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https://issues.apache.org/jira/browse/PDFBOX-822?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Timo Boehme updated PDFBOX-822:
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Attachment: pdfbox_issue822.patch
patch correcting the PNG predictor bug
> Wrong handling of PNG predictors with FlateDecode, patch attached
> -----------------------------------------------------------------
>
> Key: PDFBOX-822
> URL: https://issues.apache.org/jira/browse/PDFBOX-822
> Project: PDFBox
> Issue Type: Bug
> Components: Parsing
> Affects Versions: 1.3.0
> Reporter: Timo Boehme
> Attachments: pdfbox_issue822.patch
>
> Original Estimate: 0.17h
> Remaining Estimate: 0.17h
>
> The current implementation of PNG predictors for FlateDecode (class
> FlateFilter) is based on a wrong interpretation of predictor semantic. It
> assumes that predictor 15 (optimum) must be specified in order to use PNG
> prediction and predictor 10 (PNG NONE) would mean no prediction. Latter one
> is correct as type for an image row but wrong in its meaning for whole image.
> As specification states if one of the PNG predictor values are defined as
> 'Predictor' parameter value it only means that PNG prediction is in use
> (independent if it is 10, 11, ..., 15).
> I have attached a patch which removes predictor value '10' from 'no
> prediction' code and which triggers PNG prediction for all values >= 10.
> The bug can be tested with
> https://www.cryptool.org/trac/CrypTool2/export/1909/trunk/Documentation/Developer/PluginHowTo/HowToDeveloper.pdf
> Here e.g. on page 6 in the screenshot image (Im3) the rows are shifted by a
> pixel each 3 lines which is a result of the not interpreted predictor byte of
> the rows. The predictor value for the image is 10 (PNG NONE).
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