Below you will find two color test images and a grayscale test image for gamma calibration. If your gamma value is set up correctly at 2.2 then the respective halfes of the horizontal and vertical areas should match exactly in brightness (the transition should not be determinable). If that is not the case, correct the gamma value using an adequate tool for system-wide gamma correction, i.e. Adobe Gamma (comes with Photoshop for Windows). The set-up tools of some graphics cards allow for such system-wide gamma corrections, too.
The first test image is an "animated GIF". (Please allow your Browser to show such images continuously.) The halfes of the horizontal and vertical areas in this image change their location two times in a second. If your Gamma calibration is correct you should see only a general flickering. If it is not, the test images flickers diagonally.
The second color image serves fine tuning of gamma calibration separated into the different RGB channels. Just begin on top and move on counter-clockwise. Setting up the blue channel is the most difficult. Always check back that the gray triangle stays pure gray. You can use the small square in the middle, as viewed from sufficient distance it always should be pure gray. Here you can find a bigger test image for controlling and calibrating gray rendition (color temperature). The third test image serves the pure gray calibration of gamma, if it is wished.
The tunnel-like construction of the test images allows for the visual examination and set-up of the display's linearity. The differences between the grayscale steps are almost similar and should be perceived as being similar. But because our visual system is fond of enhancing contrasts, for the first test image the differences in brightness seem to increase the more we get to the centre - the inner-most dark square seems to be too dark.
This is not the case with the color images. Its brightness differences seem to be more moderate. In fact, they are not - the upper triangle contains exactly the same gray tones as the gray scale image. But the "eye" is misleading us less in this case. For this reason, if you are correcting your display's linearity visually, you should primarily use the first and the second test image.
Mac OS X allows for such linearizations easily, as ColorSync is able to correct the display's gamma at different brightness levels. Even though, you should use our color test image instead of the much too small "Apple" test image that is used by Mac OS's calibrator.
Please enlarge this window to fullscreen size and provide for dimmed ambient light without reflections.
The areas of the test images below are partly homogenous (solid gray/colors, upper right and lower left quarter of the images), partly set up of 1-pixel-wide light and dark lines. View the images from a distance where the lines cannot be distinguished any longer.