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3D Motion Blur

Learn how to use Turtle's 3D Motion Blur.

Project files: 3dmotionblur.zip

The aim of this tutorial is to explain how to use Turtle's 3D Motion Blur. First, we need a simple animated Maya scene.

The scene consists of a moving propeller and a checkboard floor.

Let's ray trace the scene. Your rendered image should look something like this:

Introduction

You'll find five parameters in Turtle's render globals to control the blur:

  • Camera Shutter Angle, that controls the time the camera shutter is open.
  • Blur length is a multiplier for the camera Shutter Angle, that allows us to achieve longer blurred trails without changing the global animation settings.
  • Time Sample Density is the number of test images in temporal space we take in order to capture the motion.
  • Max Time Samples are the number of smoothing time samples between each time sample.

  • Color Contrast sets the error threshold when to resample a pixel in the temporal domain. The role of each parameter is illustrated in the examples below.

    Camera Shutter Angle & Blur Length

    Enable 3D Motion Blur under Turtle's Render Globals, but don't change the default settings. Render the scene. You should have a scene like this:

    Try to change the Camera Shutter Angle to 50. Render again. The camera shutter shutter time has decreased and we see that the blurred trail is shorter.

    Try experimening with the Blur Length parameter. This allows you to have longer shutter times. If you increase the Blur Length, you are likely to see sampling artifacts, which we will deal with in the next paragraph.

    Time Sample Density & Max Time Samples

    Set the Camera Shutter Angle to 140 and the Blur Length to 2.0. Render. You will see an unsatsifactorially blurred image like:

    In order to deal with longer blurred trails, we have to increase the Time Sample Density parameter. Set it to 3. Also, set the Color Contrast parameter to 0, to make the resampling algorithm as sensitive as possible.

    Note that this increases the rendering time. Each time sample is expensive, and are to be used only when needed. You will still be able to see some temporal aliasing though. Increase the Max Time Samples parameter to 8. This will resample the moving regions of the image further, and is relatively cheap. Render again, and you will have a result like:

    Long Trails

    We want to simulate a photo of a propeller rotating with high speed, and thus want a longer trail. In this final section, I will describe the steps needed to adjust the blur setings for a good result.

    First, set Max Time Samples to zero, and adjust the Time Sample Density so that the trail is covered with samples. If we have too few time samples, the algorithm won't correctly identify the moving regions in the image. Once satisfied, raise the Max Time Samples until the temporal alias effects disappears. The Color Contrast parameter should be kept low, to ensure that even minor contrast changes indicates a moving pixel.



    Camera Shutter Angle 140
    Blur Length 4.0
    Time Sample Density 5
    Max Time Samples 6
    Color Contrast 0



    Camera Shutter Angle 140
    Blur Length 10.0
    Time Sample Density 10
    Max Time Samples 5
    Color Contrast 0

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    • Last modified 2006-07-12