Desktop Radiance allows for real time, interactive rendering. The image pixels refine on the screen and start to give you an idea of what the scene will look like. Rview is not meant to be a high resolution rendering tool but more for deciding viewpoints and validating scene geometry (make sure window normals are correct, furniture not floating in midair, walls meet, etc). The rview interactive rendering is the default mode for simulation. To produce high quality images, select Batch mode in the Camera Simulation Setup box.