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https://issues.apache.org/jira/browse/PDFBOX-1870?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13886050#comment-13886050
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John Hewson commented on PDFBOX-1870:
-------------------------------------
Excellent. I've been having some strange behaviour from tint-transform
functions in color spaces and was beginning to get suspicious about Type0 (and
possibly Type2) functions.
> PDFunctionType0 incorrect
> -------------------------
>
> Key: PDFBOX-1870
> URL: https://issues.apache.org/jira/browse/PDFBOX-1870
> Project: PDFBox
> Issue Type: Sub-task
> Components: PDModel
> Affects Versions: 2.0.0
> Reporter: Tilman Hausherr
> Priority: Minor
> Attachments: PDFunctionType0.patch
>
>
> 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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