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.
This command only operates on color images.