Motion Blur

The exposure of a film camera takes a certain time period. Non-static objects move and change their appearance during the exposure time. Because the film records everything that happens during the exposure time, such objects do not appear sharp but blurred in the picture. This phenomenon is called motion blur and can be simulated in Realsoft 3D.

Motion blur can be used as an effect to increase the realism of images. It also improves the quality of animations. Common video and film standards show 20-30 frames per second. At such frame rates and without motion blur, the animation of a rapidly moving object may not appear continuous. Various strobing artifacts may also become visible.

The effect of motion blur is visible (and necessary) only when the animation contains objects moving a certain amount per frame. As a general rule, an object should move at least 10 pixels between two frames before the blur produces noticeable results. The use of motion blur makes rendering slower. For example, 9 motion samples usually at least triple the rendering time.

The motion blur feature of Realsoft 3D works by simulating physical reality accurately. Moving objects, shadows of moving objects, animated textures and materials become blurred if they change during the exposure of a single frame. If the camera moves itself, the whole world becomes blurred.

Rendering a motion blurred animation

When building a scene, you do not have to worry about motion blur. If you decide to use motion blur after the animated scene is finished, all you have to do is to set some options in the animation and rendering settings. The following example demonstrates this:

Tutorial level: Medium

Example project: 'tutorprojects\rendering\missile'

A missile follows a path

1. Create the animation in the usual way. For example, model a missile and draw a path (a NURBS curve) for it. Multi select the missile and the path and apply Animation/Path/Directed from the main menu.

2. Go to the Rendering settings section of the select window. Select the settings you plan to use for rendering. Open the property window from the select window's popup menu and go to the Ray Tracing tab. The rendering settings can be as usual, but set the anti-aliasing Mode to Stochastic and Level to zero. The motion blur system will take several samples per pixel over time, and therefore the usual anti-aliasing is not necessary. Only when using a minimal amount of motion samples, e.g. 4 samples between each frames, you should define some anti-aliasing, for example level 2. This step is important because it will save a lot of time in rendering the animation. Close the property window.

Defining anti-aliasing settings for motion blur
Activate motion blur and select the amount of motion samples

3. Open the Animation Settings window from the Windows menu of the main menu bar. Check the Motion Blur option and set Samples to 9. Nine motion samples are enough for most purposes, and does not slow the rendering too much. Close the window.

5. Let's preview the motion blur on the view window first. Drag and drop the rendering settings object, which was prepared in step 2, to the view window (this is not necessary if you know that the view already uses the correct settings). Open the view property window, go to the Render tab and activate the Continuous rendering option. Close the view property window.

6. Open the animation window from the View main menu (if it is not already open). Hit the Play forward button. The program starts playing the animation, and renders the view after each time change because of the enabled continuous rendering option. The first rendered images look quite bad, because anti-aliasing is disabled.

Wait until nine images have been rendered. At that point, the program computes and displays a motion-blurred image in the view. You may stop the animation playback now. Open the view property window and turn off Continuous rendering option. Then rewind the animation. If the blur quality was not good enough (the missile moves too much between the motion blur samples) adjust the amount of samples to 16 using the animation settings window.

Moving missile appears blurred

7. The final step is rendering to a file. Select File/Render from the main menu. Prepare file rendering the usual way, like instructed in the manual section 'Rendering Still Images and Animations to a File', but remember to select the correct Rendering settings. Then start file rendering by hitting the Play button.

Rendering settings for motion blurred file rendering include stochastic 0-level anti-aliasing