Rendering with mental ray and 3ds Max 6.4.2 Motionblureffect In the real physical world, there is no such thing as motion blur; it is the result of an illusion that we have become accustomed to seeing in film. Because film or video is played back at a rate between 24 and 30 frames per second, fast-moving objects appear blurred in the individual frames because of the relative movement of the objects during that time span. Fast-moving objects can cover quite a distance in 1/30 of a second or longer, and the "film" can see the objects during the entire time. Over the years of watching movies, we have become so accustomed to seeing this blur effect that the visualiza- tion industry has spent a lot of time and money helping us create the effect in 3D animation. But, as with any other special effect, you should use it only when it actually is important to the story you are trying to convey to the viewer because motion blur can slow production considerably. There are basically two circumstances in which motion blur is used: individual fast-moving objects in a scene such as a speeding bullet or a spinning propeller, or when the entire scene is blurred because of a fast-moving camera similar to what you would get if you point a camera out the side window of a car. With motion blur, you need to balance cost and quality. Cost, in this case, is the amount of time you can afford in the production schedule. Another variable in the cost versus quality equation is whether the presentation will be still images or animation. Higher quality is usually required for still images, which are generally rendered at a higher resolution, as well. For animation, the rapid movement means that you can get away with lower quality motion blur because you won't be able to detect problems that might occur. In 3ds Max there are two important steps to making motion blur work: Enable object properties. Enable motion blur. You must select the objects that you want to blur in the scene and set their object properties to Object Motion Blur. Then you must enable motion blurring itself in the renderer. In the next few exercises, you'll learn to make object motion blur help the illusion of spinning fan blades in an industrial setting. You'll do this by using several methods of motion blur, with the goal of making the effect convincing and efficient to render. One notable feature of motion blur in mental ray is that it is also possible to blur the shadows of objects and the reflections of objects, neither of which is possible with the scanline render. 6.4.2.1 Exercise:Enablingmotionblurobjectproperties 1. Open the scene called Ch06_motion_blur_01.max from the CD-ROM and save it to your hard drive with the name Ch06_motion_blur_02.max. To make the rendering more efficient, let's set the scene to render only the region where we see the fan in the back wall. In the main toolbar, click the Rendered Frame Window button to open it and then click the Render button in the Rendered Frame Window to render the entire scene. In the Area to Render drop-down list, choose Region and then adjust the region to be a bit larger than the fan opening (see Figure 6.53). Any subsequent renders will now render only the region, but you will still be able to see the full scene. 2. Advance the frame slider to some frame other than frame 0, perhaps frame 20, for example. Because there is no motion for the fan blades at frame 0, there can be no motion blur about what the settings are. 176