Gaussian Blur Operator

The Gaussian Blur operator is a real-time video effect that applies a smooth blur to the video image. It's commonly used for softening video, creating depth-of-field effects, background blurring, and preparing content for compositing. The operator features adjustable blur radius, directional blur options, quality presets, and an optional edge-preserving mode.

Overview

Gaussian blur is one of the most widely used blur algorithms in image and video processing. It works by averaging pixel values using weights from a Gaussian (bell curve) distribution, which creates a natural, smooth blur effect. In Composer, the Gaussian Blur operator is GPU-accelerated for real-time performance, even at higher blur radii.

Common use cases:

• Softening skin or reducing fine details in video
• Creating depth-of-field effects for focus transitions
• Blurring backgrounds behind overlays or lower thirds
• Pre-processing video for compositing workflows
• Creating motion blur effects using directional blur
• Reducing noise or grain in video content

Settings

Blur Settings

Show advanced options - Toggle to show/hide advanced options. The default value is off.

Blur radius - Sets the blur radius in pixels. A higher radius creates a stronger blur effect. The range is 0-20 pixels, where 0 means no blur is applied. The default value is 5.

Performance note: Higher blur radii require more processing power. For 4K content with large blur radii, consider using the Fast quality preset.

Blur strength (%) - Controls the blend between the original image and the blurred result. At 0%, the original image is shown unchanged. At 100%, the fully blurred image is shown. Values in between create a partial blend. The range is 0-100%, and the default value is 100%.

Direction - Selects the blur direction. The options are:

• Both - Full 2D Gaussian blur in all directions (default)
• Horizontal - Blur only in the horizontal direction
• Vertical - Blur only in the vertical direction

Directional blur can be used to create motion blur effects or to blur in a specific direction for creative purposes.

Quality - Selects the quality/performance preset. The options are:

• Fast - Optimized for performance, uses adaptive sampling for larger radii. Recommended for 4K content or when using multiple blur operators.
• Standard - Balanced quality and performance (default). Suitable for most use cases.
• High - Maximum quality with full sampling. Best for final output or when quality is critical.

Reset to defaults (button) - Resets all blur settings to their default values.

Advanced Settings

The advanced settings provide additional control over the blur behavior. Enable "Show advanced options" to access these settings.

Sigma Control

Sigma (0 = auto) - Controls the Gaussian sigma value, which determines the shape of the blur falloff. A higher sigma creates a softer, more spread-out blur. The range is 0-200 (representing 0.0-20.0 internally).

When set to 0 (default), the sigma is automatically calculated based on the blur radius using the formula: sigma = radius / 2. This provides a good balance for most use cases.

Tip: Manually adjusting sigma can be useful when you want a softer blur without increasing the radius, or when matching blur characteristics from other software.

Blur alpha channel - When enabled, the blur is also applied to the alpha channel. This is useful when you want the transparency to be blurred along with the RGB channels. The default value is off.

Edge Preservation

The edge preservation feature provides bilateral-like filtering that maintains sharp edges while blurring smooth areas. This is particularly useful for:

• Skin smoothing while keeping eyes and hair sharp
• Background blur that respects object boundaries
• Noise reduction without losing detail

Preserve edges - Enables edge-aware blurring. When enabled, the blur algorithm detects edges and reduces blur strength across them. The default value is off.

Edge threshold (%) - Sets the luminance difference threshold for edge detection. Higher values make edge detection less sensitive, allowing more blur across moderate edges. Lower values preserve more edges. The range is 0-100%, and the default value is 20%.

Note: Edge preservation adds processing overhead. For maximum performance, leave this option disabled unless the effect is needed.

Debug

Show original (debug) - When enabled, bypasses the blur effect and shows the original input image. Useful for A/B comparison during configuration. The default value is off.

Keyboard Shortcuts

When the Gaussian Blur operator is selected, the following function keys can be used:

Practical Examples

Example 1: Soft Background Blur

For creating a soft background blur effect behind a keyed subject:

1. Add the Gaussian Blur operator after your keyer
2. Set Blur radius to 8-12 pixels
3. Set Quality to Standard
4. Leave Direction as Both

Example 2: Motion Blur Effect

To create a horizontal motion blur for a transition or speed effect:

1. Set Direction to Horizontal
2. Set Blur radius to 15-20 pixels
3. Adjust Blur strength to control the intensity
4. Use Quality: Fast for better performance

Example 3: Skin Smoothing

For subtle skin smoothing while preserving facial features:

1. Set Blur radius to 3-5 pixels
2. Enable Preserve edges
3. Set Edge threshold to 15-25%
4. Adjust Blur strength to 40-60% for a natural look

Example 4: Noise Reduction

For reducing noise or grain in low-light footage:

1. Set Blur radius to 2-4 pixels
2. Enable Preserve edges
3. Set Edge threshold to 10-15%
4. Set Quality to High for best results

Performance Considerations

The Gaussian Blur operator is GPU-accelerated and designed for real-time performance. However, performance can be affected by:

• Blur radius: Larger radii require more samples and processing time
• Quality setting: High quality uses more samples than Fast mode
• Edge preservation: Adds additional calculations per pixel
• Resolution: 4K content requires proportionally more processing than 1080p

Recommendations for optimal performance:

• Use the Fast quality preset for 4K content or when stacking multiple effects
• Avoid blur radii above 15 for 4K content in real-time scenarios
• Disable edge preservation unless specifically needed
• Use directional blur (Horizontal or Vertical) instead of Both when appropriate, as it requires fewer calculations