[Poppler-bugs] [Bug 11421] New: Low-quality scaling makes JSTOR document unreadable at normal size

[bugzilla-daemon at freedesktop.org]

http://bugs.freedesktop.org/show_bug.cgi?id=11421

           Summary: Low-quality scaling makes JSTOR document unreadable at
                    normal size
           Product: poppler
           Version: unspecified
          Platform: x86-64 (AMD64)
        OS/Version: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: cairo backend
        AssignedTo: poppler-bugs at lists.freedesktop.org
        ReportedBy: njs at pobox.com


The attached PDF, downloaded from JSTOR, appears to have originally been
scanned, and so the text is bitmapped.  Evince 0.8.1 using poppler 0.5.4 (cairo
backend) renders it very poorly at normal scaling factors, as if it were using
a low quality scaler -- the text is essentially unreadable.

This is not due to the original scan simply being of too low quality -- if I
zoom in far enough in evince the text becomes clear, and if I then use the
gimp's bicubic scaler to scale it back down to equivalent size, the text
remains readable.  It is something evince/poppler's scaling that is failing --
perhaps just using a linear instead of bicubic scaler as a speed optimization,
which would be a very poor tradeoff for this document.

Similarly, xpdf renders the text entirely readably.

Attached files:
  test.pdf -- look at, say, equation (2) on the second page, and surrounding
text
  evince.png -- screenshot of evince showing this text, very ugly
  xpdf.png -- screenshot of xpdf showing the same text, perfectly readably
  evince-then-scaled-down-by-gimp.png -- zooming in in evince, then taking a
screenshot and scaling the screenshot back down to equivalent size, results in
readable text


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