[Tig] Colour Correction, telecine or DI.

[Richard Jackson]

    The concept for the original SMPTE levels (64/940) is that there  
can be peak video content that legitimately goes above white or below  
black - such as specular highlights, etc. You don't want to reduce  
entire video level just to accomodate the worst-case peak, but  
neither do you want to hard-clip the peaks (which causes other  
distortions down the line). In analog TV transmitters, "transient  
peaks" above 100% modulation are legal for the same reason. This  
ability to handle transients is the main advantage of using 64-940  
processing - but of course the disadvantage is giving up resolution  
in the Black-White range. The SMPTE numbers are a compromise.

    - Richard Jackson
      AJA Video


P.S. Historical note: at the time the SMPTE numbers were formulated  
most of the existing equipment in TV stations was analog. SMPTE also  
wanted to leave a little extra "headroom" above white/below black to  
accomodate less-than-perfect analog levels without hard-clipping.



On Oct 12, 2006, at 9:59 AM, Bob Friesenhahn wrote:

> <snip>
> I argue that if there is valuable data there, then the video source  
> must be mis-adjusted and the problem is best corrected at the source.
>