[poppler] Supporting PDF 1.6 UserUnit

[Leonard Rosenthol]

At 04:15 AM 7/9/2005, Brad Hards wrote:
>Until PDF 1.6, the universe was scaled to 72dpi.

         That's not really true.

         It is correct to say that default user space was 
functionally equivalent to 72dpi.


>That isn't true anymore - there is now a per-page dictionary value that
>specifies the resolution. It is called UserUnit (see pg 122 of the spec).

         UserUnits do NOT effect the resolution of the image - they 
effect the scaling of the user space coordinates in order to enable 
larger then 32K pixels per dimension.


>Now I don't have any PDF documents that use this, and I can't figure out how
>to make Acrobat 7.0.2 produce one.

         Here is one that I used for testing during Acro7 beta.


>So maybe it isn't that widely used.

         It is only currently generated by the Visio & AutoCAD 
PDFMakers when the output is larger than 32Kx32K.


>However a quick scan of the poppler source tree suggests that this might not
>be a fairly widespread change, so maybe we should get to it soon?
         Depends on how you intend to support this.

         What is your thinking about what it means to have a UserUnit 
present with respect to rendering?  Do you see it simply as a 
measurement?  Do you plan to use the value as a scale/transform 
ratio?  Do you plan to use that to effect the size of the output?


Leonard 
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Leonard Rosenthol                            <mailto:leonardr at pdfsages.com>
Chief Technical Officer                      <http://www.pdfsages.com>
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