Show HN: PDF Differ • Hacker News Board

Re: Show HN: PDF Differ

#11

Post by e12e » Thu, Jul 20, 2023, 3:00 PM UTC

ketanmaheshwari wrote: post #10

Slightly related, I recently discovered that `less` can read pdf files out of the box. Seems like it is working on Linux but not on macOS.

MacOS comes with an old version of less (581.2) - as Apple fears and avoids GPL v3.

Brew etc holds newer versions - but this particular issue probably has to do with missing lesspipe:

https://github.com/wofr06/lesspipe#42-list-of-preprocessed-f...

Re: Show HN: PDF Differ

#12

Post by cubefox » Thu, Jul 20, 2023, 5:24 PM UTC

Suggestion: When highlighting text, you want to use "multiply" blend mode (a.k.a. subtractive color mixing) instead of opacity. Opacity makes black text lighter/greyish, which is not how physical text markers work, or colored sheets of transparent plastic.

Re: Show HN: PDF Differ

#13

Post by layer8 » Thu, Jul 20, 2023, 7:44 PM UTC

ketanmaheshwari wrote: post #10

Slightly related, I recently discovered that `less` can read pdf files out of the box. Seems like it is working on Linux but not on macOS.

This is likely lesspipe.sh used via LESSOPEN. Less itself certainly doesn’t understand PDF, but it allows automatic custom preprocessing of its input, which many Linux distributions have preconfigured as the system default.

Re: Show HN: PDF Differ

#14

Post by m4rc1e » Thu, Jul 20, 2023, 8:36 PM UTC

cubefox wrote: post #12

Suggestion: When highlighting text, you want to use "multiply" blend mode (a.k.a. subtractive color mixing) instead of opacity. Opacity makes black text lighter/greyish, which is not how physical text markers work, or colored sheets of transparent plastic.

Thanks for the suggestion. I plan on having user selectable blend modes. Currently, it's using the "difference" blend mode. This mode makes it easy to spot shifted images.

Re: Show HN: PDF Differ

#15

Post by progfix » Fri, Jul 21, 2023, 3:38 PM UTC

The black and white mode doesn't look very useful. Check out how Autodesk is visualising changes. They use three colours: blue=only in first pdf, red=only in second pdf, black=in both pdfs.

https://help.autodesk.com/view/BIM360D/ENU/?guid=GUID-08779B...

Re: Show HN: PDF Differ

#16

Post by yencabulator » Fri, Jul 21, 2023, 5:22 PM UTC

Open source & Linux alternatives:

https://www.qtrac.eu/diffpdf-foss.html

https://github.com/vslavik/diff-pdf https://vslavik.github.io/diff-pdf/

Re: Show HN: PDF Differ

#17

Post by m4rc1e » Mon, Jul 24, 2023, 3:43 PM UTC

cubefox wrote: post #12

Suggestion: When highlighting text, you want to use "multiply" blend mode (a.k.a. subtractive color mixing) instead of opacity. Opacity makes black text lighter/greyish, which is not how physical text markers work, or colored sheets of transparent plastic.

I've just implemented user selectable blend modes. I've included the multiply mode as well. Thanks for your feedback.

Re: Show HN: PDF Differ

#18

Post by cubefox » Mon, Jul 24, 2023, 11:32 PM UTC

m4rc1e wrote: post #17

cubefox wrote: post #12

Suggestion: When highlighting text, you want to use "multiply" blend mode (a.k.a. subtractive color mixing) instead of opacity. Opacity makes black text lighter/greyish, which is not how physical text markers work, or colored sheets of transparent plastic.

I've just implemented user selectable blend modes. I've included the multiply mode as well. Thanks for your feedback.

Cool!