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https://issues.apache.org/jira/browse/PDFBOX-2853?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14616651#comment-14616651
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Jakob Pyttlik commented on PDFBOX-2853:
---------------------------------------
Thank you for looking into this - Unfortunately, I cannot provide a public
document because of copyright reasons. The attached image is the best I can do
for now, without getting into trouble.
> CCITT: Background is rendered as transparent color
> --------------------------------------------------
>
> Key: PDFBOX-2853
> URL: https://issues.apache.org/jira/browse/PDFBOX-2853
> Project: PDFBox
> Issue Type: Bug
> Components: Rendering
> Affects Versions: 1.8.9
> Reporter: Jakob Pyttlik
> Labels: easyfix
> Attachments: ccittbug.png
>
>
> CCITT-Images with colorspace different from PDIndexed are created using
> PDCCitt.java/getRGBImage:
> {code}
> if (colorspace instanceof PDIndexed)
> {
> ...
> }
> else
> {
> byte[] map = new byte[] { (byte) 0x00, (byte) 0xFF };
> colorModel = new IndexColorModel(1, map.length, map, map, map,
> Transparency.OPAQUE);
> }
> {code}
> The value Transparency.OPAQUE (=1) is provided for the parameter
> "transparentIndex" - this creates an image, in which the white color is
> treated as transparent.
> This bug is especially annoying for some OCR-documents I had to work with
> (using PageDrawer). They consist of rendered text (as result of the OCR),
> that has the original content as image rendered on top, fully covering the
> text. When the white background is rendered as transparent, the rendered page
> gets messed up, because both texts can be seen,
> *Proposed Fix/Patch*
> Replace the value *Transparency.OPAQUE* with *-1*, so that no color is
> transparent.
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