Zsmooth - cross-platform, cross-architecture video smoothing functions for Vapoursynth, written in Zig

Goals

• Clean, easy to read code, with a standard scalar (non-SIMD) implementation for every algorithm.
• Support for 8-16 integer, and 16-32 float bit depths. (See FP16 note below)
• Tests for all filters, covering the scalar and vector implementations.
• Support for RGB, YUV, and GRAY colorspaces (assuming an algorithm isn't designed for a specific color space).
• Support Linux, Windows, and Mac.
• Support x86_64 and aarch64 CPU architectures, with all architectures supported by the Zig compiler being possible in theory.
• (Eventually) Vapoursynth and Avisynth support. (Whenever I get the spare time and motivation.)

Note: FP16 support is a work in progress. All functions support it but some are much slower than they need to be. I'm currently suspecting that this is a bug in Zig's compiler, as explicitly processing FP16 data with FP32 operations is much faster. The Zig compiler should really be handling this FP16->FP32 processing on its own, so I'm currently investigating the issue.

Implemented Features/Functions

• TemporalMedian
• TemporalSoften
• RemoveGrain
• FluxSmooth
• Repair
• Clense
• MiniDeen
• DegrainMedian
• TTempSmooth
• CCD
• Dogway's IQM/IQM5/IQMV/IQMST/IQMS functions
• Avisynth support

Function Documentation

Temporal Median

TemporalMedian is a temporal denoising filter. It replaces every pixel with the median of its temporal neighbourhood.

This filter will introduce ghosting, so use with caution.

core.zsmooth.TemporalMedian(clip clip[, int radius = 1, int[] planes = [0, 1, 2]])

Parameter	Type	Options (Default)	Description
clip	8-16 bit integer, 16-32 bit float, RGB, YUV, GRAY		Clip to process
radius	int	1 - 10 (1)	Size of the temporal window from which to calculate the median. First and last radius frames of a clip are not filtered.
planes	int[]	([0, 1, 2])	Which planes to process. Any unfiltered planes are copied from the input clip.

Temporal Soften

TemporalSoften averages radius * 2 + 1 frames. A pixel is included in the average only if the absolute difference between it and the middle frame's corresponding pixel is less than the threshold.

If the scenechange parameter is greater than 0, TemporalSoften will not average frames from different scenes.

core.zsmooth.TemporalSoften(clip clip[, int radius = 4, float[] threshold = [], int scenechange = 0, bool scalep=False])

Parameter	Type	Options (Default)	Description
clip	8-16 bit integer, 16-32 bit float, RGB, YUV, GRAY		Clip to process
radius	int	1 - 7 (4)	Size of the temporal window. This is an upper bound. At the beginning and end of the clip, only legally accessible frames are incorporated into the radius. So if radius if 4, then on the first frame, only frames 0, 1, 2, and 3 are incorporated into the result.
threshold	float[]	0 - 255 8-bit, 0 - 65535 16-bit, 0.0 - 1.0 float ([4,4,4] RGB, [4, 8, 8] YUV, [4] GRAY)	If the difference between the pixel in the current frame and any of its temporal neighbors is less than this threshold, it will be included in the mean. If the difference is greater, it will not be included in the mean. If set to -1, the plane is copied from the source.
scenechange	int	0 - 255 (0)	Calculated as a percent internally (scenechange/255) to qualify if a frame is a scenechange or not. Currently requires the SCDetect filter from the Miscellaneous filters plugin, but future plans include specifying custom scene change properties to accomidate other scene change detection mechanisms.
scalep	bool	(False)	Parameter scaling. If set to true, all threshold values will be automatically scaled from 8-bit range (0-255) to the corresponding range of the input clip's bit depth.

RemoveGrain

RemoveGrain is a spatial denoising filter.

Modes 0-24 are implemented. Different modes can be specified for each plane. If there are fewer modes than planes, the last mode specified will be used for the remaining planes.

Note on RGSF differences: This plugin operates slightly differently than RGSF, the 'single precision' floating point Vapoursynth implementation of RemoveGrain. Specifically, RGSF isn't actually 'single precision' - it's double precision. Even for operations that don't benefit from increased floating point precision. This means that RGSF is actually significantly slower than it needs to be for some/most operations.

The implementation in this plugin properly uses single precision floating point for all modes. This is exactly the same approach that the Avisynth version of RgTools takes. It does mean that for some operations, the output will very sligtly differ between RGSF and this plugin, as RGSF is technically doing higher precision (but much slower) calculations.

core.zsmooth.RemoveGrain(clip clip, int[] mode)

Parameters:

Parameter	Type	Options (Default)	Description
clip	8-16 bit integer, 16-32 bit float, RGB, YUV, GRAY		Clip to process
mode	int	1-24	For a description of each mode, see the docs from the original Vapoursynth documentation here: https://github.com/vapoursynth/vs-removegrain/blob/master/docs/rgvs.rst

FluxSmooth(S|ST)

core.zsmooth.FluxSmoothT(clip clip[, float[] temporal_threshold = 7, bool scalep=False])
core.zsmooth.FluxSmoothST(clip clip[, float[] temporal_threshold = 7, float[] spatial_threshold = 7, bool scalep = False])

FluxSmoothT (T\ emporal) examines each pixel and compares it to the corresponding pixel in the previous and next frames. Smoothing occurs if both the previous frame's value and the next frame's value are greater, or if both are less than the value in the current frame.

Smoothing is done by averaging the pixel from the current frame with the pixels from the previous and/or next frames, if they are within temporal_threshold.

FluxSmoothST (S\ patio\ T\ emporal) does the same as FluxSmoothT, except the pixel's eight neighbours from the current frame are also included in the average, if they are within spatial_threshold.

The first and last rows and the first and last columns are not processed by FluxSmoothST.

Parameter	Type	Options (Default)	Description
clip	8-16 bit integer, 16-32 bit float, RGB, YUV, GRAY		Clip to process
temporal_threshold	float[]	-1 - bit depth max ([7,7,7])	Temporal neighbour pixels within this threshold from the current pixel are included in the average. Can be specified as an array, with values corresonding to each plane of the input clip. A negative value (such as -1) indicates that the plane should not be processed and will be copied from the input clip.
spatial_threshold	float[]	-1 - bit depth max ([7,7,7])	Spatial neighbour pixels within this threshold from the current pixel are included in the average. A negative value (such as -1) indicates that the plane should not be processed and will be copied from the input clip.
scalep	bool	(False)	Parameter scaling. If set to true, all threshold values will be automatically scaled from 8-bit range (0-255) to the corresponding range of the input clip's bit depth.

Building

All build artifacts are placed under zig-out/lib.

Native builds

To build for the operating system and architecture of the current machine:

zig build -Doptimize=ReleaseFast

Cross-compiling

Zig has excellent cross-compilation support, letting us create Windows, Mac, or Linux compatible libraries from any of those same operating systems and architectures.

To generate Windows compatible DLLs, with AVX2 support:

zig build -Doptimize=ReleaseFast -Dtarget=x86_64-windows -Dcpu=x86_64_v3

To generate Windows compatible DLLs with AVX512 support:

zig build -Doptimize=ReleaseFast -Dtarget=x86_64-windows -Dcpu=x86_64_v4
# or the following for specific targeting of AMD Zen4 CPUs
zig build -Doptimize=ReleaseFast -Dtarget=x86_64-windows -Dcpu=znver4

See https://en.wikipedia.org/wiki/AVX-512#CPUs_with_AVX-512 for a better breakdown on which CPUs support AVX512 features.

To generate Mac (x86_64) compatible libraries:

zig build -Doptimize=ReleaseFast -Dtarget=x86_64-macos

To generate Mac (aarch64) ARM compatible libraries:

zig build -Doptimize=ReleaseFast -Dtarget=aarch64-macos 

To generate Mac (aarch64) ARM compatible libraries for a specific CPU (like M1, M2, etc):

zig build -Doptimize=ReleaseFast -Dtarget=aarch64-macos -Dcpu=apple_m1

Use zig targets to see an exhaustive list of all architectures, CPUs, and operating systems that Zig supports.

References

The following open source software provided great inspiration and guidance, and this plugin wouldn't exist without the hard work of their authors.

• Avisynth RemoveGrain: https://github.com/pinterf/RgTools
• Vapoursynth RemoveGrain: https://github.com/vapoursynth/vs-removegrain
• Vapoursynth TemporalSoften: https://github.com/dubhater/vapoursynth-temporalsoften2
• Vapoursynth TemporalMedian: https://github.com/dubhater/vapoursynth-temporalmedian
• Neo Temporal Median: https://github.com/HomeOfAviSynthPlusEvolution/neo_TMedian
• Vapoursynth FluxSmooth: https://github.com/dubhater/vapoursynth-fluxsmooth/