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https://issues.apache.org/jira/browse/PDFBOX-3000?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14940964#comment-14940964
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Petr Slaby commented on PDFBOX-3000:
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Being the original author of the transparency groups contribution in 
PDFBOX-2104, I have tried to look into this again. The good news is that the 
file attached to PDFBOX-2104 renders fine with the patch from John. It might be 
correct for the first time ever, the image shadow on the first page is missing 
in all the 2.0 reference renderings I have in my repository since December 
2014. Unfortunately, I have no older renderings, so I cannot tell whether we 
got it wrong already at the beginning or whether it got broken later. We have 
this working correctly in our source code based on PDFBox 1.7, but it seems to 
be too hard for me to figure out what exactly needs to be done to successfully 
port our implementation to PDFBox 2.0.

The only thing I do not like about John's patch is that it creates a full page 
bitmap to render the transparency group. I have tried to bring back the 
original idea of creating a bitmap according to the intersection of the 
bleeding box of the group and of the current clip path. After some trials, I 
get the same results as John on my test documents using the attached patch. 
Maybe someone with more insight into all the transforms can use it as a 
starting point to get this right.

> Transparency Group issues
> -------------------------
>
>                 Key: PDFBOX-3000
>                 URL: https://issues.apache.org/jira/browse/PDFBOX-3000
>             Project: PDFBox
>          Issue Type: Bug
>          Components: Rendering
>    Affects Versions: 2.0.0
>            Reporter: John Hewson
>             Fix For: 2.1.0
>
>         Attachments: softmask-rewrite.patch
>
>
> This is a follow-up issue for transparency group issues from PDFBOX-2423. 
> More details to come.



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