User guide

Quantity One User Guide
16-10
Any pixels inside the volume that have the same intensity as the background
pixels will be reduced to zero, thereby eliminating them from the
quantitation.
Global Background Subtraction
Note: If you select Global Background Subtraction in the Volume Report
Options dialog, but do not define a background volume as outlined
below, you will effectively select no background subtraction.
Global background subtraction calculates a single background intensity for
the entire gel. This average background intensity is then subtracted from all
the volumes in the gel. The steps for calculating global background
subtraction are:
1. Create a volume using one of the volume tools in a representative
background region of your image (i.e., a region where there is no data
and where the average pixel intensity appears to be the same as the
background intensity surrounding your data).
2. Double-click on the volume. This will open the Volume Properties dialog
box. Select the Background option button.
Fig. 16-8. Defining a background volume object.