (3*96) device pixels, which is about 4% short of a true inch.  Basically, something has to give:
> * 96 CSS px/in
> * integer relationship
> * true measurements
> If you anchor in true measurements, and the 96 px/in is inviolable, then it has to be the integer relationship that gives.  I think in print media in particular, people expect inches to be inches, not 4% wrong.

OK. That makes sense, and is not far from what I thought the reasoning might be. I was thinking of tiny inaccuracies being multiplied into bigger differences over large distances, but it is a similar problem. Physical measurements in print should be accurate. 
Received on Tuesday, 29 June 2010 17:56:25 UTC

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