Andrea, why do you need to merge captures? This in itself is the best possible quality source of a WEB-DL. Plus this is 1080p. Do you have another 1080p source?
Yes, of course! This capture is great, but the one I have is very good, too; merging them would lead to delete eventual noise, while reveal some details; of course, it should be tested, as it not happen all the time. But, until now, I’ve seen that, even with seemlingly perfect sources, when merged with another (or other two, that’s even better), the quality usually improves - from a bit to a lot.