When this checkbox is marked, a plot is shown of the default tonal response character
of the monitor. That is, the tonal characteristics of the monitor in its uncalibrated state
before any adjustment has been performed. You will usually see, to some degree,
three lines for this plot because the Red, Green and Blue channels of the uncalibrated
monitor do not have the same tonal response characteristics.
Calibrated
When this checkbox is marked, a plot is shown of the tonal response character of the
monitor after it has been calibrated by the application. This plot should very closely
follow the plot of the Target curve. This is an indication of how well the calibration
actually adjusted the monitor’s behavior from the uncalibrated state to match the
desired (target) state. You may want to toggle the Target curve display off and on to
compare it with the Calibrated curve.
Correction
When this checkbox is marked, a plot is shown of the actual correction curves that are
downloaded to the lookup table (LUT) in the video card. This lookup table is calculated
to adjust the tonal response of the monitor from the uncalibrated behavior to the
desired (target) behavior.
The Correction curves are plotted using the actual values for input and output in the
range of 0-255.
Linear vs non-linear
If monitors were linear devices then the graph of their tonal response would be a
diagonal line from 0,0 to 255,255. However, monitors do not behave in a linear
fashion. Generally their tonal response character follows a power curve represented by
the Gamma function (typically in the range of Gamma 2.2.)
For example, if the response were linear, then an input value of 128 would result in an
output value of 128. With a monitor that has a response of Gamma 2.2 an input value
of 128 results in an output value of (128/255)
2.2
= 56.
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