Doc:Tutorials/Animation/BSoD/Principles of Animation/Tutorials/P1-Strobing

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[edit] Introduction

[edit] About

This is too small to deserve being called a tutorial. We're just playing with the idea of using stretching to fight jerkiness (strobing) and comparing it with Blender's motion blur.

For the actual comparison we need to see the example in motion. For that all you need to do is to download the .blend file referenced below, open it in Blender and follow the simple instructions written there (press "ANIM" to animate, without and then with "MBLUR" turned on).

[edit] File

[edit] Tutorial

For our test we will use a sphere rotating ("orbiting") around a point outside of it.

1) Sphere parented to empty, so the sphere can be animated orbiting that point.

[edit] Basic Setup

1. Add an empty:

   SPACE >> Add >> Empty.

2. Add a sphere:

   SPACE >> Add >> Mesh >> UV Sphere.

3. Move the sphere away from the origin. Preferably move it either horizontally or vertically, that will make it easier to stretch it in the right direction later.

   G.

4. Parent the sphere to the empty:

   Select sphere, then select the empty, so that it is the active object, then press...

   Ctrl P.

Image #1 shows an example of the expected result.

If you're not sure why we have to use an empty: with it as parent of the sphere, we can animate the sphere orbiting around the empty's location, by keyframing rotations for the empty. Clean, trivial, but powerful.

[edit] Keyframing the rotations

1. Select the empty and insert a rotation keyframe at frame 1:

   I Insert Key >> Rot.

2. Advance to frame 51:

   Press Up four times)

3. We want the animation to "wrap around", so we will insert another keyframe with a rotation of 360° and put the end frame right before it. The best way to do this is via the Transform Properties panel:

   N in the 3D View, set the appropriate (*) rotation axis to 360º.

   (*) It depends on the plane where the empties are rotating, of course: in Top View it's RotZ, for example.

4. For linear rotations, choose Extrapolation in the Ipo Curve Editor: >> Curve >> Extend Mode menu.
5. Set to 50 the final frame ("End") either in the Anim panel of the Scene Buttons window (F10) or in the header of the Timeline window.

[edit] Duplicating and Stretching

We want to compare spheres with and without stretching, so it's time to duplicate the objects:

1. Select both the sphere and the empty:

    RMB to select the first, Shift RMB to select the second without losing the previous selection.

2. Duplicate them:

   Shift D.

3. Move them away from the original pair, far enough for both spheres to rotate without overlapping each other.

2) Normal and stretched spheres to test if the stretched one looks better and prevents strobing during animations.

Finally, choose one of the spheres and stretch it a little.

1. Select sphere, then use the Transform Properties panel in the 3D View:

   N to open the panel.

2. Set the scaling values, we've used (0.85, 0.85, 1.2) for the one at the right in image #2.

We also added sticks between each empty and its corresponding sphere (image #2), to give a better idea in these still pictures about the points around which the spheres rotate.

Rendering an animation now will show us whether the stretched sphere looks better when animated. The speed of rotations is surely an important factor, the faster, the worse the unstretched sphere will look moving, with a bad case of strobing, too.

So indeed stretching helps here. But... is it the only way to give the impression of fast movement and to fight jerkiness? No. Is it the best alternative, then? Let's see...

3) Motion Blur (MBLUR) and blur factor (Bf) buttons.

[edit] Motion Blur

The motion blur effect can be used to prevent jerkiness in computer generated images and also reproduce how real cameras record fast action.

Blender's old Motion Blur functionality is very easy to apply, but it increases render time, because more images have to be rendered to composite each frame.

There are 3 buttons that control motion blur, all of them in the Render panel of the Scene Buttons window (F10), shown in image #3:

MBLUR

toggle to enable or disable motion blur.

OSA levels

the buttons with numbers below "OSA" button, they define how many images are created to composite each frame.

Bf

blur factor, controls how pronounced (spread away) the blur will be.

[edit] Conclusion

Images #3 and #4 below give examples of renderings without and with MBLUR turned on. We've used two pairs of rotating spheres (lollipops?), the bottom one turning twice as fast as the ones at the top.

3) Rotating spheres with motion blur: left: normal, right: stretched; top: slow, bottom: fast.

4) Same as image #3, but with motion blur: blur factor (Bf) = 1.0.

As written in the introduction, for the actual comparison we need the rendered animations that can be created following this tutorial or using the provided .blend file. That also gives you the chance to play with different blur factors and many other possibilities (check the first suggested exercise below).

[edit] Suggested exercises

[edit] Simple tests

There are many things we can experiment with using the example in this tutorial. Here are a few ideas:

• Try different blur factor (Bf) values.
• Change the speed of the animation (there are many ways to do this: fps, editing curves or keyframes, speed ipo, etc.).
• Consider what effect camera movement or different lighting setups would have in making strobing more or less pronounced. Then make a few experiments to know for sure.

[edit] "Complex" movements

Parenting objects is a great way to animate seemingly complex movements. If you haven't already, we suggest you experiment with it to get a taste of the possibilities.

Examples:

• Pendulums.
• Amusement rides, like carousels.

Summer of documentation 2006 -- Willian 01:56, 20 August 2006 (CEST)

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