Thanks for that thorough information, really helpful! It actually seems like I got it kind of right altough my terminology is not so precise. I did think that calibration is getting the screen "back to neutral" so it behaves nice and well within its color space (and adjusting whitepoint, brightness, gamma, that was what I meant by desired target), and profiling is measuring and modeling what that neutral really is. However, I need to study more how the data in these tables are actually used. The source of all this was that I expected vcgt values at 0,0,0 to be 0,0,0 with the -k 0.0 parameter to dispcal, but clearly that is not the case and now I need to find out why (or go mad, or both). /Anders On Wednesday 27 October 2010, Sam Berry wrote: > On 27 October 2010 15:21, Anders Torger <torger@xxxxxxxxxxx> wrote: > > On Wednesday 27 October 2010, Graeme Gill wrote: > > > Please take some time to understand the difference between > > > calibration and profiling. > > > > This is what people keep saying to beginners like me :-). However, > > it seems to me quite easy. Calibration = through translation > > (matrix or lut) make the monitor display colours closer to some > > desired target. > > This is profiling. > > > Profiling = measuring the screen to see how it actually does > > display colours. One can profile a calibrated display or an > > uncalibrated display. > > This is profile/calibration validation. > > Calibration = Ensuring that display channels perform *individually* > as expected. Normally via display settings and 3 1-dimensional LUTs. > This does not alter colour in a major way, other than perhaps > altering the white point. A perfect monitor will show no change > after calibration. This process ensures the monitor conforms to a > 2.2 gamma response with a D65 white point, for example. > > Profiling = Modelling the display using a matrix or a set of 1D LUTs > and a *3-dimensional* LUT. This is the step that allows the graphics > application to ensure the display shows the correct colours, > regardless of varying gamut. Prior calibration improves the > effectiveness of profiling. > > Validation = Ensuring that the final result of both of these steps is > adequate by measuring a set of patches and comparing to those > predicted by the profile. > > > However, a source of confusion may be that I have misunderstood > > where the data is. I thought that for an .icc profile from dispcal > > vgct = calibration curves and rTRC/gTRC/bTRC = profile (*after* > > vcgt applied)... but I'm no longer that sure. I must try to look > > further into this, source code if I must. It will be impossible > > for me to find the source to my experienced (or imagined) problems > > if I don't have full understanding how calibration and profiling > > is applied. > > The xTRC curves are there to allow the colour correction to be > performed in linear space, rather than in gamma space. Matrix gamma > transformation operations are meaningless unless performed on linear > data. The curves allow this transformation and its inverse to be > performed. > > > Anyway, I'm sorry for being clueless, I know it's not fun educating > > clueless beginners like me... I'm trying not to say clueless > > things, but it seems today like I need to spend some more time on > > this before leaving the clueless stage :-). > > > > /Anders > > Sam Berry > www.satsumatree.co.uk