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Since | 11.0 |

The Volume Blur operation blurs the voxels of a volume.

It does this by computing for each neighborhood around a voxel a single value according to some property of that neighborhood. The resulting voxel is then set to that value. The neighborhood regions are always cubic in shape, despite the term radius being used.

Note

The volume is treated as a piecewise linear function between the voxel centers, not as a step function. This usually results in expected behavior for sub-voxel sized filters, but may be surprising if you are attempting to work with discrete data. Consider the Volume Convolve 3×3×3 for those cases.

Note

This node currently only works with standard Houdini volumes. It does not work with VDBs.

## Parameters

Source Group

The volume primitives to be reduced.

Use Voxel Radius

Determine if the radius will be computed from world sizes or voxel sizes.

Radius

The world space radius to use for reduction. This defines the cubic region of voxels that will be valid for reduction. In the case of tapered volumes, this is approximate since the same voxel size blur will be used for all voxels.

With the exception of the median reduction, these reductions take about the same amount of time regardless of the radius.

Note

The world space radius is converted to voxels, and this is then capped at 5× the voxel resolution.

Note

The **Maximum**, **Minimum** and **Median** reductions only work on integer voxel radiuses.

Voxel Radius

The number of voxels to perform the reduction in along each axis.

Reduction

The types of reduction to be performed.

Maximum

Find largest element of the neighborhood. This is a sort of dilate operator that will expand a fog into surrounding voxels.

Minimum

Find smallest element of the neighborhood. This is a sort of erode operator that will shrink a fog.

Maximum of Absolute

Find largest absolute element of the neighborhood.

Minimum of Absolute

Find smallest absolute element of the neighborhood.

Average

Find the mean of the neighborhood. This is equivalent to a box blur of the same radius.

Median

Returns the median, or 50th percentile, of the voxels in the neighborhood. The true median is not computed, instead an approximation is made by using a separable median, ie, finding the median along each axis in turn.

Sum

The total of all voxels in the neighborhood.

Sum of Absolute

The total of the absolute value of all the voxels in the neighborhood.

Sum of Squares

The total of the square each voxel in the neighborhood.

Root Mean Square

The square root of the average of the squares of all of the voxels in the neighborhood.

Passes

An approximation of a gaussian blur can be achieved by doing four box blurs of smaller radius. For a cone blur, multiply the radius by 0.454545 and use two passes. For a gaussian, multiply the radius by 0.33 and use four passes.

Override Border

Overrides the volume’s border conditions for the blur.

Use Volume

Use the volume’s border settings.

Constant

Treat exterior voxels as having a constant value.

Repeat

Wrap voxel values from one side of the volume to the other.

Streak

Extend boundary voxels.

Border Value

The value of the border to use when overridden with constant border conditions.

## Examples

volumeblur Example for Volume Blur geometry node

This example demonstrates how the Volume Blur SOP can be used to apply local filters to volume values, such as blurring, dilating, or eroding.

See also |