The Color Balance command only works on color images. The color balance of an image can be adjusted in two ways. A simple scaling can be performed on each of the planes, or a background level can be subtracted from each image plane.
Color images from DSLRs and CCD cameras typically require a background level adjustment. This is accomplished by equalizing the background level (or bias) in each color plane. Each of the Background Level values is subtracted from every image pixel in its color plane, then the average of the three values is added back in. Any pixel values that become negative are forced to zero. Any pixel values that become negative are forced to zero. The Reset button resets the background level subtraction to zero on all planes. The Auto button automatically determines the settings necessary to equalize the image background in all three color planes.
Scaling adjustment (percent) allows you to compensate for transmittance differences between the filters used to acquire the three color planes. Values of 100% result in no change. The scaling percentages can be typed in or adjusted using the spin controls. The Preview Image is particularly helpful in monitoring the results when using the spin controls. The Reset Scaling button resets to 100% on all three planes.
The Click On White Area to Set Scaling check box enables the operation of the mouse to set the scaling. Set the Background level first, then click on a white object (e.g. a neutral-colored star) in the image (not the preview) with the mouse. The Scaling settings will automatically be adjusted to make the selected point appear white. If an area of the image is known to be white (or gray), this is an easier way to determine the scaling factors, and can be used to instantly color balance the image.
A handy procedure for calibrating colors based on G2V "solar analog" stars is outlined in the section for the Color Balance command. Using this command you can simply click on a G2V star to calibrate your color balance.
This command only operates on color images.