RESOLVE FX · UNDERSTAND THE EFFECT
Box Blur.
Control the softness.
Keep the intent.
From a quiet background to a controlled local blur. Understand Strength, axes, channels and edges — then choose the result deliberately, not by guessing at a slider.
Strength + H/V
Iterations + Border
Alpha + Blend
Try “Edge test” and change the border mode. Compare Blend with radius: the two are not interchangeable.
INPUTBOX BLURChannels and alpha in the model
Each multiplier applies to both axes here. Resolve exposes separate horizontal and vertical channel controls.
Teaching model, not Resolve: radii are demo pixels, not Strength. Repeated passes keep a fixed radius. Alpha is filtered in premultiplied RGB; color management and OFX internals are not reproduced.
A practical reference with actual interface screenshots.
14 controls · 4 scenarios01THE BLUR MODEL
One filter. Several different decisions.
The equal-weight neighborhood explains the look. The lab shows that principle; it does not substitute for Resolve’s own rendering.
Not pixelation. Averaging.
Imagine a small rectangular window over a pixel. A box filter averages the values inside it, then moves across the image. Fine changes soften: text loses definition, thin lines spread and bright points become patches. This is not Mosaic Blur: large discrete pixel cells are not the intended result.
Strength and Blend answer different questions.
Strength changes the blur itself. Blend mixes the processed frame with its input. A strong blur at half Blend is therefore not equivalent to half the blur strength: the original sharp structure returns over the soft patch. Establish the blur shape first; then decide how much original detail to restore.
Iterations is not a free quality switch.
Repeated averaging smooths the rectangular profile: multiple box passes create a smoother response. At the fixed radius used in this teaching model, the patch also spreads. Iterations is not merely artifact removal: reassess blur strength and processing time after changing it. Resolve’s exact radius normalization is not reproduced here.
Box-filter principle: NVIDIA BoxFilter ↗
02THE ACTUAL CONTROLS
Know what every control changes.
Five verified screenshots, fourteen controls. Values in the captures are reference values, not a preset for every shot or a claimed parameter range.
01 · Strength and axes
Establish the shape before the channels.
- Strength
Overall blur strength when the axes are controlled together. Increasing it blends neighboring detail more strongly. It is neither effect opacity nor a documented pixel radius.
CheckBegin with a small change at Blend 1.000. Compare fine text or a high-contrast edge at 100% Viewer zoom, not only Fit.
- Split Horizontal and Vertical
Separate control allows different horizontal and vertical softness. Unequal axes create an elongated patch; matching axes create a symmetrical one. The axis controls depend on the switch state.
CheckKeep the axes linked for ordinary softening. H/V refers to the image axes, not an arbitrary blur angle; explore Directional Blur for diagonal streaks.
02 · Horizontal Channel Adjustment
Four horizontal channel controls.
- Red · Horizontal
Changes horizontal red-channel blur relative to the overall setting. Blurring red more than green and blue can introduce red or cyan fringes on an otherwise neutral edge.
CheckKeep Red, Green and Blue matched for a neutral result. Introduce differences deliberately, not as a white-balance correction.
- Green · Horizontal
Controls horizontal mixing of the green component. It does not translate the image like a Transform: it changes the spread of neighboring channel values.
CheckInspect fine white text: mismatched color spreads are especially visible on neutral detail.
- Blue · Horizontal
Sets horizontal blue-channel softness. A larger value than R/G can produce a blue halo and a complementary tint around transitions.
CheckDo not confuse channel-specific blur with optical chromatic aberration: this is blur stylization, not a lens model.
- Alpha · Horizontal
Controls the horizontal component of transparency blur when alpha processing is enabled. It is not Power Window strength or Global Blend.
CheckEvaluate it on genuinely transparent media over a contrasting background. On an opaque area with constant alpha, a change may not be visible.
03 · Vertical Channel Adjustment
The same components on the other axis.
- Red · Vertical
Vertical red-channel blur. In split mode it allows red softness to spread vertically without imposing the same horizontal profile.
CheckCompare vertical and horizontal Red settings. Colored trails should be intentional, not an accidental mismatch.
- Green · Vertical
Vertical softness of the green channel. It acts on the color component, not just on a green object in the shot.
CheckUse a mask or Qualifier to isolate an object; the channel name is not a selection.
- Blue · Vertical
Vertical averaging of the blue component. A mismatch with R/G changes the color of fine detail and high-contrast horizontal edges.
CheckInspect several frames: motion can make colored halos more obvious than a still does.
- Alpha · Vertical
Vertical transparency processing when Blur Alpha is enabled. Together with horizontal Alpha it shapes the softened silhouette.
CheckIf soft RGB is cut off by hard transparency, check Blur Alpha, both Alpha axes and the source alpha interpretation.
04 · Advanced Controls
Profile, boundaries and transparency.
- Number of Iterations
The number of repeated box-blur passes. It changes the averaging profile and fine detail. It is not the number of neighboring frames: this remains a spatial effect, not temporal denoising.
CheckCompare one and several passes on a point or white line. Then revisit Strength; do not increase the pass count automatically.
- Border Type
The rule for samples outside the image boundary. Modes can look identical in the center; differences appear near the edge and grow with blur size.
CheckTest a bright object near the frame boundary. No mode knows the actual off-screen scene. Black, Replicate, Reflect and Wrap-Around are explained below.
- Blur Alpha
Enables alpha processing alongside color. On opaque footage, it does not turn a Color window into a transparent cutout. A correction mask and the media alpha channel are different things.
CheckFor alpha graphics, inspect the result on black, white and colored backgrounds. Dark halos can involve premultiplied versus straight alpha, not just blur radius.
05 · Global Blend
Mix the result after shaping it.
- Blend
Final mixing of the input and processed image: 0 returns the input; 1.000 shows the full effect. An intermediate value does not reduce the pass count or correct a wrong Border Type.
CheckFor soft stylization you may restore some sharp detail. For hiding information this is risky: Blend below 1 brings the original structure back. Check the final export.
03BEYOND THE FRAME
An edge is a missing-data problem.
Use the edge-test chart in the hero and compare the same radius across modes. In the middle of an image there may be no visible difference.
Black
0 0 | A B C | 0 0Out-of-image samples are zero. On opaque imagery this can darken a boundary; with alpha processing, also inspect transparency.
Do not mistake a dark rim for a vignette. Compare the edge before and after.
Replicate
A A | A B C | C CEdge values extend outward. No new scene is created beyond the frame: the last available row or column is repeated.
A high-contrast edge object can produce a stretched color band.
Reflect
B A | A B C | C BThe boundary is extended by reflection. The transition often avoids the dark edge caused by black padding, but mirrored detail can become visible.
Letters, lamps and bright points make reflections easy to spot. The diagram is conceptual: exact edge-pixel repetition is implementation-dependent.
Wrap-Around
B C | A B C | A BSampling continues from the opposite side of the image. Useful for a periodic pattern, but ordinary footage can pick up unrelated color from the other edge.
Inspect both left/right and top/bottom boundaries. This does not reconstruct a cropped scene.
The letters illustrate edge extension, not a literal pixel sequence from Resolve. The Box Blur screenshot shows Reflect in a closed menu; no synthetic menu screenshot is used.
04FROM SIGNAL TO RESULT
Give the blur its own node.
Select the intended Color node, open Effects, find Box Blur in Resolve FX Blur and drag it onto that node. Keep balancing decisions separate.
Box Blur on a serial Color node
Drag Box Blur onto this node. Add and track a Power Window on the same node to limit the effect. The window is not a separate graph node or an output-alpha connection.
Green connections carry the image. The dashed annotation is not a signal connection. This is a teaching diagram, not a Resolve screenshot.
More on node connections ↗ · Power Windows / Tracker ↗
05BUILD IT IN RESOLVE
Four tasks. Four acceptance checks.
These are teaching exercises, not “one-click” promises. Use your own clip; choose the amount by the intended result and inspect a short export.
A local detail in motion
Soften a small distracting area without blurring the entire shot.
PrepareA short shot with clear detail. Put Box Blur on a dedicated serial node, initially without a window.
- 01
Use the full effect: Blend 1.000 and matched RGB. Choose Strength by inspecting the detail, not the overall impression.
- 02
Add a Power Window to that same node. It limits the result’s influence; it is not another FX node in the graph.
- 03
Track forward and backward from the reference frame. Check turns, occlusions and frame exits; correct manually where needed.
- 04
Review the full shot at 100% and export a short segment. Where anonymity is essential, do not rely on weak blur: use adequate coverage and check every problem frame separately.
The processing boundary is unobtrusive and the window stays on the target. For privacy, validate unreadability in the export rather than merely the presence of an effect.
A quieter background for a title
Simplify the background while keeping the title sharp.
PrepareVideo plus a separate text layer on Edit. Apply Box Blur to the background clip, not to the composite that already includes the text.
- 01
First inspect the background alone. Keep H/V linked and RGB matched.
- 02
Adjust Strength until texture competes less with the letters while the composition remains readable.
- 03
Compare one and several Iterations on small highlights. Check Reflect and Replicate at the boundaries.
- 04
View the title again. Reduce Blend to restore texture if useful; evaluate text contrast separately because blur does not guarantee it.
Letter edges remain sharp, the background is softer and the frame boundary has no unexpected darkening or streaking.
Blur along one axis
Create controlled horizontal softness without accidental colored smear.
PrepareA frame with vertical lines or short text. Start with Blend 1.000 and matched RGB.
- 01
Enable Split Horizontal and Vertical. Make horizontal blur stronger than vertical blur.
- 02
Compare vertical and horizontal lines: vertical edges spread farther horizontally.
- 03
Change one color channel, inspect the fringe, then restore it. This is a learning check, not a required styling step.
- 04
For a diagonal trail, compare Directional Blur. When suggesting motion, check the subject direction: H/V blur does not analyze velocity.
You can explain why the detail spreads in that direction and why color fringes appeared.
Soft graphics with transparency
Soften an RGBA element without a clipped glow or dark outline.
PrepareAn image or render with a real alpha channel, placed over a contrasting background. Black inside a JPEG is not transparency.
- 01
Compare the original silhouette on black and white. Check Straight/Premultiplied interpretation for the source.
- 02
Enable Blur Alpha and match both Alpha axes to the intended soft contour.
- 03
Temporarily disable Blur Alpha. Find where softened RGB no longer fits inside the hard silhouette.
- 04
Restore the appropriate setting and test an alpha-capable export. Enabling Blur Alpha does not add transparency to a format that cannot preserve it.
The edge remains soft on different backgrounds without an unexpected dark halo; transparency survives in the exported file.
06CHOOSE THE RIGHT MODEL
Blur is a family, not a single look.
| FX | What shapes the result | What to explore it for |
|---|---|---|
| Box Blur | Rectangular averaging, repeated passes, H/V and channels. | Controlled softening and axis/channel experiments. |
| Gaussian Blur ↗ | Smoothly weighted profile instead of equal neighbor weights. | Even softness when the box-pass character is not the goal. |
| Directional Blur ↗ | Direction is set by an angle. | Diagonal or other directional smear. |
| Lens Blur ↗ | Optical patch character and aperture shape. | Shaping bokeh character, rather than simply increasing Strength. |
| Mosaic Blur ↗ | Large discrete cells instead of continuous softness. | Pixelation or graphic concealment; adequacy must be checked separately. |
| AI CineFocus ↗ | Focus and depth rather than one blur radius across the frame. | Different scene-depth planes. See its own guide for version and edition requirements. |
07DIAGNOSE BEFORE RESETTING
A symptom tells you where to look.
01Nothing changes+
Check the selected clip/node, global bypass, FX enable state, Strength and Global Blend. Temporarily remove the local mask: it may exclude the area you are examining.
02The whole shot blurs+
Confirm that the Window/Qualifier belongs to the node containing Box Blur. White in the matte should match the affected area. Choose inversion deliberately.
03The mask looks like a patch+
Check the window shape, softness and tracking. Strong blur mixes neighboring values; mask feathering does not reconstruct the background hidden behind a subject.
04A dark frame-edge band+
Compare Black with Reflect and Replicate. Check transparency and any baked-in black border: Border Type handles the available image boundary, not an automatically detected letterbox.
05White detail develops color fringes+
Check R/G/B matching on both axes. Do not try to fix it with white balance when the cause is different channel-blur geometry.
06Lower Blend reveals the text again+
This is expected: the input is being mixed back in. For concealment, Blend is not an automatically safe intensity control. Check adequate processing and the entire export.
07A soft element is clipped by a hard silhouette+
Check for a real alpha channel, Blur Alpha, both Alpha axes and premultiplication. Compare the source without FX: the defect may predate processing.
08A still looks fine but motion does not+
Check tracking drift, keyframes, subject scale changes and frame-edge contact. Compare a short final render: caching or the preview mode can obscure changes.
Animation without jumps
The diamond next to a parameter creates a keyframe. For a blur-to-sharp reveal, animate effect strength on one clip and inspect the in-between frames. Smoothness depends on the change curve as well as endpoints. Avoid animating several controls together until each contribution is clear.
Node order matters
Blur mixes the current signal values. Results may differ before and after a nonlinear contrast or color transform. The teaching graph places balance before Box Blur as an organizational example, not a universal CST/RCM rule. Grain added before blur also softens, so place texture deliberately.
Check at working resolution
Assess fine detail at 100% and in the target export. A reduced preview already smooths fine structure through scaling. Higher resolution and additional passes increase work, but actual speed depends on the GPU, version and effect chain. Check playback FPS and a short render before deciding on caching.
08BEFORE YOU DELIVER
Check the shot, not just the settings.
A checked box is a reminder, not automated certification. Judge the image in motion and in the actual delivery file.
09QUESTIONS THAT MATTER
Keep these distinctions clear.
Does Box Blur create Mosaic Blur-style squares?
No. “Box” refers to the averaging neighborhood. It smooths transitions rather than splitting the image into large pixel cells. Its geometry is easiest to see on a bright point with few passes.
Does Strength 0.250 mean a 25-pixel radius?
That correspondence is not established here. The screenshot shows 0.250, but it cannot be converted to pixels without a verified specification. The lab explicitly uses demo-buffer pixels, not the Resolve scale.
Are more Iterations always better?
No. The profile, appearance and processing cost change. Repeated passes may help create a smoother character, but Strength and detail must be reassessed afterwards.
Does Blur Alpha blur my Power Window?
Do not treat them as interchangeable. Blur Alpha concerns processed-media alpha; Window softness defines the transition of the correction region. Inspect the result and matte separately.
Can it replace noise reduction?
It smooths some fine variation but removes useful texture with it. It does not analyze noise across time. First decide whether you need a less detailed background, noise removal or optical defocus.
Is this the same Box Blur as in Fusion?
This guide covers Resolve FX Box Blur on a Color node. Similarly named Fusion tools or effects in other programs do not guarantee matching controls or scales. Check the actual tool panel.
Why is there no perfect preset for every shot?
Detail size, working resolution, effect placement and goals differ. Screenshot values are reference points; the exercises explain how to choose a result and how to evaluate it.
Sources and the scope of this guide
Parameter names and screenshots were checked against the source images in the site archive. The interactive example is an independent mathematical model. It does not claim Resolve’s Strength mapping, exact edge sampling, color-management behavior or rendering speed.
Controls shown in the screenshots are the reference for this article. Check your installed version for edition availability and UI differences. Exercises have not been certified by a live Resolve run in this site update.