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From Duncan McGregor <dun...@oneeyedmen.com>
Subject Re: Transparent Text
Date Mon, 02 Mar 2009 15:14:22 GMT
Thank you

At present the text-behind-image trick is doing it for me, but when I  
find its limitations I'll look into potentially patching fop.

Cheers

Duncan

On 2 Mar 2009, at 15:03, Jay Berkenbilt wrote:

> 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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