Choose the background subtraction method used in ratio calculations. By default, the background subtraction is zero. Provide background constants for the numerator and denominator in the event that they are known. When the region of interest (i.e. the box) is known to contain background areas, the background intensity can be statistically estimated and separated from the objects within the region. To control which pixels are identified as background, adjust the Confidence slider.
Open Background Subtraction Options by choosing Options | Background Subtraction from the Data Inspector window.