PDF export issue involving transparency and elliptical gradients

[garrettm30]

I am having a PDF export issue. It started with a real document, but when I observed a problem, I kept distilling down to the core issue and changing the design in random ways until I could home in on the issue, and here is the odd design that I landed on that illustrates the core problem. Please observe this screenshot:

 

On the left is the Publisher document (attached). In the middle are the export settings used, namely the “PDF (digital - small size)” preset, which if I am not mistaken was a default preset. On the right, the resulting PDF export (also attached) as viewed in Apple Preview.

Notice the gradient that is overlaid (with darken blending mode) over the triangle object. On the left part of the export, the transparency is lost, while on the right, transparency is as expected for darken mode. Those are two different rectangles with similar gradients applied. I duplicated the one on the left, moved it to the right, and changed the gradient method from elliptical to linear.

As far as I can tell, that is the only difference between the two rectangles. Therefore I conclude that elliptical gradients do not get exported correctly with regards to transparency.

Some observations:

• If I use the same preset but change the export color space to CMYK, then Apple Preview displays correctly (this despite the document and elements defined as RGB).
• The “incorrect” PDF that shows the issue in the screenshot displays correctly in Acrobat Reader DC.
• I can export using the PDF/X-4 preset and open correctly in Apple Preview.
• I used Publisher 1.9.3 but also tested beta 1.9.4.1076 with the same results. I am on macOS 10.14.6 with Preview 10.1.

The different results when viewed in Apple Preview vs. Adobe Acrobat does suggest that this is possibly an Apple Preview issue—though not necessarily. I know from web programming that different browsers handle incorrect HTML differently, as each tries to guess the correct intent in different ways, so perhaps there is a little issue with the PDF that Acrobat does a better job at second-guessing. Maybe not, but as commonly as PDFs are viewed by Apple Preview or the similar technology that renders PDFs in iOS, it is at least worth looking into.

PDF alpha issue.afpub PDF alpha issue.pdf

[thomaso]

I see the same results with your 2 files as shown in your screenshots.

…

Most obvious is that in macOS's Preview.app for PDF the page transparency is not shown but white instead (I have set transparency color to pale yellow). Whereas Preview shows transparency if exported as PNG. So this specific page white handling seems to be a matter of Preview, possibly meant as feature.

If I export not as page but as "Selection Only" to force paper/background transparency then both apps, Preview and Acrobat, fail in displaying transparency, while Acrobat still shows it for paper white but for none of the objects. [ For my trials I moved the left rectangle to see an obvious gap / and I did all exports with preset "(for print)". ]PDF alpha issue_darken_selection.pdf

If I open this PDF (darken mode exported as 'selection only') in APub then the gradients are set to "normal", so this Darken mode issue is caused by Affinity exported as "Selection Only".

If I switch blend modes to "Darker Colour" or "Multiply" and export with preset "(for print)" then it seems Preview has problems with "Multiply" only – but does handle "Darker Color" correctly – which is quite strange since "Multiply" (and "Darken") are a supported transparency modes in the PDF specs – while Darker Colour is not.

[thomaso]

This topic is possibly related to that, with shadows in darken mode not exporting correctly:

 

[SPaceBar]

Hi @garrettm30 Sorry for the delay in replying to your post. I haven't been able to reproduce the issue when using Acrobat or Preview. 

[garrettm30]

44 minutes ago, SPaceBar said:

I haven't been able to reproduce the issue when using Acrobat or Preview.

Can you confirm that the PDF export that I attached in the original post is displayed correctly in Preview?

If it appears correctly in Preview, then I conclude it is a difference in the version of Preview in your version of macOS and versus my macOS 10.14.6.

If the PDF I shows the same error on computer, then we will have more work to do to figure out why you could export correctly and I could not.

[SPaceBar]

Hi @garrettm30 It does display correctly in my version of Preview on macOS 11.4.

In the attached image Acrobat is the larger PDF at the back and Preview at the front. I know I have an iMac with macOS 10.12.6 but I will see if any of my colleagues have macOS 10.14.6.

[thomaso]

46 minutes ago, SPaceBar said:

I will see if any of my colleagues have macOS 10.14.6.

Just in case, this is the appearance of Garrett's PDF to me in macOS 10.14.6 in Preview, and below in Apub + Acrobat:

 

 

[garrettm30]

For what it is worth, my original PDF does display correctly on my 2020 iPhone SE with iOS 14.something. That seems to reduce the severity of the issue in my mind. It may well be just an issue with older copies of Preview, but it might still be worth taking a look at in case there is some little syntax foible in the export that the older Preview chokes at.

[SPaceBar]

I tried the Preview that I have on my Sierra iMac and that was ok too. It's possible it's an issue with specific macOS's but I will get back to you on that.

I've just sent it to my very old iPhone 6 and the issue is visible on there too.

[SPaceBar]

@garrettm30 One of my colleagues with Mojave also saw the issue when using Preview but not on their PC. We're currently looking into it. 

UPDATE: For us it displays incorrectly on Preview 10.1 but looks fine on Preview 11 - one of us has this installed on Mojave. This suggests its only an issue with older versions of Preview and is more of a reader issue.

[thomaso]

2 hours ago, SPaceBar said:

This suggests its only an issue with older versions of Preview and is more of a reader issue.

Good to know, thanks!
(Do you know how the colleague got Preview 11 in their Mojave? As a copy taken from a newer macOS installation?)

What is with this gradient issue if the objects get exported as selection? As mentioned above then to me also Acrobat appears to fail with transparency. It seems, both gradient types don't show transparency in both viewer apps.

 

[SPaceBar]

Sorry @garrettm30 & @thomaso there was a little bit of cross-communication there. They were on macOS 11.4 not on Preview 11. The fact that it works with an update does seem to suggest it was more with the reader. It also worked fine on my macOS 10.12.6 iMac too.

I can look into the "export as selection" issue. I know there have been a few gradient issues reported but on a quick check could not see that.

[thomaso]

10 minutes ago, SPaceBar said:

seem to suggest it was more with the reader. It also worked fine on my macOS 10.12.6 iMac too.

As supplement: Garrett's PDF also opens fine on a PDF viewer app on my Android phone (v7.0, ~2018).

41 minutes ago, SPaceBar said:

I can look into the "export as selection" issue. I know there have been a few gradient issues reported but on a quick check could not see that.

How about the export-as-selection PDF I had uploaded above? Does it display transparency for any gradient / in any viewer to you?