Hi, I am trying to understand how the RGB separation graph is computed and what it is telling me. I have read Ted's explanations here
, and here
, but I still have some questions.
My initial assumption was that at each point, it is plotting the expected luminance (x-axis) of both the greyscale and primary RGB patches against the measured luminance (y-axis). This would make sense except for that the greyscale line is always perfectly
linear, and I know that my display does not match the target 2.4 gamma exactly (nevermind measurement error/noise, etc.).
My next thought was that the greyscale measurements are used to normalize the measurements at each point, so the greyscale measurements always lie on the perfect 1:1 line and the RGB measurements are computed as (measured R/G/B Y)/(measured grey Y)*3
. This would imply that if (at all luminance levels) the RGB balance was perfect and the display was perfectly additive, all three of the R, G, and B lines would match up with the 1:1 greyscale line.
However, this would also mean that if the display was not
perfectly additive such that the greyscale luminance was less
than the sum of the R, G, and B luminances, we would see the R, G, or B lines above
the greyscale line. Ted's says here
that will never happen, so I'm wondering if my understanding is wrong or Ted simply meant that it does not (usually) happen in practice, because most real-displays that are not perfectly additive (like WRGB OLED) have the sum of the color luminances less than the greyscale luminance:
In summary, can someone explain how exactly the RGB separation plot is computed?
R,G,B lines closer to the White line of ColourSpace (or black line in LightSpace) define a good RGB Separation.
The post-calibration will have a great RGB Separation also.
Note that the RGB lines will not go above the White/Black line.
Lastly, what is the Error
checkbox on the graph supposed to do? I am toggling it back and forth and not seeing any difference.