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Re: Learning to Create Tiny DJVU files

Posted: 04 May 2014, 23:48
by daniel_reetz
dtic wrote:Very useful posts Richard!
Agreed 100%. These posts are, as far as I can see, a unique resource on the internet. Thanks for taking the time, RichardT.

Re: Learning to Create Tiny DJVU files

Posted: 05 May 2014, 00:24
by jera2
I too want to chime in and express my thanks, Richard, for all your posts. Very informative, and if I ever get around to working with this area on my own, I will study your posts again!

Re: Learning to Create Tiny DJVU files

Posted: 24 Jul 2014, 12:05
by RichardT
Thanks, all, for the kind words! As I come across interesting or confusing books I'll be sure to make more posts, but in truth most books are very easy to compress with the techniques already here. Between scanTailor and imageMagick and minidjvu and djvuLibre, we have a pretty complete suite of tools. I still wish a free replacement for msepdjvu existed, but the truth is for complicated pages you get much better results splitting the imagery out by hand anyway.

Re: Learning to Create Tiny DJVU files

Posted: 16 Jul 2015, 23:42
by RichardT
Hi all! It's been a year since my last post, and really not much has changed for my process. I scan a lot fewer books these days, since my whole library has been scanned and I try to avoid buying paper books unless that's the only form available.

One thing I've started doing since getting a large desktop machine is using a RAM disk. In a typical scenario, making tweaks to a book, I will split out a DjVu or PDF into one PNG per page, do some kind of image processing on the PNGs, and then recombine them into a DjVu or PDF. So, it has always bothered me that I have to write sometimes like 800 intermediate files to disk, then re-open and read them back in to edit, then just erase them again as soon as I'm done.

Well like I mentioned, I got a new desktop with lots of RAM to spare, so I tried making a ram disk for those files. Now, all the intermediate files never hit a physical disk! And it's faster as well.

All the main platforms can mount a ram disk. I'm on OS X these days, and the command will look like:

Code: Select all

diskutil erasevolume HFS+ 'RAM Disk' `hdiutil attach -nomount ram://xxxxxx`
.... where xxxxx is the size you want in megabytes * 2048.

Anyway, if you are computer-savvy, have lots of RAM, and are careful to create the final product on a physical disk, it can be a nice way to handle all those temporary files.

Re: Learning to Create Tiny DJVU files

Posted: 21 Jul 2015, 01:13
by RichardT
I know I've mentioned this before in some posts, but I used this technique today and I thought I'd add it to the thread as its own tip...

Tip: If all the text on the page is one color (say, blue text), you don't have to make a foreground color map. djvumake will create a minimal one for you.

So today the ugly scan I cleaned up had blue text on page 2. Here's what I did:
  1. Clean up the image in scantailor or imagemagick, and set it to black-and-white output. Let it make the text black.
  2. Generate an indirect DjVu file of all the pages with minidjvu like always. Now each page has its own DjVu file.
  3. Move the page that should have colored text out of the way. (e.g., mv p0002.djvu x0002.djvu)
  4. Create a djvu page with Sjbz set to the b/w text page you just moved, and FGbz set to the hex value of the color you want the text to be.
So, that last step will look something like:

Code: Select all

djvumake.exe p0002.djvu INFO=,,600 INCL=p0001.iff Sjbz=x0002.djvu FGbz=#5478bc
Here's a close-up from my file today (left is original bad jpeg scan, right is much nicer product):
b3s.png
side-by-side
b3s.png (11.15 KiB) Viewed 9241 times
I know, the crisp "B3" on the right looks a little ragged, but at 100% zoom it looks great. That's as good as it gets when starting with these horrible jpeg scans, unfortunately.

Sadly, I paid money for this scan... if anyone here happens to know a Wizards of the Coast exec, let them know they can hire me to make their scanned product offerings look great, if they want. ;)

Re: Learning to Create Tiny DJVU files

Posted: 15 Mar 2016, 13:04
by Amjad
This post is priceless.
Richard rocks !