ShiftLinesHorizontally not working as intended

[Selur]

A user got a clip where I wanted to shift some lines horizontally.
So I wrote the following script:

import vapoursynth as vs
core = vs.core

def ShiftLinesHorizontally(clip: vs.VideoNode, shift: int, ymin: int, ymax: int) -> vs.VideoNode:
    # Validate clip format and subsampling
    if clip.format.color_family != vs.YUV or clip.format.subsampling_w != 0 or clip.format.subsampling_h != 0:
        raise ValueError("ShiftLinesHorizontalRange: only YUV444 input is supported.")
    
    # Ensure ymin and ymax are within valid range
    if ymin < 0 or ymin >= clip.height:
        raise ValueError(f"ShiftLinesHorizontalRange: ymin ({ymin}) is out of range.")
    if ymax < ymin or ymax >= clip.height:
        raise ValueError(f"ShiftLinesHorizontalRange: ymax ({ymax}) is out of range.")
    
    # If no shift is needed, return original clip
    if shift == 0:
        return clip

    width = clip.width
    height = clip.height

    # Create shifted version of just the target lines
    mid = clip.std.CropAbs(width=width, height=ymax-ymin+1, left=0, top=ymin)
    black = core.std.BlankClip(mid, width=abs(shift), height=mid.height, color=[0, 128, 128])
    
    if shift > 0:
        shifted_mid = core.std.StackHorizontal([black, mid.std.CropRel(right=shift)])
    else:
        shifted_mid = core.std.StackHorizontal([mid.std.CropRel(left=-shift), black])
    
    shifted_mid = shifted_mid.resize.Point(width=width, height=mid.height)

    # Build the output clip by stacking:
    # 1. Lines above ymin (unchanged)
    # 2. Shifted lines (ymin to ymax)
    # 3. Lines below ymax (unchanged)
    parts = []
    
    if ymin > 0:
        parts.append(clip.std.CropAbs(width=width, height=ymin, left=0, top=0))
    
    parts.append(shifted_mid)
    
    if ymax < height - 1:
        parts.append(clip.std.CropAbs(width=width, height=height-ymax-1, left=0, top=ymax+1))
    
    return core.std.StackVertical(parts)

and called it using:

import misc
clip = misc.ShiftLinesHorizontally(clip, shift=-24, ymin=468, ymax=479)

But something is wrong.
The 12 line I wanted are shifted (hurray), but the 12 lines above them got shifted too, and I don't see where I got it wrong.


=> does anybody see where my mistake is?

Cu Selur

[_Al_]

I don't know about posted script, but resize can shift nicely, positive or negative, then using overlay:

import vapoursynth as vs
from vapoursynth import core
import havsfunc
clip = ...

HORIZONTAL_SHIFT = 24
Y = 468
STRIP_HEIGHT = 12

shifted = clip.resize.Bicubic(src_left=HORIZONTAL_SHIFT)
masks = []
masks.append(core.std.BlankClip(clip, height=Y))
masks.append(core.std.BlankClip(clip, height=STRIP_HEIGHT, color=(255,128,128)))
try:
    masks.append(core.std.BlankClip(clip, height=clip.height-(Y+STRIP_HEIGHT)))
except vs.Error:
    pass
mask = core.std.StackVertical(masks)
clip = havsfunc.Overlay(base=clip, overlay=shifted, mask=mask)   
clip.set_output()

[Selur]

Thanks, I'll try that tomorrow and report back.
(still interested in what I did wrong)

Cu Selur

[Selur]

using, whole script https://pastebin.com/rQgHyftP and like you suggested:

def ShiftLinesHorizontally(clip: vs.VideoNode, shift: int, ymin: int, ymax: int) -> vs.VideoNode:
  # Validate clip format and subsampling
  if clip.format.color_family != vs.YUV or clip.format.subsampling_w != 0 or clip.format.subsampling_h != 0:
      raise ValueError("ShiftLinesHorizontalRange: only YUV444 input is supported.")
  
  # Ensure ymin and ymax are within valid range
  if ymin < 0 or ymin >= clip.height:
      raise ValueError(f"ShiftLinesHorizontalRange: ymin ({ymin}) is out of range.")
  if ymax < ymin or ymax >= clip.height:
      raise ValueError(f"ShiftLinesHorizontalRange: ymax ({ymax}) is out of range.")
  
  # If no shift is needed, return original clip
  if shift == 0:
      return clip
  # shifted version
  shift_height = ymax-ymin+1
  shifted = clip.resize.Bicubic(src_left=shift)
  # masking
  masks = []
  masks.append(core.std.BlankClip(clip, height=ymin))
  masks.append(core.std.BlankClip(clip, height=shift_height, color=(255,128,128)))
  
  try:
      masks.append(core.std.BlankClip(clip, height=clip.height-(ymin+shift_height)))
  except vs.Error:
      pass
  mask = core.std.StackVertical(masks)
  clip = Overlay(base=clip, overlay=shifted, mask=mask, opacity=1)   
  return clip

I get the same effect:

(last few lines get shifted, but so do the lines above)

Cu Selur

Ps.: I also tried first saving a temp clip, after the deinterlacing, and using that as source, but the result is the same.
PPs.: Alternative link to source.

[StainlessS]

I dont speak Parseltongue (Python/Vapoursynth), but your clip [TFF] seems to require different shift for even/odd field.
I would expect better result if doing field shifts prior to deinterlace.

I could not see any logic problems in your script [tryin' to understand logic], perhaps it is the differing shift that is causing/contributing to
your suspected problem. [shift after QTGMC deinterlace]

EDIT: [clickme to see independently shifted fields <not deinterlaced>]


EDIT: Is there an Avisynth version of ShiftLinesHorizontally(), I did search but neither D9 nor Google (ShiftLinesHorizontally Site:forum.doom9.org)
found an equivalent (not even in this thread), feels like a JMac698 function.

[Selur]

The function is something I came up with.
I was planning to use this function in a broader context later, where I would shift different lines differently, but since my simple approach didn't work as expected, I assume I'm missing something obvious.

[_Al_]

I downloaded source. It is only bottom 6 lines, not 12. They wiggle left, right.
If using 12 lines, like you posted it shifts good 6 lines to the left.

[Selur]

AAAAARRRRGGGGH,... you are right. So easy.
Thanks!

[Selur]

Since I couldn't get the whole idea working with plain Vapoursynth I ended up using also numpy.
Script: https://pastebin.com/0qe12xVH
numpyhelper.py: https://pastebin.com/Zau8pGsj (can probably be improved to be faster => https://pastebin.com/zZP8Sxbe)
Not perfect, but way more stable:


Cu Selur

[Chortos-2]

FYI when you really do just want to shift some lines, you can do it in one line using akarin Expr:

clip.akarin.Expr('Y 476 >= x[24,0]:c x ?')

[Selur]

Nice. Thanks for the info!
So AutoFixLineBorders in numpyhelper could be rewritten to not use numpy? That would be nice and probably a lot faster!

[Chortos-2]

From a quick glance at the code, it seems to dynamically compute the amount of faded columns in each row, right? It’s not impossible to do that in Expr (for a fixed input resolution), but it wouldn’t be pretty, because Expr doesn’t have loops/jumps. NumPy is probably your best bet besides building a native-code plugin.

[Selur]

Yes, it checks every line. Thanks for the info, so for now it is numpy.