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https://issues.apache.org/jira/browse/PDFBOX-4095?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16362467#comment-16362467
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Jani Pehkonen commented on PDFBOX-4095:
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{quote}some blendmodes don't work properly against the page background
{quote}
The "unmarked space" simply means a raster buffer (like BufferedImage) that is
initially fully transparent. This makes the blend modes work. No new graphics
engine is needed.
See how Mozilla PDF.js has implemented it
[here|https://github.com/mozilla/pdf.js/blob/ea3d8450d218dd53619c72c934547fe57f22530f/src/display/canvas.js#L731].
If a PDF page uses any blend modes [other than
Normal|https://github.com/mozilla/pdf.js/blob/ea3d8450d218dd53619c72c934547fe57f22530f/src/core/evaluator.js#L226],
PDF.js renders everything on a fully transparent RGBA canvas. Finally when the
page has been rendered, PDF.js draws the RGBA canvas on a white canvas.
When rendering graphics like this in a fully transparent buffer, you are
actually implementing _page groups_, which are explained in the PDF 32000
standard in section 11.4.7.
> Non Separable Blend Modes implementation(HUE, SATURATION, COLOR, LUMINOSITY)
> ----------------------------------------------------------------------------
>
> Key: PDFBOX-4095
> URL: https://issues.apache.org/jira/browse/PDFBOX-4095
> Project: PDFBox
> Issue Type: Improvement
> Components: Rendering
> Affects Versions: 2.0.8
> Reporter: savan patel
> Priority: Major
> Attachments: BlendComposite.java.patch, BlendMode.java.patch,
> COSName.java.patch, blendmodes.pdf, gs-bugzilla690477.pdf,
> gs-bugzilla697433-1.pdf
>
>
> I have a patch for implementation of non separable blend modes...
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