Describing figures vs letting figures speak for themselves
It is evidently true that figures/images can convey things difficult to convey in words (e.g., see Edward Tufte's The Visual Display of Quantitative Information).

On the other hand, the exercise of verbally approximating what may be visually apparent is in itself highly informative in various ways. Among others, your verbal approximation of the visual will partly explain to your readers your own interpretation of it, to which they can add or contrast their own. Or, they might otherwise fail to see in it what you see.

That is, with regard to the latter point, it is often good to "state the obvious", because the notion of "obvious" turns out to be subjective.