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Date: Mon, 17 Dec 2001 10:31:55 -0600
From: Joel Schumacher <jschumac@jcpenney.com>
To: Juergen May <j.may@speed-print.co.uk>
Cc: tiff@olympiakos.com
Subject: Re: Newbie need help! Please!
Message-ID: <20011217103155.F25043@jcpenney.com>
References: <B84399E7.1AA9%j.may@speed-print.co.uk>
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You're right about looking at offset 182.

A rational is a composition of 2 numbers, a numerator and a divisor.
You divide the first one by the second one.

In the first number you have, 0,45,198,192, or in hex: 00 2D C6 C0
In decimal, 2DC6C0 is 3,000,000.

For the second number, you have 0,0,39,16, or in hex: 00 00 27 10
In decimal, 2710 is 10,000.

You divide 3,000,000 by 10,000 and you get 300.

I've seen some wierd combinations of the x/y values that seem an
awfully strange way to represent something like 300 dpi or 200 dpi.
How about 629145600/2097152 for 300dpi???

Why not just make y=1 and make x=300 or 200 or whatever the dpi is?
I don't know.

The important thing to remember is to divide the two and use the
result.  4/2 = 6/3 = 10/5 = 2/1.  Don't expect the numerator or
divisor to be any particular value.

Juergen May (j.may@speed-print.co.uk) wrote :
> I'm a newbie and have a problem understanding the TIFF data structure.
> 
> I need to get the resolution of a bi-level TIFF image but can't seem to get
> the value. I know the resolution is 300 so I'm expecting to find contiguous
> bytes with the values 1 and 44 (decimal).
> 
> Now, if I'm right, the value bytes in the tag 282 (x resolution) act as a
> pointer. In my instance, the values are as follows -
> 
> 1    26    - Tag 282
> 0    5     - Rational type
> 0    0    0    1    - Count
> 0    0    0    182  - ???
> 
> I don't understand what 182 means!? Is this an offset from the start of the
> file? If so, the value from 182 are -
> 
> 0    45    198    192
> 0    0    39    16
> 0    45    198    192
> 0    0    39    16
> 
> The expected values (1, 44) are at offset 342 -
> 
> 1    44    0    0    0    1    0    2
> 
> But then I don't know what 0, 1, 0, 2 refer to...
> 
> 
> Can someone please help!
> 
> Thanks in advance.
> 
> Juerg
> 
> 
> To subscribe or unsubscribe email tiff-request@olympiakos.com with subscribe
> or unsubscribe in the email body.  Libtiff home page: http://www.libtiff.org
-- 
______________________________________________________________________
Joel Schumacher                    JCPenney Co. - UNIX Network Systems
jschumac@jcpenney.com              12700 Park Central Pl   M/S 6021
(972) 591-7543                     Dallas TX  75251

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