feeblemind

For Blender: 2.42 - Version française disponible() - Artykuł dostępny po polsku()

The main thing to understand is that the object to which the Motion Blur should be applied should have been animated beforehand. This means that the object must follow a curve, or be animated using IPOs. In fact, the rendered picture will be turned into a 3D model with depth and a speed vector will be calculated for each pixel of the picture. As a post-process, the Composite editor will add the motions to the final pic in a blurred way. This is why defining the motion of the object (through any mean of your choice, but the use of IPO curves would certainly be the most common) is absolutely mandatory.

Example of IPO curves effecting a moving object

A very brief example file of such an animation can be found at the following URL: http://feeblemind.tuxfamily.org/dotclear/images/atelier-improbable/vector-blur/vectorblur_example.blend

Here's how would look a regular animation rendering, without vector based motion blur (Click a thumbnail to enlarge)

A step by step of the Vector Blur process

At first, you will need to turn one of your 3D views into a Node Editor view. It is done by clicking on the grid-like icon at the left end of the header of the view. A menu will pop-up and let you define the type of view needed. Choose the Node Editor.

Turn one of the views into the Node Editor

In the header of the Node Editor, you will find a menu for the view (View, Select, Add, Node) and then two icons: the first one enables Material Nodes (the grey sphere icon), the second one enables Composite Nodes (the small face picture icon). Please click on the second one.

Click on the Composite mode icon and then activate the Use Nodes button.

The default Composite nodes network should be displayed on the screen. Using [left button] of the mouse device, draw a box that will cross the link between the Render Layer node and the Composite node: the link should disappear. Now, use the Add menu: Add >> Filters >> Vector Blur. A new node should appear, titled Vector Blur. Move it between the two previous default nodes, and start the magic: connect the output Image, Z and Speed from the Render Layer node to the input Image, Z and Speed from the Vector Blur node, using the [left button] of the mouse device. Once done, connect the output Image from the Vector Blur node to the Image input of the Composite node.

The Composite nodes are set to deliver a Vector Blur based rendering

But, as almost anything in Blender, taking into account the effect of the Vector Blur is nothing but a option. You need to tell Blender that it must do the post-processing simulating the motion blur explictely. This is done in the Scene [F10] menu, in the Render buttons, in the Anim panel. You will have to activate the Do Composite button. And as a final pre-requisite for Vector Blur motions, you will need to activate the Vec option in the Render Layers tab.

Do not forget to activate the Do Composite button in the Anim panel and the Vec button in the Render Layers tab !

You can now render your picture in two ways:

• You obviously already know the [F12] shortcut or the RENDER button in the Render panel
• You can also render the picture using the tiny Render icon in the Render Layer node

Here's how would look the same animation rendering, with vector based motion blur enabled (Click a thumbnail to enlarge)

Some explanations on the Vector Blur node

This node only has a few settings, most of them could work quite well with their default values. But sometimes (if not everytime!), you need to go beyond default settings to get real cool results. There are four settings to know about.

The Vector Blur node

• Samples: this setting controls the blur effect intensity: the higher the samples, the more blurred the object will look
• MinSpeed: if everything is blurred but if some objects are a lot slower than others (or totally static, as the background of the pic, for example) then this parameter will help differenciating high velocity objects from null velocity or slow velocity of the objects. Really useful during camera movement or slight background movements.
• MaxSpeed: if you have extremely fast objects in the scene but if the blur does not render well enough, then you can make use of this parameter to better the vector blur. Note that a 0.0 value means that no maximum is used.
• BlurFac: this parameter will scale the vector speeds calculating from the movements of the object. The visual effect is close to the shutter speed of a regular camera.

Concerning the use of Vector Blur, a good tip is to put fast moving objects on a Render Layer, slow or static objects on another, and to specify independant parameters for each, for a better control. Moreover, large objects not entirely seen from the camera should be subdivided so that at least some of the normals of the object are actually seen from the camera, or the blur effect could be drawn on the wrong side, compared to the movement.

But there also some limitations that you should know of, due to the fact the Vector Blur is a post-process effect:

• if an object is vector blurred, its shadow is not!
• if a vector blurred object is moving behing a (ZTransp or RayTransp) glass, it won't appear blurred through the glass
• if a vector blurred object is moving in front of a (EnvMap or RayMir) mirror, it won't appear blurred in the reflection