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https://issues.apache.org/jira/browse/PDFBOX-6156?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18055212#comment-18055212
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Tilman Hausherr commented on PDFBOX-6156:
-----------------------------------------
While working on a simple BitBlit, I noticed that setPixel() could not set a 0
pixel, I have fixed that.
> RegionBitmap bit blit slightly too large
> ----------------------------------------
>
> Key: PDFBOX-6156
> URL: https://issues.apache.org/jira/browse/PDFBOX-6156
> Project: PDFBox
> Issue Type: Sub-task
> Components: JBIG2
> Affects Versions: 3.0.4 JBIG2
> Reporter: Tilman Hausherr
> Priority: Major
> Attachments: bitmap-composite-and-xnor.pdf,
> bitmap-composite-and-xnor.png
>
>
> The result rendering looks like this:
> !bitmap-composite-and-xnor.png!
> The XNOR is detected and works properly, the real cause is that we have a
> white region (on the left) that has the width 141, but the actual width after
> the blt operation is 144. It turns out that 144 is a multiple of 8 so
> {{Bitmaps.blit()}} botches the last byte somehow.
> Another thing I learned while working on this is that in the specification, 0
> is white and 1 is black. The page starts with default 1 = all black. So the
> chaos starts when the next region image (on the right) is blited at x=141
> with XNOR on the white stripe, resulting in a black stripe.
> 141 pixels = 17 bytes + 5 bits => 3 bits of the destination should be left
> untouched at the end.
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