When I use the RGB merge to merge a slightly opaque layer with other layers, why is the resultant image of poor quality, and why is detail in the opaque layer lost?

Technical Note: 144
Reads: 6269
Creation Date: 09/08/2000
Modification Date: 12/02/2004

To merge layers that have a degree of opacity and/or a combination of brightfield and fluorescent layers, merge using "Merge to Composite" from the Layers menu.