Temporal Cleaner

The Temporal Cleaner was designed to be a severely modified version of VirtualDub's internal temporal smoother filter that only averages pixels between frames that are within certain thresholds. This has the effect of blending away much of the random video noise that appears in one frame, but not another, but it does not blend motion leading to ghosting effects. It also has a feature dubbed "pixel lock" whereby pixels that do not change much between multiple frames end up being set to the same value.

This feature, can substantially reduce or remove video noise by ignoring tiny pixel changes, and should aid MPEG-1, 2 or 4 compression, especially for moderately noisy video sources. The filter can operate either in YUV or RGB modes. In YUV mode it can be more aggressive in blending and pixellocking situations where the luminance difference is small but the chrominance difference is larger. The values that are compared are now biased so that differences in very dark or very bright areas are increased to make Temporal Cleaner more sensitive to them.

With this new version, MANY new settings have been introduced, and the settings have new values. The options available for the filter are a scene detection threshold value, YUV mode option, a luminance blending threshold value, a luminance pixellocking value, a chrominance blending value, a chrominance pixellocking value, a "show motion" option, and a luminance locking option. The default settings I programmed in seem to work well with most of my video sources, but you should experiment with them all to find your optimal settings.

The scene detection threshold defines the percent of pixels in a frame that exceeds the threshold in order for the filter to assume a new scene has begun. When a new scene is detected, all locked pixels are ignored and the filter passes the new frame untouched. This was necessitated since "pixel lock" would often keep some pixels from previous scenes even after scene changes.

The YUV mode option decides whether or not to process the thresholding in YUV or RGB mode. RGB mode is the native mode of VirtualDub and is thus quicker since there is no need to convert the pixels. In YUV mode you can threshold the luminance and chrominance values seperatly. In RGB mode only the luminance thresholds are used to compare against the Red, Green and Blue color channels. (in fact, the filter will simply duplicate the luminance values into the chrominance values once you hit OK in RGB mode) The RGB->YUV colorspace conversions will not effect image quality in any way unless the luminance locking option is enabled.

The blending thresholds can be anywhere from 0 to 255, and defines the maximum difference between a pixel in the current frame and the pixel in the previous frame in which the program will blend the two together. Higher thresholds blend more motion together, but will also blend more video noise away.

The "pixel lock" threshold values defines the maximum difference between pixels between frames where the pixel from the previous frame can replace the pixel in the current frame. It is recommended that the "pixel lock" thresholds be set to a value less than the main threshold values.

The "show motion" option, inspired by the equivalent function in Donald Graft's Smart Deinterlacer, will turn any pixel in the current frame that exceeds the threshold black. It also turns any pixels that are "pixel locked" blue and pixels that are being luminance locked gray. This will show you the areas of the frame that the filter considers to be moving and the areas the filter considers static. Do NOT leave this option on when you are actually converting your files. (note: this setting is NOT saved for batch operations or when you save processing settings, since this option is meant only for "debugging" ones settings)

The "luminance locking" option will decide whether or not to allow yet another option for output for compared pixels. If a pixel's luminance is with the Luminance pixellocking threshold of the previous pixel's luminance, but the chrominance difference is only within the chrominance blending threshold, Temporal Cleaner will keep the luminance of the previous pixel and blend the chrominance of the previous pixel and the current one.

This option only works in YUV mode, and may or may not help noise reduction. BTW: Since I cache the last frame internally within the filter and do not rely on VirtualDub to keep track of it, this filter can (and perhaps should) be run multiple times within a filter chain to further blend out noise.