Use the Color Operators Function
In the Step Name textbox, enter a descriptive name for the step.
Select one of the operators from the Operators list.
Select either the Constant or Image option. The Constant option uses a constant and the current image in the operation. The Image option uses the current image and an image stored in an image buffer. Note For the Mask operator, you can select only the Image option. For the Multiply Divide operator, you must specify an Image and a Constant.
Enter the constant or select the image buffer that contains the image you are adding to the source image or enter the constant value.
Click OK to add the step to the script and close the Parameters window.
Note You must already have an image stored in an image buffer before you can perform an operation using the current image and another image. The buffered image must be the same size as the source image and must be an 8-bit or RGB image.