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From Jay Berkenbilt <...@ql.org>
Subject Re: Transparent Text
Date Mon, 02 Mar 2009 15:03:47 GMT
Duncan McGregor <duncan@oneeyedmen.com> wrote:

> Hi
>
> I'm trying to work out how to write transparent text to overlay OCR
> data on top of its source image.
>
> I've seen it done in PDFs, but cannot find how to represent
> transparency in xsl:fo
>
> Thanks in anticipation
>
> Duncan McGregor

To fill in a bit of missing information here, transparent text in PDFs
is not done by tweaking aspects of how the text is displayed, like
transparent text or white on white.  It is a specific feature
supported by the PDF specification.  Specifically, there is an
argument to the Tr (text rendering) operator.  If you place

3 Tr

after your BT to begin a text stream, the resulting text will be
invisible.  This is the correct way of putting "hidden text" in a PDF
for overlaying OCR data on top of an image.

I suppose the PDF output system in fop would have to specifically
support this.

Hope that helps...

-- 
Jay Berkenbilt <ejb@ql.org>


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