When using DreamGuard Protex 3, we recommend you coat the entire image, or wall. It is likely that there will be a noticeable difference in the “sheen” if it is only partially coated.
A common scenario we are asked is by installers who are trying to save some of the cost of coating. For example, they have a tall wall and only want to coat the lower portion which is more likely to be scuffed / damaged. We do not recommend doing this as there could be a difference in the way the un-coated and coated portions reflect light.