Blur: Low Pass Video Filter

Applies a low-pass spatial filter to the video clip, attenuating high-frequency detail while preserving low-frequency structures.
In practical terms, it removes fine texture and noise before it removes larger shapes and edges.

This filter is based on the same conceptual idea as a low-pass filter in signal processing: allow slow variations to pass, suppress rapid changes.

What “low pass” means

In images:

• Low frequencies correspond to:

  • Large shapes
  • Smooth gradients
  • Broad lighting changes

• High frequencies correspond to:

  • Fine detail
  • Texture
  • Noise
  • Sharp edges

A low-pass filter reduces high-frequency content while keeping low-frequency information intact.

Note:

Low-pass blur removes detail first, not structure.

Parameters

Amount (0.0 - 100.0%)

Controls how strongly high-frequency detail is suppressed.

• 0.0%
  No filtering; the image is unchanged.

• Low values (5% - 20%)
  Fine texture and noise are reduced. Edges remain mostly intact.

• Medium values (20% - 60%)
  Noticeable softening. Small details disappear, larger forms remain readable.

• High values (60% - 100%)
  Strong smoothing. The image becomes flat and diffuse, with minimal fine structure.

Important behavior

• The effect increases rapidly at low values.
• Amount controls frequency suppression, not a blur radius in pixels.

Keyframes

The Amount parameter can be keyframed.

This enables:

• Progressive smoothing or reveal of detail
• Temporal separation of detail and structure
• Transitions between sharp and abstract states

Visual characteristics

• Smooth, uniform softening
• Reduced fine texture and noise
• Edges fade gradually rather than haloing
• Less “spread” than Gaussian blur at comparable strength

Comparison with other blur filters

Gaussian Blur

• Uniform spatial blur
• Radius-based
• Spreads pixels evenly in all directions
• Produces visible haloing at higher values

Low Pass Blur

• Frequency-based smoothing
• Suppresses detail before structure
• More controlled edge degradation
• Less haloing, more matte appearance

Exponential Blur

• Rapid falloff from edges
• Perceptual, localized softening
• Not frequency-oriented

Summary comparison

Recommended use cases

• Reducing fine digital noise
• Preprocessing before Posterize or Dither
• Softening textures while preserving shapes
• Creating abstract or painterly looks
• Preparing footage for heavy compression

Limitations

• Not a physical lens simulation
• Single control only
• Can flatten contrast at high values
• Not suitable when edge precision must be preserved