Question regarding "unknown decode filter"

[Lolf1010]

Hi everyone,

at work we use veraPDF to validate pdf files uploaded by our users of our platform.
We have seen the log-message "Unknown decode filter" a couple of times recently.
The log comes from org.verapdf.cos.filters.COSFilterRegistry#getDecodeFilter, see here.

Questions
Is it possible to add the name of the filter to the log-message so that we can see which unsupported filter was used?

Are there any known filters that are currently not supported by veraPDF?
I have found a couple online that are not in the registry (RunLengthDecode, JBIG2Decode, DCTDecode) but they did not cause the log-message. I probably did not use them correctly or, even more likely, dont understand that part of pdf-files completely ;)

And, since the log-level is SEVERE: should we report unsupported filters to you so they can be added or can they be ignored when validating a pdf-file?

Thanks.

[bdoubrov]

Hi @Lolf1010

Is it possible to add the name of the filter to the log-message so that we can see which unsupported filter was used?

Thanks for the suggestion. We've added this extra info in the latest dev build.

veraPDF does not decode images and as such does not support image-specific filters: RunLengthDecode, CCITTFaxDecode, JBIG2Decode, DCTDecode, JPXDecode.

Normally, such filters are not used for any data parsed by veraPDF. So, this log message on "Unknown decode filter" looks a somewhat suspicious. It would be great if you could provide any sample document where you've seen this message.

[Lolf1010]

Thanks for the feedback and adjustment.
Sadly i cannot provide such file as of today. The files that are uploaded by our users are private.
I will continue to try and find a file that causes the log message.
It may require some weird data - who knows what kind of stuff people put in their pdfs^^

I think for now the issue can be closed.
When i have found such file i may create a new issue specifically for that filter.