[tig] b+w stock question

bobineinc at yahoo.com bobineinc
Tue May 4 06:01:36 BST 2004


Timothy Balenger wrote:
<<One thing to consider when using colour stocks to
produce B+W from most colour telecines is the failure
of "the principle of constant luminance", which is a
well known deficiency/distortion to students of such
matters=2E=
What I mean by that is that due to the way gamma
correction is applied in the video chain of a telecine
or camera the brightness (luminance) level o=f
coloured areas will be lower than they should be when
looking at the B+W output of the telecine or on a B+W
monitor/TV=2E This is because the matri=x which
produces Y (luminance) from RGB in a telecine or
camera comes after the gamma correction=2E If there's
a matrix to produce Y, just for B+W, before gamma
correction then this distortion doesn't exist=2E
I guess most people would produce B+W from a colour
film on a colour telecine by switching the chroma off,
turning the saturation to zero or just using the Y
signal from the telecine output=2E However some
telecines= have a Colour/Mono switch which switches in
a pre-gamma Y matrix=2E The ol=d Cintel MkIII
telecines have one although it will only work properly
when transferring print, not neg=2E I have a feeling
that the URSA doesn't have= one and don't know about
other models=2E=20>>
 
Interesting but when converting a color image to B&W
mode in telecine with mono/desaturation switch, it is
bases on the resulting gray values on the viewed
lightness of the Y, but more important pre gamma or
post gamma, mono/desaturation switch does not takes
the average of the strongest and weakest color
elements to creates a B&W with that average value.

<<So if you feel that the look of your monochromised
pictures are not quite right it could be because of
this=2E The effect is not insignificant: for
example if you take the case of full amplitude 100%
saturated red the brightness displayed will be
aproximately a quarter of the correct value=2E=
Timothy Balenger>>

There is ways to convert a color to a B&W value with
a weighted average of the color elements. If the
original weight average is Red=30% Green=59% Blue=11%
you can adjust the green and blue channels to
black 0% and Red channel to 100% in any telecine
suite. 

Jais @ bobine (pronounce bo been)










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