Gerhard Fuernkranz wrote:
For a LCD, yes, you'll likely need rather many samples. But many CRT
monitors can be characterized reasonably accurate with a simple
Matrix/GGO model - and such a model has only 5x3 degrees of freedom (if
the "upper right end" of the TRC is constrained to [1,1]), so five
independent samples should be basically enough in order that the problem
is not underdetermined and the model parameters can be solved. Of course
that's an absolute minimum, and more samples are better in order to
average out measurement errors, spatial variations, etc.
(Btw, depending on the chosen number of orders used for modeling the
TRC, Argyll's shaper model may have some more degrees of freedom than
GGO, but it is still a rather reasonably low number)
For reasons that I haven't looked into, I found a dramatic difference
between the fit of a shaper/matrix model to a calibrated vs. uncalibrated
display. After I'd calibrated my display (which takes out any zero
offset in each channel, makes each channel have a fixed response
curve, and makes the three channels mix together properly to
form white), the fit was very good. On an uncalibrated display,
the fit was rather poor.
Graeme Gill.
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