Directionality/position-based meaning precedence is a cultural thing. Left-right has precedence in Western culture, so I personally would interpret my little color depth example to mean "increase" in color depth.
As an aside:
Precedence/directionality is not only left-right-top-bottom, but also "most recent/least recent", typically indicated by "in front/behind".
For instance, in the Image Resize example #1 (posted above), from a Westerner's point of view there are two possible interpretations of the precedence of the components:
1. Smaller on left, larger on right suggests "small-to-large" (since by convention left occurs first in time).
2. Smaller in front, larger behind suggests "large-to-small" (since behind -underneath- occurs first in time).
So that icon is ambiguous.