Tilman Hausherr created PDFBOX-1870:
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Summary: PDFunctionType0 incorrect
Key: PDFBOX-1870
URL: https://issues.apache.org/jira/browse/PDFBOX-1870
Project: PDFBox
Issue Type: Sub-task
Affects Versions: 2.0.0
Reporter: Tilman Hausherr
Priority: Minor
Type 0 (Sampled) Functions are described in 3.9.1 of the pdf spec and
bascially, its cheating: there's an n-dimensional grid of values ("samples")
and the function shall return these values or something in-between.
PDFunctionType0 has two bugs:
1) it does not do any interpolation. The function interpolate() is called
several times, but only adjust values between ranges etc, not to calculate the
color between 2^n samples - that part is "outputValues[i] =
(outputValuesPrevious[i] + outputValuesNext[i]) / 2". The spec does not tell
much, only that "Interpolation is used to determine output values from the
nearest surrounding values in the sample table". I have done a linear/bilinear
interpolation implementation for 1D/2D inputs. I did not do an interpolation
implementation for 3D and higher, because its unclear whether this is actually
used. Instead, I return random (!) values.
2) the sample bits are not collected correctly, the current code ignores the
leftover bits when a row is done. The spec tells us "Successive values are
adjacent in the bit stream; there is no padding at byte boundaries". Luckily,
that one is easy to correct, three lines must be moved up. Alternatively, one
might use the bit-io lib I mention in PDFBOX-615.
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