tkgamma is released under the GPL, see the file GPL in the
distribution for more details.

this is a front end to the xgamma command with an image to help calibrate
a monitor. its a simple script i wrote because there were no other
programs to help do this for XFree86 at the time (there may be
now) 

in the beginning of the script are 3 variables,

reference_image is the image displayed. its a variable in case you want to 
use another. it will take anything your implementation of tk can handle. since
GIF is now "evil" and PNG is not supported by all tk implementations, i used
a ppm file. make sure tkgamma can find it. you should make it an absolute 
path so you dont have to be in the same directory when you run it.

default_gamma is what gamma value the script starts with. defaults to 1.

gamma_max is the maximum available from the sliders, the default is 5. 
setting a lower default may give you more percision while dragging
with the mouse. because xgamma goes to 3 digits of percision, so does
tkgamma. 

if you just want an even gamma curve to look at rendered images like those 
from BMRT, just move the slider until the grey box in the middle of the black 
and white stripes is the same brightness. it helps to unfocus your
eyes or look "past" the screen to purposely blur the image as you
adjust it. then just set brightness and contrast to taste. the blue
box blurs the most because our eyes cant tell the difference as well.

if you need more carefull calibration you should first set the
lighting in the room to a constant. if you have windows, blank them in
some way. aluminum foil them works nicely and also helps keep heat out
if you live in a hot place.

set your lights where they will not glare on the monitor. behind the
monitor is a good place. flurecent lights are evil.

system gamma is where to the white slider is when the grey rectangle
in the top middle square is even with and is close to blending with
the stripes to its sides. blurring your eyes and or leaning back can
help.

gamma correction is system gamma / target gamma. for example video is
2.2, so if your system gamma is 2.5 (common for PCs) then you want to
set gamma correction to 2.5/2.2=1.136 heres some other common values.
note that lower numbers mean the scree is generally "brighter"

PC		2.5 (this varies alot)
tv/video/web	2.2 (this often does too)
mac		1.8 (so does this, but not as much)
sgi		1.5
next		1.0 aka linear gamma

set contrast and brightness to thier highest levels. then lower 
brightness until you can see the top half of the dark rectangle
in the midle of the black square, but not the lower half. lower
contrast until you can see the light grey square in the white area,
you may have to adjust brightness again until you can see both.

once your done, you should add that to your X startup scripts with 
something like 

echo xgamma -gamma 1.136 >> ~/.xsession

This is not the same level of control you would get with photoshop on
a mac for example, but it should be ok for most print work (match to a
good example of your printers output), and just fine for video, web,
etc.

I choose tcl/tk because its everywhere and simple. almost
anyone with XFree86 and a card whose XFree86 server can accept gamma
correction can be expected to have it. but it has a problem. the
command are run when a slider gets focus instead of just when it
moves. the result of this is when you have seperate setting for
individual colors and the mouse happens to go over the white slider,
that activates the white sliders commands. those three color sliders 
are rarely usefull (if you need them just to get ok color, concider a
new monitor) but they can be fun to play with and/or a quick way to
to look at color casts.

tkgamma is only tested on XFree86 4.x and will only work with cards
that support hardware gamma correction. these include anything by ati,
nvidia, and probably matrox. a few others probably as well, even some
laptops (like my a21p).

for more information see http://pixel.fairyden.net/tkgamma