Added docs

skimage/graph/rag.py

@@ -3,8 +3,30 @@ import _construct
 from skimage import util
 
 class RAG(nx.Graph):
+    """
+    The class for holding the Region Adjacency Graph (RAG).
+
+    Each region is a contiguous set of pixels in an image, usuall
+    sharing some common property.Adjacent regions have an edge 
+    between their corresponding nodes.
+    """
+
+    def merge_nodes(self,i,j):
+    """Merges nodes `i` and `j`.
+
+    The new combined node is adjacent to all the neighbors of `i`
+    and `j`. In case of conflicting edges, edge with higher weight
+    is chosen.
+
+    Parameters
+    ----------
+    i : int
+        Node to be merged.
+    j : int
+        Node to be merged.
+
+    """
 
-    def merge_nodes(i,j):
         if not self.has_edge(i, j):
             raise ValueError('Cant merge non adjacent nodes')
 
@@ -24,7 +46,28 @@ class RAG(nx.Graph):
         self.node[j]['labels'] += self.node[i]['labels'] 
         self.remove_node(i)
 
-def rag_meancolor(img,labels):
+
+def rag_meancolor(img, labels):
+    """Computes the Region Adjacency Graph of a color image using
+    difference in mean color of regions as edge weights.
+
+    Given an image and its segmentation, this method constructs the
+    corresponsing Region Adjacency Graph (RAG).Each node in the RAG
+    represents a contiguous pixels with in `img` the same label in
+    `arr`
+
+    Parameters
+    ----------
+    img : (width, height, 3) or (width, height, depth, 3) ndarray
+        Input image.
+    arr : (width, height) or (width, height, depth) ndarray
+        The array with labels.
+
+    Returns
+    -------
+    out : RAG
+        The region adjacency graph.
+    """
 
     img = util.img_as_ubyte(img)
     if img.ndim == 4 :