Deoldify Vapoursynth filter

[Dan64]

Hello Selur,

  sorry to bother you but I have a problem with Vapoursynth that I can't understand.

  In order to improve the "chroma limiter", I was thinking to add the possibility to repeat the filter more times (max 5).
  To do that I wrote this piece of code

def _clip_chroma_limiter_ex(clip: vs.VideoNode = None, deviation: float = 0.05, steps: int = 1, tht: int = 10) -> vs.VideoNode:
   
    max_steps = max(min(steps, 5), 1)
       
    clip_limited = vs_clip_chroma_stabilizer(clip, deviation=deviation)
    for i in range(1, max_steps):
        clip_limited=vs_clip_chroma_stabilizer(clip_limited, deviation=deviation)
   
    if tht < 1 or tht > 255:
        return clip_limited

    # calculate motion mask
    clipMask = clip
    clipMask = clipMask.resize.Bicubic(format=vs.GRAY8, matrix_s="470bg", range_s="limited")
    clipMask = vs.core.motionmask.MotionMask(clip=clipMask, th1=tht, th2=tht, tht=tht) # pixels with abs(diff) < tht will be black (static parts)
    clipMask = vs.core.std.InvertMask(clip=clipMask) # invert so that static parts are white (weight=1)
    # merge in YUV color space       
    clipMask = clipMask.resize.Bicubic(format=vs.YUV444PS, matrix_s="470bg", range_s="limited")
    clip_limited = clip_limited.resize.Bicubic(format=vs.YUV444PS, matrix_s="470bg", range_s="limited")
    clip = clip.resize.Bicubic(format=vs.YUV444PS, matrix_s="470bg", range_s="limited")
    clip = vs.core.std.MaskedMerge(clipa=clip, clipb=clip_limited, mask=clipMask) # MotionMask
    # restore RBG24 color space
    clip = clip.resize.Bicubic(format=vs.RGB24, matrix_in_s="709", range_s="limited", dither_type="error_diffusion")
   
    return clip

Now the problem:

If I set "tht=0" the motion mask is not applied and I can see the filter working:

Here with steps=1



Here with steps=5



But if I set "tht" with a value > 1 and < 255, independently from the value I get always the same image:



like the Mask was always filled with weights=0

Do you have any idea on the reason ?

Dan