Re: [docbook-apps] imagedata scale problem

["Bob Stayton" <bobs@sagehill.net>]

Hi Fabien,
The basic problem is that the HTML img element does not let you specify a percentage 
scale of an image's intrinsic size.  The width attribute on img can be either as 
pixels (and a plain integer is interpreted as pixels), or as percentage.  But the img 
percentage is of the page width (window width in a browser), so the image would be 
scaled to take up 80% of the window width, not 80% of each image's intrinsic image 
size.  Thus all images would be the same size if the stylesheet just passed 80% to the 
img width attribute.

This leaves scaling the intrinsic image size up to the XSLT processor.  The problem in 
XSLT processing is figuring out what the intrinsic image width is so that a scale="80" 
can be applied.  Without the intrinsic image width, the processor has to guess.  It 
does so by using the 'nominal.image.width' stylesheet param, which is set to 6 times 
the 'pixels.per.inch' param, which is set to 90 by default.  Thus the 
nominal.image.width value is 540, and 80% of that is 432, which is what you see in 
your output.

For the stylesheet to get the intrinsic image size, Norm Walsh wrote an Java extension 
program that opens the graphic and determines its size (if it can).  Then it uses that 
information to scale the graphic.  That extension is included in the DocBook XSL 
distribution and is described here:

http://www.sagehill.net/docbookxsl/ImageSizing.html#ImageSizeExt

It does require using a Java XSLT processor such as Saxon or Xalan.  It will not work 
with xsltproc.

Bob Stayton
Sagehill Enterprises
bobs@sagehill.net


----- Original Message ----- 
From: "Fabien Tillier" <f.tillier@cerep.fr>
To: <docbook-apps@lists.oasis-open.org>
Sent: Thursday, August 04, 2011 12:51 AM
Subject: [docbook-apps] imagedata scale problem


Hi List.
I have some troubles when rendering images specified as

<equation>
      <title>Mitochondrial Membrane Potential</title>
<alt/>
<mediaobject>
<imageobject>
             <imagedata role="analysis" fileref="/images/xml/53_2.png" scale="80" 
format="PNG"/>
</imageobject>
      </mediaobject>
</equation>

When using the HTML DB5 stylesheet, the result for the image is

<div class="equation-contents">
      <div class="mediaobject">
<img width="432" src="/images/xml/53_2.png">
</div>
</div>


My images all have the same resolution, thus different size but uniform display 
appearance of the equation they contains. As they are a bit too big, I use scale=80" 
to reduce their size by 20%. My problem is that the result gives for all images an 
<img width="432"...>  whatever the intrinsic image size is. Thus my equations appears 
now all with different display sizes on the HTML page, which is not the expected 
output.
As a hint, when using xsl-fo output, I get
<fo:block id="d68e38942">
<fo:external-graphic src="url(/images/xml/53_2.png)" width="auto" height="auto" 
content-width="80%" content-height="80%" content-type="content-type:image/png"/>
</fo:block>
Which is correct.

Any ideas ?
Regards,
Fabien

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