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From Clay Leeds <cle...@medata.com>
Subject Re: Image Size Calculations
Date Wed, 09 Jun 2004 04:20:49 GMT
Greetings,

On Jun 8, 2004, at 1:55 PM, J.Pietschmann wrote:
> Darn, the mail server failed yesterday. Resending.

And I thought it was just me...

> Peter B. West wrote:
> > I think the problem is that pixels are not well-defined.  In 
> general, a pixel is an output-dependent unit.  On a printer, a pixel 
> might be 1/2400 inch, on the screen, 1/96".  The Recommendation warns 
> about this in 5.9.13.1 Pixels.  I suggest that anyone tempted to 
> define lengths in "px" read that section of the Recommendation.  It's 
> not so bad if the units are completely "internal", that is, that it 
> only affects text, tables and the like.  But when you import an image 
> constructed externally, and defined in pixels for God knows what 
> output device, you are asking for trouble.
>
> Well, perhaps we should use wording like this in graphics.xml:
>
> "FOP always assumes a resolution of 72dpi on encountering pixel
> measurements, regardless of the output device, and converts all length
> measured in pixels in millipoints using 1/72 pixels per inch as
> conversion factor. The layout stage doesn't use pixels, even if the
> final rendering is on a bitmapped device like the monitor. A bitmapped
> image without explicit measurements is assumed to have the actual pixel
> counts as measurements. Any resolution declaration in the image 
> metadata
> is ignored."

I was about to make these changes, when I realized I wasn't certain 
where these edits would be made:

Overview of Graphics Support
http://xml.apache.org/fop/graphics.html#support-overview

Graphics Resolution
http://xml.apache.org/fop/graphics.html#resolution

I am leaning towards the latter. Which leads to the question: replace 
the first paragraph?

BTW, nice work, Jorg!

> BTW does someone know how resolution is stored in GIFs, and whether
> the Java image API can retrieve this?

I was under the impression GIF files were always 8-bit (256 color) at 
72dpi.

This search gave me some nice hits:
http://www.google.com/search?q=GIF+resolution&ie=UTF-8&oe=UTF-8

> > Bottom line - don't define *anything* in px.
>
> Yeah, double this. I have no idea why people are confused to no
> end by this issue.
>
> J.Pietschmann

If we put it on the site in a WARNING box, it'll resonate...

Web Maestro Clay


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