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