We present an efficient implementation of the ultimate attribute opening operator. In this implementation, the ultimate opening is computed by processing the image maxtree representation. To show the efficiency of this implementation, execution time is given for various images at different scales. A quasi-linear dependency with the number of pixels is observed. This new implementation makes the ultimate attribute opening usable in real time. Moreover, the use of the maxtree allows us to process specific zones of the image independently, with a negligible additional computation time.