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https://issues.apache.org/jira/browse/PDFBOX-2681?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jon Wu updated PDFBOX-2681:
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Attachment: purple-gradient-comparison.jpg
[~jahewson] your explanation makes sense that shading must be done in the
source color space. I'd agree that the only issue left here is that there's a
bug in the shading calculation with CMYK.
purple-gradient-comparison.jpg is just another side by side example from
another file - same design but with a purple gradient (with default ICC, not
the Adobe one). This is very similar to the example [~jahewson] just attached
but you can see how "washed out" the PDFBox version looks due to the bad
shading calculation.
In my example here, there was somebody's face (not shown) and we've seen that
the bug here makes a huge difference such that if there's a gradient over
somebody's face that should barely be visible, it ends up completely taking
over the photo as seen in purple-gradient-comparison.jpg.
> Colors inaccurate rastered CMYK source w/ gradient + photo
> ----------------------------------------------------------
>
> Key: PDFBOX-2681
> URL: https://issues.apache.org/jira/browse/PDFBOX-2681
> Project: PDFBox
> Issue Type: Bug
> Components: Rendering
> Affects Versions: 2.0.0
> Environment: Tested on OS X 10.10, Java 1.6 / 1.8
> Reporter: Jon Wu
> Attachments: Shading2Function2CMYK.pdf, Shading2Function2CMYK.ps,
> acrobat-vs-pdfbox-swop.png, gradient-test-illustrator.jpg,
> gradient-test-pdfbox.jpg, gradient-test-photo-illustrator.jpg,
> gradient-test-photo-pdfbox-us-web-coated-swop-v2.jpg,
> gradient-test-photo-pdfbox.jpg, gradient-test-photo-rgb-illustrator.jpg,
> gradient-test-photo-rgb-pdfbox.jpg, gradient-test-photo-rgb.pdf,
> gradient-test-photo.pdf, gradient-test.pdf, purple-gradient-comparison.jpg
>
>
> In the attached gradient-test-photo.pdf, there's a photo with a gradient on
> top of it. The colors in the gradient are CMYK. When rasterizing this test
> file with PDFBox 2.0.0 SNAPSHOT 20150209, the resulting image's gradient is
> different from the original and the colors of the photo under the gradient
> look significantly different vs the display in Adobe tools like Illustrator
> or other compliant PDF readers.
> Issues:
> - Color hue is wrong. Is this a CMYK to RGB issue?
> - Opacity of gradient is wrong and much different. The jpg from Illustrator
> shows much more of the photo without a gradient over it.
> Without a photo, there's still a difference, but it's much harder to see.
> Example in gradient-test.pdf where the same gradient is drawn over a grey
> rectangle.
> If I convert the PDF to RGB in Illustrator first and rasterize the RGB PDF
> with PDFBox, the result is nearly identical between Illustrator and PDFBox so
> this seems like a CMYK conversion issue in both the general color conversion
> and maybe how the gradient is calculated.
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