Use this parameter to create an opaque white box under your barcode.
Note: For ITF, UCP and PDF417 bar codes, the box will be transparent, with bearer bars around
it.
Use the Top, Bottom, Left and Right fields to add a white margin around your barcode and make the box bigger.
By default, Dynamic Barcodes links the four margins' values so that when you change one of them, the other ones are updated automatically.
If you want to change them independently, click the link symbol to make it
look detached 
.