I've note, that addition of R=G=B patches isn't meant that there will be gray patches at printer output, because of printer may be not linearized and gray-balanced. The optimum way is the selection of wanted gray points in Lab, then icclu conversion of this points to RGB data by preliminary profile. Of course, RGB data may be converted to XYZ by icclu too.If I've understand correctly I have to start the above procedure with a preliminary profile... It's ok if I make a preliminary profile with only 441 patches or I have to do this with the 882 patches target?As I wrote yesterday: 1. Computing LAB data array in table processor2. Converting LAB array to RGB: icclu -fb -ir -s100 <LAB.txt >RGB.txt PreProf.icc3. Computing XYZ data for *.ti1: icclu -ff -ia -s100 <RGB.txt >XYZ.txt4. Combining patch numbers, RGB and XYZ data in one table by table processor5. Inserting this table into *.ti1 file.
You can't just add gray RGB by -g key because it changes OFP-spread in the *.ti1 file, but You can generate separate file only with grays and combine two ti1, one OFPS, one GRAYS into one big *.ti1 with "standard" OFPS and additional grays. I'd not recommend You to do regular gray spread across gray axis as in JPEGs You shown. Randomized distribution may be more reasonable for profiling (ask Graeme here).
Ok I trust you!
See my MS Excel example how to add 101 Lab patches randomly placed in radius 7dE from gray axis.
Thanks a lot! it is vary clear! Is it ok if I use a 7dE radius or is it better something else? If I have understand I have to write down all the neutral gray patches and the random "semi-gray" patches in a unique LAB.txt and after that I have to start the 2-5 procedure
is it correct? thanks daniele
