BM4D

The reference. BM3D plus time: it searches for similar blocks not only across the frame but also in a window of neighboring frames (±4 frames) — and averages them in groups stretched across time.

What it does

Everything BM3D can do, but groups of similar blocks are assembled both across the frame and across neighboring frames (shifted to follow the motion). Noise is averaged over many frames at once — on static shots this gives a cleanliness no spatial algorithm can reach; detail matches between frames and is therefore reinforced rather than blurred.

When to pick it

• A final render where quality matters more than time.
• Medium and heavy noise.
• Static and moderately moving scenes — always with Motion Compensation and the Analyze Motion cache.
• When you've tried everything and the picture is still noisy.

When not to pick it: drafts, real time, weak hardware, or footage without noise (overkill). This is the slowest algorithm in the plugin.

Parameters in plain words

The set is almost the same as BM3D:

• Sigma — how strong the noise must be to count as noise. The main slider.
• Block Size — the block size (4–8, 8 by default).
• Block Step — the step of the block grid (4 by default).
• Group Size — the size of the group of similar blocks (1–16, 8 by default).
• Search Range — the radius for searching similar blocks (9 by default).
• Match Step — the step at which positions are traversed during the search.
• Match Threshold — how strict block similarity must be for a group.
• Hard Threshold — the hard cleanup threshold in the second stage (2.7 by default).
• Planes — which planes to process.
• Wiener Stage — the second stage, a polish based on the first estimate. On by default; turning it off makes things roughly twice as fast, but quality is lower.

In Simple: Denoise moves Sigma, Balance moves the search sizes (further left is faster, further right is better quality).

Prerequisite: Analyze Motion

BM4D takes frames from a ±4 window. So that the averaging doesn't produce ghosting, those frames must be shifted to follow the motion — that is what Motion Compensation does. On a long clip it makes sense to compute the motion vectors in advance: run Analyze Motion once, and every render after that reads the cache.

How it works inside

Expand

The difference from BM3D is the dimensionality of the groups: BM3D groups similar 2D blocks of a single frame, BM4D groups 3D groups made of blocks from neighboring frames. Averaging over such a group cancels noise more strongly (each frame brings independent noise), and motion compensation keeps the structure matching over time. The first stage (hard threshold) estimates the "clean" signal, the second (Wiener) polishes based on that estimate.

If it didn't help

• Ghosting on motion → Motion Compensation Enable, Analyze Motion, Temporal Gate in Motion + Cut.
• Very slow → turn Wiener Stage off, soften Search Range / Block Step, Precision of motion → Fast.
• Softness → lower Sigma, smaller Group Size.
• Flicker remains → the window takes more frames with compensation; check that the Analyze Motion cache is up to date (not reset).

Next — FAQ or back to the algorithm comparison.