Thanks for Yifan Lu for providing his excellent jailbreak and simple_usbnet hack, without which my meager success would NOT have been possible. Obviously :-)
So, I have always HATED the default kindle fonts for one main reason....they are just not QUITE big enough for my 51-year-old lasik eyes. On my K2 and K3, I always did the font hack thing, which kind hackers made extremely simple (thanks everyone). I usually ended up replacing Caecilia with Georgia, but I can live without that. The main thing was, whatever font I used, I made them 25% faller and 15% wider than the defaults. HUGE help to the contrast.
There are 8 kindle font sizes. 7 and 8 are HUGE, and 6 is just NOT QUITE BIG ENOUGH for me. This is the problem I wanted to fix.
So, I got a Kindle Touch Wi-Fi only for Christmas, and though I like the device, again, I HATE the font (sizes). Well, after several hours of futzing with this today, I got it working just fine. So, this proves it's pretty easy and hopefully people a LOT smarter than me will package this up so others can do it simply.
I WOULD NOT RECOMMEND THAT ANYONE DO WHAT I JUST DID UNLESS YOU ARE WILLING TO BRICK YOUR DEVICE!!!! I "almost did" a couple or times. Also, I will forget everything I did within a few days, and I hardly ever visit these forums, so don't expect support from me :-)
I have some rudimentary knowledge of ttf files, linux, ssh, scp, etc. If you do not, PLEASE DO NOT TRY THIS.
All I did was:
1) installed the jailbreak: http://yifan.lu/p/kindle-touch-jailbreak/
2) installed usbnet (download at the same page as above)
3) set my root password (see readme file in usbnet) and gained root ssh access via putty and winscp
4) using putty, I ssh'ed in as root, and then did "mntroot rw" command to mound the rootfs as writeable
5) using winscp, I "SCP'ed" into the device as root. navigate to /usr/java/lib/fonts. I made a local copy of the entire "fonts" directory. Then I made another copy so I could revert any file changes I was about to make.
I had to revert my first few attempts at replacing the font files SEVERAL times and like I said nearly bricked it. What I learned was that older font files I used on K3 do not work. But, no worries, all I really wanted to do was increase the size of the fonts, so I figured I had better start with the files already on the device.
Some time ago, I bought "Font Creator" from http://www.high-logic.com/
. I used this to increase the font sizes. You open each file, click on "Tools --> Glyph Transformer". The expand "Outlines" on the left, select "Scale" and enter "115.00" in Horizonal % and "125.00" in Verical %. And save the file. You can also futz with the font weight (boldness) and other stuff. Very powerful program.
I did this for all of the files that start with "Caecilia..." and "Helvetica...".
Then using WinSCP I copied them back to the original location on the Kindle.
The Kindle pretty much freaks out and reboots itself after disconnecting, and if not you can hopefully navigate to the settings menu and choose restart.
Once restarted, the difference is DRAMATIC. The list of books uses Caecilia, so it was instantly more readable for me. The menus use Helvetica, so they look better as well. And now I can read books on this one just like on my K3...without having to have a bright light or reading glasses.
Attached are the files I modified. (hope this doesn't violate any copyrights...mods, if it does feel free to remove the attachment)
YMMV. Be Careful!