Message-ID: 001d01bf3fd2$c3d87c50$5101a8c0@ivo
To: "Kambiz Asrar Haghighi" <kambiz@interchange.ubc.ca>, "TIFF Mailing List" <tiff@olympiakos.com>
Subject: Re: X & Y Resolution
From: "Ivo Penzar" <ivo.penzar@infolink-software.com>
Date: Mon, 6 Dec 1999 11:14:54 +0100
References: <Pine.GSO.4.20.9912051208170.14305-100000@inch.interchange.ubc.ca>
Sender: owner-tiff@olympiakos.com


> Hi,
>
> I've tried to understand what Xresolution and Yresolution are from the
> tiff specification, but I still don't understand how I would go about
> deciding the values for these fields based on the number of pixels I have
> in my image. I know the value of the width and height, but is there any
> correlation between these and the above values?
>
> Thanks in advance,
> Kambiz

E.g., if your document was scanned as 300 dots per inch, X and Y resolutions
would be both 300/1 (or 600/2, 900/3, 1500/5, etc. - TIFF stores X and Y
resolutions as rational numbers, either as number of dots per inch or per
centimeter). If that document was 3 by 4 inches (original), the
corresponding width and height would be 900 x 1200 pixels. Now, the smart
viewer (or printer driver) knows how to recalculate the original size (3 by
4 inches) from the width and height (in pixels) and from X and Y
resolutions.
It is mostly useful for technical documentation, maps, etc. Most images do
not have meaningful X and Y resolutions: paintings, photos and alike;
sometimes this information is not written (some image formats do not provide
fields to store them), or is just stored as "default" value 72 or 75 dots
per inch.

Ivo



