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From "Lars Torunski (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (PDFBOX-4516) PDFBox text and images are blurry even after rendering with high DPI
Date Mon, 29 Apr 2019 19:17:00 GMT

    [ https://issues.apache.org/jira/browse/PDFBOX-4516?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16829637#comment-16829637
] 

Lars Torunski commented on PDFBOX-4516:
---------------------------------------

Some years ago I had to resize/downscale images for thumbnails. I got best quality results
with VALUE_INTERPOLATION_BICUBIC and a multi step rescale operation.

See https://blog.nobel-joergensen.com/2008/12/20/downscaling-images-in-java/
"when downscaling to something less than factor 0.5, you get the best result by doing multiple
downscaling with a minimum factor of 0.5 (in other words: each scaling operation should scale
to maximum half the size)."

Unfortunately the referenced blog "Chris Campbell’s blog The Perils of Image.getScaledInstance()"
isn't available anymore. An similiar implementation can be found at
https://github.com/martinheidegger/java-image-scaling/blob/master/src/main/java/com/mortennobel/imagescaling/MultiStepRescaleOp.java

> PDFBox text and images are blurry even after rendering with high DPI
> --------------------------------------------------------------------
>
>                 Key: PDFBOX-4516
>                 URL: https://issues.apache.org/jira/browse/PDFBOX-4516
>             Project: PDFBox
>          Issue Type: Bug
>          Components: Rendering
>    Affects Versions: 2.0.15
>         Environment: Oracle Java 8 update125 on both Mac OS X and centos
>            Reporter: Jack
>            Priority: Major
>              Labels: interpolation, quality
>         Attachments: PDFBOX-4516-59.png, PDFBOX-4516-output-default.png, PDFBOX-4516-output-improved.png,
PDFBox4516.java, defaultDPI.png, highDPI.png, lowDPI.png, original.pdf
>
>
> I tried to render image with different DPI, found PDFBOX performs poorly on the input
pdf file, I have to put a very high DPI to get a reasonable good image. Could anyone pls help
take a look?  Thanks



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