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https://issues.apache.org/jira/browse/PDFBOX-5370?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17484369#comment-17484369
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Maruan Sahyoun commented on PDFBOX-5370:
----------------------------------------
To add a little context. The issues started when Hans Bärfuss approached me
with him getting a different rendering than Adobe. There is some additional
information I'd like to share:
Translated from German:
{quote}
The (PDFBox) results. RGB as an alternate colorspace are very rare for NChannel
in the field. The explanation for the green color: I created the tint transform
for the DeviceN color in a different color than the color of the different
separations so one can see the differences in rendering engines as most
rendering are only supporting deviceN but not NChannel.
{quote}
Please also see the part from ISO-32000-2 mentioned above (10.8.3)
{quote}
The results of the simulation should match those produced by the following
steps:
a) Process the PDF as if separations were to be created for a simulated device
that supports subtractive
process colourants and possibly spot colours. The PDF processor determines what
process colours and
possible spot colours the simulated device is to have. A default
DestOutputProfile, if available for a
subtractive device, or ColorantTable values, if available for a subtractive
device, should be consulted to
determine the process colours to use (see 14.11.5, "Output intents").
b) Convert each separation into "flat XYZ" (no gamma) and using a background
matte of all white.
c) Blend the resulting separations into a single result using a multiply blend
(see "Table 133 — Variables
used in the basic compositing formula").
d) Convert the result to the actual device colour space and output it.
{quote}
Maybe that clarifies the expected processing to get the sample results
> DeviceN/NChannel Seperation fails for rgb
> -----------------------------------------
>
> Key: PDFBOX-5370
> URL: https://issues.apache.org/jira/browse/PDFBOX-5370
> Project: PDFBox
> Issue Type: Bug
> Components: Rendering
> Affects Versions: 2.0.25, 2.0.26, 3.0.0 PDFBox
> Reporter: Maruan Sahyoun
> Priority: Major
> Attachments: NChannel-Pantone-1.BMP, NChannel-Pantone-1.PNG,
> NChannel-Pantone.bmp, NChannel-Pantone.pdf, NChannel-cmyk-1.BMP,
> NChannel-cmyk-1.PNG, NChannel-cmyk.bmp, NChannel-cmyk.pdf,
> NChannel-rgb-1.BMP, NChannel-rgb-1.PNG, NChannel-rgb.bmp, NChannel-rgb.pdf,
> NChannel-rgb2.pdf, Patch_PDFBOX-5370.txt, image-2022-01-29-10-51-18-421.png,
> image-2022-01-29-10-51-44-286.png, image-2022-01-30-13-46-16-080.png
>
>
> The files NChannel-xx.pdf use different color modes for separation which is
> described in chapter 10.8.3 of the PDF spec. The matching .bmp files show
> the expected results. The -1.BMP and -1.PNG files show the results generated
> by PDFBox trunk (2.0 is the same result).
> As can be seen the results for cmyk and Pantone are fine/close with the rgb
> rendering failing.
> The PDFs and expected results have been provided by Hans Bärfuss, PDF Tools
> AG. Thank you for contributing the samples.
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