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https://issues.apache.org/jira/browse/PDFBOX-6199?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18077611#comment-18077611
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Tilman Hausherr edited comment on PDFBOX-6199 at 5/1/26 9:53 AM:
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I wrote a "dumb" version of the decoder:
{code:java}
private byte getPixelSafe(Bitmap bitmap, int x, int y)
{
if (x < 0 || y < 0)
return 0;
if (x >= bitmap.getWidth() || y >= bitmap.getHeight())
return 0;
return bitmap.getPixel(x, y);
}
private void decodeTypicalPredictedLineTemplate1Dumb(final int lineNumber,
final int width,
final int rowStride, final int refRowStride, final int paddedWidth,
final int deltaRefStride, int byteIndex, final int currentLine, int
refByteIndex)
throws IOException
{
for (int x = 0; x < width; ++x)
{
int bit;
// i)
// Page 49
byte b1 = getPixelSafe(referenceBitmap, x - 1, lineNumber - 1);
byte b2 = getPixelSafe(referenceBitmap, x, lineNumber - 1);
byte b3 = getPixelSafe(referenceBitmap, x + 1, lineNumber - 1);
byte b4 = getPixelSafe(referenceBitmap, x - 1, lineNumber);
byte b5 = getPixelSafe(referenceBitmap, x , lineNumber);
byte b6 = getPixelSafe(referenceBitmap, x + 1, lineNumber);
byte b7 = getPixelSafe(referenceBitmap, x - 1, lineNumber + 1);
byte b8 = getPixelSafe(referenceBitmap, x, lineNumber + 1);
byte b9 = getPixelSafe(referenceBitmap, x + 1, lineNumber + 1);
if (b1 == b2 && b2 == b3 && b3 == b4 && b4 == b5 && b5 == b6 && b6
== b7 && b7 == b8 && b8 == b9)
{
bit = b1;
}
else
{
// Otherwise, explictly decode the current pixel using the
methodology of steps 3(c)i through 3(c)iii above.
// Figure 13: 10-pixel refinement template
byte c1 = getPixelSafe(regionBitmap, x - 1, lineNumber - 1);
byte c2 = getPixelSafe(regionBitmap, x, lineNumber - 1);
byte c3 = getPixelSafe(regionBitmap, x + 1, lineNumber - 1);
byte c4 = getPixelSafe(regionBitmap, x - 1, lineNumber);
byte c5 = getPixelSafe(referenceBitmap, x, lineNumber - 1);
byte c6 = getPixelSafe(referenceBitmap, x - 1, lineNumber);
byte c7 = getPixelSafe(referenceBitmap, x, lineNumber);
byte c8 = getPixelSafe(referenceBitmap, x + 1, lineNumber);
byte c9 = getPixelSafe(referenceBitmap, x, lineNumber + 1);
byte c10 = getPixelSafe(referenceBitmap, x + 1, lineNumber + 1);
int context = c1 << 9 | c2 << 8 | c3 << 7 | c4 << 6 | c5 << 5
| c6 << 4 | c7 << 3 | c8 << 2 | c9 << 1 | c10;
cx.setIndex(context);
bit = arithDecoder.decode(cx);
}
regionBitmap.setPixel(x, lineNumber, (byte) (bit & 1));
}
}
{code}
Result when using 8 as the SLTP context:
!screenshot-4.png!
This is quite close. Either there's a bug misunderstanding in my code, or
there's a bug in the non-SLTP decoding.
Update: I traced to see when the dumb method is called last, it is at line 309.
That is just above from where the problems start.
was (Author: tilman):
I wrote a "dumb" version of the decoder:
{code:java}
private byte getPixelSafe(Bitmap bitmap, int x, int y)
{
if (x < 0 || y < 0)
return 0;
if (x >= bitmap.getWidth() || y >= bitmap.getHeight())
return 0;
return bitmap.getPixel(x, y);
}
private void decodeTypicalPredictedLineTemplate1Dumb(final int lineNumber,
final int width,
final int rowStride, final int refRowStride, final int paddedWidth,
final int deltaRefStride, int byteIndex, final int currentLine, int
refByteIndex)
throws IOException
{
for (int x = 0; x < width; ++x)
{
int bit;
// i)
// Page 49
byte b1 = getPixelSafe(referenceBitmap, x - 1, lineNumber - 1);
byte b2 = getPixelSafe(referenceBitmap, x, lineNumber - 1);
byte b3 = getPixelSafe(referenceBitmap, x + 1, lineNumber - 1);
byte b4 = getPixelSafe(referenceBitmap, x - 1, lineNumber);
byte b5 = getPixelSafe(referenceBitmap, x , lineNumber);
byte b6 = getPixelSafe(referenceBitmap, x + 1, lineNumber);
byte b7 = getPixelSafe(referenceBitmap, x - 1, lineNumber + 1);
byte b8 = getPixelSafe(referenceBitmap, x, lineNumber + 1);
byte b9 = getPixelSafe(referenceBitmap, x + 1, lineNumber + 1);
if (b1 == b2 && b2 == b3 && b3 == b4 && b4 == b5 && b5 == b6 && b6
== b7 && b7 == b8 && b8 == b9)
{
bit = b1;
}
else
{
// Otherwise, explictly decode the current pixel using the
methodology of steps 3(c)i through 3(c)iii above.
// Figure 13: 10-pixel refinement template
byte c1 = getPixelSafe(regionBitmap, x - 1, lineNumber - 1);
byte c2 = getPixelSafe(regionBitmap, x, lineNumber - 1);
byte c3 = getPixelSafe(regionBitmap, x + 1, lineNumber - 1);
byte c4 = getPixelSafe(regionBitmap, x - 1, lineNumber);
byte c5 = getPixelSafe(referenceBitmap, x, lineNumber - 1);
byte c6 = getPixelSafe(referenceBitmap, x - 1, lineNumber);
byte c7 = getPixelSafe(referenceBitmap, x, lineNumber);
byte c8 = getPixelSafe(referenceBitmap, x + 1, lineNumber);
byte c9 = getPixelSafe(referenceBitmap, x, lineNumber + 1);
byte c10 = getPixelSafe(referenceBitmap, x + 1, lineNumber + 1);
int context = c1 << 9 | c2 << 8 | c3 << 7 | c4 << 6 | c5 << 5
| c6 << 4 | c7 << 3 | c8 << 2 | c9 << 1 | c10;
cx.setIndex(context);
bit = arithDecoder.decode(cx);
}
regionBitmap.setPixel(x, lineNumber, (byte) (bit & 1));
}
}
{code}
Result when using 8 as the SLTP context:
!screenshot-4.png!
This is quite close. Either there's a bug misunderstanding in my code, or
there's a bug in the non-SLTP decoding.
> Template 1 handling with TPGRON not supported
> ---------------------------------------------
>
> Key: PDFBOX-6199
> URL: https://issues.apache.org/jira/browse/PDFBOX-6199
> Project: PDFBox
> Issue Type: Sub-task
> Components: JBIG2
> Affects Versions: 3.0.4 JBIG2
> Reporter: Maruan Sahyoun
> Priority: Minor
> Attachments: image-2026-04-28-12-27-28-955.png,
> image-2026-04-28-12-28-19-575.png, image-2026-04-28-12-29-21-038.png,
> screenshot-1.png, screenshot-2.png, screenshot-3.png, screenshot-4.png
>
>
> {{bitmap-refine-template1-tpgron.jbig2}} tests the folling features of JBIG2:
> - Refinement region
> - Template 1
> - TPGRON
> - Reference bitmap reuse
> We currently produce garbled output when decoding
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