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https://issues.apache.org/jira/browse/PDFBOX-5970?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17932957#comment-17932957
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Tilman Hausherr edited comment on PDFBOX-5970 at 3/6/25 3:46 PM:
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I think that what you mean is this: the CMYK colors are [0 0 0 1], but the RGB
colors are [0.08917373, 0.08673228, 0.08380255]. I tried our old CMYK ICC
profile (USWebCoatedSWOP), there we get [0.13707179, 0.12234684, 0.12568857].
I also asked ChatGPT:
{quote}When converting *CMYK (0,0,0,1)* (pure black) to sRGB using the {*}US
Web Coated (SWOP) v2 ICC profile{*}, the result is *not exactly (0,0,0)* due to
the characteristics of the ICC profile.
h3. *ICC Profile Considerations*
* The *US Web Coated SWOP v2* profile is designed for printing on coated paper
using a web press.
* Unlike a direct mathematical conversion, ICC profiles use lookup tables and
tone curves to account for ink behavior and paper reflectivity.
* {*}Black (K=100%) in CMYK does not always map to pure black (0,0,0) in
sRGB{*}, because real-world printing inks are not perfectly black.
h3. *Expected Conversion Result*
Using the *Adobe Color Converter* or other ICC-aware software, the typical
conversion of *CMYK (0,0,0,1) in US Web Coated SWOP v2* results in an sRGB
value around:
*sRGB (33, 31, 32)*
This means:
{quote} *
{quote}The black is *not absolute black* but rather a {*}dark grayish
tone{*}.{quote}
*
{quote}This happens because of how the ICC profile models ink absorption and
dot gain.{quote}
was (Author: tilman):
I think that what you mean is this: the CMYK colors are [0 0 0 1], but the RGB
colors are [0.08917373, 0.08673228, 0.08380255]. I tried our old CMYK ICC
profile (USWebCoatedSWOP), there we get [0.13707179, 0.12234684, 0.12568857].
I also asked ChatGPT:
!screenshot-1.png!
> CMYK color converted to RGB
> ---------------------------
>
> Key: PDFBOX-5970
> URL: https://issues.apache.org/jira/browse/PDFBOX-5970
> Project: PDFBox
> Issue Type: Bug
> Reporter: Simon Steiner
> Priority: Major
> Attachments: adobe4.pdf, screenshot-1.png
>
>
> In pdfbox 2, if i set a breakpoint on PageDrawer:
> protected Paint getPaint(PDColor color) throws IOException
> And call org.apache.pdfbox.tools.PDFToImage
> I see cmyk black text is converted to RGB, i expect result should be
> Color.black as pdfbox used to do via:
> float[] components = color.getComponents();
> return new Color(new DeviceCMYKColorSpace(), components, 1);
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