Polymesh objects can be rendered as volumes. This gives many creative opportunities for rendering solid objects in varied and interesting ways. This short 'making of' tutorial shows how to combine a polymesh with a volume by combining their shading using the displacement attribute of a standard_volume shader. We will also cover how to reproduce the above-animated effect using the cell_noise, color_correct, ramp_rgb and range shaders connected to volume_displacement of the standard_volume shader.

An example of a free to use head scan model can be found here.

The polymesh should be closed and not have anything self-intersecting, otherwise, the volume may not render correctly.

Step Size

• First of all, we need to convert the head mesh to a volume. Select the mesh and under its Arnold attributes, increase the step_size to 0.1. When the step_size is positive, it turns a polymesh into a volume and its value is used as the base step for raymarching the volume.

More information about volume step_size can be found here.

A basic scene file can be found here. |

Standard Volume

• Assign a standard_volume shader to the polymesh and increase the density to a very high value of around 4000. This will ensure that the displacement texturing looks more defined later.

_{Head mesh rendered as volume}

Range

• Connect a range shader to the volume_displacement of the standard_volume shader.
• Increase its output_max value to around 30. This will increase the effect of the volume_displacement once we connect the cell_noise shader to it.

Camera Projection

To animate the effect from top to bottom we will project a ramp through the V direction.

• Create a camera_projection shader and connect it to the input of the range shader.

• Remember to select the render camera that you want to use for the camera_projection.

Ramp RGB

• Create a ramp_rgb shader and connect it to the projection_color of the camera_projection shader.

Color Correct

• Connect a color_correct shader and connect it to the input of the ramp_rgb shader. You can use this to fine-tune the cell_noise shading effect.

Cell Noise

• Create a cell_noise shader.
• Change the pattern to cell1.
• Disable additive.
• Ensure that the coord_space is set to object.
• You will need to adjust the scale according to your scene size. In this case, the cell_noise is thinner because Y and Z are less than X.
• Increase the density to 1 and set randomness to around 0.2 to add some irregular shapes.

^{_{Final cell_noise settings}}

Animation

• Keyframe the black color of the ramp_rgb from left to right over time to see the effect move bottom to top across the head volume.
• Keyframe the time attribute of the cell_noise shader to animate the cell_noise effect.

Conclusion

That's it. Remember to increase the volume_samples for any lights in the scene when rendering the final animation.

_{Further example with cell_noise scaled in Y}

_{Final shading network}