around <code class="docutils literal"><span class="pre">StepIterator</span></code> and uses it
to navigate vertically, while its base iterator is used to navigate
horizontally.</p>
<p>Combining fundamental iterator and step iterator allows us to create locators
that describe complex pixel memory organizations. First, we have a choice of
iterator to use for horizontal direction, i.e. for iterating over the pixels
on the same row. Using the fundamental and step iterators gives us four
choices:</p>
<ul class="