Alex Brollo, 13/05/2016 09:02:
I presume that this complex structure is somewhat
similar of djvu
background/foreground segmentation into djvu files, and artifacts are
similar.
Sure.
So, pdf images are not only "compressed", but deeply processed and
segmented images.
...which is what I call "compression". I still recommend to try and
increase the fixed-ppi parameter in such a case of excessive compression.
I also still need an answer to
https://it.wikisource.org/?diff=1733473
Is something of this complex IA image processing path
documented
anywhere?
What do you mean? Are you asking about details of their derivation plan
for books? What we know has been summarised over time at
https://en.wikisource.org/wiki/Help:DjVu_files#The_Internet_Archive , as
always. As the help page IIRC states, the best way to understand what's
going on is to check the item history and read the derive.php log, like
https://catalogd.archive.org/log/487271468 which I linked.
The main difference compared to the past is, I think, that they're no
longer creating the luratech b/w PDF, probably because the "normal" PDF
now manages to compress enough. They may have not realised that the
single PDF they now produce is too compressed for illustrations and for
cases where the original JP2 is too small.
Nemo