Glow

Extracts bright areas and composites a blurred, tinted version over the original for a bloom or glow effect.

Category: Effects Menu path: Effects > Glow

Ports

Port	Type	Direction	Description
in	imageRgba16f	input	Input image
out	imageRgba16f	output	Image with glow applied

Parameters

Param	Type	Default	Description
threshold	scalar	0.5	Luminance cutoff for bright area extraction (0-1). Only pixels brighter than this contribute to the glow. Lower it to make more of the image bloom. Keyframeable.
intensity	scalar	1.0	Multiplier for the extracted brightness. Higher values produce a stronger glow. Keyframeable.
blur (Radius)	scalar	40	The glow's reach in pixels — how far light visibly travels from the source. Crank it and the whole scene blooms out from even a small shape. Keyframeable.
falloff	enum	Natural	The glow's shape, by look: Soft — one wide gaussian, the classic soft glow. Natural — a bright core with a natural halo. Long Tail — a tight core with long atmospheric tails that carry light far past the source.
stretch	vec2	1, 1	Per-axis reach multiplier (linked pair). Unlink and raise X for a horizontal anamorphic streak, or Y for a vertical one.
color	color	white (1,1,1,1)	Tint color for the glow. Multiply against the extracted brightness.
blendMode	enum	Add	How the glow is composited over the original. Add: additive (brightens). Screen: screen blend (softer, non-clipping). Hidden when output is Glow Only.
output	enum	Composite	Composite: glow over the source (default). Glow Only: the isolated glow with no source underneath — grade it, distort it, or composite it yourself downstream.

Expose Channels

When enabled (E button on node header), adds input ports that override params via edge connections:

Port	Type	Overrides
threshold_in	scalar	threshold
intensity_in	scalar	intensity
blur_in	scalar	blur

How It Works

The glow effect is a three-stage operation:

1. Threshold pass: Extracts pixels above the luminance threshold using a smoothstep with a ±0.1 transition band. The extracted brightness is multiplied by the intensity and tint color.
2. Blur stage: With Soft falloff, one gaussian blur at the full radius. With Natural / Long Tail, the extraction is blurred at a stack of doubling radii (the widest equals the Radius value; the octave count is derived automatically) and the octaves are summed with decaying weights — a sum of gaussians that closely approximates a true exponential radial falloff. The tightest octave always contributes at full strength, so the core stays bright and wider octaves add bloom on top.
3. Merge pass: The glow is composited over the original image using Add or Screen blend mode — or returned as-is with output set to Glow Only.

Glow expands content bounds (like Blur) by Radius × Stretch, so the engine computes overscan to prevent clipping at comp edges.

Usage Examples

Basic: Bloom on highlights

1. Add a Glow node after your image source
2. Set threshold to 0.7, intensity to 1.0, blur to 30
3. Bright areas (specular highlights, light sources) bloom outward

Creative: Colored glow

1. Set the color param to a warm orange for a candlelight glow
2. Lower threshold to 0.5 to include more of the image in the glow
3. Use Screen blend mode for a softer, more natural bloom

Advanced: Pulsing neon glow

1. Keyframe intensity from 0.5 to 2.0 in a sine pattern using Time + Math nodes
2. Feed the result into intensity_in via expose channels
3. The glow rhythmically pulses

Advanced: Bloom the whole scene from a small source

1. Set falloff to Long Tail and push Radius to 300+ — light from even a small bright shape carries across the frame while the source stays crisp
2. Raise intensity to taste; Screen blend keeps the long tails from clipping
3. Unlink Stretch and raise X for an anamorphic-style streak

Advanced: Isolated glow as a graph ingredient

1. Set output to Glow Only — the node emits just the glow
2. Grade it (Colorize, Levels), distort it (UV Remap, Roughen), or use it as a matte or Draw Instances source
3. Composite back over the source with a Merge when ready

Tips

• Screen blend mode prevents values from exceeding 1.0 (no clipping), while Add can push values above 1.0 for a more aggressive bloom
• Lower threshold values include more of the image in the glow -- at 0, the entire image glows
• Radius is the glow's actual reach: 20-60 for subtle halos, 150+ for scene-wide bloom
• Natural and Long Tail cost a few blur passes instead of one (the count scales with radius, capped at 6) — still cheap, but Soft is the fastest
• For cinematic bloom, use a slight warm tint color, Long Tail falloff, and Screen blend mode
• Old projects load with Soft falloff automatically — identical to the original single-blur glow

Related Nodes

• Blur -- the blur stage used internally; standalone blur without the threshold/composite steps
• Merge -- the compositing stage; can replicate glow manually with more control
• Threshold -- similar bright-area extraction without the blur/composite
• DropShadow -- similar multi-pass architecture but darkens instead of brightens