测试环境：
Acer Aspire 5750G
NVIDIA GeForce GT630M
Ubuntu 12.04 x86_64
其他情况解决方法类似。
调节屏幕亮度
Fn不能调节屏幕的亮度。因为fn调节的是/sys/class/backlight/acpi_video0/brightness文件，而I卡的文件是/sys/class/backlight/intel_backlight/brightness。
一、测试代码
启动系统，出现grub菜单时，按“e”编辑，在有linux内核路径那一行，添加“acpi_backlight=vendor”，如：
linux /boot/vmlinuz-3.2.0-30-generic root=UUID=75c414be-2e17-407a-b699-94f6a398dff7 ro acpi_backlight=vendor quiet splash
一旦能正常启动，且用fn能调节屏幕亮度，说明成功，接着下一步。
二、修改grub
sudo vi /etc/default/grub
找到：
GRUB_CMDLINE_LINUX=""
改为：
GRUB_CMDLINE_LINUX="acpi_backlight=vendor“
我的grub文件如下：
# If you change this file, run 'update-grub' afterwards to update
# /boot/grub/grub.cfg.
# For full documentation of the options in this file, see:
# info -f grub -n 'Simple configuration'
GRUB_DEFAULT=0
#GRUB_HIDDEN_TIMEOUT=0
GRUB_HIDDEN_TIMEOUT_QUIET=true
GRUB_TIMEOUT=3
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
GRUB_CMDLINE_LINUX="acpi_backlight=vendor"
# Uncomment to enable BadRAM filtering, modify to suit your needs
# This works with Linux (no patch required) and with any kernel that obtains
# the memory map information from GRUB (GNU Mach, kernel of FreeBSD ...)
#GRUB_BADRAM="0x01234567,0xfefefefe,0x89abcdef,0xefefefef"
# Uncomment to disable graphical terminal (grub-pc only)
#GRUB_TERMINAL=console
# The resolution used on graphical terminal
# note that you can use only modes which your graphic card supports via VBE
# you can see them in real GRUB with the command `vbeinfo'
#GRUB_GFXMODE=640x480
# Uncomment if you don't want GRUB to pass "root=UUID=xxx" parameter to Linux
#GRUB_DISABLE_LINUX_UUID=true
# Uncomment to disable generation of recovery mode menu entries
#GRUB_DISABLE_RECOVERY="true"
# Uncomment to get a beep at grub start
#GRUB_INIT_TUNE="480 440 1"
更新grub.cfg
~ sudo update-grub
查看grub.cfg 发现其中每个启动项都加入了“acpi_backlight=vendor”
~ vi /boot/grub/grub.cfg
设定屏幕初始亮度
重启后发现，屏幕亮度又恢复为最大亮度。
查看影响屏幕亮度的文件
~ vi /sys/class/backlight/intel_backlight/brightness
调节几次屏幕亮度发现其中数值会改变，我的笔记本数值范围为0～976。
手动修改该数值，会发现屏幕亮度随之改变（需要root用户执行）：
~ su
Password:
root@ www :/home/congbo# echo 500 > /sys/class/backlight/intel_backlight/brightness
因此，将该语句添加到 /etc/rc.local 就能开机自动设定屏幕初始亮度了。
修改/etc/rc.local如下（需要root用户执行）：
#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will “exit 0″ on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.
echo 500 > /sys/class/backlight/intel_backlight/brightness
exit 0
调节gamma值
~ xgamma -gamma .7
-> Red 1.000, Green 1.000, Blue 1.000
<- Red 0.700, Green 0.700, Blue 0.700