BoxBlur

BoxBlur is a spatial image filter: every output pixel is computed from neighboring pixels in the current frame. It does not analyze motion, scene depth, faces or semantic objects, and it does not reconstruct hidden detail.

The key box-filter idea is equal-weight averaging inside a rectangular neighborhood. With a low iteration count this can retain a more geometric character than Gaussian Blur.

Strength controls the overall blur scale, but Blackmagic does not publish a literal Strength-to-pixel-radius mapping. Do not present Inspector values as documented pixel radii.

Split Horizontal and Vertical decouples the two image axes. This can create elongated H/V softness, but it does not turn BoxBlur into an arbitrary-angle motion blur.

Horizontal Channel Adjustment affects horizontal spread. Vertical Channel Adjustment does the same vertically; matching values produce a neutral baseline while different values create anisotropic behavior.

Red, Green and Blue are component controls, not object selectors. Unequal RGB values can create colored fringes around neutral high-contrast edges.

Alpha refers to transparency in the RGBA source. On fully opaque footage, alpha-channel changes may be difficult or impossible to see, so test alpha behavior on genuinely transparent graphics.

Number of Iterations repeats the box filtering. Additional passes smooth the profile and can change the apparent footprint, so reassess Strength after changing Iterations.

Iterations is not temporal accumulation and does not replace temporal denoising. BoxBlur remains a current-frame spatial effect.

Border Type controls how samples beyond the image boundary are supplied. This is independent from Strength and Iterations and becomes visible primarily when the footprint reaches a frame edge.

Black supplies zero values outside the frame. Strong edge blur can therefore pull dark values inward; on alpha-sensitive material, inspect transparency separately as well.

Replicate extends the boundary value outward. It is often stable for technical work, although a bright edge can create a stretched band of the last available color.

Reflect mirrors image data beyond the boundary. It often avoids a dark rim, but recognizable text, lights or geometry may reveal the reflection.

Wrap-Around samples the opposite side of the frame. It fits periodic or tileable textures but can introduce unrelated content on ordinary footage.

Effect Mask is not a second image input and not a blur-radius map. It limits where BoxBlur contributes according to Fusion mask behavior while the primary image still arrives through Input.

BoxBlur.Output remains a normal 2D RGBA image stream. A downstream blue mask socket still expects mask-type data rather than an arbitrary blurred image.

For local censorship or softening, stabilize the mask and tracking before pushing blur strength. Heavy blur can hide coverage errors that become obvious in motion.

Keep image blur separate from mask feather. Rectangle or Polygon Soft Edge changes mask coverage; BoxBlur filters image RGBA and therefore solves a different problem.

With premultiplied RGBA, a dark halo may involve alpha interpretation rather than Border Type alone. Check transparent graphics over several backgrounds and use an explicit Alpha Divide/Multiply workflow when required.

A small BoxBlur before EdgeDetect or Threshold can suppress high-frequency noise, but it can also erase useful thin features. Judge technical prefiltering around 100% Viewer scale.

BoxBlur before Merge affects only that branch; BoxBlur after Merge filters the assembled composite. Flow placement can matter more than a small Strength adjustment.

Several moderate iterations and one very large Strength are not interchangeable. They change the profile differently, so Iterations should not be treated as a meaningless quality-up switch.

The current Fusion captures verify Controls, Split H/V, Strength, both Channel Adjustment sections, Number of Iterations and Border Type. Controls seen on the Color-page Resolve FX panel are not imported into this Fusion article unless the current Fusion capture verifies them.

Before publishing numeric presets, live-check the target Resolve build. Bundled captures verify labels and menu choices but not proprietary kernel math, exact Strength-to-radius mapping or target-build premultiplication behavior.