[poppler] Scanned images in PDFs and DPI

[Ralph]

> You could use pdftoimages to extract the embedded images and check the
> resolution.

I actually gave that a try, seems that it's a 16k x 12k pixel pbm file embedded inside… wonderful.  Seems that the plotter used to scan these things scans at 400 dpi, because that would make the resulting images a perfect 42" x 30".

We're going to use that as a sanity check at least.  Thanks for the suggestions!   

--  
Ralph G.
(co-founder of plangrid.com, blueprints on the iPad)


On Thursday, February 9, 2012 at 12:26 AM, Adrian Johnson wrote:

> On 09/02/12 11:30, Ralph wrote:
> > Hi Folks,
> >  
> > This isn't really a poppler issue, but I was hoping that someone on
> > the list might have some experience dealing with this edge case.
> >  
> > The PDFs that we process with pdftoppm are regularly sized 42" x 30"
> > and often contain scans of rasterized data. Once in a while,
> > whomever made the scans screws up and puts in 8.5 x 11, even though
> > it's *actually* 42" x 30". Obviously the 150 dpi is far too low and
> > the output quality is horrible.
> >  
> > There's a slight chance that the PDFs might actually be 8.5" x 11" so
> > doing a brute force DPI increase might not be a good idea. Does
> > anyone have any good workflows for these sorts of mess-ups? Or is
> > scaling the DPI based on the size difference (544 x 388 -> 3168x2448)
> > the only approach?
>  
>  
>  
> You could use pdftoimages to extract the embedded images and check the
> resolution.
>  
> >  
> > Here's the pdfinfo dump of the failure: ---- Tagged: no Pages: 1  
> > Encrypted: no Page size: 544.32 x 388.8 pts Page rot: 0 File size:
> > 881061 bytes Optimized: no
> >  
> > PDF version: 1.6 ----
> >  
> > Here's a pdf dump of what we expect: ---- Pages: 1 Encrypted: no Page
> > size: 3168 x 2448 pts Page rot: 0 File size: 523131 bytes Optimized:
> > no PDF version: 1.4
> >  
> >  
> > ----
> >  
> > I'd be happy to mail anyone the original files if needed (there
> > semi-sensitive, so I didn't want to post them to the list). Thanks
> > for anything :) We *really* enjoy using poppler.
>