Thierry,
About the grain:
I had to underexpose the settings so as not to blow out the bright yellows. That made the reflection pretty dark. When I began editing it the reflection in the dark brown water looked so painterly I decided to give the yellow petals as much texture (grain) as possible.
I think it has a soft, subtle quality that I like. But it's very much unlike what I was looking at from my kayak.
Hope this makes sense.
Take good care,
Richard