RESOLVE FX · SHAPE SOFTNESS
Gaussian Blur.
Softness looks simple.
Its geometry is not.
Start with one clean blur amount. Split horizontal and vertical only when the shot needs an axis. Keep RGB neutral unless color separation is intentional, then solve frame edges and alpha before you touch the final Blend.
Strength
Split H/V + Channels
Border + Alpha + Blend
Open the Shape chart in the lab. Keep Split off first, then enable it and reduce one vertical channel. You will see why “blur amount” and “blur footprint” are different decisions.
INPUTGAUSSIANHorizontal Channel Adjustment
Vertical Channel Adjustment
Enable Split Horizontal and Vertical to edit the vertical axis independently.
Alpha and model notes
This is an independent separable Gaussian-like teaching renderer. Strength is mapped to a small demo radius; it does not reproduce Resolve’s internal OFX algorithm or numeric scale.
Teaching visualization, not a Resolve renderer. Use the actual screenshots below for the real control names and panel structure.
Actual Resolve captures + an explicitly independent teaching renderer.
13 controls · 5 captures · 4 exercises01THE SOFTNESS MODEL
Strength is only the first question. Shape, channels and edges decide whether the blur stays clean.
Gaussian Blur is less dramatic than a vector or lens effect, which is exactly why small technical mistakes can be mistaken for “just softness.” Separate the decisions and the effect becomes predictable.
A smoothly weighted kernel
Gaussian Blur is useful when softness should remain even and neutral, without an explicit motion vector or aperture shape. In the teaching model below, neighboring samples lose weight with distance along a Gaussian-like curve; that explains the visual principle without claiming Resolve’s internal OFX implementation.
Split H/V turns a circle into an ellipse
Without axis separation, horizontal and vertical behavior stays linked as one soft shape. Split Horizontal and Vertical matters when one axis needs a different character or per-channel amount, such as wider horizontal softening with much less vertical spread.
Channels, edges, and mix are separate decisions
Red, Green, Blue, and Alpha scale each channel’s participation in the blur, Border Type only governs samples beyond the frame, Blur Alpha controls transparency processing, and Blend is the final dry/wet. Keeping those decisions separate makes troubleshooting much easier.
Version anchor and channel semantics: Blackmagic Design · Resolve 21.1 support ↗ · Resolve 19.1 Blur FX Channel Adjustment ↗
02THE ACTUAL INSPECTOR
Thirteen controls, grouped by the question they answer.
The screenshots are actual Gaussian Blur interface captures from the project archive. Captured values describe those frames only; they are not declared defaults or recommended settings.
Base shape
Set the overall softness first; split the axes only when the shot needs it.
- Split Horizontal and Vertical
Separates horizontal and vertical behavior so their per-channel multipliers can be used independently. A normal symmetrical soft blur often does not need it; anisotropic blur or deliberate channel styling does.
CheckCompare the shot with split disabled first. If the linked shape already solves the problem, do not add independent axes just for complexity.
- Strength
Sets the overall Gaussian Blur amount before per-channel adjustments. The screenshot shows 0.400 as one captured panel state; it is not a recommendation or universal preset.
CheckJudge more than the center of the frame: high Strength exposes Border Type problems sooner, removes texture, and can make local masks easier to notice.
Horizontal contribution
Horizontal Channel Adjustment scales blur per channel along the horizontal axis.
- Red
Horizontal blur multiplier for the red channel relative to overall Strength. A value of 1.000 is neutral relative to the base amount; it does not mean “100% red”.
CheckIf Red differs from Green/Blue, colored fringing can appear on high-contrast vertical edges.
- Green
Horizontal Green multiplier. For technically neutral softening it normally matches Red and Blue.
CheckCheck white titles, graphics, and fine lines; accidental channel separation shows there first.
- Blue
Horizontal Blue multiplier. Deliberately separating it from R/G can create colored softness or a chromatic smear without changing the axis geometry itself.
CheckDo not confuse stylization with a defect: on neutral subjects, verify that colored fringing is actually intentional.
- Alpha
Horizontal alpha-channel multiplier. Its practical effect appears on keyed or transparent elements and works together with Blur Alpha.
CheckOn fully opaque footage you may not see a difference at all. Test it in the real composite.
Vertical contribution
Vertical Channel Adjustment shapes the second axis of the same model.
- Red
Vertical blur multiplier for Red. After Split H/V it lets you change the vertical red spread independently relative to overall Strength.
CheckWhen horizontal and vertical components differ strongly, inspect round highlights and point details; the elliptical footprint is easiest to see there.
- Green
Vertical Green multiplier. Equal RGB and H/V values keep the blur neutral; separating one axis makes it anisotropic.
CheckDo not separate H/V for ordinary defocus-like softening; the elongated shape can resemble an optical or scaling artifact.
- Blue
Vertical Blue multiplier. It can be combined with horizontal channel values for deliberately colored blur geometry.
CheckInspect at several viewer zoom levels: a subtle blue fringe may disappear at Fit and become obvious at 100%.
- Alpha
Vertical Alpha multiplier. It matters when a transparent edge needs different vertical softness from RGB or when diagnosing matte behavior.
CheckDo not use Alpha as a substitute for a correct matte/compositing pipeline: it is a blur multiplier, not a bad-key repair tool.
Edges and transparency
A strong blur inevitably asks: what exists beyond the frame?
- Border Type
Defines how Resolve supplies samples when the kernel extends beyond the image. The actual captured menu shows Black, Replicate, Reflect, and Wrap-Around; the difference appears mainly near frame edges, not in the center.
CheckInspect frames where a bright subject, face, text, or high-contrast line touches the border. That is where the wrong mode reveals itself first.
- Blur Alpha
Includes the alpha channel in the blur process. On keyed graphics, titles, and other transparent elements it helps RGB and matte softness move together; on ordinary opaque footage the difference may be invisible.
CheckIf RGB is already soft but the transparency edge stays hard or produces a halo, compare Blur Alpha states and inspect premultiplication/compositing.
Final mix
Blend does not reshape the kernel; it mixes the result after it has been built.
- Blend
The Global Blend control mixes the processed result with the unaffected image. Fix Strength, Split H/V, channels, Border Type, and Alpha first, then use Blend as the final dry/wet.
CheckIf the blur is stretched, colored, or broken at an edge, lowering Blend only hides the cause. Fix the source of the problem first.
03WHEN THE KERNEL REACHES THE EDGE
Border Type is not a style preset. It is an answer to missing image data.
The center of the image may look identical under every mode. The difference appears when a blur sample asks for pixels outside the frame, so inspect the worst edge case on purpose.
Black
… ABC | ···Outside the frame there is no useful picture, so strong blur can pull dark values inward.
Useful for exposing the issue; rarely the best choice for a bright subject touching the border.
Replicate
AAA | ABC | CCCExtends the nearest edge pixel. It avoids black contamination but can stretch the edge color into a band.
Inspect flat walls, sky, and bright frames; stretched bands show there more clearly.
Reflect
CBA | ABC | CBAMirrors the image across the border. It often looks smooth on organic footage, but faces, text, and straight lines can create an obvious duplicate.
Check motion as well as a still frame near the edge; reflected detail can flicker as a tracked mask moves.
Wrap-Around
BCA | ABC | ABCTakes samples from the opposite edge. It can be useful for cyclic graphics but easily imports unrelated detail across the frame on normal footage.
Watch opposite edges together for content that has no physical reason to appear there.
The letter strings are explanatory edge-extension diagrams, not literal Resolve pixels. The actual open-menu screenshot on this page shows Black, Replicate, Reflect, and Wrap-Around, with Reflect selected in that capture.
04ISOLATE THE SOFTENING
A blur is easier to trust when it has one job and one node.
Privacy work, background cleanup and graphics all benefit from the same discipline: keep the base grade separate, localize only when necessary, and leave the FX easy to bypass.
The isolated softening node
Apply Gaussian Blur here and constrain it with a tracked Power Window or matte when the job is local. Set Strength first, then decide whether Split H/V, channel adjustments, Border Type, or Blur Alpha are actually necessary.
Green lines show image flow. The dashed matte annotation is not a separate node. For privacy work, the tracker belongs to the localization stage; for an animated transition, keyframe only the controls the motion actually needs. This is a teaching diagram, not a Resolve screenshot.
Related Color workflow: node pipeline ↗ · Power Windows / Tracker ↗
05BUILD IT IN RESOLVE
Four exercises expose four different reasons to use Gaussian Blur.
These are teaching workflows, not magic values. Keep the exact Strength and channel numbers subordinate to what the shot must accomplish.
Hide a face or detail locally
Create effective privacy blur without an obvious rectangular edge or blurring the whole frame.
PrepareUse a dedicated FX node, a Power Window around the subject, and tracking. Start with linked H/V and equal RGB values.
- 01
Set the Window slightly wider than the recognizable region and track it through the shot.
- 02
Raise Strength until identifying detail is no longer readable rather than pushing blur to the maximum.
- 03
Add Window softness so the local-effect boundary does not reveal itself.
- 04
Check Border Type on edge frames rather than judging only the center.
The face/detail is no longer identifiable, the Window edge is invisible, and tracking does not create sharp edge flashes.
Reduce distracting background detail
Calm a busy background while keeping the subject sharp, without pretending to create true optical bokeh.
PrepareSeparate the subject with a mask/matte and apply Gaussian Blur to the background rather than the entire image.
- 01
Check the mask around hair, fine objects, and motion before setting Strength.
- 02
Increase Strength until the background stops competing without turning all texture into plastic.
- 03
Leave Split H/V off unless there is a specific reason for an elongated blur footprint.
- 04
Finally compare Blend 1.0 with a reduced mix during real playback.
The subject stays clean, the background is calmer, and the blur does not announce itself as an effect.
Build controlled H/V anisotropic blur
Make blur substantially wider along one axis without turning it into a directional streak.
PrepareUse graphics, an abstract background, or a technical case where axis-based shaping is justified.
- 01
Find the base Strength with linked axes.
- 02
Enable Split Horizontal and Vertical only after the base softness is clear.
- 03
Keep RGB equal and change only the needed axis so you can see pure geometry first.
- 04
Inspect round highlights and fine detail; they reveal the elliptical footprint most clearly.
The blur is elongated along the intended axis without a directional trail or accidental RGB fringing.
Blur transparent graphics without a hard matte edge
Keep RGB and transparency softness consistent on a title or keyed element.
PrepareUse an element with real alpha over a contrasting background.
- 01
First inspect the composite without the effect and rule out an existing halo or premultiplication issue.
- 02
Set Strength and RGB for the desired visual softness.
- 03
Compare Blur Alpha on/off and adjust Alpha multipliers if needed.
- 04
Check against both light and dark backgrounds; alpha errors may appear on only one.
RGB and matte soften together without a hard transparency edge or a new halo.
06CHOOSE THE RIGHT BLUR MODEL
Smoothness, iterations, vectors and bokeh are four different problems.
| FX | What shapes the result | Explore it for |
|---|---|---|
| Box Blur ↗ | A more structural box profile where Number of Iterations is part of the behavior. | When Iterations matter or a box-like character is desired. |
| Directional Blur ↗ | Blur along an angle/vector with Realistic/Stylized and Symmetric Blur. | For motion-like streaks and explicitly directional geometry. |
| Gaussian Blur | Smooth neutral blur with optional Split H/V and per-channel control. | For softening, privacy blur, backgrounds, matte softness, and clean axis shaping. |
| Lens Blur ↗ | Optical bokeh-oriented blur with aperture/lens controls. | When bokeh shape and lens character matter more than simple softness. |
07READ THE FAILURE
Every ugly blur leaves a clue about the wrong control family.
01A dark band appears along the frame edge.+
Do not lower Blend first. Compare Border Type: Black can deliberately pull darkness inward, while Replicate/Reflect use different outside-frame samples.
02White graphics develop a colored fringe.+
Compare Red/Green/Blue in both Channel Adjustment groups. Match RGB for neutral blur; keep differences only as deliberate stylization.
03The blur looks stretched even though ordinary softening is intended.+
Check Split Horizontal and Vertical and differences between Horizontal/Vertical multipliers. Restore linked behavior or matching H/V values.
04RGB is soft on transparent graphics but the matte remains hard.+
Compare Blur Alpha, Alpha multipliers, and the original premultiplied composite. Gaussian Blur does not automatically repair a bad key.
05A local privacy blur reads as a separate patch.+
Check Power Window softness/size and tracking. FX Strength should not be used to hide a hard mask boundary.
06The image looks plastic after strong blur.+
Return to the goal: reduce Strength, localize the effect, or restore more source through Blend. If natural optical defocus is the goal, compare Lens Blur.
Inspect at 100%
Fit view can hide fine halos and channel fringing. Perform the final technical check on at least a few frames at 100%.
Watch playback, not only a still
Tracking, masks, and frame edges can look clean on one frame and fail a few frames later. Watch the full effect in motion.
Compare against the right neighboring FX
If the task becomes about motion streaks, bokeh, or Iterations, do not force Gaussian Blur into another tool’s job; compare Directional, Lens, or Box Blur.
08BEFORE YOU DELIVER
Certify the image, not the slider position.
No Strength number is a quality certificate. Inspect the actual edge, motion, transparency and mask behavior at the resolution you will deliver.
09COMMON CONFUSIONS
Keep the Resolve FX, the Blur palette and optical defocus conceptually separate.
How is Gaussian Blur different from the Color page Blur palette?
It is a separate Resolve FX with its own Strength, Split H/V, per-channel adjustments, Border Type, Blur Alpha, and Global Blend controls. The Color page Blur palette is a different tool with a different control set; do not treat numeric values as interchangeable.
Should Split Horizontal and Vertical always be enabled?
No. Linked behavior is simpler and safer for normal symmetrical soft blur. Split is useful when H/V must differ or when you deliberately shape axis/per-channel geometry.
Why do Horizontal and Vertical each have four channels?
Red, Green, Blue, and Alpha let you scale blur independently by channel and axis. Equal RGB values give a neutral result; differences create channel-specific softness or colored fringing.
Should I use Replicate or Reflect?
There is no universal answer. Replicate extends the edge pixel; Reflect mirrors the image. Choose based on the actual frame edge and watch motion, especially near faces, text, or geometry.
Do I need Blur Alpha on ordinary video?
On fully opaque footage its effect may be invisible. It matters on graphics, keyed material, and other elements with real transparency.
When should I switch to Lens Blur?
When the goal is no longer simple softness but optical defocus: aperture-shaped bokeh, lens character, and related optical controls. Gaussian Blur remains simpler and more direct for technical softening.
Sources and the limits of this guide
Visible control names, menu options, and captured values were checked against the actual Gaussian Blur screenshots in this project. The current product/version anchor is Blackmagic Design’s Resolve 21.1 support documentation, while the official Resolve 19.1 New Features Guide explicitly documents the per-channel Blur FX Channel Adjustment semantics. The interactive lab is a separate teaching renderer.
The exercises were not live-certified through a Resolve render during this website update. Edition availability, tiny UI differences, and production behavior should always be verified in the installed build used for delivery.