### 3.9.9 Average Function

Now things get interesting. Above, we began to see how pigments and normals can fade from one to the other when we used them in maps. But how about if we want a smooth blend of patterns all the way through? That is where a new feature called `average` can come in very handy. Average works with pigment, normal, and texture maps, although the syntax is a little bit different, and when we are not expecting it, the change can be confusing. Here is a simple example. We use our standard includes, camera and light source from above, and enter the following object.

      plane { -z, 0
        pigment { White }
        normal {
          average
          normal_map {
            [1, gradient x ]
            [1, gradient y ]
          }
        }
      }

What we have done here is pretty self explanatory as soon as we render it. We have combined a vertical with a horizontal gradient bump pattern, creating crisscrossing gradients. Actually, the crisscrossing effect is a smooth blend of gradient x with gradient y all the way across our plane. Now, what about that syntax difference?

We see how our normal map has changed from earlier examples. The floating point value to the left-hand side of each map entry has a different meaning now. It gives the weight factor per entry in the map. Try some different values for the 'gradient x' entry and see how the normal changes.

The weight factor can be omitted, the result then will be the same as if each entry had a weight factor of 1.