For those not desiring to upgrade their Kindle DX to 3.2.1 in order to get PDF contrast, here is a replacement that allows setting contrast (and more!) throughout the whole system. It replaces a kernel module and adds a simple watcher so that you can modify the contrast with the keyboard. In addition to contrast, you can also reduce the number of shades so that page turns are faster and/or flashless. The README is duplicated below. Enjoy!
Code:
NOTE: This has been tested on a Kindle DX Graphite 2.5.8. You must update your
Kindle DX to this version before installing the update! Installing on the
3.2.1+ adaptation should be okay but hasn't been tested.
INSTALLATION INSTRUCTIONS
1. Plug your Kindle into your computer.
2. Copy update_contrast_0.1_install.bin to the root of the Kindle.
3. Eject/unplug the Kindle DXG.
4. Go to the Home screen, press the Menu key, and select Settings.
5. Press the Menu key again, and select Update Your Kindle.
6. Select Ok when prompted if you want to perform an update.
USAGE INSTRUCTIONS
1. While holding Shift, press up/down to move among 5 contrast levels.
2. While holding Shift, press left/right to move among 3 bit depths.
(16 shades is default; 4 shades has faster updates; 2 shades has no flashes)
3. While holding Shift, press the five way to invert the screen.
UNINSTALLATION INSTRUCTIONS
1. Plug your Kindle into your computer.
2. Copy update_contrast_0.1_uninstall.bin to the root of the Kindle.
3. Eject/unplug the Kindle DXG.
4. Go to the Home screen, press the Menu key, and select Settings.
5. Press the Menu key again, and select Update Your Kindle.
6. Select Ok when prompted if you want to perform an update.
INTERNAL DOCUMENTATION
It adds a command 99 to /proc/eink_fb/update_display which takes 16 numbers as
arguments. These are the shades 0-15 that each shande should be mapped to before
it is displayed. This allows you to set up pretty much any mapping you want. e.g.
echo "99 0 3 6 9 12 15 15 15 15 15 15 15 15 15 15 15" >/proc/eink_fb/update_display
LICENSE AND DISCLAIMER
You may freely use and share unmodified versions of this software so long as
you do not charge a fee for redistribution. This software may not be bundled,
preloaded on devices, included in collections, or otherwise aggregated without
prior written consent of the copyright holder. All other rights reserved to
the maximum extent permitted by applicable law.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.