8 bit Video Levels: 16-235 ---> 18% black (grey) would fall at 195.
8 bit Graphics: 0-255 ---> 18% black (grey) would fall at 209.
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Since RGB is additive, I'm looking at 18% grey as 82% WHITE (or 82% of the
maximum of all 3 colour channels).
For GRAPHICS levels - there are 256 unique shades of white --
[0,0,0] is the first and [255,255,255] is the 256th
The half-way point would be the 128th value or [127,127,127] which would be
50% white (or 50% black).
Therefore, let's view 18% grey as really 82% white - and 82% of 256 is
209.92. If we subtract 1 from that figure (to adjust for the numbering) we
arrive at 208.92 or approximately 209.
For VIDEO levels - there are only 220 unique shades of white --
[16,16,16] is the first and [235,235,235] is the 220th
The half-way point would be the 110th value or [109,109,109] which would be
50% white (or 50% black).
Again, 18% grey can really be considered as 82% white - and 82% of 220 is
180.4 - but we have to adjust that figure to take into account we start our
numbering at "16" and not at "0."
We adjust as we did above by subtracting 1 from 180.4 --> 179.4, then add 16
to that figure to adjust for our starting point. Therefore, we arrive at
195.4 or approximately 195 as our 18% grey.
You can use this method as a starting point to compute 18% black (grey) for
10 bit, and logrithmic scales...
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