I want to render a single frame of an animation and would like to have some of the moving objects to be rendered as a trail between either
- the beginning of the animation (frame 0),
- a particular number of n frames or
- the previous keyframe,
and the current frame.
The objects I want the trail to be rendered of are markers on a human body (like, little red dots, i.e. spheres with a 100% emissive red material, on the shoulder, elbow, hand of a humanoid figure)
The reason that I want the animation being rendered as a trail of the markers is that I want to use the image in a printed technical documentation that describes a particular motion. For obvious reasons an actual animation is not possible in this case.
I have already tried rendering the trail of the markers by using motion blur but the results were far from what I would like them to look. Furthermore the motion blur does for some reason not really follow the actual trail of the markers (I don't know why) and is also influenced by motion of the camera.
I would like to avoid post-composition of multiple frames by hand.
One idea would be to render only the markers for the n frames before the current frame with transparent background, fully render only the current frame and blend the frames together.
Is this possible in blender? Can it be automated? How?