[jira] [Commented] (PDFBOX-4267) Incorrect rendering when /Matte entry

["Jani Pehkonen (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PDFBOX-4267?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16580066#comment-16580066 ] 

Jani Pehkonen commented on PDFBOX-4267:
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When decoding an image, you must reverse the operation by solving for c. You get: c = (c' - m) / alpha + m. The variable c' is the color stored in the PDF file. If alpha == 0, avoid division by zero and just set the alpha of the pixel to zero. Note that the equations assume all color components are in range 0.0-1.0. The code of PDF.js has colors in range 0-255.

> Incorrect rendering when /Matte entry
> -------------------------------------
>
>                 Key: PDFBOX-4267
>                 URL: https://issues.apache.org/jira/browse/PDFBOX-4267
>             Project: PDFBox
>          Issue Type: Bug
>          Components: Rendering
>    Affects Versions: 2.0.11, 3.0.0 PDFBox
>            Reporter: Tilman Hausherr
>            Priority: Major
>         Attachments: bugzilla888437.pdf, gs-bugzilla688797-reduced.pdf, gs-bugzilla688797.pdf
>
>
> The image softmask in the attached file has a {{/Matte 0 0 0}} entry. PDFBox displays the PDF differently than Adobe Reader, the reflection shown by PDFBox is barely visible. When the /Matte entry is deleted, then it is barely visible in Adobe Reader too. So the /Matte entry does make some difference, although I don't understand how.
> In the PDF specification, the formula shown is c' = m + α x (c - m). So 0 should have no effect?!
> I looked at the code of PDF.js, they have a special handling when alpha is 0, don't know why.



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