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https://issues.apache.org/jira/browse/PDFBOX-6155?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18074260#comment-18074260
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Tilman Hausherr edited comment on PDFBOX-6155 at 4/17/26 2:32 PM:
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Re "undefined results" in that documentation commit, I just spent some time
working on bitmap-symbol-symhuffrefine-textrefine.pdf without success. Whatever
happens is when calling GenericRefinementRegion.getRegionBitmap(). It starts
with a good bitmap and ends with a complete mess. It's with ID 9 in case it is
investigated from elsewhere. The source is image ID 8 and has a "gap" but I
suspect this is on purpose because it is meant to be improved by the refinement
process.
!GenericRefinementRegion215-1776436118615-1.png!
!GenericRefinementRegion267-null-1776436118627.png!
was (Author: tilman):
Re "undefined results" in that documentation commit, I just spent some time
working on bitmap-symbol-symhuffrefine-textrefine.pdf without success. Whatever
happens is when calling GenericRefinementRegion.getRegionBitmap(). It starts
with a good bitmap and ends with a complete mess. It's with ID 9 in case it is
investigated elsewhere. Image ID 8 has a "gap" but I suspect this is on purpose
because it is meant to be improved by the refinement process.
!GenericRefinementRegion215-1776436118615-1.png!
!GenericRefinementRegion267-null-1776436118627.png!
> AT (Adaptive template pixels) -1 byte skipped
> ---------------------------------------------
>
> Key: PDFBOX-6155
> URL: https://issues.apache.org/jira/browse/PDFBOX-6155
> Project: PDFBox
> Issue Type: Sub-task
> Components: JBIG2
> Affects Versions: 3.0.4 JBIG2
> Reporter: Tilman Hausherr
> Assignee: Tilman Hausherr
> Priority: Major
> Attachments: GenericRefinementRegion215-1776436118615-1.png,
> GenericRefinementRegion267-null-1776436118627.png,
> bitmap-symbol-textrefine-customat.pdf,
> bitmap-symbol-textrefine-negative-delta-width.pdf,
> bitmap-symbol-textrefine.pdf
>
>
> bitmap-symbol-textrefine-customat.pdf has a garbled shape, however
> bitmap-symbol-textrefine.pdf doesn't. The difference is that the problematic
> one has 4 AT bytes.
> [https://github.com/SerenityOS/serenity/blob/master/Tests/LibGfx/test-inputs/jbig2/json/bitmap-symbol-textrefine-customat.json]
> {code:json}
> "refinement_adaptive_template_pixels": [
> 10,
> -1,
> 4,
> 15
> ],
> {code}
> After a lot of reading and searching and trying I was able to trace it to
> {{GenericRefinementRegion.updateOverride()}} which ignores AT bytes if they
> are -1. However the specification says no such thing:
> 6.3.5.3 Fixed templates and adaptive templates
> The AT pixel RA1 can be located anywhere in the field shown in Figure 7, not
> including the current pixel. The AT pixel
> RA2 can be located anywhere in the range (-128, -128) to (127, 127) in the
> reference bitmap.
> See also figure 7 earlier in the specification, which has (-1,-1) values.
> Just removing the two lines fixes the problem but ruins
> bitmap-symbol-textrefine-negative-delta-width.pdf, which has all -1 so I'll
> research that.
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