On Dec 7, 2007 12:30 PM, Graeme Gill <graeme@xxxxxxxxxxxxx> wrote: > > The last hack was made to give white level around 140 Cd/m^2 using > > dispcal -yl -r. > > This also gives correct reading for maximum brightness according to > > monitor specifications. > > It's hard to justify this unless you've got another instrument > that you trust to compare it with though. (ie. the monitor > specs could be quite different to the actual monitor behaviour). Sure, it was just a quick hack to get a somewhat sensible reading. > > The right spot for an absolute scale factor is in > i1disp_take_XYZ_measurement(). > > > It works like a dream, though I cannot rely on the absolute value of gamma. > > Setting -g1.75 in dispcal gives a final gamma of 2.2 (according to my > > gamma swatches, downloaded from Timo Autiokari). > > It's probably more reliable to check for yourself using dispwin and spotread. > Read the Y for 100% and 50%. Gamma = log(50%Y/100%Y) / log(0.5) > Oh yes. I have noticed before that different gamma swatches often have rather big errors. I have made correction layers to the gamma swatches I use in Photoshop. Then I can drag the swatches across the screen and can see the variations in error. I have just changed video card, because I wanted to test Nvidia's GPU computing, and found that the old card had a broken fan. After I changed the card, I may have messed up with old .cal files. I have made new calibration files now, and they work perfectly, mostly hitting target gamma within 0.05 according to spotread/dispcal. I have also uninstalled all irrelevant icc profiles, after I noticed that Microsofts Picture and Fax Viewer displayed images using ColorMatch instead of an embedded sRGB profile. > > I'm leaving Nvidias settings from installation time untouched. > > > > I do not understand the black point setting, as I see it in the > > calibration file: > > BEGIN_DATA > > 0.0000 0.019102 0.018301 0.017533 > > 3.9216e-003 0.025279 0.024478 0.024011 > > 7.8431e-003 0.031338 0.030534 0.030370 > > > > I don't understand why is it not going down to more near zero. > > It doesn't necessarily follow that zero device value is the threshold > where the display starts to turn on. Some devices have a dead zone > from zero where nothing happens, so it's important to > set the calibrated zero at the threshold where something starts > to happen, otherwise the display characteristic isn't invertible, > and a calibration curve can't be created. > > Having said that, it doesn't mean that I think the current > calibration algorithm is perfect in what it achieves for > the black point. > Got it! > Thanks for the feedback on the Chroma 4 - I'll see about > adding your changes into the code, if you can clarify what > the actual version number and sub-model ID is. > Version no: 5.008 Sub model id (vv): -1 USB driver inf file: MonacoOptix.inf Thanks for your help Preben Soeberg