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https://issues.apache.org/jira/browse/PDFBOX-6065?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18018959#comment-18018959
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Tilman Hausherr edited comment on PDFBOX-6065 at 9/9/25 6:50 AM:
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Thank you, it also works with my test files and improves the rendering of the
files from PDFBOX-2989. Amusingly I once asked ChatGPT (shortly after it came
out) to optimize the LZW code and the code failed the unit test. So ChatGPT has
evolved a lot.
was (Author: tilman):
Thank you, it also works with my test files. Amusingly I once asked ChatGPT
(shortly after it came out) to optimize the LZW code and the code failed the
unit test. So ChatGPT has evolved a lot.
> LZWFilter crashes, probably not handling the KwKwK special case
> ---------------------------------------------------------------
>
> Key: PDFBOX-6065
> URL: https://issues.apache.org/jira/browse/PDFBOX-6065
> Project: PDFBox
> Issue Type: Bug
> Components: Parsing
> Affects Versions: 2.0.34, 3.0.5 PDFBox
> Reporter: Daniel Persson
> Priority: Minor
> Fix For: 2.0.35, 3.0.6 PDFBox, 4.0.0
>
> Attachments: elvis5.pdf, lzwfilter.patch
>
>
> The parsing throws an exception when trying to parse an image with the words
> "The Legend" in the PDF.
> java.io.IOException: negative array index: -1 near offset 1
> at org.apache.pdfbox.filter.LZWFilter.checkIndexBounds(LZWFilter.java:136)
> at org.apache.pdfbox.filter.LZWFilter.doLZWDecode(LZWFilter.java:110)
> at org.apache.pdfbox.filter.LZWFilter.decode(LZWFilter.java:70)
>
> I've not looked into the Lempel-Ziv algorithm since the 90s, so I'm not up to
> date with all the papers that have been published. And also, I've never read
> the original welsh paper:
> [https://courses.cs.duke.edu/spring03/cps296.5/papers/welch_1984_technique_for.pdf]
> But it seems that ChatGPT was able to find this paper and suggest a patch by
> rewriting the function handling all cases, not needing the bounds check at
> all. Not saying that this is the right solution to the problem, but I ran it
> against our 50k pages from multiple publishers and newspapers without any
> visual artifacts, and it also works with the example provided in this issue.
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