Emulgator
19th June 2012, 20:44
I guess this is a well-known fault,
but I saw this only a few times in NTSC footage and oops, there he is now on my table.
Maybe someone can help.
Attempted restoration of a NTSC-DVD 98,77% Film
Most prominent fault: Scrolling NTSC Checkerboard Moiré:
In encoded NTSC frames (pulldown ignored) in coloured parts a scrolling 2x2 checkerboard moiré becomes visible.
But the fault lies in Y plane only ! Greyscale() (forcing U,V to 127) keeps the fault, Forcing Y to 0 or 127 shows clean U,V planes.
This fault is moving vertically through the lines stepping height down by 1-2-1, so pattern is repeating every 4 frames:
Frame 0:
Y of lines 0+1 modulated into positive direction
AND Y of lines 2+3 modulated into negative direction
Frame 1: (Fault steps 1 line down):
Y of line 0 modulated into negative direction
AND Y of lines 1+2 modulated into positive direction
AND Y of Line 3 modulated into negative direction
Frame 2: (Fault steps 2 lines down, so pattern is reversed to Frame 1):
Y of line 0 modulated into positive direction
AND Y of lines 1+2 modulated into negative direction
AND Y of Line 3 modulated into positive direction
Frame 3: (Fault steps 1 line down):
Y of lines 0+1 modulated into positive direction
AND Y of lines 2+3 modulated into negative direction.
I get the impression as if strong U,V gradients are leaking into Y
and modulate Y-values of neighboring 2x2 squares checkerboardwise in opposite directions under certain conditions.
Y values are modulated in 2x2 pixel squares, one square has its Y-value modulated to (Y+F),
the surrounding squares have their Y-values modulated to (Y-F).
For a vertical border at a given x the arithmetical mean value of Y-values in lines (n,n+1) and (n+2,n+3)
would give the correct Y-values,
the affected vicinity around the vertical border is +-3 to +-4 pixels wide.
The colour of the border element (blue/red) influences the phase !
At right border: skyblue and orange wings trigger different line pairs !
Local Condition: A contour where saturation (U,V) rises/falls more than a certain amount per pixel.
In vicinity of U,V deviating more than +-30(?) from 127(?) the fault occurs and the stronger the saturation, the stronger is F.
A purely saturated area does not exhibit this fault.
A strong chroma signal change is needed to watch this fault.
Strong vertical black/blue or black/red or black/orange or black/green borders will show best how it behaves.
Black/Grey/White changes do not trigger the fault.
A short sample is here:
http://www.dvd-manufactur.de/files/TC_VTS_01_3a.VOB
but I saw this only a few times in NTSC footage and oops, there he is now on my table.
Maybe someone can help.
Attempted restoration of a NTSC-DVD 98,77% Film
Most prominent fault: Scrolling NTSC Checkerboard Moiré:
In encoded NTSC frames (pulldown ignored) in coloured parts a scrolling 2x2 checkerboard moiré becomes visible.
But the fault lies in Y plane only ! Greyscale() (forcing U,V to 127) keeps the fault, Forcing Y to 0 or 127 shows clean U,V planes.
This fault is moving vertically through the lines stepping height down by 1-2-1, so pattern is repeating every 4 frames:
Frame 0:
Y of lines 0+1 modulated into positive direction
AND Y of lines 2+3 modulated into negative direction
Frame 1: (Fault steps 1 line down):
Y of line 0 modulated into negative direction
AND Y of lines 1+2 modulated into positive direction
AND Y of Line 3 modulated into negative direction
Frame 2: (Fault steps 2 lines down, so pattern is reversed to Frame 1):
Y of line 0 modulated into positive direction
AND Y of lines 1+2 modulated into negative direction
AND Y of Line 3 modulated into positive direction
Frame 3: (Fault steps 1 line down):
Y of lines 0+1 modulated into positive direction
AND Y of lines 2+3 modulated into negative direction.
I get the impression as if strong U,V gradients are leaking into Y
and modulate Y-values of neighboring 2x2 squares checkerboardwise in opposite directions under certain conditions.
Y values are modulated in 2x2 pixel squares, one square has its Y-value modulated to (Y+F),
the surrounding squares have their Y-values modulated to (Y-F).
For a vertical border at a given x the arithmetical mean value of Y-values in lines (n,n+1) and (n+2,n+3)
would give the correct Y-values,
the affected vicinity around the vertical border is +-3 to +-4 pixels wide.
The colour of the border element (blue/red) influences the phase !
At right border: skyblue and orange wings trigger different line pairs !
Local Condition: A contour where saturation (U,V) rises/falls more than a certain amount per pixel.
In vicinity of U,V deviating more than +-30(?) from 127(?) the fault occurs and the stronger the saturation, the stronger is F.
A purely saturated area does not exhibit this fault.
A strong chroma signal change is needed to watch this fault.
Strong vertical black/blue or black/red or black/orange or black/green borders will show best how it behaves.
Black/Grey/White changes do not trigger the fault.
A short sample is here:
http://www.dvd-manufactur.de/files/TC_VTS_01_3a.VOB