[Tig] Re: SMPTE Bars/Pluge

[Joe Owens]

Steve, I always thought the pluge was plus-or-minus 2.5 IRE on either  
side of pedestal, making  the little stripes 5, 7.5, 10.  True, the  
lower one should disappear relative to overall pedestal and the upper  
should be "just" visible.
And all this is totally dependent on ambient illumination.
I sort of don't follow the "eight" black bars...  If this is "SMPTE  
SPLIT" with a row of reverse order hues , then there would be some  
black separator bars on the second row of hue patches.  The majority  
of the picture would contain from left to right, "TV white", yellow,  
cyan, green, magenta, red, and blue.  The second row might contain a  
representation that goes blue, black, magenta, black, cyan, black, TV  
white.  I say TV white because it is not 100 IRE white (Peak), it is  
really (80? IRE or 78 or something like that)...
The second row of colours is to do a 'cheat setup' for hue and  
saturation.  If you can "blue-only" the monitor, you can fairly  
accurately setup those parameters by matching the grey-scale  
intensity of the blue/white outside bars for saturation and then  
balance the cyan/magenta pair for hue.  The reasoning is this:  the  
overall saturation of the picture will be correct if the blue  
component of TV white matches the pure blue bar, and the  hue will be  
correct if the blue content of the cyan and magenta bars is matched--  
ie, one is blue+green, the other is blue+red.
      The strategy stems from the idea that colour bars are generated  
using a single uniform square-wave that is x2 (frequency doubled), re- 
added to the original, x2 again, re-added again to come up with the  
combination/progression that we all know and love...
It goes like this:  the original square wave is "1" or TTL "high" for  
White, yellow, cyan, green, then "0" or "low", for magenta, red, and  
blue -- notice this translates as 1=presence of green, 0=absence of  
green.  The first multiplied x2 wave represents "red" and is present  
in white/yellow, and magenta/ pure red (of course).  The 4x wave (=  
blue) exists as "1" in white, cyan, magenta, and pure blue.   The  
second row of colours is generated by inverting the green high/low  
wavetrain, red only in Magenta and white, and the blue wavetrain.   
There is no yellow, pure green, or pure red in the second row, those  
are your three "black bars"(?)...
      Reminds me of a little story...
Now there was the father bar, the mother bar and the baby bar.  One  
day they went for a walk in the woods... (don't go there...)   and  
there was a little girl with blonde hair also walking ... and oh  
forget it.  This was just going to wind up with brown bars being  
"just right", but... never mind.



Joe Owens
Presto!Digital Colourgrade
302-9664 106 Avenue
Edmonton, Alberta T5H0N4
+1 780 421-9980
jpo at prestodigital.ca