PDF icon thumbnail: binder & paging consistency

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PDF icon thumbnail: binder & paging consistency

I always thought that the presence of the binder in PDF icon thumbnail (and a possible "peek through" to the following page) means single-page vs. multi-page PDF. Nonetheless the two files below are both basically the same documents, multipage PDFs, generated the same way:

Both are PDF 1.7 files created from the same app, only the left one was downloaded via Safari from the web, the other one from Mail (or another native app), OS versions do not matter (in this case the left one is from macOS 10.14 via Finder and the right one from iOS 14 via iCloud, nonetheless I have both types of thumbnails coming from one OS at a given time…)

Both are the same dimensions, multi-page, authored in the same SW.

Is there a rule I'm missing between the two file representations, or the thumbnail generation is more random than I thought?

Thanks! –Jan

iMac 27″, 11.2

Posted on Feb 15, 2021 4:31 PM

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Answer 1

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VikingOSX

Level 10

123,422 points

Feb 17, 2021 7:43 AM in response to jbrasna

Well, this is turning out to be a detective mystery. It does not appear to be tied to a specific PDF version, and if the PDF is created on macOS using Apple's Quartz PDFContext, or Apple's PDFKit framework, and happens to be a multi-page PDF, then it gets the icon black binding. Ostensibly, this may be to visually indicate that the PDF is more than one page in length.

Applications that use their own PDF library (e.g. LibreOffice v7.1) do not generate multi-page PDF with black binding on their document icon. If I download the 453 page LO Writer User Guide using Safari 14.0.3, the downloaded PDF icon has the black binding, even though that User Guide was created with LO Writer at the Document Foundation.

When I generate a PDF from single-page content, it receives no icon binder, and 100% of the time, when it is multi-page, the icon receives a binding. All created on the Mac using: 1) cupsfilter, 2) printInfo, 3) pstopdf, 4) Preview, 5) Pages v10.3.9, and custom PDFKit framework applications.

If I read a multi-page PDF with a custom script and split the first page into its own PDF file, that one-page document has no icon binding, but the remainder of the multi-page PDF does have an icon binding.

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Answer 2

Camelot

Level 9

58,473 points

Feb 17, 2021 12:48 PM in response to VikingOSX

I suspect it has something to do with the kMDItemNumberOfPages metadata:

% mdls -n kMDItemNumberOfPages SinglePage.pdf
kMDItemNumberOfPages = 1

For all the (small number of) PDFs I checked here, all the single-page icons had a value of 1, whereas multi-page PDFs had a greater number, indicating the number of pages.

The bigger question may be who/what/where is setting (or not setting) this value.

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Answer 3

VikingOSX

Level 10

123,422 points

Feb 17, 2021 3:58 PM in response to Camelot

Apple's Quartz PDFContext and PDFKit have been creating these plain, single-page, and black-bound, multi-page PDF icons since at least El Capitan. If I generate a multi-page PDF from LibreOffice v7.1 using its own PDF library, then I get a plain PDF icon.

However, if I download a 453 page PDF that was created by LibreOffice Writer using either Safari 14.0.3 or Firefox 85.0.2, then that PDF once written to macOS bears a black, multi-page PDF icon binding. This leads me to believe that the decision is not being made by the browsers about the icon style, but by some Apple framework that the browsers are accessing to write that PDF to the filesystem. The page count is determined and the appropriate icon is generated, perhaps my qlmanage.

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Answer 4

VikingOSX

Level 10

123,422 points

Feb 15, 2021 7:59 PM in response to jbrasna

It is late here, and my primary Desktop is macOS 11.2.1. The one consistency that I see with the black binder PDF icons is that their producer is Apple's Quartz PDFContext, AppendMode 1.1. Without that AppendMode 1.1, and generated by just Quartz PDFContext, they are plain icons without the PDF stamp on them. I will look into this tomorrow after I move a foot of snow at both houses.

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Answer 5

jbrasna Author

Level 1

10 points

Feb 22, 2021 5:38 PM in response to Camelot

Interestingly enough, for the two documents in the original question above it's correct in both cases, yet only the latter receives the multi-page treatment.

% mdls -n kMDItemNumberOfPages DH77999.pdf
kMDItemNumberOfPages = 7

% mdls -n kMDItemNumberOfPages WD99613.pdf
kMDItemNumberOfPages = 5

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Answer 6

jbrasna Author

Level 1

10 points

Feb 22, 2021 5:32 PM in response to VikingOSX

Well, this is turning out to be a detective mystery.

Indeed. Thank you both for elaborating and confirming my thoughts — for something that ought to be simple and consistent I kept seeing wild variations, and now I know it's not my perception betraying me, but it might be the framework used to write the file sometimes failing to count the pages etc. Interesting!

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PDF icon thumbnail: binder & paging consistency

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