Tell me how I can remove the background of a yellowed old book I have to read or print for my research side-project with a PDF file. I don't understand dismissive generalisations about a tool coming from people that don't use it. For the purpose it was designed for it does the job better than a format designed for an entirely different thing.
Frankly I don't expect having to read PDF files 50 years from now, but if I were thinking about preservation, the timeproof archiving medium still is acid-free paper –better yet, vellum– and probably India ink. As for the need of any technology, beyond stone tools and fire nobody really needs anything, it's just convenient.
Tell me how I can remove the background of a yellowed old book I have to read or print for my research side-project with a PDF file.
I think you may be confusing tools with file formats. There are any number of ways to do this with .PDFs, none of which I've personally had to explore.
Frankly I don't expect having to read PDF files 50 years from now, but if I were thinking about preservation, the timeproof archiving medium still is acid-free paper –better yet, vellum– and probably India ink. As for the need of any technology, beyond stone tools and fire nobody really needs anything, it's just convenient.
I just can open this djvu file with a viewer and display foreground, done. I can focus on reading it, which is the whole point of me accessing this file. I don't have to process a bloated PDF version with any other tools you just don't even know, me neither.
Exactly, in this planet we still can read, for instance, books printed by Gutenberg, yet try to convert some Word files rotting in a low-density macintosh floppy from 25 years ago. Paper beats everything else because it's a passive medium that lasts centuries and comes with all the hardware you need. A computer file needs a whole ecosystem and being copied around often.
Will we even use files in 2068? I don't know. Maybe in 2047 PDFs will be out of mainstream support because 99% of customers will be using the next better format or workflow.
Exactly, in this planet we still can read, for instance, books printed by Gutenberg, yet try to convert some Word files rotting in a low-density macintosh floppy from 25 years ago.
Meanwhile, a .PDF from the same era would still be perfectly readable. There's a lesson there.
There was no way no create a pdf file with a Mac back in 1993. It didn't take off until Acrobat 3 a few years later, and then you couldn't make decent pdfs unless you bought Acrobat 4 and use Distiller. You'd typically share your doc (or whatever) files, and if you wanted portability you'd use PostScript. Which still is a better format if you have to make changes at the very last stage before printing.
Ordinary users just couldn't make pdfs without paying for additional publishing software until some ten years ago.
The lesson is that some formats become de facto standards, then people forget how that happened (and that it could happen again), and ignore better technical solutions for specific jobs.
Djvu certainly may fall out of use some day, but I think you are greatly underestimating how popular the format is if you really think think there won't be programs around to read it. It's not an obscure format, and there are widely used open source libraries to do so.
50 years from now, you are not going to have any trouble finding a .PDF viewer, but DjVu is a different question entirely.