Houdini 22.0 Nodes Copernicus nodes

Filter Frequencies Copernicus node

Boosts or suppresses spatial frequencies in an image.

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Since 22.0

Every image can be described as a sum of spatial frequencies: low frequencies are the broad, slowly varying content such as gradients and lighting, while high frequencies are the fine detail such as texture and edges. This node boosts or suppresses frequencies across that spectrum, letting you amplify, attenuate, or remove detail at a chosen scale. The Frequency and Width controls select which part of the spectrum to act on, and the Anisotropy controls narrow that selection to an angular wedge, so you can target frequencies running in a particular direction.

Internally the node transforms the source image into frequency space with an FFT, multiplies it by a mask built from these controls, and transforms back. For full control you can build the frequency mask yourself and wire it into the filter input instead of using the procedural controls.

Parameters

Signature

The layer type this node filters. See Signatures for more information.

Scale

Multiplies the filtered result. Use values above 1 to boost the kept band or below 1 to attenuate it. The default of 1 passes the band through unchanged.

Frequency

The radial band of the mask. These controls are disabled when an image is wired into the filter input, since that image supplies the mask directly.

Frequency

The center of the kept band, as a normalized radial frequency from 0 to 1. A value of 0 is the lowest frequency (the broad, slowly varying content at the center of the transform) and 1 is the highest frequency the image can represent (the finest detail). The default of 0 keeps the lowest frequencies.

Width

The full width of the kept band around Frequency, so the band spans Frequency - Width/2 to Frequency + Width/2. Wider values keep more of the spectrum; a narrow width isolates a single, tightly defined frequency.

Smooth

Gives the band a soft falloff at its edges instead of a hard cutoff. A hard cutoff in frequency space can produce ringing artifacts in the result, so smoothing the band usually gives a cleaner image.

Anisotropy

Restricts the radial band to an angular wedge, so only frequencies running in a chosen direction are kept. These controls are disabled when an image is wired into the filter input.

Angle

The center direction of the wedge, in degrees from 0 to 360. Frequencies oriented along this direction are kept.

Width

The angular extent of the wedge, in degrees. The default of 360 keeps all directions, leaving the filter isotropic. Smaller values narrow the wedge so only frequencies near Angle survive.

Smooth

Gives the wedge a soft falloff at its angular edges instead of a hard cutoff.

Reflect

Mirrors the wedge to the opposite direction, so a wedge at Angle also covers Angle + 180. Because the frequency spectrum of a real image is symmetric about its center, you usually want this on so the filter treats a direction and its opposite alike.

Inputs

source

The image to filter.

filter

An optional image used directly as the frequency-domain mask. When wired, the Frequency and Anisotropy controls are disabled and this image multiplies the source’s transform instead.

Outputs

filtered

The filtered image.

See also

Copernicus nodes