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https://issues.apache.org/jira/browse/PDFBOX-3902?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16138495#comment-16138495
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Tilman Hausherr commented on PDFBOX-3902:
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Well yes... 144 dpi will look poor. Even a high resolution fax is 200 dpi and
still looks poor. Scans start to look good at 300 dpi. Your glyph images are
"blocky" at their native resolution. That it looks better with high resolution
and then downscale is because interpolation is done. Maybe Adobe is doing some
magic like rendering the tiny b/w images at a higher resolution without
interpolation and then doing downscale to gray. If we'd do that we'd be slower
too. This is not something where I would put any energy... there's a reason
that since the 80/90ies fonts are defined as vector graphics and not bitmaps.
Bitmaps in type 3 fonts are used by some converter applications because they
don't want to embed the fonts for some reason.
> PDFs with Bitmap Fonts are getting rendered poorly
> --------------------------------------------------
>
> Key: PDFBOX-3902
> URL: https://issues.apache.org/jira/browse/PDFBOX-3902
> Project: PDFBox
> Issue Type: Bug
> Reporter: Yannick Haser
> Attachments: 144dpi.jpeg, 432dpi_scaledDown.jpeg, test.pdf
>
>
> I have a problem with converting some special PDFs to JPEGs. Those "special"
> PDFs have a bitmap Font for their text-representation, after converting to
> JPEG the text is not readable.
> Converting the PDF to a higher resolution and scaling it down manually fixes
> that issue (Problem: Higher Converting Cost).
> The problem for the ticket is, that I'm not allowed to present those PDFs and
> I still cannot reproduce those perfectly.
> My best shot is the attached PDF.
> Problem-Setup:
> Converting the PDF to JPEG with 144 DPI.
> {code:java}
> BufferedImage image = renderer.renderImageWithDPI(0, 144, ImageType.RGB);
> {code}
> Fix-Setup:
> Converting the PDF to Jpeg with 432 DPI and scale it down with an external
> Scaling Algorithm.
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