sample_mode=4|5 introduces banding

[q3cpma]

Hello,

tried the new mode with this input picture, here are the results:

sample_mode=2:

sample_mode=5:

Using the following script:

import vapoursynth as vs

core = vs.core

src = core.imwri.Read($(dquote "$in"))
src = core.resize.Bilinear(src, format=vs.YUV444P8, matrix=1)
src = core.neo_f3kdb.Deband(src, sample_mode=X, range=15})
src = core.resize.Bilinear(src, format=vs.RGB24)
src = core.imwri.Write(src, "PNG", $(dquote "$out"), overwrite=True)

src.set_output()

EDIT: sample_mode=4 has the same output as 5 here. I guess it's just corner case?