How to get started with Onion Skinning in Houdini.

Onion Skinning is a viewport visualization for animation, which displays an animated object on multiple frames. It is often an important task when creating a 3D configurator. The current frame is displayed normally and the other animation frames or “onion skinning” are displayed as partially transparent ghosts. By showing the object across multiple frames, the designer develops a sense of their movement.

Onion Skinning is activated in Houdini for a geometry object via the “Onion Skinning” menu on the “Other” tab. The number of frames displayed, the frame step and the opacity of the skin can all be set on the Viewport tab of the 3D display options.

Enable Onion Skinning.

Onion Skinning can be activated for a geometry object by setting the Onion Skinning parameter to “Transform Only” or “Full Deformation”.

Transform Only.

The geometry of the current frame is used while the object transformation is animated. This is faster than full deformation if the underlying geometry changes over time.

Full Deformation.

The geometry is retransformed at each frame along with the object transformation.

Onion skinning can also be deactivated globally by deactivating Onion Skinning in the menu. If you activate the “Global Onion Skinning” option, the onion skinning will be restored for the objects for which it is activated.

Note: Onion skinning is not displayed for hosted objects. If Onion Skinning is enabled for an object and another object is entered in the SOP layer, Onion Skinning is disabled.

Onion Skinning Options.

There are several display options for Onion Skinning on the View Window tab of the 3D Display Options:

• The number of skins before and after the current frame.
• The increment of the frame between the skins.

• The coloring of skins before and after the coloring, independently of each other.
• The opacity of the skins, from 0 to 100%.

Increasing the number of skins displayed has a negative effect on playback performance, especially when using Full Deformation mode.

Tips for Onion Skinning.

• Use Onion Skinning only on one or a few objects at a time. The performance hit can slow down scrubbing and playback.
• If the deformation of the geometry is minimal, try Transform Only to improve performance.
• Reducing the number of skins can also improve performance.
• If you want to move animations slowly, expand the Frame Step display option to make the animation easier to see. Also, fast animations can be better visualized with a small frame step.
• The Skin Opacity setting can help in situations where the skin is overstrained.

I hope we were able to give you a short overview of Onion Skinning.

Thank you very much for your visit.