vcm

StepFilter

The script call is:

vcm.StepFilter(clip [ , int add = 1][,int limit = 0][ ,float boost = 1.0][,int segmenthor = 60][,int segmentvert = 60])

clip: Input RGB, YUV, and Gray except Compat and half float formats.
add: If set 0, noise is multiplicative, else additive
limit: If non zero then assumes values higher than averages were probably clipped and will not alter them.
boost: The reference value for correction are multiplied by this value. 0.5 to 5.0 allowed.
segmenthor:average over this width to find correction. If set to zero then full width of frame is used. range 0, 16 to width / 2.
segmentvert:average over this height to find correction. If set to zero then full height of frame is used. range 0, 16 to height / 2.

In some vhs video transfers horizontal bars are seen. This function can be used to correct images similar to horizontal bars in a doom9 forum thread. Using F1Quiver or F2Quiver are other (better) options. StepFilter is simpler to use. Boost and limit can be tried to improve. However the margins may deteriorate, but can be cropped later.