Glow Node

A Glow is created by blurring an image, and then brightening the blurred result and mixing it back with the original. The Glow node provides a variety of variations on this theme. For example, a Bartlett glow is a high-quality glow with a smoother drop-off; however, it is more processor-intensive at larger sizes.

Glow Node Inputs

The Glow node has three inputs: an orange one for the primary 2D image input, a blue one for an effect mask, and a third white input for a Glow mask.

• Input: The orange input is used for the primary 2D image that has the glow applied.
• Effect Mask: The blue input is for a mask shape created by polylines, basic primitive shapes, paint strokes, or bitmaps from other tools. Connecting a mask to this input restricts the source of the glow to only those pixels within the mask. An effect mask is applied to the tool after it is processed.
• Glow Mask: The Glow node supports pre-masking using the white glow mask input. A Glow premask filters the image before applying the glow. The glow is then merged back over the original image. This is different from a regular effect mask that clips the rendered result.

The Glow mask allows the glow to extend beyond the borders of the mask, while restricting the source of
the glow to only those pixels within the mask.

Glow masks are identical to Effect masks in every other respect.

Glow Node Setup

The Glow node receives a 2D image like the MediaIn1 shown below. The output continues the node tree by connecting to another 2D image-processing node or a Merge node.

Glow Node Controls Tab

The Controls tab contains all the primary controls necessary for customizing the glow operation. A Color Scale section at the bottom of the Inspector can be used for tinting the glow.

• Filter
  Use this menu to select the method of Blur used in the filter. The selections are described below.
  • Box: A simple but very fast Box filter.
  • Bartlett: Bartlett adds a softer, subtler glow with a smoother drop-off but may take longer to render than Box.
  • Multi-box: Multi-box uses a Box filter layered in multiple passes to approximate a Gaussian shape. With a moderate number of passes (e.g., four), a high-quality blur can be obtained, often faster than the Gaussian filter, and without any ringing.
  • Gaussian: Gaussian adds a soft glow, blurred by the Gaussian algorithm.
  • Fast Gaussian: Fast Gaussian adds a soft glow, blurred by the Gaussian algorithm. This is the default method.
  • Blend: Blend adds a nonlinear glow that is evenly visible in the whites and blacks.
  • Hilight: Hilight adds a glow without creating a halo in the surrounding pixels.
  • Solarize: Solarize adds a glow and solarizes the image.
• Color Channels (RGBA)
  This filter defaults to operating on R, G, B, and A channels. Selective channel filtering is possible by clicking each channel to make them active or inactive.
• Lock X/Y
  When Lock X/Y is checked, both the horizontal and vertical glow amounts are locked. Otherwise, separate amounts of glow may be applied to each axis.
• Glow Size
  Glow Size determines the size of the glow effect. Larger values expand the size of the glowing highlights of the image.
• Num Passes
  Only available in Multi-box mode. Larger values lead to a smoother distribution of the effect, but also increase render times. It’s good to find the line between desired quality and acceptable render times.
• Glow
  The Glow slider determines the intensity of the glow effect. Larger values tend to completely blow the image out to white.
• Clipping Mode
  This option determines how edges are handled when performing domain-of-definition rendering. This is profoundly important for nodes like Blur, which may require samples from portions of the image outside the current domain.
  • Frame: The default option is Frame, which automatically sets the node’s domain of definition to use the full frame of the image, effectively ignoring the current domain of definition. If the upstream DoD is smaller than the frame, the remaining area in the frame is treated as black/transparent.
  • Domain: Setting this option to Domain respects the upstream domain of definition when applying the node’s effect. This can have adverse clipping effects in situations where the node employs a large filter.
  • None: Setting this option to None does not perform any source image clipping at all. This means that any data required to process the node’s effect that would normally be outside the upstream DoD is treated as black/transparent.
• Blend
  The Blend slider determines the percentage of the affected image that is mixed with original image. It blends in more of the original image as the value gets closer to 0.
  
  This control is a cloned instance of the Blend slider in the Common Controls tab. Changes made to this control are simultaneously made to the one in the common controls.
• Apply Mode
  Three Apply Modes are available when it comes to applying the glow to the image.
  • Normal: Default. This mode simply adds the glow directly over top of the original image.
  • Merge Under: Merge Under places the glow beneath the image, based on the Alpha channel. Threshold mode permits clipping of the threshold values.
  • Threshold: This control clips the effect of the glow. A new range slider appears. Pixels in the glowed areas with values below the low value are pushed to black. Pixels with values greater than high are pushed to white.
  • High-Low Range Control: Available only in Threshold mode. Pixels in the glowed areas with values below the low value are pushed to black. Pixels with values greater than high are pushed to white.
• Color Scale (RGBA)
  These Scale sliders can be used to adjust the amount of glow applied to each color channel individually, by tinting the glow.

Glow Node Settings Tab

The Settings tab in the Inspector is also duplicated in other Blur nodes. These common controls are described in detail HERE.