Problem with text color using exclusion blend mode

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maximilian

I have a document where I have yellow text on a background image that is mostly dark blue. I have the text on a separate layer for which I have set the blend mode to exclusion. When I export the document as a PDF/X-4, intended for printer, the yellow of the text appears much darker when viewing the PDF file in Adobe Acrobat Reader than it looked like in Scribus. After investigating this problem, I believe that the reason for the discrepancy is that, in the exported PDF file, the blending color space of the text object seems to be set to the color space of the document's output intent, which is in CMYK mode, even though Scribus performs all color blending operations in RGB (as I believe I have read somewhere). Can someone confirm this? Is this a bug in Scribus?

I have attached a sample Scribus document as well as the exported PDF file together with a screenshot of how the PDF file looks in Acrobat Reader.

AdmFubar

Quote from: maximilian on August 25, 2025, 09:48:17 AMAfter investigating this problem, I believe that the reason for the discrepancy is that, in the exported PDF file, the blending color space of the text object seems to be set to the color space of the document's output intent, which is in CMYK mode, even though Scribus performs all color blending operations in RGB (as I believe I have read somewhere). Can someone confirm this? Is this a bug in Scribus?
No not a bug, this is how it would look as printed, as CMYK has smaller color space than RGB.

Do you have color management turned on for Scribus? or your operating system? You can set up your system to reflect how it will look on screen when printed.
Using Scribus1.6.1, 1.7.0 openSUSE 15.6
Advanced hobbyist

maximilian

#2
Yes, I have color management set up, and I am also aware that CMYK color spaces tend to be smaller than RGB color spaces.

Alright, let's test your hypothesis that the resulting PDF file is correct and that the reason for the difference between the color seen in Scribus and the color rendered by Acrobat Reader is merely because the CMYK gamut is smaller than the RGB gamut. I have added another rectangle to the document with exactly the same dark blue color as the first one. On top of this rectangle, I have placed a text field equivalent to the text in front of the first dark blue rectangle. The visible color of the second text is almost exactly the same as the visible color of the first text. However, the second text is in a different layer that does not have a blend mode set, but instead, the text has the visible color of the first text applied to it directly (I calculated the result color of the color blend using the formula specified in the PDF standard). If your hypothesis is correct, then the two colors should look nearly identical in the generated PDF file when opened in Acrobat Reader.

However, this is not the case. Presumably because the blend color space of the text in the PDF document is set to the document's destination CMYK color space, whereas the blending in Scribus is performed in the working RGB color space.

UPDATE: I have modified the sample document so that the first text field is now directly above the second one in front of the same dark blue rectangle. This way, the effect can be observed even more clearly.

a.l.e

In the bug tracker there seem to be a few tickets that are close to your issue (like https://bugs.scribus.net/view.php?id=16940).

But I could not find this exact use case.

Would you mind opening a ticket with your sample files?

maximilian


AdmFubar

I'm not sure if i'm right about this, but the blend mode for text only seems to work with text and not other objects.

I was playing with the file posted by max and was adjusting the wording of the text to reflect what text was which as i tried different options. the text wrapped in the text frame and the exclusion mode was applied to the text, I added a background color to the text as well and got more exclusion effect applied.

See the attached file.

Using Scribus1.6.1, 1.7.0 openSUSE 15.6
Advanced hobbyist

maximilian

#6
Quote from: AdmFubar on August 26, 2025, 11:18:13 PMI'm not sure if i'm right about this, but the blend mode for text only seems to work with text and not other objects.
I am not sure if I understand what you mean by that. Do you mean that, if there are different objects in a layer that has a blend mode assigned, the blend mode will only affect text in that layer and not other objects? If so, this does not seem to be the case. I have created a circle in the layer with the blend mode with the same source color as the text in that layer and the circle is displayed in exactly the same color as the text.

Quote from: AdmFubar on August 26, 2025, 11:18:13 PMI was playing with the file posted by max and was adjusting the wording of the text to reflect what text was which as i tried different options. the text wrapped in the text frame and the exclusion mode was applied to the text, I added a background color to the text as well and got more exclusion effect applied.
Is this related to the original topic of this thread, to the observation you made in the first sentence of your message, or to neither of the two? Because I do not see any connection and I wonder if I am missing something.

AdmFubar

Ok I did a little checking and found this on Adobe's site

Difference
Looks at the color information in each channel and subtracts either the blend color from the base color or the base color from the blend color, depending on which has the greater brightness value. Blending with white inverts the base color values; blending with black produces no change.

Exclusion
Creates an effect similar to but lower in contrast than the Difference mode. Blending with white inverts the base color values. Blending with black produces no change.

In Scribus this seems to work as indicated here. The darker the color present the less change there is until you get to black and then there is no change.

Now when you are exporting to the pdf, in the window that opens there are a set of tabs for adjusting the export options, one is marked "Color". In that tab there is an intended output option, "Screen/Web", "Printer", or "Grayscale", Whst option are you using?
Using Scribus1.6.1, 1.7.0 openSUSE 15.6
Advanced hobbyist

maximilian

Quote from: AdmFubar on August 27, 2025, 01:59:39 AMIn Scribus this seems to work as indicated here. The darker the color present the less change there is until you get to black and then there is no change.
Yes, I have manually calculated the result color of the blend, assuming it were performed in RGB, and have even documented it in the ODS file attached to my bug report, and the calculated color matches the color that is rendered by Scribus as a result of applying the exclusion blend mode (by the way, I have included a third text in the sample SLA file in the bug report that has the result color of the color blend being performed in CMYK explicitly assigned to it).

Quote from: AdmFubar on August 27, 2025, 01:59:39 AMNow when you are exporting to the pdf, in the window that opens there are a set of tabs for adjusting the export options, one is marked "Color". In that tab there is an intended output option, "Screen/Web", "Printer", or "Grayscale", Whst option are you using?
When selecting PDF/X-4 in the General tab, the "Output Intended For" option in the Color tab is greyed out and set to "Printer" (understandably). But when I tried exporting to PDF 1.6 (which is apparently the standard that PDF/X-4 is based on), I selected "Printer" and the problem is present in the exported PDF file as well.

a.l.e

Thanks for the ticket.

We will see if jghali will have something to say about that...